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NO. ll.- R. P. A. CHEAP REPRINTS.
A Historic Work
&
The Origin of
Species
CHARLES DARWIN
WATTS & Co.,
17, JOHNSON’S COURT, FLEET STREET, LONDON, E.C.
(issued
for the rationalist press association, limited)
............................... .........................
The Next R.P.A. CHEAP REPRINT will be “LECTURES AND ESSAYS.”
�2S. 6d. net, by post 2s.
An Easy Outline
of Evolution.
By DENNIS HIRD
(Principal of Ruskin College).
>
�^2377
$£
— -ry
ON THE ORIGIN OF SPECIES
.I
yr ■
�PUBLISHERS’ NOTE
This edition of The Origin of Species is an exact reprint
of the first edition (published 1859-60), which has now
gone out of copyright. The third and subsequent editions
were considerably revised and amplified by Mr. Darwin,
but without any alteration of fundamental importance
being made. He strengthened, but did not rebuild, the
structure.
Mr. John Murray, the original publisher, is now
issuing the final edition in cloth binding at 2s. 6d. net,
and in paper covers at is. net. Students and all
admirers of Darwin should compare the first and last
editions of this great work in order to fully understand
the development of the doctrine of Evolution.
�ON THE
ORIGIN OF SPECIES
BY MEANS OF NATURAL SELECTION
THE PRESERVATION OF FAVOURED RACES IN
THE STRUGGLE FOR LIFE
BY
CHARLES DARWIN, M.A.
[issued
for the rationalist press association, limited]
WATTS & CO.,
17, JOHNSON’S COURT, FLEET STREET, LONDON, E.C.
1903
��CONTENTS
PAGE
CHAPTER
Introduction
y
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I. Variation under Domestication
II. Variation under Nature
III. Struggle for Existence
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n
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25
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31
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IV. Natural Selection
.....
39
V. Laws of Variation
.....
58
VI. Difficulties of Theory
....
VII. Instinct
VIII. Hybridism
73,,
87-
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10a
IX. On the Imperfection of the Geological Record
114
X. On the Geological Succession of Organic Beings
127
XI. Geographical Distribution
....
XII.Geographical Distribution—Continued
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-
140
154
XIII. Mutual Affinities of Organic Beings : Morpho
logy
: Embryology : Rudimentary Organs
XIV. Recapitulation and Conclusion
Index
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165
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183
196
�> . *■
3 p
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k
k
ii
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*'*s
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�ON THE ORIGIN OF SPECIES
INTRODUCTION
When on board H. M. S. Beagle, as [ this Abstract.
naturalist, I was much struck with certain
facts in the distribution of the inhabitants
of South America, and in the geological
relations of the present to the past
inhabitants of that continent. These
facts seemed to me to throw some light
on the origin of species—that mystery
of mysteries, as it has been called by one
of our greatest philosophers. On my
return home, it occurred to me, in 1837,
that something might perhaps be made
out on this question by patiently accumu
lating and reflecting on all sorts of facts
which could possibly have any bearing
on it. After five years’ work, I allowed
myself to speculate on the subject, and
drew up some short notes; these I
enlarged in 1844 into a sketch of the
conclusions, which then seemed to me
probable : from that period to the present
day I have steadily pursued the same
object. I hope that I may be excused
for entering on these personal details, as
I give them to show that I have not been
hasty in coming to a decision. My work is now nearly finished ; but
as it will take me two or three more years
to complete it, and as my health is far
from strong, I have been urged to publish
I have more especially
been induced to do this, as Mr. Wallace,
who is now studying the natural history
of the Malay archipelago, has arrived at
almost exactly the same general conclu
sions that I have on the origin of species.
Last year he sent me a memoir on this
subject, with a request that I would
forward it to Sir Charles Lyell, who sent
it to the Linnean Society, and it is
published in the third volume of the
Journal of that Society. Sir C. Lyell
and Dr. Hooker, who both knew of my
work—the latter having read my sketch
of 1844—honoured me by thinking it
advisible to publish, with Mr. Wallace’s
excellent memoir, some brief extracts
from my manuscripts.
This Abstract, which I now publish,
must necessarily be imperfect. I cannot
here give references and authorities for
my several statements; and I must trust
to the reader reposing some confidence
in my accuracy. No doubt errors will
have crept in, though I hope I have
always been cautious in trusting to good
authorities alone. I can here give only
the general conclusions at which I have
arrived, with a few facts in illustration,
but which, I hope, in most cases will
�8
ON THE ORIGIN OF SPECIES
suffice. No.one can feel more sensible
than I do of the necessity of hereafter
publishing in detail all the facts, with
references, on which my conclusions
have been grounded; and I hope in a
future work to do this. For I am well
aware that scarcely a single point is dis
cussed in this volume on which facts
cannot be adduced, often apparently
leading to conclusions directly opposite
to those at which I have arrived. A
fair result can be obtained only by fully
stating and balancing the facts and argu
ments on both sides of each question;
and this cannot possibly be here done.
I much regret that want of space pre
vents my having the satisfaction of
acknowledging the generous assistance
which I have received from very many
naturalists, some of them personally
unknown to me. I cannot, however, let
this opportunity pass without expressing
my deep obligations to Dr. Hooker, who
for the last fifteen years has aided me in
every possible way by his large stores of
knowledge and his excellent judgment.
In considering the Origin of Species,
it is quite conceivable that a naturalist,
reflecting on the mutual affinities of
organic' beings, on their embryological
relations, their geographical distribution,
geological succession, and other such
facts, might come to the conclusion that
each species had not been independently
created, but had descended, like varieties,
from other species. Nevertheless, such
a conclusion, even if well founded, would
be unsatisfactory, until it could be shown
how the innumerable species inhabiting
this world have been modified, so as to
acquire that perfection of structure and
coadaptation which most justly excites
our admiration. Naturalists continually
refer to external conditions, such as
climate, food, etc., as the only possible
cause of variation. In one very limited
sense, as we shall hereafter see, this may
be true; but it is preposterous to attri
bute to mere external conditions the
structure, for instance, of the wood
pecker, with its feet, tail, beak, and
tongue, so admirably adapted to catch
insects under the bark of trees. In the
case of the mistletoe, which draws its
nourishment from certain trees, which
has seeds that must be transported by
certain birds, and which has flowers with
separate sexes absolutely requiring the
agency of certain insects to bring pollen
from one flower to the other, it is equally
preposterous to account for the structure
of this parasite, with its relations to
several distinct organic beings, by the
effects of external conditions, or of habit,
or of the volition of the plant itself.
The author of the Vestiges of Creation
would, I presume, say that, after a certain
unknown number of generations, some
bird had given birth to a woodpecker,
and some plant to the mistletoe, and
that these had been produced perfect as
we now see them; but this assumption
seems to me to be no explanation, for it
leaves the case of the coadaptations of
organic beings to each other and to their
physical conditions of life untouched
and unexplained.
It is, therefore, of the highest impor
tance to gain a clear insight into the
means of modification and coadaptation.
�INTRODUCTION
At the commencement of my observa
tions it seemed to me probable that a
careful study of domesticated animals
and of cultivated plants would offer the
best chance of making out this obscure
problem. Nor have I been disappointed;
in this and in all other perplexing cases
I have invariably found that our know
ledge, imperfect though it be, of variation
under domestication, afforded the best
and safest clue.
I may venture to
express my conviction of the high
value of such studies, although they
have been very commonly neglected by
naturalists.
From these considerations I shall
devote the first chapter of this Abstract
to Variation under Domestication. We
shall thus see that a large amount of
hereditary modification is at least pos
sible; and, what is equally or more
important, we shall see how great is the
power of man in accumulating by his
Selection successive slight variations.
I will then pass on to the variability
of species in a state of nature; but I
shall, unfortunately, be compelled to
treat this subject far too briefly, as it
can be treated properly only by giving
long catalogues of facts. We shall,
however, be enabled to discuss what
circumstances are most favourable to
variation.
In the next chapter the
Struggle for Existence among all organic
beings throughout the world, which inevi
tably follows from the high geometrical
ratio of their increase, will be treated of.
This is the doctrine of Malthus, applied
to the whole animal and vegetable king
doms. As many more individuals of
9
each species are born than can possibly
survive, and as, consequently, there is
a frequently recurring struggle for exis
tence, it follows that any being, if it vary
however slightly in any manner profitable
to itself, under the complex and some
times varying conditions of life, will
have a better chance of surviving, and
thus be naturally selected. From the
strong principle of inheritance, any
selected variety will tend to propagate
its new and modified form.
This fundamental subject of Natural
Selection will be treated at some length
in the fourth chapter; and we shall
then see how Natural Selection almost
inevitably causes much Extinction of
the less improved forms of life, and
leads to what I have called Divergence
of Character. In the next, chapter I
shall discuss the complex and little
known laws of variation and of correla
tion of growth. In the four succeeding
chapters the most apparent and gravest
difficulties on the theory will be given—
namely, first, the difficulties of transi
tions, or in understanding how a simple
being or a simple organ can be changed
and perfected into a highly-developed
being or elaborately-constructed organ;
secondly, the subject of Instinct, or the
mental powers of animals; thirdly,
Hybridism, or the infertility of species
and the fertility of varieties when inter
crossed; and, fourthly, the imperfection
of the Geological Record. In the next
chapter I shall consider the geological
succession of organic beings throughout
time; in the eleventh and twelfth,* their
geographical distribution throughout
�IO
ON THE ORIGIN OF SPECIES
space; in the thirteenth, their classifica
tion or mutual affinities, both when
maturp and in an embryonic condition.
In-the last chapter I shall give a brief
recapitulation of the whole work, and a
few concluding remarks.
No one ought to feel surprise at much
remaining as yet unexplained in regard
to the origin of species and varieties, if
he makes due allowance for our profound
ignorance in regard to the mutual rela
tions of all the beings which live around
us. Who can explain why one species
ranges widely and is very numerous, and
why another allied species has a narrow
range and is rare ? Yet these relations
are of the highest importance, for they
determine the present welfare, and, as I
believe, the future success and modifica
tion of every inhabitant of this world.
Still less do we know of the mutual
relations of the innumerable inhabitants
of the world during the many past geo
logical epochs in its history. Although
much remains obscure, and will long
remain obscure, I can entertain no
doubt, after the most deliberate study
and dispassionate judgment of which I
am capable, that the view Mitch most
naturalists entertain, and which I
formerly entertained—namely, that each
species has been independently created
—is erroneous. I am fully convinced
that species are not immutable; but that
those belonging to what are called the
same genera are lineal descendants of
some other and generally extinct species,
in the same manner as the acknow
ledged varieties of any one species are1
the descendants of that species. Further
more, I am convinced that Natural
Selection has been the main, but not
exclusive, means of modification.
�Chapter I.
VARIATION UNDER DOMESTICATION
Causes of Variability—Effects of Habit—Correla
tion of Growth—Inheritance—Character of
Domestic Varieties—Difficulty of distinguish
ing between Varieties and Species—Origin of
Domestic Varieties from one or more Species—■
Domestic Pigeons, their Differences and Origin
—Principle of Selection anciently followed,
its Effects—-Methodical and Unconscious
Selection—Unknown Origin of our Domestic
Productions — Circumstances favourable to
Man’s power of Selection.
When we look to the individuals of the
same variety or sub-variety of our older
cultivated plants and animals, one of the
first points which strikes us is, that they
generally differ more from each other than
do the individuals of any one species or
variety in a state of nature. When we
reflect on ;the vast diversity of the plants
and animals which have been cultivated,
and which have varied during all ages
under the most different climates and
treatment, I think we are driven to con
clude that this great variability is simply
due to our domestic productions having
been raised under conditions of life not so
uniform as, and somewhat different from,
those to which the parent-species have
been exposed under nature. There is also,
I think, some probability in the view pro
pounded by Andrew Knight, that this
variability may be partly connected with
excess of food. It seems pretty clear that
organic beings must be exposed during
several generations to the new conditions
of life to cause any appreciable amount of
variation ; and that when the organisation
has once begun to vary, it generally con
tinues to vary for many generations. No
case is on record of a variable being ceasing
to be variable under cultivation.
Our
oldest cultivated plants, such as wheat,
still often yield new varieties ; our oldest
domesticated animals are still capable of
rapid improvement or modification.
It has been disputed at what period of
life the causes of variability, whatever they
may be, generally act; whether during the
early or late period of development of the
embryo, or at the instant of conception.
Geoffroy St. Hilaire’s experiments show
that unnatural treatment of the embryo
causes monstrosities; and monstrosities
cannot be separated by any clear line of
distinction from mere variations. But I
am strongly inclined to suspect that the
most frequent cause of variability, may be
attributed to the male and female repro
ductive elements having been affected prior
to the act of conception. Several reasons
make me believe in this ; but the chief
one is the remarkable effect which confine
ment or cultivation has on the function
of the reproductive system, this system
appearing to be far more susceptible than
any other part of the organisation to the
action of any change in the conditions of
life. Nothing is more easy than to. tame
an animal, and few things more difficult .
than to get it to breed freely under con
finement, even in the many cases when
the male and female unite. How many
animals there are which will not breed,
though living long under not very close
confinement in their native country! This
is generally attributed to vitiated instincts;
but how many cultivated plants display
the utmost vigour, and yet rarely or never
seed ! In some few such cases it has been
discovered that very trifling changes, such
as a little more or less water at some
particular period of growth, will determine
whether or not the plant sets a seed. I
cannot here enter on the copious details
which I have collected on this curious
subject ; but to show how singular the laws
are which determine the reproduction of
animals under confinement, I may just
mention that carnivorous animals, even
from the tropics, breed in this country
pretty freely under confinement, with the
exception of the plantigrades or bear family;
whereas carnivorous birds, with the rarest
exceptions, hardly ever lay fertile eggs.
Many exotic plants have pollen utterly
worthless, in the same exact condition as
in the most sterile hybrids. When, on the
�12
ON THE ORIGIN OF SPECIES
one hand, we see domesticated animals
and plants, though often weak and sickly,
yet breeding quite freely under confine
ment ; and when, on the other hand, we
see individuals, though taken young from
a state of nature, perfectly tamed, longlived, and healthy (of which I could give
numerous instances), yet having their repro
ductive system so seriously affected by
unperceived causes as to fail in acting, we
need not be surprised at this system, when
it does act under confinement, acting not
quite regularly, and producing offspring not
perfectly like their parents.
Sterility has been said to be the bane of
horticulture ; but on this view we owe
variability to the same cause which pro
duces sterility ; and variability is the source
•of all the choicest productions of the
garden. I may add that, as some organ
isms will breed freely under the most
unnatural conditions (for instance, the
rabbit and ferret kept in hutches), showing
that their reproductive system has not
Been thus affected ; so will some animals
and plants withstand domestication or
cultivation, and vary very slightly—perhaps
hardly more than in a state of nature.
A long list could easily be given of
“sporting plants”; by this term gardeners
mean a single bud or offset, which suddenly
assumes a new and sometimes very different
character from that of the rest of the plant.
Such buds can be propagated by grafting,
■etc., and sometimes by seed. These
“ sports ” are extremely rare under naturfe,
but far from rare under cultivation ; and
in this case we see that the treatment of the
parent has affected a bud or offset, and not
the ovules or pollen. But it is the opinion
of most physiologists that there is no
essential difference between a bud and an
ovule in their earliest stages of formation ;
so that, in fact, “ sports ” support my view,
that variability may be largely attributed
to the ovules or pollen, or to both, having
been affected by the treatment of the parent
prior to the act of conception. These cases
anyhow show that variation is not neces
sarily connected, as some authors have
supposed, with the act of generation.
Seedlings from the same fruit and the
young of the same litter, sometimes differ
considerably from each other, though both
the young and the parents, as Muller has
remarked, have apparently been exposed
to exactly the same conditions of life ; and
this shows how unimportant the direct
effects of the conditions of life are in com
parison with the laws of reproduction, of
growth, and of inheritance; for had the
action of the conditions been direct, if any
of the young had -varied, all would probably
have varied in the same manner. To judge
how much, in the case of any variation, we
should attribute to the direct action of
heat, moisture, light, food, etc., is most
difficult: my impression is, that with
animals such agencies have produced very
little direct effect, though apparently more
in the case of plants. Under this point of
view, Mr. Buckman’s recent experiments
on plants are extremely valuable. When
all or nearly all the individuals exposed to
certain conditions are affected in the same
way, the change at first appears to be
directly due to such conditions; but in
some cases it can be shown that quite
opposite conditions produce similar changes
of structure. Nevertheless, some slight
amount of change may, I think, be attri
buted to the direct action of the conditions
of life—as, in some cases, increased size
from amount of food, colour from particular
kinds of food or from light, and perhaps
the thickness of fur from climate.
Habit also has a decided influence, as in
the period of flowering with plants when
transported from one climate to another.
In animals it has a more marked effect ;
for instance, I find in the domestic duck
that the bones of the wing weigh less and
the bones of the leg more, in proportion to
the whole skeleton, than do the same bones
in the wild duck; and I presume that this
change may be safely attributed to the
domestic duck flying much less, and walking
more, than its wild parent. The great and
inherited development of the udders in
cows and goats in countries where they are
habitually milked, in comparison with the
state of these organs in other countries, is
another instance of the effect of use. Not
a single domestic animal can be named
which has not in some country drooping
ears ; and the view suggested by some
authors, that the drooping is due to the
disuse of the muscles of the ear, from the
animals not being much alarmed by danger,
seems probable.
There are many laws regulating varia
tion, some few of which can be dimly seen,
and will be hereafter briefly mentioned.
I will here only allude to what may be
called correlation of growth. Any change
in the embryo or larva will almost certainly
entail changes in the mature animal.
In monstrosities the correlations between
quite distinct parts are very curious ; and
many instances are given in Isidore Geoffroy
�VARIATION UNDER DOMESTICATION
St. Hilaire’s great work on this subject.
Breeders believe that long limbs are almost
always accompanied by an elongated head.
Some instances of correlation are quite
whimsical: thus cats with blue eyes are
invariably deaf; colour and constitutional
peculiarities go together, of which many
remarkable cases could be given among ani
mals and plants. From the facts collected
by Heusinger, it appears that white sheep
and pigs are differently affected from
coloured individuals by certain vegetable
poisons. Hairless dogs have imperfect
teeth ; long-haired and coarse-haired ani
mals are apt to have, as is asserted, long
or many horns ; pigeons with feathered feet
have skin between their outer toes ; pigeons
with short beaks have small feet, and those
with long beaks large feet. Hence, if man
goes on selecting, and thus augmenting, any
peculiarity, he will almost certainly uncon
sciously modify other parts of the structure,
owing to the mysterious laws of the correla
tion of growth.
The result of the various, quite unknown,
or dimly-seen laws of variation is infinitely
complex and diversified. It is well worth
while carefully to study the several treatises
published on some of our old cultivated
plants, as on the hyacinth, potato, even the
dahlia, etc.; and it is really surprising to
note the endless points in structure and
constitution in which the varieties and sub
varieties differ slightly from each other.
The whole organisation seems to have
become plastic, and tends to depart in
some small degree from that of the parental
type.
.
.
. , . , .
Any variation which is not inherited is
unimportant for us. But the number and
diversity of inheritable deviations of struc
ture, both those of slight and those of
considerable physiological importance, is
endless. Dr. Prosper Lucas’s treatise, in
two large volumes, is the fullest and the
best on this subject. No breeder doubts
how strong is the tendency to inheritance :
like produces like is his fundamental belief:
doubts have been thrown on this principle
by theoretical writers alone. When any
deviation of structure often appears, and
we see it in the father and child, we cannot
tell whether it may not be due to the same
cause having acted on both ; but when
among individuals, apparently exposed to
the same conditions, any very rare devia
tion, due to some extraordinary combination
of circumstances, appears in the parent—
say, once among several million individuals
—and it reappears in the child, the mere
13
doctrine of chances almost compels us to
attribute its reappearance to inheritance.
Every one must have heard of cases of
albinism, prickly skin, hairy bodies, etc.,
appearing in several members of the same
family. If strange and rare deviations of
structure are truly inherited, less strange
and commoner deviations may be freely
admitted to be inheritable. Perhaps the
correct way of viewing the whole subject
would be to look at the inheritance of every
character whatever as the rule, and non
inheritance as the anomaly.
The laws governing inheritance are quite
unknown; no one can say why a peculiarity
in different individuals of the same species,
or in individuals of different species, is
sometimes inherited and sometimes not
so ; why the child often reverts in certain
characters to its grandfather or grand
mother or other more remote ancestor
why a peculiarity is often transmitted from
one sex to both sexes, or to one sex alone,
more commonly but not exclusively to the
like sex. It is a fact of some little impor
tance to us, that peculiarities appearing in
the males of our domestic breeds are often
transmitted either exclusively, or in a much
greater degree, to males alone. A much
more important rule, which I think may be
trusted, is that, at whatever period of life a
peculiarity first appears, it tends to appear
in the offspring at a corresponding age,
though sometimes earlier. In many cases
this could not be otherwise: thus the
inherited peculiarities in the horns of cattle
could appear only in the offspring when
nearly mature; peculiarities in the silk
worm are known to appear at the corre
sponding caterpillar or cocoon stage. But
hereditary diseases and some other facts
make me believe that the rule has a wider
extension, and that when there is no appa
rent reason why a peculiarity should appear
at any particular age, yet that it does tend
to appear in the offspring at the same
period at which it first appeared in the
parent. I believe this rule to be of the
highest importance in explaining the laws
of embryology. These remarks are of
course confined to the first appearance of
the peculiarity, and not to its primary
cause, which may have acted on the ovules
or male element ; in nearly the same
manner as in the crossed offspring from a
short-horned cow by a long-horned bull,
the greater length of horn, though appearing
late in life, is clearly due to the male element.
Having alluded to the subject of rever
sion, I may here refer to a statement often
�14
ON THE ORIGIN OF SPECIES
made by naturalists—namely, that our
domestic varieties, when run wild, gradually
but certainly revert in character to their
aboriginal stocks. Hence it has been
argued that no deductions can be drawn
from domestic races to species in a state
of nature. I have in vain endeavoured to
discover on what decisive facts the above
statement' has so often and so boldly been
made. There would be great difficulty in
proving its truth : we may safely conclude
that very many of the most strongly-marked
domestic varieties could not possibly live
in a wild state. In many cases we do not
know what the aboriginal stock was, and
so could not tell whether or not nearly
perfect reversion had ensued. It would be
quite necessary, in order to prevent the
effects of intercrossing, that only a single
variety should be turned loose in its new
home. Nevertheless, as our varieties cer
tainly do occasionally revert in some of
their characters to ancestral forms, it seems
to me not improbable that, if we could
succeed in naturalising, or were to cultivate,
during many generations, the several races,
for instance, of the cabbage, in very poor
soil (in which case, however, some effect
would have to be attributed to the direct
action of the poor soil), that they would to
a large extent, or even wholly, revert to
the wild aboriginal stock. Whether or not
the experiment would succeed is not of
great importance for our line of argument;
for by the experiment itself the conditions
■of life are changed. If it could be shown
that our domestic varieties manifested a
strong tendency to reversion—that is, to
lose their acquired characters, while kept
under the same conditions, and while kept
in a considerable body, so that free inter
crossing might check, by blending together,
any slight deviations in their structure—in
such case I grant that we could deduce
nothing from domestic varieties in regard
to species. But there is not a shadow of
evidence in favour of this view : to assert
that we could not breed our cart and race
horses, long and short horned cattle, and
poultry of various breeds, and esculent
vegetables, for an almost infinite number
of generations, would be opposed to all
experience. I may add that, when under
nature the conditions of life do change,
variations and reversions of character pro
bably do occur ; but natural selection, as
will hereafter be explained, will determine
how far the new characters thus arising
shall be preserved.
When we look to the hereditary varieties 1
or races of our domestic animals and plants,
and compare them with closely-allied
species, we generally perceive in each
domestic race, as already remarked, less
uniformity of character than in true species.
Domestic races of the same species, also,
often have a somewhat monstrous character;
by which I mean that, although differingfrom
each other, and from other species of the
same genus, in several trifling respects, they
often differ in an extreme degree in some one
part, both when compared one with another,
and more especially when compared with
all the species in nature to which they are
nearest allied. With these exceptions (and
with that of the perfect fertility of varieties
when crossed—a subject hereafter to be
discussed), domestic races of the same
species differ from each other in the same
manner as, only in most cases in a lesser
degree than, do closely-allied species of
the same genus in a state of nature. I
think this must be admitted, when we find
that there are hardly any domestic races,
either among animals or plants, which have
not been ranked by competent judges as
mere varieties, and by other competent
judges as the descendants of aboriginally
distinct species. If any marked distinction
existed between domestic races and species,
this source of doubt could not so per
petually recur. It has often been stated
that domestic races do not differ from each
other in characters of generic value. I
think it could be shown that this statement
is hardly correct; but natmalists differ
widely in determining what characters are
of generic value, all such valuations being
at present empirical. Moreover, on the
view of the origin of genera which I shall
presently give, we have no right to expect
often to meet with generic differences in
our domesticated productions.
When we attempt to estimate the amount
of structural difference between the domestic
races of the same species, we are soon
involved in doubt, from not knowing
whether they have descended from one or
several parent species. This point, if it
could be cleared up, would be interesting ;
if, for instance, it could be shown that the
greyhound, bloodhound, terrier, spaniel,
and bull-dog, which we all know propagate
their kind so ti;uly, were the offspring of
any single species, then such facts would
have great weight in making us doubt
about the immutability of the many very
closely-allied natural species—for instance,
of the many foxes—inhabiting different
quarters of the world. I do not believe, as
�VARIATION UNDER DOMESTICATION
we shall presently see, that the whole
amount of difference between the several
breeds of the dog has been produced under
domestication ; 1“ believe that some small
part of the difference is due to their being
descended from distinct species. In the
case of some other domesticated species,
there is presumptive, or even strong evi
dence, that all the breeds have descended
from a single wild stock.
It has often been assumed that man has
chosen for domestication animals and
plants having an extraordinary inherent
tendency to vary, and likewise to withstand
diverse climates. I do not dispute that
these capacities have added largely to the
value of most of our domesticated produc
tions ; but how could a savage possibly
know, when he first tamed an animal,
whether it would vary in succeeding genera
tions, and whether it would endure other
climates ? Has the. little variability of the
ass or guinea-fowl, or the small power of
endurance of warmth by the reindeer, or of
cold by the common camel, prevented their
domestication ? I cannot doubt that if
other animals and plants, equal in number
to our domesticated productions, and
belonging to equally diverse classes and
countries, were taken from a state of
nature, and could be made to breed for an
equal number of generations under domes
tication, they would vary on an average as
largely as the parent species of our existing
domesticated productions have varied.
In the case of most of our anciently
dom^ifcated animals and plants, I do not
think it is possible to come to any definite
conclusion, whether they have descended
from one or several wild species. The
argument mainly relied on by those who
believe in the multiple origin of our domestic
animals is, that we find in the most ancient
records, more especially on the monuments
of Egypt, much diversity in the breeds ;
and that some of the breeds closely
resemble, perhaps are identical with, those
still existing. Even if this latter fact were
found more strictly and generally true than
seems to me to be the case, what does it
show but that some of our breeds originated
there four or five thousand years ago?
But Mr. Horner’s researches have rendered
it in some degree probable that man suffi
ciently civilised to have manufactured
pottery existed in the valley of the Nile
thirteen or fourteen thousand years ago ;
and who will pretend to say how long
before these ancient periods savages, like
those of Tierra del Fuego or Australia, who
15
possess a semi-domestic dog, may not have
existed in Egypt ?
The whole subject must, I think, remain
vague; nevertheless, I may, without here
entering on any details, state that, from
geographical and other considerations, I
think it highly probable that our domestic
dogs have descended from several wild
species. Knowing, as we do, that savages
are very fond of taming animals, it seems
to me unlikely, in the case of the dog-genus,
which is distributed in a wild state through
out the world, that since man first appeared
one single species alone should have been
domesticated. In regard to sheep and
goats I can form no opinion. I should
think, from facts communicated to me by
Mr. Blyth on the habits, voice, and con
stitution, etc., of the humped Indian cattle,
that these had descended from a different
aboriginal stock from our European cattle ;
and several competent judges believe that
these latter have had more than one wild
parent. With respect to horses, from
reasons which I cannot give here, I am
doubtfully inclined to believe, in opposition
to several authors, that all the races have
descended from one wild stock. Mr. Blyth,
whose opinion, from his large and varied
stores of knowledge, I should value more
than that of almost anyone, thinks that all
the breeds of poultry have proceeded from
the common wild Indian fowl (Gallus
bankiva). In regard to ducks and rabbits,
the breeds of which differ considerably from
each other in structure, I do not doubt that
they have all descended from the common
wild duck and rabbit.
The doctrine of the origin of our several
domestic races from several aboriginal
stocks has been carried to an absurd
extreme by some authors. They believe
that every race which breeds true, let the
distinctive characters be ever so slight, has
had its wild prototype. At this rate there
must have existed at least a score of species
of wild cattle, as many sheep, and several
goats in Europe alone, and several even
within Great Britain. One author believes
that there formerly existed in Great Britain
eleven wild species of sheep peculiar to it.
When we bear in mind that Britain has
now hardly one peculiar mammal, and
France but few distinct from those of
Germany, and conversely, and so with
Hungary, Spain, etc., but that each of these
kingdoms possesses several peculiar breeds
of cattle, sheep, etc., we must admit that
many domestic breeds have originated in
Europe ; for whence could they have been
�i6
ON THE ORIGIN OF SPECIES
derived, as these several countries do not
possess a number of peculiar species as
distinct parent-stocks ? So it is in India.
Even in the case of the domestic dogs
of the whole world, which I fully admit
have probably descended from several wild
species, I cannot doubt that there has been
an immense amount of inherited variation.
Who can believe that animals closely
resembling the Italian greyhound, the
bloodhound, the bull-dog, or Blenheim
spaniel, etc.—so unlike all wild Canidae—
ever existed freely in a state of nature?
It has often been loosely said that all our
races of dogs have been produced by the
crossing of a few aboriginal species; but
by crossing we can only get forms in some
degree intermediate between their parents ;
and, if we account for our several domestic
races by this process, we must admit the
former existence of the most extreme
forms, as the Italian greyhound, blood
hound, bull-dog, etc., in the wild state.
Moreover, the possibility of making distinct
races by crossing has been greatly exagge
rated. There can be no doubt that a
race may be modified by occasional crosses,
if aided by the careful selection of those
individual mongrels which present any
desired character ; but that a race could
be obtained nearly intermediate between
two extremely different races or species,
I can hardly believe. Sir J. Sebright
expressly experimentised for this object,
and failed. The offspring from the first
cross between two pure breeds is tolerably
and sometimes (as I have found with
pigeons) extremely uniform, and everything
seems' simple enough ; but when these
mongrels are crossed one with another for
several generations, hardly two of them
will be alike, and then the extreme diffi
culty, or rather utter hopelessness, of the
task becomes apparent. Certainly a breed
intermediate between two very distinct
breeds could not be got without extreme
care and long-continued selection ; nor can
I find a single case on record of a per
manent race having been thus formed.
On the Breeds of the Domestic Pigeon.—
Believing that it is always best to study
some special group, I have, after delibera
tion, taken up domestic pigeons. I have
kept every breed which I could purchase
or obtain, and have been most kindly
favoured with skins from several quarters
of the world, more especially by the Hon.
W. Elliot from India, and by the Hon. C.
Murray from Persia. Many treatises in
different languages have been published
on pigeons, and some of them are very
important, as being of considerable anti
quity. I have associated with several
eminent fanciers, and have been permitted
to join two of the London Pigeon Clubs.
The diversity of the breeds is something
astonishing. Compare the English carrier
and the short-faced tumbler, and see the
wonderful difference in their beaks, entailing
corresponding differences in their skulls.
The carrier, more especially the male bird,
is also remarkable from the wonderful
development of the carunculated skin
about the head, and this is accompanied
by greatly elongated eyelids, very large
external orifices to the nostrils, and a wide
gape of mouth. The short-faced tumbler
has a beak in outline almost like that of a
finch ; and the common tumbler has the
singular inherited habit of flying at a great
height in a compact flock, and tumbling in
the air head over heels. The runt is a bird
of great size, with long, massive beak and
large feet; some of the sub-breeds of runts
have very long necks, others very long
wings and tails, others singularlMj short
tails. The barb is allied to the carrier,,
but, instead of a very long beak, has a very
short and very broad one. The pouter
has a much elongated body, wings, and
legs ; and its enormously developed crop,
which it glories in inflating, may well
excite astonishment and even laughter.
The turbit has a very short and conical
beak, with a line of reversed feathers down
the breast; and it has the habit of con
tinually expanding slightly the upper part
of the oesophagus. The Jacobin has the
feathers so much reversed along the back
of the neck that they form a hood, and
it has, proportionally to its size, much
elongated wing and tail feathers. The
trumpeter and laugher, as their names,
express, utter a very different coo from the
other breeds. The fantail has thirty or
even forty tail feathers, instead of twelve
or fourteen, the normal number in all
members of the great pigeon family ; and
these feathers are kept expanded, and are
carried so erect that in good birds the
head and tail touch ; the oil-gland is quite
aborted. Several other less distinct breeds
might be specified.
In the skeletons of the several breeds
the development of the bones of the face
in length and breadth and curvature differs
enormously. The shape, as well as the
breadth and length of the ramus of the
lower jaw, varies in a highly remarkable
manner. The number of the caudal and
�VARIATION UNDER DOMESTICATION
sacral vertebrae vary ; as does the number
of the ribs, together with their relative
breadth and the presence of processes.
The size and shape of the apertures in
the sternum are highly variable ; so is the
degree of divergence and relative size of
the two arms of the furcula. The propor
tional width of the gape of mouth, the
proportional length of the eyelids, of the
orifice of the nostrils, of the tongue (not
always in strict correlation with the length
of beak), the size of the crop and of the
upper part of the oesophagus ; the develop
ment and abortion of the oil-gland; the
number of the primary wing and caudal
feathers ; the relative length of wing and
tail to each other and to the body; the
relative length of leg and of the feet ; the
number of scutellae on the toes, the develop
ment of skin between the toes, are all
points of structure which are variable. The
period at which the perfect plumage is
acquired varies, as does the state of the
down with which the nestling birds are
clothed when hatched. The shape and
size of the eggs vary. The manner of
flight differs remarkably ; as does in some
breeds the voice and disposition. Lastly,
in certain breeds, the males and females
have come to differ to a slight degree from
each other.
Altogether at least a score of pigeons
might be chosen which, if shown to an
ornithologist, and he were told that they
were wild birds, would certainly, I think,
be ranked by him as well-defined species.
Moreover, I do not believe that any ornitho
logist would place the English carrier,
the short-faced tumbler, the runt, the barb,
pouter, and fantail in the same genus ;
more especially as in each of these breeds
several truly-inherited sub-breeds, or species
as he might have called them, could be
shown him.
Great as the differences are between the
breeds of pigeons, I am fully convinced
that the common opinion of naturalists is
correct—namely, that all have descended
from the rock-pigeon (Columba livia),
including under this term several geo
graphical races or sub-species, which differ
1 from each other in the most trifling respects.
As several of the reasons which have led
me to this belief are in some degree appli
cable in other cases, I will here briefly
give them. If the several breeds are not
varieties, and have not proceeded from the
rock-pigeon, they must have descended
from at least seven or eight aboriginal
stocks ; for it is impossible to make the
17
present domestic breeds by the crossing of
any lesser number: how, for instance,
could a pouter be produced by crossing
two breeds unless one of the parent-stocks
possessed the characteristic enormous crop?
The supposed aboriginal stocks must all
have been rock-pigeons—that is, not breed
ing or willingly perching on trees. But
besides C. livia, with its geographical sub
species, only two or three other species of
rock-pigeons are known ; and these have
not any of the characters of the domestic
breeds. Hence the supposed aboriginal
stocks must either still exist in the countries
where they were originally domesticated,
and yet be unknown to ornithologists
(and this, considering their size, habits,
and remarkable characters, seems very
improbable), or they must have become
extinct in the wild state. But birds breeding
on precipices, and good fliers, are unlikely
to be exterminated; and the common rock
pigeon, which has the same habits with the
domestic breeds, has not been exterminated
even on several of the smaller British islets,
or on the shores of the Mediterranean.
Hence the supposed extermination of so
many species having similar habits with
the rock-pigeon seems to me a very rash
assumption. Moreover, the several abovenamed domesticated breeds have been
transported to all parts of the world, and,
therefore, some of them must have been
carried back again into their native country ;
but not one has ever become wild or feral,
though the dovecot-pigeon, which is the
rock-pigeon in a very slightly altered state,
has become feral in several places. Again,
all recent experience shows that it is most
difficult to get any wild animal to breed
freely under domestication; yet, on the
hypothesis of the multiple origin of our
pigeons, it must be assumed that at least
seven or eight species were so thoroughly
domesticated in ancient times by half
civilised man as to be quite prolific under
confinement.
An argument, as it seems to me, of great
weight, and applicable in several other
cases, is that the above-specified breeds,
though agreeing generally in constitution,
habits, voice, colouring, and in most parts
of their structure, with the wild rock-pigeon,
yet are certainly highly abnormal in other
parts of their structure : we may look in
vain throughout the whole great family of
Columbidse for a beak like that of the
English carrier, or that of the short-faced
tumbler, or barb ; for reversed feathers like
those of the Jacobin ; for a crop like that
c
■
�18
ON THE ORIGIN OF SPECIES
of the pouter; for tail-feathers like those
of the fantail. Hence it must be assumed
not only that half-civilised man succeeded
in thoroughly domesticating several species,
but that he intentionally or by chance
picked out extraordinarilyabnormal species;
and, further, that these very species have
since all become extinct or unknown. So
many strange contingencies seem to me
improbable in the highest degree.
Some facts in regard to the colouring of
pigeons well deserve consideration. The
rock-pigeon is of a slaty-blue, and has a
white rump (the Indian sub-species, C.
intermedia of Strickland, having it bluish);
the tail has a terminal dark bar, with the
bases of the outer feathers externally
edged with white; the wings have two
black bars; some semi-domestic breeds
and some apparently truly wild breeds
have, besides the two black bars, the wings
chequered with black. These several
marks do not occur together in any other
species of the whole family. Now, in
every one of the domestic breeds, taking
thoroughly well-bred birds, all the above
marks, even to the white edging of the
outer tail-feathers, sometimes concur per
fectly developed. Moreover, when two
birds belonging to two distinct breeds are
crossed, neither of which is blue or has any
of the above-specified marks, the mongrel
offspring are very apt suddenly to acquire
these characters; for instance I crossed
some uniformly white fantails with some
uniformly black barbs, and they produced
mottled brown and black birds ; these I
again crossed together, and one grandchild
of the pure white fantail and pure black
barb was of as beautiful a blue colour, with
the white rump, double black wing-bar,
and barred and white-edged tail-feathers,
as any wild rock-pigeon ! We can under
stand these facts, on the well-known prin
ciple of reversion to ancestral characters,
if all the domestic breeds have descended
from the rock-pigeon. But if we deny this,
we must make one of the two following
highly improbable suppositions. Either,
firstly, that all the several imagined
aboriginal stocks were coloured and
marked like the rock-pigeon, althoug'h no
other existing species is thus coloured and
marked, so that in each separate breed
there might be a tendency to revert to the
very same colours and markings. Or,
secondly, that each breed, even the purest,
has within a dozen or, at most, within a
score of generations, been crossed by the
rock-pigeon : I say within a dozen or |
twenty generations, for we know of no fact
countenancing the belief that the child ever
reverts to some one ancestor, removed by
a greater number of generations. In a
breed which has been crossed only once
with some distinct breed, the tendency to
reversion to any character derived from
such cross will naturally become less and
less, as in each succeeding generation there
will be less of the foreign blood ; but when
there has been no cross with a distinct
breed, and there is a tendency in both
parents to revert to a character which has
been lost during some former generation,
this tendency, for all that we can see to
the contrary, may be transmitted un
diminished for an indefinite number of
generations. These two distinct cases are
often confounded in treatises on inheritance.
Lastly, the hybrids or mongrels from
between all the domestic breeds of pigeons
are perfectly fertile. I can state this from
my own observations, purposely made, on
the most distinct breeds. Now, it is diffi
cult, perhaps impossible, to bring forward
one case of the hybrid offspring of two
animals clearly distinct being themslves
perfectly fertile. Some authors believe that
long-continued domestication eliminates
this strong tendency to sterility : from the
history of the dog I think there is some
probability in this hypothesis, if applied to
species closely related together, though it
is unsupported by a single experiment.
But to extend the hypothecs so far as to
suppose that species, aboriginally as distinct
as carriers, tumblers, pouters, and fantails
now are, should yield offspring perfectly
fertile, inter se, seems to me rash in the
extreme.
From these several reasons—namely, the
improbability of man having formerly got
seven or eight supposed species of pigeons
to breed freely under domestication ; these
supposed species being quite unknown in
a wild state, and their becoming nowhere
feral; these species having very abnormal
characters in certain respects, as compared
with all other Columbidse, though so like
in most other respects to the rock-pigeon ;
the blue colour and various marks occa
sionally appearing in all the breeds, both
when kept pure and when crossed ; the
mongrel offspring being perfectly fertile—
from these several reasons, taken together,
I can feel no doubt that all our domestic
breeds have descended from the Columba
livia with its geographical sub-species.
In favour of this view, I may add, firstly,
that C. livia, or the rock-pigeon, has been
�VARIATION UNDER DOMESTICATION
19
knowing well how true they bred, I felt
found capable of domestication in Europe
fully as much difficulty in believing that
and in India ; and that it agrees in habits
they could have descended from a common
and in a great number of points of structure
parent as any naturalist could in coming
with all the domestic breeds. Secondly,
to a similar conclusion in regard to the
although an English carrier or short-faced
many species of finches, or other large
tumbler differs immensely in certain cha
groups of birds, in nature. One circum
racters from the rock-pigeon, yet by com
stance has struck me much—namely, that
paring the several sub-breeds of these
all the breeders of the various domestic
varieties, more especially those brought
animals and the cultivators of plants with
from distant countries, we can make an
whom I have ever conversed, or whose
almost perfect series between the extremes
treatises I have read, are firmly convinced
of structure. Thirdly, those characters
that the several breeds to which each has
which are mainly distinctive of each breed—
attended are descended from so many
for instance, the wattle and length of beak
aboriginally distinct species. Ask, as I
of the carrier, the shortness of that of the
have asked, a celebrated raiser of Here
tumbler, and the number of tail-feathers in
ford cattle whether his, cattle might not
the fantail—are in each breed eminently
have descended from long-horns, and he will
variable; and the explanation of this fact
will be obvious when we come to treat of laugh you to scorn. I have never met a
pigeon, or poultry, or duck, or rabbit
selection. Fourthly, pigeons have been
fancier who was not fully convinced that
watched, and tended with the utmost care,
each main breed was descended from .a
and loved by many people. They have
been domesticated for thousands of years
distinct species. Van Mons, in his treatise
in several quarters of the world; the
on pears and apples, shows how utterly he
earliest known record of pigeons is in the
disbelieves that the several sorts, for
fifth Egyptian dynasty, about 3000 B.C., as
instance a Ribston-pippin or Codlin-apple,
was pointed out to me by Professor Lepsius;
could ever have proceeded from the seeds
of the same tree. Innumerable other
but Mr. Birch informs me that pigeons are
given in a bill of fare in the previous
examples could be given. The explanation,
dynasty. In the time of the Romans, as
I think, is simple : from long-continued
we hear from Pliny, immense prices were
study they are strongly impressed with the
given for pigeons ; “ nay, they are come to
differences between the several races ; and
this pass, that they can reckon up their
though they well know .that each race varies
pedigree and race.” Pigeons were much
slightly, for they win their prizes by
valued by Afefe&ikKhan in India, about the
selecting such slight differences, yet they
year 1600 ; never less than 20,000 pigeons
ignore all general arguments, and refuse to
were taken with the court. “The monarchs
sum up in their minds slight differences
of Iran and Turan sent him some very
accumulated during many successive gene
rare birds”; and, continues the courtly
rations. May not those naturalists who,
historian, “ His Majesty by crossing the
knowing far less of the laws of inheritance
breeds, which method was never practised
than does the breeder, and knowing no
before, has improved them astonishingly.”
more than he does of the intermediate links
About this same period the Dutch were as
in the long lines of descent, yet admit that
eager about pigeons as were the old
many of our domestic races have descended
Romans. The paramount importance of
from the same parents—may they not
these considerations in explaining the
learn a lesson of caution when they
immense amount of variation which pigeons
deride the idea of species in a state of
have undergone will be obvious when we
nature being lineal descendants of other
treat of selection. We shall then, also,
species ?
see how it is that the breeds so often have
Selection.—Let us now briefly consider
a somewhat monstrous character. It is
the steps by which domestic races have
also a most favourable circumstance for
been produced, either from one or from
the production of distinct breeds that male
several allied species. Some little effect
and female pigeons can be easily mated
may, perhaps, be attributed to the direct
for life ; and thus different breeds can be
action of the external conditions of life,
kept together in the same aviary.
and some little to habit ; but he would be
I have discussed the probable origin of a bold man who would account by such
domestic pigeons at some, yet quite insuffi
agencies for the differences of a dray- and
cient, length ; because when I first kept
race-horse, a greyhound and bloodhound,
.pigeons and watched the several kinds,
a carrier and tumbler pigeon. One of the
�20
ON THE ORIGIN OF SPECIES
most remarkable features in our domesti
cated races is that we see in them adapta
tion, not indeed to the animal’s or plant’s
own good, but to man’s use or fancy.
Some variations useful to him have probably
arisen suddenly, or by one step; many
botanists, for instance, believe that the
fuller’s teasel, with its hooks, which cannot
be rivalled by any mechanical contrivance,
is only a variety of the wild Dipsacus;
and this amount of change may have sud
denly arisen in a seedling.
So it has
probably been with the turnspit dog ; and
this is known to have been the case with
the ancon sheep. But when we compare
the dray-horse and race-horse, the drome
dary and camel, the various breeds of sheep
fitted either for cultivated land or mountain
pasture, with the wool of one breed good
for one purpose, and that of another breed
for another purpose ; when we compare the
many breeds of dogs, each good for man in
very different ways ; when we compare the
game-cock, so pertinacious in battle, with
other breeds so little quarrelsome, with
“everlasting layers” which never desire to
sit, and with the bantam so small and
elegant; when we compare the host of
agricultural, culinary, orchard, and flowergarden races of plants, most useful to man
at different seasons and for different
purposes, or so beautiful in his eyes, we
must, I think, look further than to mere
variability. We cannot suppose that all the
breeds were suddenly produced as perfect
and as useful as we now see them; indeed,
in several cases, we know that this has not
been their history. The key is man’s
power of accumulative selection : nature
gives successive variations ; man adds
them up in certain directions useful to him.
In this sense he may be said to make for
himself useful breeds.
The great power of this principle of
selection is not hypothetical. It is certain
that several of our eminent breeders have,
even within a single, lifetime, modified to a
large extent some breeds of cattle and
sheep. In order fully to realise what they
have done, it is almost necessary to read
several of the many treatises devoted to
this subject, and to inspect the animals.
Breeders habitually speak of an animal’s
organisation as something quite plastic,
which they can model almost as they
please. If I had space, I could quote
numerous passages to this effect from highly
competent authorities. Youatt, who was
probably better acquainted with the works
of agriculturists than almost any other in
dividual, and who was himself a very good
judge of an animal, speaks of the principle
of selection as “that which enables the
agriculturist, not only to modify the char
acter of his flock, but to change it altogether.
It is the magician’s wand, by means of
which he may summon into life whatever
form and mould he pleases.” Lord Somer
ville, speaking of what breeders have done
for sheep, says : “It would seem as if
they had chalked out upon a wall a form
perfect in itself, and then had given it
existence.” That most skilful breeder, Sir
John Sebright, used to say, with respect to
pigeons, that “ he would produce any given
feather in three years, but it would take
him six years to obtain head and beak.”
In Saxony the importance of the principle
of selection in regard to merino sheep is so
fully recognised that men follow it as a
trade : the sheep are placed on a table and
are studied, like a picture by a connoisseur;
this is done three times at intervals of
months, and the sheep are each time
marked and classed, so that the very best
may ultimately be selected for breeding.
What English breeders have actually
effected is proved by the enormous prices
given for animals with a good pedigree ;
and these have now been exported to
almost every quarter of the world. The
improvement is by no means generally due
to crossing different breeds; all the best
breeders are strongly opposed to this
practice, except sometimes among closely
allied sub-breeds. And when a cross has
been made, the closest selection is far more
indispensable even than in ordinary cases.
If selection consisted merely in separating
some very distinct variety, and breedingfrom it, the principle would be so obvious as
hardly to be worth notice ; but its impor
tance consists in the great effect produced
by the accumulation in one direction, during
successive generations, of differences abso
lutely inappreciable by an uneducated eye
—differences which I for one have vainly
attempted to appreciate. Not one man in
a thousand has accuracy of eye and judg
ment sufficient to become an eminent
breeder. If gifted with these qualities, and
he studies his subject for years, and devoteshis lifetime to it with indomitable perse
verance, he will succeed, and may make
great improvements ; if he wants any of
these qualities, he will assuredly fail. Few
would readily believe in the natural
capacity and years of practice requisite to
become even a skilful pigeon-fancier.
The same principles are followed by
�VARIATION UNDER DOMESTICATION
horticulturists ; but the variations are here
often more abrupt. No one supposes that
out choicest productions have been pro
duced by a single variation from the
aboriginal stock. We have proofs that
this is not so in some cases, in which exact
records have been kept; thus, to give a
very trifling instance, the steadily-increas
ing size of the common gooseberry may be
quoted. We see an astonishing improve
ment in many florists’ flowers, when the
flowers of the present day are compared
with drawings made only twenty or thirty
years ago. When a race of plants is once
pretty well established, the seed-raisers do
not pick out the best plants, but merely go
over their seed-beds, and pull up the
“ rogues,” as they call the plants that
deviate from the proper standard. With
animals this kind of selection is, in fact,
also followed; for hardly anyone is so
careless as to allow his worst animals to
breed.
In regard to plants, there is another
means of observing the accumulated effects
of selection—namely, by comparing the
diversity of flowers in the different varieties
of the same species in the flower-garden ;
the diversity of leaves, pods, or tubers, or
whatever part is valued, in the kitchen
garden, in comparison with the flowers of
the same varieties ; and the diversity of
fruit of the same species in the orchard, in
comparison with the leaves and flowers of
the same set of varieties. See how different
the leaves of the cabbage are, and how
extremely alike the flowers ; how unlike
the flowers of the heartsease are, and how
alike the leaves ; how much the fruit of the
different kinds of gooseberries differ in size,
colour, shape, and hairiness, and yet the
flowers present very slight differences. It
is not that the varieties which differ largely
in some one point do not differ at all in
other points ; this is hardly ever, perhaps
never, the case. The laws of correlation
of growth, the importance of which should
never be overlooked, will ensure some
differences; but, as a general rule, I cannot
doubt that the continued selection of slight
variations, either in the leaves, the flowers,
or the fruit, will produce races differing
from each other chiefly in these characters.
It may be objected that the principle of
selection has been reduced to methodical
practice for scarcely more than threequarters of a century; it has certainly
been more attended to of late years, and
many treatises have been published on the
subject; and the result has been, in a
21
corresponding degree, rapid and important.
But it is very far from true that the prin
ciple is a modern discovery. I could give
several references to the full acknowledg
ment of the importance of the principle in
works of high antiquity. In rude and
barbarous periods of English history choice
animals were often imported, and laws
were passed to prevent their exportation :
the destruction of horses under a certain
size was ordered, and this maybe compared
to the “ rogumg ” of plants by nurserymen.
The principle of selection I find distinctly
given in an ancient Chinese encyclopaedia.
Explicit rules are laid down by some of the
Roman classical writers. From passages
in Genesis, it is clear that the colour of
domestic animals was at that early period
attended to. Savages now sometimes cross
their dogs with wild canine animals, to
improve the breed, and they formerly did
so, as is attested by passages in Pliny.
The savages in South Africa match their
draught cattle by colour, as do some of the
Esquimaux their teams of dogs. Living
stone shows how much good domestic
breeds are valued by the negroes of the
interior of Africa who have not associated
with Europeans. Some of these facts do
not show actual selection, but they show
that the breeding of domestic animals was
carefully attended to in ancient times, and
is now attended to by the lowest savages.
It would, indeed, have been a strange fact
had attention not been paid to breeding,
for the inheritance of good and bad
qualities is so obvious.
At the present time eminent breeders
try by methodical selection, with a distinct
object in view, to make a new strain or
sub-breed superior to anything existing in
the country. But, for our purpose, a kind
of Selection, which may be called Uncon
scious, and which results from everyone
trying to possess and breed from the best
individual animals, is more important.
Thus, a man who intends keeping pointers
naturally tries to get as good dogs as he
can, and afterwards breeds from his own
best dogs, but he has no wish or expecta
tion of permanently altering the breed.
Nevertheless, I cannot doubt that this pro
cess, continued during centuries, would
improve and modify any breed, in the same
way as Bakewell, Collins, etc., by this very
same process, only carried on more metho
dically, did greatly modify, even during
their own lifetimes, the forms and qualities
of their cattle. Slow and insensible changes
of this kind could never be recognised
�ON THE ORIGIN OF SPECIES
unless actual measurements or careful
drawings of the breeds in question had
been made long ago, which might serve
for comparison. In some cases, however,
unchanged, or but little changed individuals
of the same breed may be found in less
civilised districts, where the breed has
been less improved. There is reason to
believe that King Charles’s spaniel has
been unconsciously modified to a large
extent since the time of that monarch.
Some highly competent authorities are
convinced that the setter is directly derived
from the spaniel, and has probably been
slowly altered from it. It is known that
the English pointer has been greatly
changed within the last century, and in
this case the change has, it is believed,
been chiefly effected by crosses with the
fox-hound; but what concerns us is that
the change has been effected unconsciously
and gradually, and yet so effectually, that,
though the old Spanish pointer certainly
came from Spain, Mr. Borrow has not
seen, as I am informed by him, any native
dog in Spain like our pointer.
By a similar process of selection, and by
careful training, the whole body of English
race-horses have come to surpass in fleetness
and size the parent Arab stock, so that the
latter, by the regulations for the Goodwood
Races, are favoured in the weights they
carry. Lord Spencer and others have
shown how the cattle of England have
increased in weight and in early maturity
compared with the stock formerly kept in
this country. By comparing the accounts
given in old pigeon treatises of carriers
and tumblers with these breeds as now
existing in Britain, India, and Persia, we
can, I think, clearly trace the stages
through which they have insensibly passed,
and come to differ so greatly from the
rock-pigeon.
Youatt gives an excellent illustration of
the effects of a course of selection, which
may be considered as unconsciously fol
lowed, in so far that the breeders could
never have expected or even have wished
to have produced the result which ensued
—namely, the production of two distinct
strains. The two flocks of Leicester sheep
kept by Mr. Buckley and Mr. Burgess, as
Mr. Youatt remarks, “have been purely
bred from the original stock of Mr.
Bakewell for upwards of fifty years. There
is not a suspicion existing in the mind of
any one at all acquainted with the subject
that the owner of either of them has
deviated in any one instance from the pure
blood of Mr. Bakewell’s flock, and yet the
difference between the sheep possessed by
these two gentlemen is so great that they
have the appearance of being quite different
varieties.”
If there exist savages so barbarous as
never to think of the inherited character of
the offspring of their domestic animals,
yet any one animal particularly useful to
them, for any special purpose, would be'
carefully preserved during famines and
other accidents, to which savages are so
liable, and such choice animals would thus
generally leave more offspring than- the
inferior ones ; so that in this case there
would be a kind of unconscious selection
going on. We see the value set on animals
even by the barbarians of Tierra del Fuego,
by their killing and devouring their old
women, in times of dearth, as of less value
than their dogs.
In plants the same gradual process of
improvement, through the occasional pre
servation of the best individuals, whether
or not sufficiently distinct to be ranked at
their first appearance as distinct varieties,
and whether or not two or more species or
races have become blended together by
crossing, may plainly be recognised in the
increased size and beauty which we now
see in the varieties of the heartsease, rose,
pelargonium, dahlia, and other plants,
when compared with the older varieties or
with their parent-stocks. No one would ever
expect to get a first-rate heartsease or dahlia
from the seed of a wild plant. No one
would expect to raise a first-rate melting
pear from the seed of the wild pear, though
he might succeed from a poor seedling
growing wild if it had come from a garden
stock. The pear, though cultivated in
classical times, appears, from Pliny’s
description, to have been a fruit of very
inferior quality. I have seen great surprise
expressed in horticultural works at the
wonderful skill of gardeners in having
produced such splendid results from such
poor materials; but the art, I cannot
doubt, has been simple, and, as far as the
final result is concerned, has been followed
almost unconsciously. It has consisted in
always cultivating the best known variety,
sowing its seeds, and, when a slightly
better variety has chanced to appear,
selecting it, and so onwards. But . the
gardeners of the classical period, who culti
vated the best pear they could procure,
never thought what splendid fruit we should
eat; though we owe our excellent fruit, in
some small degree, to their having naturally
�VARIATION UNDER DOMESTICATION
chosen and preserved the best varieties
they could anywhere find.
A large amount of change in our culti
vated plants, thus slowly and unconsciously
accumulated, explains, as I believe, the
well-known fact that in a vast number of
cases we cannot recognise, and therefore
do not know, the wild parent-stocks of the
plants which have been longest cultivated
in our flower and kitchen gardens. If it
has taken centuries or thousands of years
to improve or modify most of our plants up
to their present standard of usefulness to
man, we cah understand how it is that
neither Australia, the Cape of Good Hope,
nor any other region inhabited by quite
uncivilised man, has afforded us a single
plant worth culture. It is not that these
countries, so rich in species, do not by a
strange chance possess the aboriginal
stocks of any useful plants, but that the
native plants have not been improved by
Continued selection up to a standard of
perfection comparable with that given to
the plants in countries anciently civilised.
In regard to the domestic animals kept
by uncivilised man, it should not be over
looked that they almost always have to
struggle for their own food, at least during
certain seasons. And in two countries, very
differently circumstanced, individuals of
the same species, having slightly different
constitutions or structure, would often
succeed better in the one country than in
the other; and thus by a process of
“natural selection,” as will hereafter be
more fully explained, two sub-breeds might
be formed. This, perhaps, partly explains
what has been remarked by some authors—namely, that the varieties kept by savages
have more of the character of species than
the varieties kept in civilised countries.
On the view here given of the allimportant part which selection by man has
played, it becomes at once obvious how it
is that our domestic races show adaptation
in their structure or in their habits to man’s
wants or fancies. We can, I think, further
understand the frequently abnormal char
acter of our domestic races, and likewise
their differences being so great in external
characters and relatively so slight in in
ternal parts or organs. Man can hardly
select, or only with much difficulty, any
deviation of structure excepting such as is
externally visible ; and indeed he rarely
cares for what is internal. He can never
act by selection, excepting on variations
which are first given to him in some slight
degree by nature. No man would ever try
23
to make a fantail till he saw a pigeon with
a tail developed in some slight degree in
an unusual manner, or a pouter till he saw
a pigeon with a crop of somewhat unusual
size ; and the more abnormal or unusual
any character was when it first appeared,
the more likely it would be to catch his
attention. But to use such an expression as
trying to make a fantail, is, I have no
doubt, in most cases, utterly incorrect. The
man who first selected a pigeon with a
slightly larger tail never dreamed what the
descendants of that pigeon would become
through long-continued, partly unconscious
and partly methodical selection. Perhaps
the parent bird of all fantails had only
fourteen tail-feathers somewhat expanded,
like the present Java fantail, or like indi
viduals of other and distinct breeds, in
which as many as seventeen tail-feathers
have been counted. Perhaps the first
pouter-pigeon did not inflate its crop much
more than the turbit now does the upper
part of its oesophagus—a habit which is
disregarded by all fanciers, as it is not one
of the points of the breed.
Nor let it be thought that some great
deviation of structure would be necessary
to catch the fancier’s eye : he perceives
extremely small differences, and it is in
human nature to value any novelty, how
ever slight, in one’s own possession. Nor
must the value which would formerly be set
on any slight differences in the individuals
of the same species be judged of by the
value which would now be set on them,
after several breeds have once fairly been
established. Many slight differences might,
and indeed do now, arise among pigeons,
which are rejected as faults or deviations
from the standard of perfection of each
breed. The common goose has not given
rise to any marked varieties ; hence the
Thoulouse and the common breed, which
differ only in colour, that most fleeting of
characters, have lately been exhibited as
distinct at our poultry shows.
I think these views further explain what
has sometimes been noticed—namely, that
we know nothing about the origin or
history of any of our domestic breeds.
But, in fact, a breed, like a dialect of a
language, can hardly be said to have had
a definite origin. A man preserves and
breeds from an individual with some slight
deviation of structure, or takes more care
than usual in matching his best animals
and thus improves them, and the improved
individuals slowly spread in the immediate
neighbourhood. But as yet they will hardly
�24
ON THE ORIGIN OF SPECIES
have a distinct name, and, from being only
slightly valued, their history will be dis
regarded. When further improved by the
same slow and gradual process, they will
spread more widely, and will get recognised
as something distinct’and valuable, and
will then probably first receive a provincial
name. In semi-civilised countries, with
little free communication, the spreading
and knowledge of any new sub-breed will
be a slow process. As soon as the points
of value of the new sub-breed are once
fully acknowledged the principle, as I have
called, it, of unconscious selection will
always tend, perhaps more at one period
than at another, as the breed rises or falls
in fashion—perhaps more in one district
than in another, according to the state of
civilisation of the inhabitants—slowly to
add to the characteristic features of the
breed, whatever they may be. But the
chance will be infinitely small of any record
having been preserved of such slow, varying,
and insensible changes.
. 1 must now say a few words on the
circumstances, favourable or the reverse, to
man’s power of selection. A high degree
of variability is obviously favourable, as
freely giving the materials for selection
to work on ; not that mere individual
differences are not amply sufficient, with
extreme care, to allow of the accumula
tion of a large amount of modification
in almost any desired direction. But as
variations manifestly useful or pleasing to
man appear only occasionally, the chance
of their appearance will be much increased
by a large number of individuals being
kept; and hence this comes to be of the
highest importance to success. On this
principle Marshall has remarked, with
respect to the sheep of parts of Yorkshire,
that “as they generally belong to poor
people, and are mostly in small lots, they
never can be improved.” On the other
hand, nurserymen, from raising large stocks
of the same plants, are generally far more
successful than amateurs in getting new
and valuable varieties. The keeping of a
large number of individuals of a species
in any country requires that the species
should be placed under favourable condi
tions of life, so as to breed freely in that
country. When the individuals of any
species are scanty, all the individuals, what
ever their quality may be, will generally be
allowed to breed, and this will effectually
prevent selection. But probably the most
important point of all is, that the animal
or plant should be so highly useful to '
man, or so much valued by him, that the
closest attention should be paid to even
the slightest deviation in the qualities or
structure of each individual. Unless such
attention be paid, nothing can be effected.
I have seen it gravely remarked that it
was most fortunate that the strawberry
began to vary just when gardeners began
to attend closely to this plant. No doubt
the strawberry had always varied since it
was cultivated, but the slight varieties had
been neglected. As soon, however, as
gardeners picked out individual plants with
slightly larger, earlier, or better fruit, and
raised seedlings from them, and again
picked out the best seedlings and bred
from them, then there appeared (aided by
some crossing with distinct species) those
many admirable varieties of the strawberry
which have been raised during the last
thirty or forty years.
In the case of animals with separate sexes,
facility in preventing crosses is an important
element of success in the formation of
new7 races, at least in a country which is
already stocked with other races. In this
respect enclosure of the land plays a part.
Wandering savages or the inhabitants of
open plains rarely possess more than one
breed of the same species. Pigeons can
be mated for life, and this is a great con
venience to the fancier, for thus many races
may be kept true, though mingled in the
same aviary ; and this circumstance must
have largely favoured the improvement and
formation of new breeds. Pigeons, I may
add, can be propagated in great numbers
and at a very quick rate, and inferior birds
may be freely rejected, as when killed they
serve for food. On the other hand, cats,
from their nocturnal rambling habits,
cannot be matched, and, although so much
valued by women and children, we hardly
ever see a distinct breed kept up ; such
breeds as we do sometimes see are almost
always imported from some other country,
often from islands. Although I do not
doubt that some domestic animals vary
less than others, yet the rarity or absence
of distinct breeds of the cat, the donkey,
peacock, goose, etc., may be attributed
in main part to selection not having been
brought into play : in cats, from the diffi
culty in pairing them ; in donkeys, from
only a few being kept by poor people, and
little attention paid to their breeding ;
in peacocks, from not being very easily
reared and a large stock not kept ; in
geese, from being valuable only for two
purposes, food and feathers, and more
�VARIATION UNDER NATURE
especially from no pleasure having been
felt in the display of distinct breeds.
To sum up on the origin of our Domestic
Races of animals and plants. I believe
that the conditions of life, from their action
on the reproductive system, are so far of
the highest importance as causing varia\ bility. I do not believe that variability is
an inherent and necessary contingency,
under all circumstances, with all organic
beings, as some authors have thought.
The effects of variability are modified by
various degrees of inheritance and of
reversion. Variability is governed by many
unknown laws, more especially by that of
correlation of growth. Something may be
attributed to the direct action of the con
ditions of life. Something must be attri
buted to use and disuse. The final result
is thus rendered infinitely complex. In
some cases I do not doubt that the inter
crossing of species, aboriginally distinct,
has played an important part in the origin
of our domestic productions. When in
25
any country several domestic breeds have
once been established, their occasional
inter-crossing, with the aid of selection, has,
no doubt, largely aided in the formation of
new sub-breeds ; but the importance of the
crossing of varieties has, I believe, been
greatly exaggerated, both in regard to
animals and to those plants which are
propagated by seed. In plants which are
temporarily propagated by cuttings, buds,
etc., the importance of the crossing both
of distinct species and of varieties is
immense; for the cultivator here quite
disregards the extreme variability both of
hybrids and mongrels, and the frequent
sterility of hybrids ; but the cases of plants
not propagated by seed are of little impor
tance to us, for their endurance is only
temporary. Over all these causes of
Change I am convinced that the accumula
tive action of Selection, whether applied
methodically and more quickly, or uncon
sciously and more slowly, but more
efficiently, is by far the predominant Power.
Chapter II.
VARIATION UNDER NATURE
\ ariability — Individual differences -— Doubtful
species—Wide ranging, much diffused, and
common species vary most—Species of the
larger genera in any country vary more than
the species of the smaller genera—Many of the
species of the larger genera resemble varieties
in being very closely, but unequally, related to
each other, and in having restricted ranges.
Before applying the principles arrived at
in the last chapter to organic beings in a
state of nature, we must briefly discuss
whether these latter are subject to any
variation.
To treat this subject at all
properly, a long catalogue of dry facts
should be given ; but these I shall reserve
for my future work. Nor shall I here discuss
the various definitions which have been
given - of the term species.
No one
definition has as yet satisfied all naturalists;
yet every naturalist knows vaguely what
he means when he speaks of a species.
Generally the term includes the unknown
element of a distinct act of creation. The
term “ variety ” is almost equally difficult
to define ; but here community of descent
is almost universally implied, though it can
rarely be proved. We have also what are
called monstrosities; but they graduate
into varieties. By a monstrosity I presume
is meant some considerable deviation of
structure in one part, either injurious to or
not useful to the species, and not generally
propagated. Some authors use the term
“variation” in a technical sense, as imply
ing a modification directly due to the
physical conditions of life; and “varia
tions” in this sense are supposed not to
be inherited ; but who can say that the
dwarfed condition of shells in the brackish
waters of the Baltic, or dwarfed plants on
Alpine summits, or the thicker fur of an
animal from far northwards, would not in
some cases be inherited for at least some
few generations ? and in this case I presume
that the form would be called a variety.
�26
ON THE ORIGIN OF SPECIES
vidual differences which seems to me
Again, we have many slight differences
extremely perplexing: I refer to those
which may be called individual differences,
genera which have sometimes been called
such as are known frequently to appear in
“ protean ” or “ polymorphic,” in which the
the offspring from the same parents, or
species present an inordinate amount of
which may be presumed to have thus
variation ; and hardly twq naturalists can
arisen, from being frequently observed _ in
agree which forms to rank as species and
the individuals of the same species in
which as varieties. We may instance
habiting the same confined locality. No
Rubus, Rosa, and Hieracium among plants,
one supposes that all the individuals of the
several genera of insects, and several
same species are cast in the very same
genera of Brachiopod shells. In most
mould. These individual differences are
polymorphic genera some of the species
highly important for us, as they afford
have fixed and definite characters. Genera
materials for natural selection to accumu
which are polymorphic in one country
late, in the ‘same manner as man can
seem to be, with some few exceptions,
accumulate in any given direction indi
polymorphic in other countries, and like
vidual differences in his domesticated
wise, judging from Brachiopod shells, at
productions. These individual differences
former periods of time. These facts seem
generally affect what naturalists consider
to be very perplexing, for they seem to
unimportant parts ; but I could show by a
show that this kind of variability is inde
long catalogue of facts that parts which
pendent of the conditions of life. I am
must be called important, whether viewed
inclined to suspect that we see in these
under a physiological or classificatory point
polymorphic genera variations in points of
of view, sometimes vary in the individuals
structure which are of no service or dis
of the same species. I am convinced that
service to the species, and which conse
the most experienced naturalist would be
quently have not been seized on and
surprised at the number of the cases of
rendered definite by natural selection, as
variability, even in important parts of
hereafter will be explained.
structure, which he could collect on good
Those forms which possess in some con
authority, as I have collected, during a
siderable degree the character of species,
course of years. It should be remembered
but which are so closely similar to some
that systematists are far from pleased at
other forms, or are so closely linked to
finding variability in important characters,
them by intermediate gradations that
and that there are not many men who will
naturalists do not like to rank them as
laboriously examine internal and important
distinct species, are in several respects the
organs, and compare them in many speci
most important for us. We have every
mens of the same species. I should never
reason to believe that many of these
have expected that the branching of the main
doubtful and closely-allied forms have per
nerves close to the great central ganglion
manently retained their characters in their
of an insect would have been variable in
own country for a long time—for as long,
the same species ; I should have expected
as far as we know, as have good and true
that changes of this nature could have been
species. Practically, when a naturalist
effected only by slow degrees ; yet quite
can unite two forms together by others
recently Mr. Lubbock has shown a degree of
having intermediate characters, he treats
variability in these main nerves in Coccus,
the one as a variety of the other, ranking
which may almost be compared to the
the most common, but sometimes the one
irregular branching of the stem of a tree.
first described, as the species and the
This philosophical naturalist, I may add,
has also quite recently shown that the j other as the variety. But cases of great
difficulty, which I will not here enumerate,
muscles in the larvae of certain insects are
sometimes occur in deciding whether or
very far from uniform. Authors sometimes
not to rank one form as a variety of another,
argue in a circle when they state that
even when they are closely connected by
important organs never vary ; for these
intermediate links ; nor will the commonlysame authors practically rank that character
assumed hybrid nature of the intermediate
as important (as some few naturalists have
links always remove the difficulty. In very
honestly confessed) which does not vary;
many cases, however, one form is ranked
and, under this point of view, no instance
as a variety of another, not because the
of an important part varying will ever be
intermediate links have actually been found,
found ; but under any other point of view
but because analogy leads the observer to
many instances assuredly can be given.
suppose either that they do now somewhere
There is one point connected with indi
�VARIATION UNDER NATURE
exist, or may formerly have existed ; and
here a wide door for the entry of doubt and
conjecture is opened.
Hence, in determining whether a form
should be ranked as a species or a variety,
the opinion of naturalists having sound
judgment and wide experience seems the
only guide to follow. We must, however,
in many cases decide by a majority of
naturalists, for few well-marked and wellknown varieties can be named which have
not been ranked as species by at least
some competent judges.
That varieties of this doubtful nature
are far from uncommon cannot be dis
puted. Compare the several floras of Great
Britain, of France, or of the United States,
drawn up by different botanists, and see
what a surprising number of forms have
been ranked by one botanist as good
species and by another as mere varieties.
Mr. H. C. Watson, to whom I lie under
deep obligation for assistance of all
kinds, has marked for me ,182 British
plants, which are generally considered as
varieties, but which have all been ranked
by botanists as species ; and in making
this list he has omitted many trifling
varieties, but which nevertheless have been
ranked by some botanists as species, and
he has entirely omitted several highly
polymorphic genera. Under genera, in
cluding the most polymorphic forms, Mr.
Babington gives 251 species, whereas Mr.
Bentham gives only 112—a difference of
139 doubtful forms 1 Among animals which
unite for each birth, and which are highly
locomotive, doubtful forms, ranked by one
zoologist as a species and by another as a
variety, can rarely be found within the
same country, but are common in separated
areas. How many of those birds and
insects in North America and Europe
which differ very slightly from each other
have been ranked by one eminent naturalist
as undoubted species, and by another as
varieties, or, as they are often called, as
geographical races ! Many years ago, when
comparing, and seeing others compare, the
birds from the separate islands of the
Galapagos Archipelago, both one with
another and with those from the American
mainland, I was much struck how entirely
vague and arbitrary is the distinction
between species and varieties. On the
islets of the little Madeira group there
are many insects which are characterised
as varieties in Mr. Wollaston’s admirable
work, but which it cannot be doubted would
be ranked as distinct species by many
entomologists. Even Ireland has a few
animals, nowgenerally regarded as varieties,
but which have been ranked as species by
some zoologists. Several most experienced
ornithologists consider our British red
grouse as only a strongly-marked race of
a Norwegian species, whereas the greater
number rank it as an undoubted species
peculiar to Great Britain. A wide distance
between the homes of two doubtful forms
leads many naturalists to rank both as
distinct species ; but what distance, it has
been well asked, willsuffice ? If that between
America and Europe is ample, will that
between the Continent and the Azores, or
Madeira, or the Canaries, or Ireland, be
sufficient? It must be admitted that many
forms considered by highly-competent
judges as varieties have so perfectly the
character of species that they are ranked
by other highly-competent judges as good
and true species. But to discuss whether
they are rightly called species or varieties,
before any definition of these terms has
been generally accepted, is vainly to beat
the air.
Many of the cases of strongly-marked
varieties or doubtful species well deserve
consideration ; for several interesting lines
of argument, from geographical distribu
tion, analogical variation, hybridism, etc.,
have been brought to bear on the attempt
to determine their rank. I will here give
only a single instance—the well-known one
of the primrose and cowslip, or Primula
vulgaris and veris. These plants differ
considerably in appearance ; they have a
different flavour, and emit a different odour;
they flower at slightly different periods ;
they grow in somewhat different stations ;
they ascend mountains to different heights ;
they have different geographical ranges ;
and, lastly, according to very numerous
experiments made during several years by
that most careful observer Gartner, they
can be crossed only with much difficulty.
We could hardly wish for better evidence
of the two forms being specifically distinct.
On the other hand, they are united by many
intermediate links, and it is very doubtful
whether these links are hybrids ; and there
is, as it seems to me, an overwhelming
amount of experimental evidence showing
that they descend from common parents,
and consequently must be ranked as
varieties.
Close investigation, in most cases, will
bring naturalists to an agreement how to
rank doubtful forms. Yet it must be con
fessed that it is in the best-known countries
�28
ON THE ORIGIN OF SPECIES
that we find the greatest number of forms
of doubtful value. I have been struck with
the fact that, if any animal or plant in a
state of nature be highly useful to man, or
from any cause closely attract his attention,
varieties of it will almost universally be
found recorded. These varieties, moreover,
will be often ranked by some authors as
species. Look at the common oak, how
closely it has been studied ; yet a German
author makes more than a dozen species
out of forms which are very generally con
sidered as varieties ; and in this country the
highest botanical authorities and practical
men can be quoted to show that the sessile
and pedunculated oaks are either good and
distinct species or mere varieties.
When a young naturalist commences the
study of a group of organisms quite
unknown to him, he is at first much per
plexed to determine what differences to
consider as specific and what as varieties ;
for he knows nothing of the amount and
kind of variation to which the group is
subject; and this shows, at least, how very
generally there is some variation. But if
he confine his attention to one class within
one country, he will soon make up his mind
how to rank most of the doubtful forms.
His general tendency will be to make many
species, for he will become impressed, just
like the pigeon or poultry fancier before
alluded to, with the amount of difference in
the forms which he is continually studying ;
and he has little general knowledge of
analogical variation in other groups and in
other countries by which to correct his first
impressions. As he extends the range of
his observations, he will meet with more
cases of difficulty ; for he will encounter a
greater number of closely-allied forms.
But if his observations be widely extended,
he will in the end generally be enabled to
make up his own mind which to call
varieties and which species ; but he will
succeed in this at the expense of admitting
much variation—and the truth of this ad
mission will often be disputed by other
naturalists. When, moreover, he comes to
study allied forms brought from countries
not now continuous, in which case he can
hardly hope to find the intermediate links
between his doubtful forms, he will have to
trust almost entirely to analogy, and his
difficulties rise to a climax.
Certainly no clear line of demarcation
has as yet been drawn between species and
sub-species—that is, the forms which in the
opinion of some naturalists come very near
to, but do not quite arrive at, the rank of
species ; or, again, between sub-species and
well-marked varieties, or between lesser
varieties and individual differences. These
differences blend into each other in an
insensible series ; and a series impresses
the mind with the idea of an actual
passage.
Hence I look at individual differences,
though of small interest to the systematist,
as of high importance for us, as being the
first step towards such slight varieties as
are barely thought worth recording in
works on natural history. And I look at
varieties which are in any degree more
distinct and permanent, as steps leading to
more strongly marked and more permanent
varieties ; and at these latter as leading to
sub-species, and to species. The passage
from one stage of difference to another and
higher stage may be, in some cases, due
merely to the long-continued action of
different physical conditions in two different
regions ; but I have not much faith in this
view ; and I attribute the passage of a
variety, from a state in which it differs very
slightly from its parent to one in which
it differs more, to the action of natural
selection in accumulating (as will here
after be more fully explained) differences
of structure in certain definite directions.
Hence I believe a well-marked variety may
be called an incipient species ; but whether
this belief be justifiable must be judged of
by the general weight of the several facts
and views given throughout this work.
It need not be supposed that all varieties
or incipient species necessarily attain the
rank of species. They may while in this
incipient state become extinct, or they may
endure as varieties for very long periods,
as has been shown to be the case by Mr.
Wollaston with the varieties of certain
fossil land-shells in Madeira. If a variety
were to flourish so as to exceed in numbers
the parent species, it would then rank as
the species, and the species as the variety;
or it might come to supplant and ex
terminate the parent species; or both
might co-exist, and both rank as indepen
dent species. But we shall hereafter have
to return to this subject.
From these remarks it will be seen that
I look at the term species as one arbitrarily
given for the sake of convenience to a set
of individuals closely resembling each
other, and that it does not essentially differ
from the term variety, which is given -to
less distinct and more fluctuating forms.
The term variety, again, in comparison
with mere individual differences, is also
�VARIATION UNDER NATURE
applied arbitrarily, and for mere con
venience’ sake.
Guided by theoretical considerations, I
thought that some interesting results might
be obtained in regard to the nature and
relations of the species which vary most,
by tabulating all the varieties in several
well-worked floras. At first this seemed a
simple task; but Mr. H. C. Watson, to
whom I am much indebted for valuable
advice and assistance on this subject, soon
convinced me that there were many diffi
culties, as did subsequently Dr. Hooker,
even in stronger terms. I shall reserve for
my future work the discussion of these
difficulties, and the tables themselves of
the proportional numbers of the varying
species. Dr. Hooker permits me to add
that, after having carefully read my manu
script and examined the tables, he thinks
that the following statements are fairly well
established. The whole subject, however,
treated as it necessarily here is with much
brevity, is rather perplexing, and allusions
cannot be avoided to the “ struggle for
existence,” “divergence of character,” and
other questions, hereaftei- to be discussed.
Alph. de Candolle and others have shown
that plants which have very wide ranges
generally present varieties ; and this might
have been expected, as they become exposed
to diverse physical conditions, and as they
come into competition (which, as we shall
hereafter see, is a far more important
circumstance) with different sets of organic
beings. But my tables further show that,
in any limited country, the species which
are most common—that is, abound most in
individuals, and the species which are most
widely diffused within their own country
(and this is a different consideration from
wide range, and to a certain extent from
commonness)—often give rise to varieties
sufficiently well marked to have been
recorded in botanical works. Hence it is
the most flourishing, or, as they may be
called, the dominant species—those which
range widely over the world, are the most
diffused in their own country, and are the
most . numerous in individuals—which
oftenest produce well-marked varieties, or,
as I consider them, incipient species. And
this, perhaps, might have been anticipated ;
for, as varieties, in order to become in any
degree permanent, necessarily have to
struggle with the other inhabitants of the
country, the species which are already
dominant will be the most likely to yield
offspring, which, though in some slight
degree modified, still inherit those advan
29
tages that enabled their parents to become
dominant over their compatriots.
If the plants inhabiting a country and
described in any Flora be divided into two
equal masses, all those in the larger genera
being placed on one side, and all those in
the smaller genera on the other side, a
somewhat larger number of the very
common and much diffused or dominant
species will be fouud on the side of the
larger genera. This, again, might have
been anticipated; for the mere fact of
many species of the same genus inhabiting
any country shows that there is something
in the organic or inorganic conditions of
that country favourable to the genus ; and,
consequently, we might have expected to
have found in the larger genera, or those
including many species, a large proportional
number of dominant species. ’ But so many
causes tend to obscure this result that I am
surprised that my tables show even a small
majority on the side of the larger genera.
I will here allude to only two causes of
obscurity. Fresh-water and salt-loving
plants have generally very wide ranges
and are much diffused, but this seems to
be connected with the nature of the stations
inhabited by them, and has little or no
relation to the size of the genera to which
the species belong. Again, plants low in
the scale of organisation are generally
much more widely diffused than plants
higher in the scale ; and here again there
is no close relation to the size of the genera.
The cause of lowly-organised plants ranging
widely will be discussed in our chapter on
geographical distribution.
From looking at species as only stronglymarked and well-defined varieties, I was
led to anticipate that the species of the
larger ger.era in each country would oftener
present varieties than the species of the
smaller genera ; for wherever many closelyrelated species (z.<?., species of the same
genus) have been formed, many varieties
or incipient species ought, as a general
rule, to be now forming. Where many
large trees grow we expect to find saplings.
Where many species of a genus have been
formed through variation, circumstances
have been favourable for variation ; and
hence we might expect that the circum
stances would generally be still favourable
to variation. On the other hand, if we
look at each species as a special act of
creation, there is no apparent reason why
more varieties should occur in a group
having many species than in one having
few.
�3°
ON THE ORIGIN OF SPECIES
To test the truth of this anticipation I
have arranged the plants of twelve countries,
and the coleopterous insects of two districts,
into two nearly equal masses, the species
of the larger genera on one side, and those
of the smaller genera on the other side,
and it has invariably proved to be the case
that a larger proportion of the species on
the side of the larger genera present
varieties than on the side of the smaller
genera. Moreover, the species of the
large genera which present any varieties
invariably present a larger average number
of varieties than do the species of the small
genera. Both these results follow when
another division is made, and when all the
smallest genera, with from only one to four.
species, are absolutely excluded from the
tables. These facts are of plain significa
tion on the view that species are only
strongly-marked and permanent varieties ;
for wherever many species of the same
genus have been formed, or where, if we
may use the expression, the manufactory
of species has been active, we ought gene
rally to find the manufactory still in action,
more especially as we have every reason
to believe the process of manufacturing
new species to be a slow one. And this
certainly is the case, if varieties be looked
at as incipient species; for my tables
clearly show as a general rule that, wherever
many species of a genus have been formed,
the species of that genus present a number
of varieties, that is of incipient species
beyond the average. It is not that all
large genera are now varying much, and
are thus increasing in the number of their
species, or that no small genera are now
varying and increasing ; for if this had
been so, it would have been fatal to my
theory ; inasmuch as geology plainly tells
us that small genera have in the lapse of
time often increased greatly in size; and
that large genera have often come to
their maxima, declined, and disappeared.
All that we want to show is, that where
many species of a genus have been formed,
on an average many are still forming ; and
this holds good.
There are other relations between the
species of large genera and their recorded
varieties which deserve notice. We have
seen that there is no infallible criterion by
which to distinguish species and wellmarked varieties ; and in those cases in
which intermediate links have not been
found between doubtful forms naturalists
are compelled to come to a determination
by the amount of difference between them,
judging by analogy whether or not the
amount suffices to raise one or both to the
rank of species. Hence the amount of
difference is one very important criterion
in settling whether two forms should be
ranked as species or varieties. Now Fries
has remarked in regard to plants, and
Westwood in regard to insects, that in
large genera the amount of difference
between the species is often exceedingly
small. I have endeavoured to test this
numerically by averages, and, as far as my
imperfect results go, they confirm the view.
I have also consulted some sagacious and
experienced observers, and, after delibera
tion, they concur in this view. In this
respect, therefore, the species of the larger
genera resemble varieties, more than do the
species of the smaller genera. Or the case
may be put in another way, and it may be
said that in the larger genera, in which a
number of varieties or incipient species
greater than the average are now manu
facturing, many of the species already
manufactured still to a certain extent
resemble varieties, for they differ from each
other by a less than usual amount of
difference.
Moreover, the species of the large genera
are related to each other, in the same
manner as the varieties of any one species
are related to each other. No naturalist
pretends that all the species of a genus are
equally distinct from each other ; they may
generally be divided into sub-genera, or
sections, or lesser groups. As-Fries has
well remarked, little groups of species are
generally clustered like satellites around
certain other species. And what are varie
ties but groups of forms, unequally related
to each other, and clustered round certain
forms—that is, round their parent-species ?
Undoubtedly there is one most important
point of difference between varieties and
species — namely, that the amount of
difference between varieties, when com
pared with each other or with their parent
species, is much less than that between the
species of the same genus. But when we
come to discuss the principle, as I call it, of
Divergence of Character, we shall see how
this may be explained, and how the lesser
differences between varieties will tend to
increase into the greater differences between
species.
There is one other point which seems to
me worth notice. Varieties generally have
much restricted ranges : this statement is
indeed scarcely more than a truism, for if
a variety were found to have a wider range
�VARIATION UNDER NATURE
than that of its supposed parent-species
their denominations ought to be reversed.
But there is also reason to believe that
those species which are very closely allied
to other species, and in so far resemble
varieties, often have much-restricted ranges.
For instance, Mr. H. C. Watson has marked
for me in the well-sifted London Catalogue
of plants (4th edition) 63 plants which are
therein ranked as species, but which he
considers as so closely allied to other
species as to be of doubtful value : these
63 reputed species range on an average
over 6.9 of the provinces into which Mr.
Watson has divided Great Britain. Now,
in this same catalogue, 53 acknowledged
varieties are recorded, and these range
over 7.7 provinces ; whereas, the species to
which these varieties belong range over 14.3
provinces.
So that the acknowledged
varieties have very nearly the same
restricted average range as have those very
closely allied forms marked for me by Mr.
Watson as doubtful species, but which are
almost universally ranked by British
botanists as good and true species.
Finally, then, varieties have the same
general characters as species, for they can
not be distinguished from species—except,
firstly, by the discovery of intermediate
linking forms ; and the occurrence of such
links cannot affect the actual characters of
the forms which they connect; and except,
secondly, by a certain amount of difference,
for two forms, if differing very little, are
generally ranked as varieties, notwith
3i
standing that intermediate linking forms
have not been discovered; but the amount
of difference considered necessary to give
to two forms the rank of species is quite
indefinite. In genera having more than
the average number of species in any
country, the species of these genera have
more than the average number of varieties.
In large genera the species are apt to
be closely but unequally allied together,
forming little clusters round certain species.
Species very closely allied to other species
apparently have restricted ranges. In all
these several respects the species of large
genera present a strong analogy with
varieties. And we can clearly understand
these analogies, if species have once existed
as varieties, and have thus originated;
whereas these analogies are utterly in
explicable if each species has been inde
pendently created.
We have also seen that it is the most
flourishing or dominant species of the
larger genera which on an average vary
most; and varieties, as we shall hereafter
see, tend to become converted into new
and distinct species. The larger genera
thus tend to become larger; and throughout
nature the forms of life which are now
dominant tend to become still more
dominant by leaving many modified and
dominant descendants.
But, by steps
hereafter to be explained, the larger genera
also tend to break up into smaller genera.
And thus the forms of life throughout the
universe become divided into groups sub
ordinate to groups.
Chapter III.
STRUGGLE FOR EXISTENCE
Bears on natural selection—The term used in a
wide sense—Geometrical powers of increase—
Rapid increase of naturalised animals and
plants—Nature of the checks to increase—
Competition universal—Effects of climate—
Protection from the number of individuals—
Complex relations of all animals and plants
throughout nature—Struggle for life most
severe between individuals and varieties of
the same species ; often severe between species
of the same genus—The relation of organism
to organism the most important of all rela
tions.
Before entering on the subject of this
chapter I must make a few preliminary
remarks, to show how the struggle for
existence bears on Natural Selection. It
has been seen in the last chapter that
�32
ON THE ORIGIN OF SPECIES
among organic beings in a state of nature
there is some individual variability; indeed,
I am not aware that this has ever been
disputed. It is immaterial for us whether
a multitude of doubtful forms be called
species or sub-species or varieties ; what
rank, for instance, the two or three hundred
doubtful forms of British plants are entitled
to hold, if the existence of any well-marked
varieties be admitted. But the mere exist
ence of individual variability and of some
few well-marked varieties, though necessary
as the foundation for the work, helps us
but little in understanding how species
arise in nature. How have all those
exquisite adaptations of one part of the
organisation to another part, and to the
conditions of life, and of one distinct
organic being to another being, been per
fected? We see these beautiful co-adaptations most plainly in the woodpecker and
mistletoe ; and only a little less plainly in
the humblest parasite which clings to the
hairs of a quadruped or feathers of a bird ;
in the structure of the beetle which dives
through the water; in the plumed seed
which is wafted by the gentlest breeze ; in
short, we see beautiful adaptations every
where and in every part of the organic
world.
#
Again, it may be asked, how is it that
varieties, which I have called incipient
species, become ultimately converted into
good and distinct species, which in most
cases obviously differ from each other far
more than do the varieties of the same
species ? How do those groups of species,
which constitute what are called distinct
genera, and which differ from each other
more than do the species of the same
genus, arise ? All these results, as we shall
more fully see in the next chapter, follow
from the struggle for life. Owing' to this
struggle for life, any variation, however
slight, a.ndfrom whatever cause proceeding,
if it be in any degree profitable to an indi
vidual of any species, in its infinitely
complex relations to other organic beings
and to external nature, will tend to the
preservation of that individual, and will
generally be inherited by its offspring.
The offspring, also, will thus have a better
chance of surviving, for, of the many indi
viduals of any species which are periodically
born, but a small number can survive. I
have called this principle, by which each
slight variation, if useful, is preserved, by
the term of Natural Selection, in order to
mark its relation to man’s power of selec
tion. We have seen that man by selection
can certainly produce great results, and can
adapt organic beings to his own uses,
through the accumulation of slight but
useful variations, given to him by the hand
of Nature. But Natural Selection, as we
shall hereafter see, is a power incessantly
ready for action, and is as immeasurably
superior to man’s feeble efforts as the
works of Nature are to those of Art.
We will now discuss in a little more
detail the struggle for existence. In my
future work this subject shall be treated, as
it well deserves, at much greater length.
The elder de Candolle and Lyell have
largely and philosophically shown that all
organic beings are exposed to severe com
petition. In regard to plants, no one has
treated this subject with more spirit and
ability than W. Herbert, Dean of Man
chester, evidently the result of his great
horticultural knowledge. Nothing is easier
than to admit in words the truth of the
universal struggle for life, or more difficult
—at least, I have found it so—than con
stantly to bear this conclusion in mind.
Yet, unless it be thoroughly engrained in
the mind, I am convinced that the whole
economy of nature, with every fact on
distribution, rarity, abundance, extinction,
and variation, will be dimly seen or quite
misunderstood. We behold the face of
Nature bright with gladness ; we often see
superabundance of food ; we do not see, or
we forget, that the birds which are idly
singing round us mostly live on insects or
seeds, and are thus constantly destroying
life; or we forget how largely these
songsters, or their eggs, or their nestlings,
are destroyed by birds and beasts of prey ;
we do not always bear in mind that, though
food may be now superabundant, it is not
so at all seasons of each recurring year.
I should premise that I use the term
Struggle for Existence in a large and meta
phorical sense, including dependence of
one being on another, and including (which
is more important) not only the life of the
individual, but success in leaving progeny.
Two canine animals in a time of dearth
may be truly said to struggle with each
other which shall get food and live. But a
plant on the edge of a desert is said to
struggle for life against the drought, though
more properly it should be said to be de
pendent on the moisture. A plant which
annually produces a thousand seeds, of
which on an average only one comes to
maturity, may be more truly said to struggle
with the plants of the same and other kinds
which already clothe the ground. The
�STRUGGLE FOR EXISTENCE
33
mistletoe is dependent on the apple and a
minimum rate of natural increase : it will
few other trees, but can only in a far-fetched
be under the mark to assume that it breeds
sense be said to struggle with these trees,
when thirty years old, and goes on breeding
for, if too many of these parasites grow on
till ninety years old, bringing forth three
the same tree, it will languish and die.
pair of young in this interval: if this be
But several seedling mistletoes, growing
so, at the end of the fifth century there
close together on the same branch, may
would be alive fifteen million elephants,
more truly be said to struggle with each
descended from the first pair.
other. As the mistletoe is disseminated by
But we have better evidence on this
birds, its existence depends on birds ; and
subject than mere theoretical calculations
it may metaphorically be said to struggle
—namely, the numerous recorded cases of
with other fruit-bearing plants, in order to
the astonishingly rapid increase of various
tempt birds to devour and thus disseminate
animals in a state of nature, when circum
its seeds rather than those of other
stances have been favourable to them
plants. In these several senses, which
during two or three following seasons.
pass into each other, I use for convenience’
Still more striking is the evidence from
sake the general term of struggle for exist
our domestic animals of many kinds which
ence.
have run wild in several parts of the world :
A strugglefor existence inevitably follows
if the statements of the rate of increase of
from the high rate at which all organic
slow-breeding cattle and horses in South
beings tend to increase. Every being
America, and latterly in Australia, had not
which during its natural lifetime produces
been well authenticated, they would have
several eggs or seeds must suffer destruc
been incredible. So it is with plants:
tion during some period of its life, and
cases could be given of introduced plants
during some season or occasional year ;
which have become common throughout
otherwise, on the principle of geometrical __ whole islands in a period of less than ten
increase, its numbers would quickly become
years. Several of the plants, such as the
so inordinately great that no country could
cardoon and a tall thistle, now most
support the product. Hence, as more indi
numerous over the wide plains of La Plata,
viduals are produced than can possibly
clothing square leagues of surface almost
survive, there must in every case be a
to the exclusion of all other plants, have
struggle for existence, either one individual
been introduced from Europe ; and there
with another of the same species, or with
are plants which now range in India, as I
the individuals of distinct species, or with
hear from Dr. Falconer, from Cape Comorin
the physical conditions of life. It is the
to the Himalaya, which have been imported
doctrine of Malthus applied with manifold
from America since its discovery. In such
force to the whole animal and vegetable
cases, and endless instances could be given,
kingdoms ; for in this case there can be
no one supposes that the fertility of these
no artificial increase of food and no pru
animals or plants has been suddenly and
dential restraint from marriage. Although
temporarily-increased in any sensible degree.
some species may be now increasing, more
The obvious explanation is that the con
or less rapidly, in numbers, all cannot do
ditions of life have been very favourable,
so, for the world would not hold them.
and that there has consequently been less
There is no exception to the rule that
destruction of the old and young, and that
every organic being naturally increases at
nearly all the young have been enabled to
so high a rate that, if not destroyed, the
breed. In such cases the geometrical ratio
earth would soon be covered by the progeny
of increase, the result of which never fails
of a single pair. Even slow-breeding man
to be surprising, simply explains the extra
has doubled in twenty-five years ; and at
ordinarily rapid increase and wide diffusion
this rate, in a few thousand years, there
of naturalised productions in their new
would literally not be standing room for
homes.
his progeny. Linnaeus has calculated that
In a state of nature almost every'- plant
if an annual plant produced only two seeds
produces seed, and among animals there
and there is no plant so unproductive as
are very few which do not annually pair.
this—and their seedlings next year pro
Hence we may confidently assert that all
duced two, and so on, then in twenty years
plants and animals are tending to increase
there would be a million plants. The
at a geometrical ratio, that all would most
elephant is reckoned the slowest breeder
rapidly stock every station in which they
of all known animals, and I have taken
could anyhow exist, and that the geometrical
some pains to estimate its probable
tendency to increase must be checked by
D
•
�34
ON THE ORIGIN OF SPECIES
destruction at some period of life. Our
number of the species will almost instan
familiarity with the larger domestic animals
taneously increase to any amount.
tends, I think, to mislead us : we see no
The causes which check the natural ten
great destruction falling on them, and
dency of each species to increase in number
we forget that thousands are annually
are most obscure. Look at the most
slaughtered for food, and that in a state
vigorous species : by as much as it swarms
of nature an equal number would have
in numbers, by so much will its tendency
somehow to be disposed of.
to increase be still further increased. We
The only difference between organisms
know not exactly what the checks are in
which annually produce eggs or seeds by
even one single instance. Nor will this
the thousand and those which produce
surprise anyone who reflects how ignorant
extremely few is, that the slow breeders
we are on "this head, even in regard to
would require a few more years to people,
mankind, so incomparably better known
under favourable conditions, a w-hole dis
than any other animal. This subject has
trict, let it be ever so large. The condor
been ably treated by several authors, and
lays a couple of eggs and the ostrich a
I shall, in my future work, discuss some of
score, and yet in the same country the
the checks at considerable length, more
condor may be the more numerous of the
especially in regard to the feral animals of
two : the Fulmar petrel lays but one egg,
South America. Here I will make only
yet it is believed to be the most numerous
a few remarks, just to recall to the reader’s
bird in the world. One fly deposits hundreds
mind some of the chief points. Eggs or
of eggs, and another, like the hippobosca,
very young animals seem generally to suffer
a single one ; but this difference does not
most; but this is not invariably the case.
With plants there is a vast destruction of
determine how many individuals of the two
seeds; but, from some observations which
species can be supported in a district. A
large number of eggs is of some importance . I have made, I believe that it is the seed
to those species which"depend on a rapidly
lings which suffer most from germinating
in ground already thickly stocked with
fluctuating amount of food, for it allows
other plants. Seedlings, also, are destroyed
them rapidly to increase in number. But
in vast numbers by various enemies ; for
the real importance of a large number of
eggs or seeds is to make up for much
instance, on a piece of ground three feet
long and two wide, dug and cleared, and
destruction at some period of Life; and this
where there could be no choking from other
period in the great majority of cases is an
plants, I marked all the seedlings of our
early one. If an animal can in any way
native weeds as they came up, and out of
protect its own eggs or young, a small
the 357 no less than 295 were destroyed,
number may be produced, and yet the
chiefly by slugs and insects. If turf which
average stock be fully kept up; but if many
has long been mown—and the case would
eggs or young are destroyed, many must
be the same with turf closely browsed by
be produced, or the species will become
quadrupeds—be let to grow, the more
extinct. It wrould suffice to-keep up the
vigorous plants gradually kill the less
full number of a tree, which lived on an
vigorous, though fully grown, plants ; thus
average for a thousand years, if a single
out of twenty species growing on a little
seed were produced once in a thousand
plot of turf (three feet by four) nine species
years, supposing that this seed were never
perished from the other species being
destroyed, and could be ensured to ger
allowed to grow up freely.
minate in a fitting place. So that in all
The amount of food for each species of
cases the average number of any animal
course gives the extreme limit to which
or plant depends only indirectly on the
each can increase ; but very frequently it is
number of its eggs or seeds.
not the obtaining food, but the serving as
In looking at Nature, it is most necessary
prey to other animals, which determines
to keep the foregoing considerations always
the average numbers of a species. Thus
in mind—never to forget that every single
there seems to be little doubt that the stock
organic being around us may be said to
of partridges, grouse, and hares on any
be striving to the utmost to increase in
large estate depends chiefly on the destruc
numbers ; that each lives by a struggle at
tion of vermin. If not one head of game
some period of its life ; that heavy destruc
were shot during the next twenty years in
tion inevitably falls-either on the young or
England, and, at the same time, if no
old during each generation or at recurrent
vermin were destroyed, there would, in all
intervals. Lighten any check, mitigate
probability, be less game than at present,
the destruction ever so little, and the
�STRUGGLE FOR EXISTENCE
although hundreds of thousands of game
animals are now annually killed. On the
other hand, in some cases, as with the
elephant and rhinoceros, none are destroyed
by beasts of prey : even the tiger in India
most rarely dares to attack a young elephant
protected by its dam.
Climate plays an important part in deter
mining the average numbers of a species,
and periodical seasons of extreme cold or
drought I believe to be the most effective
of all checks. I estimated that the winter
of 1854-55 destroyed four-fifths of the birds
in my own grounds ; and this is a tremen
dous destruction, when we remember that
ten per cent, is an extraordinarily severe
mortality from epidemics with man. The
action of climate seems at first sight to be
quite independent of the struggle for exis
tence ; but, in so far as climate chiefly acts
in reducing food, it brings on the most
severe struggle between the individuals,
whether of the same or of distinct species,
which subsist on the same kind of food.
Even when climate, for instance extreme
cold, acts directly, it will be the least
vigorous, or those which have got least food
through the advancing winter, which will
suffer most. When we travel from south
to north, or from a damp region to a dry,
we invariably see some species gradually
getting rarer and rarer, and finally disap
pearing ; and the change of climate being
conspicuous, we are tempted to attribute
the whole effect to its direct action. But
this is a false view : we forget that each
species, even where it most abounds, is
constantly suffering enormous destruction
at some period of its life, from enemies or
from competitors for the same place and
food ; and if these enemies or competitors
be in the least degree favoured by any
slight change of climate, they will increase
in numbers, and, as each area is already
fully stocked with inhabitants, the other
species will decrease.
When we travel
southward and see a species decreasing in
numbers, we may feel sure that the cause
lies quite as much in other species being
favoured as in this one being hurt. So it
is when we travel northward, but in a some
what lesser degree, for the number of
species of all kinds, and therefore of com
petitors, decreases northwards ; hence in
going northward, or in ascending a moun
tain, we far oftener meet with stunted
forms, due to the directly injurious action
of climate, than we do in proceeding south
wards or in descending a mountain. When
we reach the Arctic regions,or snow-capped
35
summits, or absolute deserts, the struggle for
life is almost exclusively with the elements.
That climate acts in main part indirectly
by favouring other species we may clearly
see in the prodigious number of plants in
our gardens which can perfectly well endure
our climate, but which never become
naturalised, for they cannot compete with
our native plants nor resist destruction by
our native animals.
When a species, owing to highly favour
able circumstances, increases inordinately
in numbers in a small tract, epidemics—at
least, this seems generally to occur with
our game animals—often ensue ; arid here
we have a limiting check independent of
the struggle for life. But even some of
these so-called epidemics appear'to be due
to parasitic worms, which have frbrn some
cause, possibly in part through facility of
diffusion among the crowded animals,
been di sproportionably favoured : and here
comes in a sort of struggle between the
parasite and its prey.
On the other hand, in many cases a.
large stock of individuals of the same
species, relatively to the numbers of its .
enemies, is absolutely necessary for its pre
servation. Thus we can easily raise plenty
of corn and rape-seed, etc., in dur fields,,
because the seeds are in great excess
compared with the number of birds which
feed on them ; nor can the birds,- though
having a superabundance of food at thisone season, increase in number propor-'
tionally to the supply of seed, as their
numbers are checked during winder; but
anyone who has tried knbws how trouble
some it is to get seed from a few wheat or
other such plants in a garden : I have in
this case lost every single seed. This
view of the necessity of a large stock of
the same species for its preservation
explains, I believe, some singular facts in
nature, such as that of very rare plants
being sometimes extremely abundant in
the few spots where they do occur; and
that of some social plarits being social, that
is, abounding in individuals, even on the
extreme confines of their range. For in
such cases we may believe that a plant
could exist only where the conditions of its
life were so favourable that many could .
exist together, and thus save the species
from utter destruction. I should add that
the good effects of frequent intercrossing,
and the ill effects of close interbreeding,
probably come into play in some of these
cases ; but on this intricate subject I will
not here enlarge.
■
■ ■- .
�36
ON THE ORIGIN OF SPECIES
Many cases are on record showing how
complex and unexpected are the checks
and relations between organic beings which
have to struggle together in the same
country. I will give only a single instance,
which, though a simple one, has interested
me. In Staffordshire, on the estate of a
relation, where I had ample means of inves
tigation, there was a large and extremely
barren heath, which had never been touched
by the hand of man ; but several hundred
acres of exactly the same nature had been
enclosed twenty-five years previously and
planted with Scotch fir. The change in
the native vegetation of the planted part of
the heath was most remarkable, more than
is generally seen in passing from one quite
different soil to another : not only the pro
portional numbers of the heath-plants were
wholly changed, but twelve species of plants
■ (not counting grasses and carices) flourished
in the plantations, which could not be found
on the heath. The effect on the insects
must have been still greater, for six insec
tivorous birds were very common in the
plantations, which were not to be seen on
the heath ; and the heath was frequented
by two or three distinct insectivorous birds.
Here we see how potent has been the
effect of the introduction of a single tree,
nothing whatever else having been done,
with the exception that the land had been
enclosed, so that cattle could not enter.
But how important an element enclosure
is I plainly saw near Farnham, in Surrey.
Here there are extensive heaths, with a
few clumps of old Scotch firs on the distant
hill-tops : within the last ten years large
spaces have been enclosed, and self-sown
firs are now springing up in multitudes,
so close together that all cannot live.
When I ascertained that these young trees
had not been sown or planted, I was so
much surprised at their numbers that I
went to several points of view, whence I
could examine hundreds of acres of the
unenclosed heath, and literally I could not
see a single Scotch fir, except the old
planted clumps. But, on looking closely
between the stems of the heath, I found a
multitude of seedlings and little trees, which
had been perpetually browsed down by the
cattle. In one square yard, at a point
some hundred yards distant from one of
the old clumps, I counted thirty-two little
trees ; and one of them, with twenty-six
rings of growth, had during many years
tried to raise its head above the stems of
the heath, and had failed. No wonder
that, as soon as the land was enclosed, it
became thickly clothed with vigorously
growing young firs. Yet the heath was so
extremely barren and so extensive that no
one would ever have imagined that cattle
would have so t closely and effectually
searched it for food.
Here we see that cattle absolutely deter
mine the existence of the Scotch fir ; but
in several parts of the world insects deter
mine the existence of cattle. Perhaps
Paraguay offers the most curious instance
of this ; for here neither cattle nor horses
nor dogs have ever run wild, though they
swarm southward and northward in a feral
state ; and Azara and Rengger have shown
that this is caused by the greater number
in Paraguay of a certain fly, which lays its
eggs in the navels of these animals when
first born. The increase of these flies,
numerous as they are, must be habitually
checked by some means, probably by birds.
Hence, if certain insectivorous birds (whose
numbers are probably regulated by hawks
or beasts of prey) were to increase in
Paraguay, the flies would decrease—then
cattle and horses would become feral, and
this would certainly greatly alter (as, indeed,
I have observed in parts of South America)
the vegetation : this again would largely
affect the insects ; and this, as we just
have seen in Staffordshire, the insectivorous
birds, and so onwards in ever-increasing
circles of complexity. We began this series
by insectivorous birds, and we have ended
with them. Not that in nature the rela
tions can ever be as simple as this. Battle
within battle must ever be recurring with
varying success ; and yet in the long-run
the forces are so nicely balanced that the
face of nature remains uniform for long
periods of time, though assuredly the
merest trifle would often give the victory
to one organic being over another. Never
theless, so profound is our ignorance, and
so high our presumption, that we marvel
when we hear of the extinction of an organic
being ; and as we do not see the cause, we
invoke cataclysms to desolate the world, or
invent laws on the duration of the forms of
life !
I am tempted to give one more instance
showing how plants and animals, most
remote in the scale of nature, are bound
together by a web of complex relations.
I shall hereafter have occasion to show
that the exotic Lobelia fulgens, in this part
of England, is never visited by insects,
and, consequently, from its peculiar struc
ture, never can set a seed. Many of our
orchidaceous plants absolutely require the
�STRUGGLE FOR EXISTENCE
visits of moths to remove their pollen
masses, and thus to fertilise them. I have
also reason to believe that humble-bees
are indispensable to the fertilisation of the
heartsease (Viola tricolor), for other bees
do not visit this flower. From experiments
which I have lately tried, I have found that
the visits of bees are necessary for the
fertilisation of some kinds of clover; but
humble-bees alone visit the red clover
(Trifolium pratense), as other bees cannot
reach the nectar. Hence I have very little
doubt that, if the whole genus of humblebees became extinct or very rare in
England, the heartsease and red clover
would become very rare, or wholly dis
appear. The number of humble-bees in
any district depends in a great degree on
the number of field-mice, which destroy
their combs and nests ; and Mr. H. New
man, who has long attended to the habits
of humble-bees, believes that “ more than
two-thirds of them are thus destroyed all
over England.” Now the number of mice
is largely dependent, as everyone knows,
on the number of cats ; and Mr. Newman
says: “Near villages and small towns I
have found the nests of humble-bees more
numerous than elsewhere, which I attribute
to the number of cats that destroy the
mice.” Hence it is quite credible that the
presence of a feline animal m large
numbers in a district might determine,
through the intervention first of mice and
then of bees, the frequency of certain
flowers in that district!
In the case of every species, many
different checks, acting at different periods
of .life, and during different seasons or
years, probably come into play ; some one
check or some few being generally the
most potent, but all concur in determining
the average number or even the existence
of the species. In some cases it can be
shown that widely-different checks act on
the same species in different districts.
When we look at the plants and bushes
clothing an entangled bank, we are tempted
to attribute their proportional numbers and
kinds to what we call chance. But how
false a view is this ! Every one has heard
that, when an American forest is cut down,
a very different vegetation springs up ; but
it has been observed that ancient Indian
ruins in the Southern United States, which
must formerly have been cleared of trees,
now display the same beautiful diversity
and proportion of kinds as in the sur
rounding virgin forests. What a struggle
between the several kinds of trees must here
37
have gone on during long centuries, each
annually scattering its seeds by the
thousand ; what war between insect and
insect—between insects, snails, and other
animals with birds and beasts of prey—all
striving to increase and all feeding on each
other or on the trees or theiP seeds and
seedlings, or on the other plants which
first clothed the ground and thus checked
the growth of the trees ! Throw up a
handful of feathers, and all must fall to the
ground according to definite laws; but how
simple is this problem compared to the
action and reaction of the innumerable
plants and animals which have determined,
in the course of centuries, the proportional
numbers and kinds of trees now growing on
the old Indian ruins!
The dependency of one organic being on
another, as of a parasite on its prey, lies
generally between beings remote in the
scale of nature. This is often the case with
those which may strictly be said to struggle
with each other for existence, as in the case
of locusts and grass-feeding quadrupeds.
But the struggle almost invariably will be
most severe between the individuals of the
same species, for they frequent the same
districts, require the same food, and are ex
posed to the same dangers. In the case of
varieties of the same species, the struggle
will generally be almost equally severe, and
we sometimes see the contest soon decided :
for instance, if several varieties of wheat
be sown together, and the mixed seed be
resown, some of the varieties which best
suit the soil or climate, or are naturally the
most fertile, will beat the others and so
yield more seed, and will consequently in a.
few years quite supplant the other varieties.
To keep up a mixed stock of even such
extremely close varieties as the variously
coloured sweet-peas, they must be each
year harvested separately, and the seed
then mixed in due proportion, otherwise the
weaker kinds will steadily decrease in
numbers and disappear. So again with the
varieties of sheep : it has been asserted
that certain mountain-varieties will starve
out other mountain-varieties, so that they
cannot be kept together. The same result
has followed from keeping together different
varieties of the medicinal leech. It may
even be doubted whether the varieties of any
one of our domestic plants or animals have
so exactly the same strength, habits, and
constitution, that the original proportions of
a mixed stock could be kept up for half-adozen generations, if they were allowed to
struggle together, like beings in a state of
�38
ON THE ORIGIN OF SPECIES
nature, and if the seed or young were not
annually sorted.
As species of the same genus have usually,
though by no means invariably, some
similarity in habits and constitution, and
always in structure, the struggle will
generally
more severe between species
■of the same genus, when they come into
competition with each other, than between
.species of distinct genera. We see this in
the recent extension over parts of the
United States of one species of swallow
having caused the decrease of another
species. The recent increase of the missel
thrush in parts of Scotland has caused the
decrease of the song-thrush. How fre
quently we hear of one species of rat taking
the place of another species under the most
different climates 1 In Russia the small
Asiatic cockroach has everywhere driven
before it its great congener. One species
:of charlock will supplant another, and so in
■ other .cases. We can dimly see why the
competition should be most severe between
allied forms, which fill nearly the same
place in the economy of nature; but
probably in no one case could we pre
cisely say why one species has been
victorious over another in the great battle
of life. :
A corollary of the highest importance
may be deduced from the foregoing
remarks—namely, that the structure of
every organic being is related, in the most
essential yet often hidden manner, to that
of all other organic beings with which it
comes, into competition for food or resi
dence, or from which it has to escape, or
on which it preys. This is obvious in the
structure of the teeth and talons of the
tiger ; and in that of the legs and claws of
the parasite which clings to the hair on the
tiger’s body. But in the beautifully plumed
seed of the dandelion, and in the flattened
and fringed legs of the water-beetle, the
relation seems at first confined to the
elements of air and water. Yet the advan
tage of plumed seeds no doubt stands in
the closest relation to the land being
already thickly clothed by other plants ;
so that the seeds may be widely distributed
and fall on unoccupied ground. In the
water-beetle, the structure of its legs, so
well adapted for diving, allows it to com
pete with other aquatic insects, to hunt for
its own prey, and to escape serving as prey
to other animals.
The store of nutriment laid up within the
seeds of many plants seems at first sight to
have no sort of relation to other plants.
But from the strong growth of young plants
produced from such seeds (as peas and
beans), when sown in the midst of long
grass, I suspect that the chief use of the
nutriment in the seed is to favour the
growth of the young seedling while
struggling with other plants ■ growing'
vigorously all around.
Look at a plant in the midst of its range ;
why does it not double or quadruple its
numbers ? We know that it can perfectly
well withstand a little more heat or cold,
dampness or dryness, for elsewhere it ranges
into slightly hotter or colder, damper or
drier, districts. In this case we can clearly
see that, if we wished in imagination to
give the plant the power of increasing in
number, we should have to give it some
advantage over its competitors, or over the
animals which preyed on it. On the con
fines of its geographical range, a change of
constitution with respect to climate would
clearly be an advantage to our plant; but
we have reason to believe that only a few
plants or animals range so far that they
are destroyed by the rigour of the climate
alone. Not until we reach the extreme
confines of life, in the Arctic regions or
on the borders of an utter desert, will com
petition cease. The land maybe extremely
cold or dry, yet there will be competition
between some few species, or between the
individuals of the same species, for the
warmest or dampest spots.
Hence, also, we can see that when a
plant or animal is placed in a new country
among new competitors, though the climate
may be exactly the same as in its former
home, yet the conditions of its life will
generally be changed in an essential
manner. If we wished to increase its
average numbers in its new home, we
should have to modify it in a different way
to what we should have done in its native
country ; for we should have to give it
some advantage over a different set of com
petitors or enemies.
It is good thus to try in our imagination
to give any form some advantage over
another. Probably in no single instance
should we know what to do so as to
succeed. It will convince us of our
ignorance on the mutual relations of all
organic beings ; a conviction as necessary
as it seems to be difficult to acquire. All
that we can do is to keep steadily in mind
that each organic being is striving to
increase at a geometrical ratio; that each
at some period of its life, during some
season of the year, during each generation
�NATURAL SELECTION
or at intervals, has to struggle for life and
to suffer great destruction. When we reflect
on this struggle, we may console ourselves
with the full belief that the war of nature
"*<
1
»
■
39
is not incessant, that no fear is felt, that
death is generally prompt, and that the
vigorous, the healthy, and the happy survive
and multiply.
Chapter IV.
NATURAL SELECTION
Natural Selection—its power compared with
man’s selection—its power on characters of
trifling importance—its power at all ages and
on both sexes—Sexual Selection—On the
-> generality of intercrosses between individuals
of the same species—Circumstances favour- •
able and unfavourable to Natural Selection,
namely, intercrossing, isolation, number of
individuals—Slow action—Extinction caused
by Natural Selection—Divergence of Char
acter, related to the diversity of inhabitants of
any small area, and to naturalisation—Action
of Natural Selection, through Divergence of
Character and Extinction, on the descendants
from a common parent—Explains the Group: ing of all organic beings.
HOW will the struggle for existence, dis
cussed too briefly in the last chapter, act
in regard to variation ? Can the principle
of selection, which we have seen is so
potent in the hands of man, apply in
nature? I think we shall see that it can
act most effectually. Let it be borne
in mind in what an endless number of.
strange peculiarities our domestic produc
tions, and, in a lesser degree, those under
nature, vary; and how strong the hereditary
tendency is. Under domestication, it may
be truly said that the whole organisation
becomes in some degree plastic. Let it
be borne in mind how infinitely complex
and close-fitting are the mutual relations
of all organic beings to each other and to
their physical conditions of life. Can it,
then, be thought improbable, seeing that
variations useful to man have undoubtedly
occurred, that other variations useful in
some way to each being in the great and
complex battle of life should sometimes
occur in the course of thousands of genera
tions ? If such do occur, can we doubt
(remembering that many more individuals
are born than can possibly survive) that
individuals having any advantage, however,
slight, over others would have the best
chance of surviving and of procreating
their kind. On the other hand, we may
feel sure that any variation in the least
degree injurious would be rigidly destroyed.
This preservation of favourable variations
and the rejection of injurious variations I
call Natural Selection. Variations neither
useful nor injurious would not be affected
by natural selection, and would be left a
fluctuating element, as perhaps we see in
the species called polymorphic.
We shall best understand the probable
course of natural selection by taking the
case of a country undergoing some physical
change, for instance, of climate. The pro
portional numbers of its inhabitants would
almost immediately undergo a change,
and some species might become extinct.
We may conclude, from what we have
seen of the intimate and complex manner
in which the inhabitants of each country
are bound together, that any change in the
numerical proportions of some of the
inhabitants, independently of the change
of climate itself, would seriously affect
many of the others. If the country were
open on its borders, new forms would
certainly immigrate, and this, also would
seriously disturb the relations of some of the
former inhabitants. Let it be remembered
how powerful the influence of a single intro
duced tree or mammal has been shown
to be. But in the case of an island, or
of a country partly surrounded by barriers,
into which new and better adapted forms
could not freely enter, we should then have
places in the economy of nature which
would assuredly be better filled up, if some
of the original inhabitants were in some
manner modified ; for, had the area been
open to immigration, these same places
would have been seized on by intruders.
In such case every slight modification
�4°
ON THE ORIGIN OF SPECIES
which in the course of ages chanced to
arise, and which in any way favoured the
individuals of any of the species by better
adapting them to their altered conditions,
would tend to be preserved ; and natural
selection would thus have free scope for the
work of improvement.
We have reason to believe, as stated in
the first chapter, that a change in the con
ditions of life, by specially acting on the
reproductive system, causes or increases
variability; and in the foregoing case the
conditions of life are supposed to have
undergone a change, and this would
manifestly be favourable to natural selec
tion by giving a better chance of profitable
variations occurring ; and, unless profitable
variations do occur, natural selection can
do nothing. Not that, as I believe, any
extreme amount of variability is necessary ;
as man can certainly produce great results
by adding up in any given direction mere
individual differences, so could Nature, but
far more easily, from having incomparably
longer time at her disposal. Nor do I
believe that any great physical change, as
of climate, or any unusual degree of
isolation to check immigration, is actually
necessary to produce new and unoccupied
places for natural selection to fill up by
modifying and improving some of the
varying inhabitants.
For, as all the
inhabitants of each country are struggling
together with nicely-balanced forces, ex
tremely slight modifications in the structure
or habits of one inhabitant would often give
it an advantage over others; and still
further modifications of the same kind
would often still further increase the
advantage. No country can be named in
which all the native inhabitants are now so
perfectly adapted to each other, and to the
physical conditions under which they live,
that none of them could anyhow be
improved ; for in all countries the natives
have been so far conquered by naturalised
productions that they have allowed
foreigners to take firm possession of the
land. And, as foreigners have thus every
where beaten some of the natives, we may
safely conclude that the natives might have
been modified with advantage, so as to have
better resisted such intruders.
As man can produce, and certainly has
produced, a great result by his methodical
and unconscious means of selection, what
may not nature effect ? Man can act only
on external and visible characters : Nature
cares nothing for appearances, except in so
far as they may be useful to any being.
She can act on every internal organ, on
every shade of constitutional difference, on
the whole machinery of life. Man selects
only for his own good ; Nature only for
that of the being which she tends. Every
selected character is fully exercised by her;
and the being is placed under well-suited
conditions of life. Man keeps the natives
of many climates in the same country ; he
seldom exercises each selected character in
some peculiar and fitting manner ; he feeds
a long and a short beaked pigeon on the
same food ; he does not exercise a longbacked or long-legged quadruped in any
peculiar manner; he exposes sheep with
long and short wool to the same climate.
He does not allow the most vigorous males
to struggle for the females. He does not .
rigidly destroy all inferior animals, but
protects during each varying season, as far
as lies in his power, all his productions.
He often begins his selection by some halfmonstrous form ; or at least by some modi
fication prominent enough to catch his eye,
or to be plainly useful to him. Under
Nature, the slightest difference of structure
or constitution may well turn the nicelybalanced scale in the struggle for life, and
so be preserved. How fleeting are the
■ wishes and efforts of man ! how short his
time ! and consequently how poor will his
products be, compared with those accumu
lated by Nature during whole geological
periods. Can we wonder, then, that
Nature’s productions should be far “truer ”
in character than man’s productions ; that
they should be infinitely better adapted to
the most complex conditions of life, and
should plainly bear the stamp of far higher
workmanship ?
It may metaphorically be said that
natural selection is daily and hourly
scrutinising, throughout the world, every
variation, even the slightest ; rejecting that
which is bad, preserving and adding up all
that is good; silently and insensibly
working, whenever and wherever oppor
tunity offers, at the improvement of each
organic being in relation to its organic and
inorganic conditions of life. We see
nothing of these slow changes in progress
until the hand of time has marked the
long lapse of ages, and then so imperfect
is our view into long past geological ages
that we only see that the forms of life are
now different from what they formerly
were.
Although natural selection can act only
through and for the good of each being,
yet characters and structures, which we
�NATURAL SELECTION
are apt to consider as of very trifling
importance, may thus be acted on. When
we see leaf-eating insects green, and bark
feeders mottled-grey, the alpine ptarmigan
white in winter, the red-grouse the colour
of heather, and the black-grouse that of
peaty earth, we must believe that these
tints are of service to these birds and
insects in preserving them from danger.
Grouse, if not destroyed at some period of
their lives, would increase in countless
numbers ; they are known to suffer largely
from birds of prey ; and hawks are guided
by eyesight to their prey—so much so, that
on parts of the Continent persons are
warned not to keep white pigeons, as being
the most liable to destruction. Hence I
can see- no reason to doubt that natural
selection might be most effective in giving
the proper colour to each kind of grouse,
and in keeping that colour, when once
acquired, true and constant. Nor ought
we to think that the occasional destruction
of an animal of any particular colour would
produce little effect: we should remember
how essential it is in a flock of white sheep
to destroy every lamb with the faintest
trace of black. In plants the down on the
fruit and the colour of the flesh are con
sidered by botanists as characters of the
most trifling importance ; yet we hear from
an excellent horticulturist, Downing, that
in the United States smooth-skinned fruits
suffer far more from a beetle, a curculio,
than those with down ; that purple plums
suffer far more from a certain disease than
yellow plums; whereas another disease
attacks yellow-fleshed peaches far more
than those with other coloured flesh. If,
with all the aids of art, these slight differ
ences make a great difference in cultivating
the several varieties, assuredly in a state
of nature, where the trees would have to
struggle with other trees and with a host
of enemies, such differences would effec
tually settle which variety, whether a smooth
or downy, a yellow or purple-fleshed fruit,
should succeed.
In looking at many small points of
difference between species, which, as far
as our ignorance permits us to judge, seem
quite unimportant, we must not forget that
climate, food, etc., probably produce some
slight and direct effect. It is, however, far
more necessary to bear in mind that there
are many unknown laws of correlation of
growth, which, when one part of the organi
sation is modified through variation, and
the modifications are accumulated by
natural selection for the good of the being,
4i
will cause other modifications, often of the
most unexpected nature.
As we see that those variations which
under domestication appear at any parti
cular period of life, tend to reappear in the
offspring at the same period—for instance,
in the seeds of the many varieties of our
culinary and agricultural plants; in the
caterpillar and cocoon stages of the varieties
of the silkworm ; in the eggs of poultry,
and in the colour of the down of their
chickens ; in the horns of our sheep and
cattle when nearly adult—so, in a state of
nature, natural selection will be enabled to
act on and modify organic beings at any
age by the accumulation of variations
profitable at that age, and by their inheri
tance at a corresponding age. If it profit
a plant to have its seeds more and more
widely disseminated by the wind, I can see
no greater difficulty in this being effected
through natural selection than in the
cotton-planter increasing and improving
by selection the down in the pods on his
cotton-trees. Natural selection may modify
and adapt the larva of an insect to a score
of contingencies wholly different from
those which concern the mature insect.
These modifications will no doubt affect,
through the laws of correlation, the struc
ture of the adult; and probably in the case
of those insects which live only for a few
hours, and which never feed, a large part
of their structure is merely the correlated
result of successive changes in the structure
of their larvae. So, conversely, modifica
tions in the adult will probably often affect
the structure of the larva ; but in all cases
natural selection will ensure that modifica
tions consequent on other modifications at
a different period of life shall not be in the
least degree injurious ; for, if they became
so, they would cause the extinction of the
species.
Natural selection will modify the structure
of the young in relation to the parent, and
of the parent in relation to the young. In
social animals it will adapt the structure
of each individual for the benefit of the
community ; if each in consequence profits
by the selected change. What natural
selection cannot do is to modify the struc
ture of one species without giving it any
advantage for the good of another species;
and, though statements to this effect may
be found in works of natural history, I
cannot find one case which will bear inves
tigation. A structure used only once in an
animal’s whole life, if of high importance
to it, might be modified to any extent by
�42
ON THE ORIGIN OF SPECIES
natural selection ; for instance, the great
jaws possessed by certain insects, used
exclusively for opening the cocoon—or the
hard tip to the beak of nestling birds, used
for breaking the egg. It has been asserted
that of the best short-beaked tumbler
pigeons more perish in the egg than are
able to get out of it; so that fanciers assist
in the act of hatching. Now, if nature had
to make the beak of a full-grown pigeon
very short for the bird’s own advantage,
the process of modification would be very
slow, and there would be simultaneously
the most rigorous selection of the young
birds within the egg which had the most
powerful and hardest beaks, for all with
weak beaks would inevitably perish ; or
more delicate and more easily broken
shells might be selected, the thickness of
the shell being known to vary like every
other structure.
Sexual Selection.—Inasmuch as pecu
liarities often appear under domestication
in one sex and become hereditarily attached
to that sex, the same fact probably occurs
under nature, and, if so, natural selection
will be able to modify one sex in its func
tional relations to the other sex, or in
relation to wholly different habits of life in
the two sexes, as is sometimes the case
with insects. And this leads me to say a
few words on what I call Sexual Selection.
This depends, not on a struggle for exis
tence, but on a struggle between the males
for possession of the females ; the result is
not death to the unsuccessful competitor,
but few or no offspring. Sexual selection
is, therefore, less rigorous than natural
selection. Generally, the most vigorous
males, those which are best fitted for their
places in nature, will leave most progeny.
But in many cases victory depends not on
general vigour, but on having special
weapons confined to the male sex. A
hornless stag or spurless cock would have
a poor chance of leaving offspring. Sexual
selection, by always allowing the victor
to breed, might surely give indomitable
courage, length to the spur, and strength
to the wing to strike in the spurred leg, as
well as the brutal Cock-fighter, who knows
well that he can improve his breed by care
ful selection of the best cocks. How low
in the scale of nature the law of battle
descends I know not; male alligators have
been described as fighting, bellowing, and
whirling round, like Indians, in a war
dance, for the possession of the females ;
male salmons have been seen fighting all
day long; male stag-beetles often bear
wounds from the huge mandibles of other
males. The war is, perhaps, severest
between the males of polygamous animals,
and these seem oftenest provided with
special weapons. The males of carnivorous
animals are already well armed ; though
to them and to others special means of
defence may be given through means of
sexual selection, as the mane to the lion,
the shoulder-pad to the boar, and the
hooked jaw to the male salmon ; for the
shield may be as important for victory as
the sword or spear.
Among birds the contest is often of a
more peaceful character. All those who
have attended to the subject believe that
there is the severest rivalry between the
males of many species to attract by singing
the females. The rock-thrush of Guiana,
birds of paradise, and some others, congre
gate ; and successive males display their
gorgeous plumage and perform strange
antics before the females, which, standing
by as spectators, at last choose the most
attractive partner. Those who have closely
attended to birds in confinement well know
that they often take individual preferences
and dislikes : thus Sir R. Heron has
described how one pied peacock was
eminently attractive to all his hen birds.
It may appear childish to attribute any
effect to such apparently weak means : I
cannot here enter on the details necessary
to support thjs view ; but if man can in a
short time give elegant carriage and beauty
to his bantams, according to his standard
of beauty, I can see no good reason to
doubt that female birds, by selecting, during
thousands of generations, the most melo
dious or beautiful males, according to their
standard of beauty, might produce a
marked effect. I strongly suspect that
some well-known laws, with respect to the
plumage of male and female birds, in com
parison with the plumage of the young,
can be explained on the view of plumage
having been chiefly modified by sexual
selection, acting when the birds have come
to the breeding age or during the breeding
season ; the modifications thus produced
being inherited at corresponding ages or
seasons, either by the males alone or by
the males and females ; but I have not
space here to enter on this subject.
Thus it is, as I believe, that when the
males and females of any animal have
the same general habits of life, but differ
in structure, colour, or- ornament, such
differences have been mainly caused by
�NATURAL SELECTION
sexual selection; that is, individual males
have had, in successive generations, some
slight advantage over other males, in their
weapons, means of defence, or charms ; and
have transmitted these advantages to their
male offspring. Yet I would not wish to
attribute all such sexual differences to this
agency ; for we see peculiarities arising and
becoming attached to the male sex in our
domestic animals (as the wattle in male
carriers, horn-like protuberances in the
cocks of certain fowls, etc.), which we
cannot believe to be either useful to the
males in battle or attractive to the females.
We see analogous cases under nature—for
. instance, the tuft of hair on the breast of
the turkey-cock, which can hardly be either
useful or ornamental to this bird ; indeed,
had the tuft appeared under domestication,
it would have been called a monstrosity.
Illustrations of the Action of Natural
Selection.—In order to make it clear how,
as I believe, natural selection acts, I must
beg permission to give one or two
imaginary illustrations. Let us take the
case of a wolf, which preys on various
animals, securing some by craft, some by
strength, and some by fleetness ; and let
us suppose that the fleetest prey—a deer
for instance, had from any change in the
country increased in numbers, or that other
prey had decreased in numbers,' during
that season of the year when the wolf is
hardest pressed for food. I canmnder such
circumstances see no reason to doubt that
the swiftest and slimmest wolves would
have the best chance of surviving, and so
be preserved or selected—provided always
that they retained strength to master their
prey at this or at some other period of the
year, when they might be compelled to
prey on other animals. I can see no more
reason to doubt this than that man can
improve the fleetness of his greyhounds by
careful and methodical selection, or by that
unconscious selection which results from
each man trying to keep the best dogs
without any thought of modifying the
breed.
Even without any change in the pro
portional numbers of the animals on which
our wolf preyed, a cub might be born with
an innate tendency to pursue certain kinds
of prey. Nor can this be thought very
improbable ; for we often observe great
differences in the natural tendencies of our
domestic animals ; one cat, for instance,
taking to catch rats, another mice ; one
cat, according to Mr. St. John, bringing
43
home winged game, another hares ofl
rabbits, and another hunting on marshy
ground and almost nightly catching wood
cocks or snipes. The tendency to catch rats
rather than1 mice is known to be inherited.
Now, if any slight innate change of habit
or of structure benefited an individual wolf,
it would have the best chance of surviving
and of leaving offspring. Some of its
young would probably inherit the same
habits or structure, and by the repetition
of this process a new variety might be
formed which would either supplant or
co-exist with the parent form of wolf. Or,
again, the wolves inhabiting a mountainous
district, and those frequenting the lowlands,
would naturally be forced to hunt different
prey ; and from the continued preservation
of the individuals best fitted for the two
sites two varieties might slowly be formed.
These varieties would cross and blend
where they met ; but to this subject of
intercrossing we shall soon have to return.
I may add that, according to Mr. Pierce,
there are two varieties of the wolf inhabiting
the Catskill Mountains in the United
States—one with a light greyhound-like
form, which pursues deer, and the other
more bulky, with shorter legs, which more
frequently attacks the shepherd’s flocks.
Let us now take a more complex case.
Certain plants excrete a sweet juice, appa
rently for the sake of eliminating something
injurious from their sap : this is effected
by glands at the base of the stipules in
some Leguminoste, and at the back of the
leaf of the common laurel. This juice,
though small in quantity, is greedily sought
by insects. Let us now suppose a little
sweet juice or nectar to be excreted by the
inner bases of the petals of a flower. In
this case insects in seeking the nectar
would get dusted with pollen, and would
certainly often transport the pollen from
one flower to the stigma of another flower.
The flowers of two distinct individuals of
the same species would thus get crossed ;
and the act of crossing, we have good
reason to believe (as will hereafter be more
fully alluded to), would produce very
vigorous seedlings, which consequently
would have the best chance of flourishing
and surviving. Some of these seedlings
would probably inherit the nectar-excreting
power. Those individual flowers which
had the largest glands dr nectaries, and
which excreted most nectar, would be
oftenest visited by insects, and would be
oftenest crossed ; and so in the long run
would gain the upper hand. Those flowers,
�44
ON THE ORIGIN OF SPECIES
also, which had their stamens and pistils
placed, in relation to the size and habits of
the particular insects which visited them,
so as to favour in any degree the transportal
of their pollen from flower to flower, would
likewise be favoured or selected. We
might have taken the case of insects visiting i
flowers for the sake of collecting pollen
instead of nectar ; and as pollen is formed
for the sole object of fertilisation, its destruc
tion appears a simple loss to the plant ;
yet if a little pollen were carried, at first
occasionally and then habitually, by the
pollen-devouring insects from flower to
flower, and a cross thus effected, although
nine-tenths of the pollen were destroyed,
it might still be a great gain to the plant;
.and those individuals which produced more
.and more pollen, and had larger and larger j|
.anthers, would be selected.
When our plant, by this process of the
-•continued preservation or natural selection
of more and more attractive flowers, had
been rendered highly attractive to insects,
they would, unintentionally on their part,
regularly carry pollen from flower to flower;
and that they can most effectually do this
I could easily show by many striking
.instances. I will give only one—-not as a
very striking case, but as likewise illus
trating one step in the separation of the
sexes of plants, presently to be alluded to.
Some holly-trees bear only male flowers,
which have four stamens producing a rather
small quantity of pollen, and a rudimentary
pistil; other holly-trees bear only female
flowers ; these have a full-sized pistil, and
four stamens with shrivelled anthers, in
which not a grain of pollen can be detected.
Having found a female tree exactly sixty
yards from a male tree, I put the stigmas
■of twenty flowers, taken from different
branches, under the microscope, and on
all, without exception, there were pollen
grains, and on some a profusion of pollen.
As the wind had set for several days from
the female to the male tree, the pollen
could not thus have been carried. The
weather had been cold and boisterous, and,
therefore, not favourable to bees ; neverthe
less, every female flower which I examined
had been effectually fertilised by the bees,
accidentally dusted with pollen, having
flown from tree to tree in search of nectar.
But to return to our imaginary case : as
soon as the plant had been rendered so
highly attractive to insects that pollen was
regularly carried from flower to flower,
another process might commence. No,
naturalist doubts the advantage of what
has been called the “ physiological division
of labour”; hence we may believe that it
would be advantageous to a plant to pro
duce stamens alone in one flower or on one
whole plant, and pistils alone in another
flower or on another plant. In plants under
culture and placed under new conditions of
life, sometimes the male organs and some
times the female organs become more or
less impotent: now, if we suppose this to
occur in ever so slight a degree under
nature, then, as pollen is already carried
regularly from flower to flower, and as a
more complete separation of the sexes of
our plant would be advantageous on the
principle of the division of labour, indi
viduals with this tendency more and more
increased would be continually favoured or
selected, until at last a complete separation
of the sexes would be effected.
Let us now turn to the nectar-feeding
insects in our imaginary case: we may
suppose the plant of which we have been
slowly increasing the nectar by continued
selection to be a common plant, and that
certain insects depended in main parton its
nectar for food. I could give many facts,
showing how anxious bees are to save
time ; for instance, their habit of cutting
holes and sucking the nectar at the bases
of certain flowers, which they can, with a
very little more trouble, enter by the
mouth. Bearing such facts in mind, I can
see no reason to doubt that an accidental
deviation in the size and form of the body,
or in the'curvature and length of the
proboscis, etc., far too slight to be appre
ciated by us, might profit a bee or other
insect, so that an individual so characterised
would be able to obtain its food more
quickly, and so have a better chance
of living and leaving descendants. Its
descendants would probably inherit a
tendency to a similar slight deviation of
structure. The tubes of the corollas of
the common red and incarnate clovers
(Trifolium pratense and incarnatum) do
not on a hasty glance appear to differ in
length ; yet the hive-bee can easily suck
the nectar out of the incarnate clover, but
not out of the common red clover, which
is visited by humble-bees alone ; so that
whole fields of the red clover offer in vain
an abundant supply of precious nectar to
the hive-bee. Thus it might be a great
advantage to the hive-bee to have a slightly
longer or differently constructed proboscis.
On the other hand, I have found by experi| ment that the fertility of clover depends on
i bees visiting and moving parts of the
�NATURAL SELECTION
corolla, so as to push the pollen on to the
stigmatic surface. Henc£, again, if humblebees were to become rare in any country,
it might be a great advantage to the red
clover to have a shorter or more deeply
divided tube to its corol^so that the hive
bee could visit its flowers. Thus I can
understand how a flower and a bee might
slowly become, either simultaneously or
one after the other, modified and adapted
in the most perfect manner to each other,
by the continued preservation of individuals
presenting mutual and slightly favourable
deviations of structure.
I am well aware that this doctrine of
natural selection, exemplified in the above
imaginary instances, is open to the same
objections which were at first urged against
Sir Charles Lyell’s noble views on “ the
modern changes of the earth, as illustrative
of geology”; but we now seldom hear the
action, for instance, of the coast-waves,
called a trifling and insignificant cause,
when applied to the excavation of gigantic
valleys or to the formation of the longest
lines of inland cliffs. Natural selection can
act only by the preservation and accumula
tion of infinitesimally small inherited modi
fications, each profitable to the preserved
being ; and as modern geology has almost
banished such views as the excavation of
a great valley by a single diluvial wave, so
will natural selection, if it be a true
principle, banish the belief of the continued
creation of new organic beings, or of any
great and sudden modification in their
structure.
On the Intercrossing of Individuals.—I
must here introduce a short digression. In
the case of animals and plants with
separated sexes, it is of course obvious that
two individuals must always (with the
exception of the curious and not wellunderstood cases of parthenogenesis) unite
for each birth ; but in the case of hermaph
rodites this is far from obvious. Neverthe
less, I am strongly inclined to believe that
with all hermaphrodites two individuals,
either occasionally or habitually, concur for
the reproduction of their kind. This view
was first suggested by Andrew Knight.
We shall presently see its importance ; but
I must here treat the subject with extreme
brevity, though I have the materials pre
pared for an ample discussion. All verte
brate animals, all insects, and some other
large groups of animals, pair for each birth.
Modern research has much diminished the
number of supposed hermaphrodites, and
45
of real hermaphrodites a large number pair;
that is, two individuals regularly unite for
reproduction, which is all that concerns us.
But still there are many hermaphrodite
animals which certainly do not habitually
pair, and a vast majority of plants arc
hermaphrodites. What reason, it may be
asked, is there for supposing in these cases
that two individuals ever concur in repro
duction ? As it is impossible here to enter
on details, I must trust to some general
considerations alone.
In the first place, I have collected so
large a body of facts, showing, in ac
cordance with the almost universal belief of
breeders, that with animals and plants a
cross between different varieties, or between
individuals of the same variety but of
another strain, gives vigour and fertility to
the offspring ; and, on the other hand, that
close interbreeding diminishes vigour and
fertility ; that these facts alone incline me
to believe that it is a general law of nature
(utterly ignorant though we be of the
meaning of the law) that no organic being
self-fertilises itself for an eternity of gene
rations ; but that a cross with another indi
vidual is occasionally—perhaps at very long
intervals—indispensable.
On the belief that this is a law of nature,
we can, I think, understand several large
classes of facts, such as the following,
which on any other view are inexplicable.
Every hybridiser knows how unfavourable
exposure to wet is to the fertilisation of a
flower, yet what a multitude of flowershave
their anthers and stigmas fully exposed to
the weather ! But if an occasional cross be
indispensable, the fullest freedom for the
entrance of pollen from another individual
will explain this state of exposure, more
especially as the plant’s own anthers and
pistil generally stand so close together that
self-fertilisation seems almost inevitable.
Many flowers, on the other hand, have
their organs of fructification closely en
closed, as in the great papilionaceous or
pea-family ; but in several, perhaps in all,
such flowers there is a very curious adapta
tion between the structure of the flower and
the manner in which bees suck the nectar;
for, in doing this, they either push the
flower’s own pollen on the stigma or bring
pollen from another flower. So necessary
are the visits of bees to papilionaceous
flowers that I have found, by experiments
published elsewhere, that their fertility is
greatly diminished if these visits be pre
vented. Now, it is scarcely possible that
bees should fly from flower to flower, and
�46
ON THE ORIGIN OF SPECIES
not carry pollen from one to the other, to
the pollen and stig’matic surface of the
the great good, as I believe, of the plant.
same flower, thqygh placed so close
Bees will act like a camel-hair pencil, and
together, as if for tne very purpose of self
it is quite sufficient just to touch the anthers
fertilisation, should in so many cases be
of one flower and then the stigma of another
mutually useless to each other 1 How
with the same brush to ensure fertilisation;
simply are thes^-ffacts explained on the
but it must not be supposed that bees
view of an occasional cross with a distinct
would thus produce a multitude of hybrids
individual being advantageous or indis
between distinct species; for if you bring
pensable !
on the same brush a plant’s own pollen and
If several varieties of the cabbage, radish,
pollen from another species, the former
ortion, and of some other plants, be allowed
will . have such a prepotent effect that it
to seed near each other, a large majority,
will invariably and completely destroy, as
as I have found, of the seedlings thus
has been shown by Gartner, any influence
raised will turn out mongrels : for instance,
from the foreign pollen.
I raised 233 seedling cabbages from some
When the stamens of a flower suddenly
plants of different varieties growing near
spring towards the pistil, or slowly move
each other, and of these only 78 were true
one after the other towards it, the con
to their kind, and some even of these were
trivance seems adapted solely to ensure
not perfectly true. Yet the pistil of each
self-fertilisation; and no doubt it is useful
cabbage-flower is surrounded not only by
for this end ; but the agency of insects is
its own six stamens, but by those of the
often required to cause the stamens to
many other flowers on the same plant.
spring forward, as Kblreuter has shown to I How, then, comes it that such a vast
be the case with the barberry; and in this I number of the seedlings are mongrelised?
very genus, which seems to have a special
I suspect that it must arise from the pollen
contrivance for self-fertilisation, it is well
of a distinct variety having a prepotent
known that, if closely-allied forms or
effect over a. flower’s own pollen, and that
varieties are planted near each other, it is
this is part of the general law of good being
hardly possible to raise pure seedlings, so
derived from the intercrossing of distinct
largely do they naturally cross. In many
individuals of the same species. When
other cases, far from there being any aids
distinct species are crossed, the case is
for self-fertilisation, there are special con
directly the reverse, for a plant’s own pollen
trivances, as I could show from the writings
is always prepotent over foreign pollen ;
of C. C. Sprengel and from my own obser
but to this subject we shall return in a
vations, which effectuallyprevent the stigma
future chapter.
. receiving pollen from its own flower: for
In the case of a gigantic tree covered
instance, in Lobelia fulgens there is a
with innumerable flowers, it may be objected
really beautiful and elaborate contrivance
that pollen could seldom be carried from
by which every one of the infinitely
tree to tree, and at most only from flower
numerous pollen-granules are swept out of
to flower on the same tree, and that flowers
the conjoined anthers of each flower before
on the same tree can ,be considered as
distinct individuals only in a limited sense.
the stigma of that individual flower is ready
: to receive them ; and as this flower is never
I believe this objection to be valid, but that
nature has largely provided against it by
visited, at least in my garden, by insects,
-it never sets a seed, though, by placing
giving to trees a strong tendency to bear
• pollen from one flower on the stigma of flowers with separated .sexes. When the
sexes are separated, although the male and
another, I raised plenty of seedlings ; and
female flowers may be produced on the
. while another species of Lobelia growing
same tree, we can see that pollen must be
close by, which is visited by bees, seeds
regularly carried from flower to flower ;
freely. In very many other cases, though
and this will give a better chance of pollen
there be no special mechanical contrivance
being occasionally carried from tree to
to prevent the stigma of a flower receiving
tree. That trees belonging to all Orders
its own pollen, yet, as C. C. Sprengel has
have their sexes more often separated than
shown, and as I can confirm, either the
other plants, I find to be the case in this
anthers burst before the stigma is ready for
country; and at my request Dr. Hooker
fertilisation or the stigma is ready before
the pollen of that flower is ready, so that
tabulated the trees of New Zealand, and
Dr. Asa Gray those of. the United States,
-these plants have in fact separated sexes,
and the result was as I anticipated. On
:and njust habitually be crossed. How
the other hand, Dr. Hooker has recently
. strange are these facts ! How strange that
�NATURAL SELECTION
informed me that hl^inds that the rule
does not hold in Australia ; and I have
made these few remarks on the sexes of
trees simply to call attention to the subject.
Turning for a very brief space to animals:
on the land there are ^^hermaphrodites,
as land-mollusca and . earth-worms ; but
these all pair. As yet I have not found a
single case of a terrestrial animal which
fertilises itself. W& can understand this
remarkable fact, which offers so strong a
contrast with terrestrial plants, on the view
of an occasional cross being indispensable,
by considering the medium in which terres
trial animals live, and the nature of the
fertilising element; for we know of no
means, analogous to the action of insects
and of the wind in the case of plants,, by
which an occasional cross could be effected
with terrestrial animals without the con
currence of two individuals. Of aquatic
animals, there are many self-fertilising
hermaphrodites ; but here currents in the
water offer an obvious means for an occa
sional cross. And, as in the case of flowers,
I have as yet failed, after consultation with
one of the highest authorities—namely,
Professor Huxley—to discover a single case
of an hermaphodrite animal with the organs
of reproduction so perfectly enclosed within
the body that access from without and the
occasional influence of a distinct individual
can be shown to be physically impossible.
Cirripedes long appeared to me to present
a case of very great difficulty under this
point of view ; but I have been enabled, by
a fortunate chance, elsewhere to prove that
two individuals, though both are self
fertilising hermaphrodites, do sometimes
cross.
It must have struck most naturalists as
a strange anomaly that in the case of both
animals and plants species of the same
family, and even of the same genus, though
agreeing closely with each other in almost
their whole organisation, yet are not rarely
some of them hermaphrodites and some
of them unisexual. But if, in fact, all
hermaphrodites do occasionally intercross
with other individuals, the difference
between hermaphrodites and unisexual
species, as far as function is concerned,
becomes very small.
From these several considerations, and
from the many special facts which I have
collected, but which I am not here able to
give, I am strongly inclined to suspect that
both in the vegetable and animal kingdoms
an occasional intercross with a distinct
individual is a law of nature. I am well
47
aware that there are, on this view, many
cases of difficulty, some of which I am
trying to investigate. Finally, then, we
may conclude that in many organic beings
a cross between -two individuals^ is an
obvious necessity for each birth ; in many
others it occurs perhaps only at long
intervals ; but in none, as I suspect, can
self-fertilisation go on for perpetuity.'
Circumstances Favourable to Natural
Selection—This, is an extremely intricate
subject. A large amount of inheritable
and diversified variability is favourable, but
I believe mere individual differences suffice
for the work. A large number of indi
viduals, by giving a better chance for the
appearance within any given period of
profitable variations, will compensate for a
lesser amount of variability in each indi
vidual, and is, I believe, an extremely
important element of success. Though
Nature grants vast periods of time for the
work of natural selection, she does not
grant an indefinite period ; for as all
organic beings are striving, it may be said,
to seize on each place in the economy of
nature, if any one species does not become
modified and improved in a corresponding
degree with its competitors, it will soon be
exterminated.
In man’s methodical selection, a breeder
selects for some definite object, and free
intercrossing will wholly stop his work.
But when many men, without intending to
alter the breed, have a nearly common
standard of perfection, and all try to get
and breed from the best animals, much
improvement and modification surely but
slowly follow from this unconscious process
of selection, notwithstanding a large amount
of crossing with inferior animals. Thus it
will be in nature ; for within a confined
area, with some place in its polity not so
perfectly occupied as might be, natural
selection will always tend to preserve all
the individuals varying in the right direc
tion, though in different degrees, so as
better to fill up the unoccupied place. But
if the area be large, its several districts will
almost certainly present different conditions
of life ; and then, if natural selection be
modifying and improving a species in the
several districts, there will be intercrossing
with the other individuals of the same
species on the confines of each. And in
this case the effects of intercrossing can
hardly be counterbalanced by natural
selection always tending to modify all the
individuals in each district in exactly the
�48
ON THE ORIGIN OF SPECIES
same manner to the conditions of each ;
only through the principle of inheritance,
for in a continuous area the physical con
and through natural selection destroying
ditions at least will generally graduate
any which depart from the proper type ;
away insensibly from one district to another.
but if their conditions of life change, and
The intercrossing will most affect those
they undergo modification, uniformity of
animals which unite for each birth, which
character can be^riven to their modified
wander much, and which do not breed at a
offspring solely by natural selection pre
very quick rate. Hence in animals of this
serving the same favourable variations.
nature—for instance, in birds—varieties will
Isolation, also, is an important element
generally be confined to separated countries;
in the process of natural selection. Ina
and this I believe to be the case. In her
confined or isolated area, if not very large,
maphrodite organisms which cross only
the organic and inorganic conditions of
occasionally, and likewise in animals which
life will generally be in a great degree
unite for each birth, but which wander
uniform; so that natural selection will tend
little, and which can increase at a very
to modify all the individuals of a varying
rapid rate, a new and improved variety
species throughout the area in the same
might be quickly formed on any one spot,
manner in relation to the same conditions.
and might there maintain itself in a body,
Intercrosses, also, with the individuals of
so that whatever intercrossing took place
the same species which otherwise would
would be chiefly between the individuals of
have inhabited the surrounding and differ
the same new variety. A local variety,
ently circumstanced districts will be pre
when once thus formed, might subsequently
vented. But isolation probably acts more
slowly spread to other districts. On the
efficiently in checking the immigration of
above principle, nurserymen always prefer
better adapted organisms, after any physical
getting seed from a large body of plants of
change, such as of climate or elevation of
the same variety, as the chance of interthe land, etc.; and thus new places in the
crossingwith othervarieties is thus lessened.
natural economy of the country are left
Even in the case of slow-breeding ani
open for the old inhabitants to struggle for,
mals, which unite for each birth, we must
and become adapted to, through modifica
not overrate the effects of intercrossing in i tions in their structure and constitution.
retarding natural selection ; for I can bring
Lastly, isolation, by checking immigration,
a considerable catalogue of facts showing
and consequently competition, will give
that within the same area varieties of the
time for any new variety to be slowly
same animal can long remain distinct, from
improved; and this may sometimes be of
haunting different stations, from breeding
importance in the production of new species.
at slightly different seasons, or from varie
If, however, an isolated area be very small,
ties of the same kind preferring to pair
either from being surrounded by barriers
together.
or from having very peculiar physical con
ditions, the total number of the individuals
Intercrossing plays a very important
supported on it will necessarily be very
part in nature in keeping the individuals of
the same species, or of the same variety,
small ; and fewness of individuals will
greatly retard the production of new species
true and uniform in character. It will
through natural selection by decreasing
obviously thus act far more efficiently with
those animals which unite for each birth ;
the chance of the appearance of favourable
variations.
but I have already attempted to show that
If we turn to nature to test the truth of
we have reason to believe that occasional
these remarks, and look at any small
intercrosses take place with all animals
isolated area, such as an oceanic island,
and with all plants. Even if these take
although the total number of the species
place only at long intervals, I am convinced
inhabiting it will be found to be small, as
that the young thus produced will gain so
we shall see in our chapter on Geographical
much in vigour and fertility over the off
Distribution ; yet of these species a very
spring from long-continued self-fertilisation,
large proportion are endemic—that is,
that they will have a better chance of sur
have been produced there, and nowhere
viving and propagating their kind ; and
else. Hence an oceanic island at first
thus, in the long run, the influence of
sight seems to have been highly favourable
intercrosses, even at rare intervals, will be
for the production of new species. But we
great. If there exist organic beings which
never intercross, uniformity of character
may thus greatly deceive ourselves, for to
ascertain whether a small isolated area, or
can be retained among them, as long as
a large open area like a continent, has been
their conditions of life remain the same,
�NATURAL SELECTION
most favourable for .the production of neworganic forms, we ought to make the com
parison within equal times; and this we
are incapable of doing.
Although I do not doubt that isolation is
of considerable importance in the produc
tion of new species, on the whole I am
inclined to believe that largeness of area is
of more importanoe, more especially in the
production of species which will prove
capable of enduring for a long period and
of spreading widely. Throughout a great
and open area not only will there be a
better chance of favourable variations
arising from the large number of individuals
of the same species there supported, but
the conditions of life are infinitely complex
from the large number of already existing
species ; and if some of these many species
become modified and improved, others will
have to be improved in a corresponding
degree, or they will be exterminated. Each
new form also, as soon as it has been
much improved, will be able to spread over
the open and continuous area, and will thus
come into competition with many others.
Hence more new places will be formed,
and the competition to fill them will be
more severe, on a large than on a small
and isolated area. Moreover, great areas,
though now continuous owing to oscilla
tions of level, will often have recently
existed in a broken condition, so that the
good effects of isolation will generally, tp a
certain extent, have concurred. Finally, I
conclude that, although small isolated areas
probably have been in some respects highly
favourable for the production of new species,
yet that the course of modification will
generally have been more rapid on large
areas ; and, what is more important, that
the new forms produced on large areas,
which already have been victorious over
many competitors, will be those that will
spread most widely, will give rise to most
new varieties and species, and will thus
play an important part in the changing
history of the organic world.
We can, perhaps, on these views, under
stand some facts which will be again
alluded to in our chapter on Geographical
Distribution ; for instance, that the pro
ductions of the smaller continent of
Australia have formerly yielded, and
apparently are now yielding, before those
of the larger Europaso-Asiatic area. Thus,
also, it is that continental productions have
everywhere become so largely naturalised
on islands. On a small island the race
for life will have been less severe, and
49
there will h ave been less modification
and less extermination. Hence, perhaps,
it comes that the flora of Madeira, according
to Oswald Heer, resembles the extinct
tertiary flora of Europe. All fresh-water
basins, taken together, make a small area
compared with that of the sea or of the
land ; and, consequently, the competition
between fresh-water productions will have
been less severe than elsewhere ; new
forms will have been more slowly formed,
and old forms more slowly exterminated.
And it is in fresh water that we find seven
genera of Ganoid fishes, remnants of a
once preponderant order; and in fresh
water we find some of the most anomalous
forms now known in the world, as the
Ornithorhynchus and Lepidosiren, which,
like fossils, connect to a certain extent
orders now widely separated in the natural
scale. These anomalous forms may almost
be called living fossils ; they have endured
to the present day from having inhabited
a confined area, and from having thus been
exposed to less severe competition.
To sum up the circumstances favourable
and unfavourable to natural selection, as
far as the extreme intricacy of the subject
permits. I conclude, looking to the future,
that for terrestrial productions a large con
tinental area, which will probably undergo
many oscillations of level, and which conse
quently will exist for long periods in a
broken condition, is the most favourable
for the production of many new forms of
life likely to endure tong and to spread
widely. For the area first existed as a
continent, and the inhabitants, at this
period numerous in individuals and kinds,
will have been subjected to very severe
competition. When converted by sub
sidence into large separate islands, there
will still exist many individuals of the same
species on each island : intercrossing on
the confines of the range of each species
will thus be checked : after physical
changes of any kind immigration will be
prevented, so that new places in the polity
of each island will have to be filled up by
modifications of the old inhabitants ; and
time will be allowed for the varieties in
each to become well modified and perfected.
When, by renewed elevation, the islands
shqjl be reconverted into a continental
area, there will again be severe competition:
the most favoured or improved varieties
will be enabled to spread ; there will be
much extinction of the less improved forms,
and the relative proportional numbers of
the various inhabitants of the renewed
E
�5o
ON THE ORIGIN OF SPECIES
continent will again be changed; and
again there will be a fair field for natural
selection to improve still further the inhabi
tants, and thus produce new species.
That natural selection will always act
with extreme slowness I fully admit. Its
action depends on there being places in
the polity of nature which can be better
occupied by some of the inhabitants of the
country undergoing modification of some
kind. • The existence of such places will
often depend on physical changes,-which
are generally very slow, and on the immi
gration of better-adapted forms having
been checked. But the action of natural
selection will probably still oftener depend
on some of the inhabitants becoming slowly
modified, the mutual relations of many
of the other inhabitants being thus dis
turbed. Nothing can be effected unless
favourable variations occur, and variation
itself is apparently always a very slow
process. The process will often be greatly
retarded by free intercrossing. Many will
exclaim that these several causes are amply
sufficient wholly to stop the action of natural
selection. I do not believe so. On the
other hand, I do believe that natural selec
tion always acts very slowly, often only at
long intervals of time, and generally on
only a very few of the inhabitants of the
same region at the same time. I further
believe that this very slow, intermittent
action of natural selection accords perfectly
well with what, geology tells us of the rate
and manner a’t which the inhabitants of
this world have changed.
Slow though the process of selection may
be, if feeble man can do much by his powers
of artificial selection, I can see no limit to
the amount of change, to the beauty and
infinite complexity of the co-adaptations
between all organic beings, one with another
and with their physical conditions of life,
which may be effected in the long course
of time by nature’s power of selection.
Extinction.—This subject will be more
fully discussed in. our chapter on Geology ;
but it must be here alluded to from being
intimately connected with natural selection.
Natural selection acts solely through the
preservation of variations in some way
advantageous, which consequently endure.
But as, from the high geometrical ratio of
increase of all organic beings, each area is
already fully stocked with inhabitants, it
follows that, as each selected and favoured
form increases in number, so will the less
favoured forms decrease and become rare.
Rarity, as geology tells us, is'the precursor
to extinction. We can also see that any
form represented by few individuals will,
during fluctuations in the seasons or in the
number of its enemies, rui^ a good chance
of utter extinction. But we may go further
than this ; for as new forms are continually
and slowly being produced, unless we believe
that the number of specific forms goes on
perpetually and almost indefinitely increas
ing, numbers inevitably must become extinct.
That the number of specific forms has not
indefinitely increased geology shows us
plainly ; and, indeed, we can see reason
why they should not have thus increased,
for the number of places in the polity of
nature is not indefinitely great—not that
we have any means of knowing that any
one region has as yet got its maximum of
species. Probably no region is as yet fully
stocked, for at the Cape of Good Hope,
where more species of plants are crowded
together than in any other quarter of the
world, some foreign plants have become
naturalised, without causing, as far as we
know, the extinction of any natives.
Furthermore, the species which are most
numerous in individuals will have the best
chance of producing within any given period
favourable variations. We have evidence
of this in the facts given in the second
chapter, showing that it is the common
species which afford the greatest number
of recorded varieties, or incipient species.
Hence, rare species will, be less quickly
modified or improved within any given
period, and they will consequently be beaten
in the race for life by the modified descen
dants of the commoner species.
From these several considerations I think
it inevitably follows that, as new species in
the course of time are formed through
natural selection, others will become rarer
and rarer, and finally extinct. The forms
which stand in closest competition with
those undergoing modification and improve
ment will naturally suffer most. And we
have seen in the chapter on the Struggle
for Existence that it is the most closelyallied forms—varieties of the same species,
and species of the same genus or of related
genera—which, from haying nearly the
same structure, constitution, and habits,
generally come into the severest competi
tion with each other. Consequently, each
new variety or species, during the progress
of its formation, will generally press hardest
on its nearest kindred, and tend to exter
minate them. We see the same process
of extermination among our domesticated
�NATURAL SELECTION
productions, through the selection of im
proved forms by man. Many curious in
stances could be given showing how quickly
new breeds of cattle, sheep, and other ani
mals, and varies of flowers, take the place
of older and inferior kinds. In Yorkshire it'
is historically known that the ancient black
cattle were displaced by the long-horns,
and that these “were swept away by the
short-horns” (I quote the words of an
agricultural writer) “ as if by some murder
ous pestilence.”
Divergence of Character.—'The principle
which I have designated by this term is of
high importance on my theory, and explains,
as I believe, several important facts. In
the first place, varieties, even stronglymarked ones, though having somewhat of
the character of species—as is shown by the
hopeless doubts in many cases how to rank
them—yet certainly differ from each other
far less than do good and distinct species.
Nevertheless, according to my view, varieties
are species in the process of formation, or
are, as I have called them, incipient species.
How, then, does the lesser difference
between varieties become augmented’into
the greater difference between species ?
That this does habitually happen we must
infer from most of the innumerable species
throughout nature presenting well-marked
differences; whereas varieties, the supposed
prototypes and parents of future well-marked
species, present slight and ill-defined dif
ferences. Mere chance, as we may call it,
might cause one variety to differ in some
character from its parents, and the offspring
of this variety again to differ from its parent
in the very same character and in a greater
degree; but this alone would never account
for so habitual and large an amount of dif
ference as that between varieties of the same
species and species of the same genus.
As has always been my practice, let us
. seek light on this head from our domestic
productions. We shall-here find some
thing analogous. A fancier is struck ’ by
a pigeon having a slightly shorter beak ;
another fancier is struck by a pigeon
having a rather longer beak; and on the
acknowledged principle that “ fanciers do
not and will not admire a medium standard,
but like extremes,” they both go on (as
has actually occurred with tumbler-pigeons)
choosing and breeding from birds with
longer and longer beaks, or with shorter
and shorter beaks. Again, we may suppose
that at-an early period one man preferred
swifter horses ; another stronger and more
5i
bulky horses. The ea£ly differences would
be very slight; in the course of time, from
the continued selection of swifter horses by
some breeders, and of stronger ones by
others, the differences would become
greater, and would be noted as forming
two sub-breeds; finally, after the lapse of
centuries, the sub-breeds would become
converted into two well-established and
distinct breeds. As the differences slowly
become greater, the inferior animals with
intermediate characters, being neither very
swift nor very strong, will have been
neglected, and will have tended to dis
appear. Here, then, we see in man’s pro
ductions the action of what may be called
the principle of divergence, causing differ
ences, at first barely appreciable, steadily
to increase, and the breeds to diverge in
character both from each other and from
their common parent.
But how, it may be asked, can any analo
gous principle apply in nature ? I believe
it can and does apply most efficiently, from
the simple circumstance that the more
diversified the descendants from any one
species become in structure, constitution,
and habits, by so much will they be better
enabled to seize on many and widely diver
sified places in the polity of nature, and so
be enabled to increase in numbers.
We can clearly see this in the case of
animals with simple habits. Take the case
of a carnivorous quadruped, of which the
number that can be supported in any
country has long ago arrived at its full
average. If its natural powers of increase
be allowed to act, it can succeed in increas
ing (the country not undergoing any change
in its conditions) only by its varying descen
dants seizing on places at present occupied
by other animals : some of them, for instance,
being enabled to feed on new kinds of prey,
either dead or alive ; some inhabiting new
stations, climbing trees, frequenting water,
and some perhaps becoming less car
nivorous. The more diversified in habits
and structure the descendants of our car
nivorous animal became, the more places
they would be enabled to occupy. What
applies to one animal will apply throughout
all time to all animals—that is, if they
vary—for otherwise natural selection can
do nothing. So it will be with plants. It
has been experimentally proved that if a
plot of ground be sown with one species
of grass, and a similar plot be sown with
several distinct genera of grasses, a greater
number of plants and a greater weight of
dry herbage can thus be raised. The same
�52
ON THE ORIGIN OF SPECIES
has been found to hold good when first one
variety and then several mixed varieties of
wheat have been sown on equal spaces of
ground. Hence, if any one species of grass
were to go on varying, and those varieties
were continually selected which differed
from each other in at all the same manner
as distinct species and genera of grasses
differ from each other, a greater number of
individual plants of this species of grass,
including its modified descendants, would
succeed in living on the same piece of
ground. And we well know that each
species and each variety of grass is annually
sowing almost countless seeds, and thus,
as it may be said, is striving its utmost to
increase its numbers. Consequently, I
cannot doubt that in the course of many
thousands of generations the most distinct
varieties of any one species of grass would
always have the best chance of succeeding
and of increasing in numbers, and thus of
supplanting the less distinct varieties ; and
varieties, when rendered very distinct from
each other, take the rank of. species.
The truth of the principle, that the greatest
amount of life can be supported by great
diversification of structure, is seen under
many natural circumstances. In an ex
tremely small area, especially if freely open
to immigration, and where the contest
between individual and individual must be
severe, we always find great diversity in its
inhabitants. For instance, I found that a
piece of turf, three feet by four in size, which
had been exposed for many years to exactly
the same conditions, supported twenty
species of plants, and these belonged to
eighteen genera and to eight orders, which
shows how much these plants differed from
each other. So it is with the plants and
insects on small and uniform islets ; and so
in small ponds of fresh water. Farmers
find that they can raise most food by a
rotation of plants belonging to the most
different orders : nature follows what may
be called a simultaneous rotation. Most
of the animals and plants which live close
round any small piece of ground could live
on it (supposing it not to be in any way
peculiar in its nature), and may be said to
be striving to the utmost to live there ;
but it is seen that, where they come into
the closest competition with each other,
the advantages of diversification of struc
ture, with the accompanying differences of
habit and constitution, determine that the
inhabitants, which thus jostle each other
most closely, shall, as a general rule, belong
to what we call different genera and orders.
The same principle is seen in the natural
isation of plants through man’s agency in
foreign lands. It might have been expected
that the plants which have succeeded in
becoming naturalised in any land would
generally have been closely allied to the
indigenes ; for these are commonly looked
at as specially created and adapted for
their own country. It might, also, perhaps
have been expected that naturalised plants
would have belonged to a few groups more
especially adapted to certain stations in
their new homes. But the case is very
different; and Alph. de Candolle has well
remarked, in his great and admirable work,
that floras gain by naturalisation, propor
tionally with the number of the native
genera and species, far more in new genera
than in new species. To give a single
instance : in the last edition of Dr. Asa
Gray’s Manual of the Flora of the Northern
United States 260 naturalised plants are
enumerated, and these belong to 162 genera.
We thus see that these naturalised plants
are of a highly diversified nature. They
differ, moreover, to a large extent from the
indigenes, for out of the 162 genera no less
than 100 genera are not there indigenous,
and thus a large proportional addition is
made to the genera of these States.
By considering the nature of the plants
or animals which have struggled success
fully with the indigenes of any country,
and have there become naturalised, we
may gain some crude idea in what manner
some of the natives would have to be
modified in order to gain an advantage
over the other natives; and we may, at
least, safely infer that diversification of
structure, amounting to new generic differ
ences, would be profitable to them.
The advantage of diversification in the
inhabitants of the same region is, in fact,
the same as that of the physiological
division of labour in the organs of the
same individual body—a subject so well
elucidated by Milne Edwards. No physio
logist doubts that a stomach adapted to
digest vegetable matter alone, or flesh
alone, draws most nutriment from these
substances. So, in the general economy of
any land, the more widely and perfectly
the animals and plants are diversified for
different habits of life, so will a greater
number of individuals be capable of there
supporting themselves. A set of animals,
with their organisation but little diversified,
could hardly compete with a set more per
fectly diversified in structure. It may be
doubted,for instance, whether the Australian
�NATURAL SELECTION
marsupials, which are divided into groups
differing but little from each other, and
feebly representing, as Mr. Waterhouse
and others have remarked, our carnivorous,
ruminant, and rodent mammals, could suc
cessfully compete with these well-proiiounced orders. In the Australian mammals
we see the process of diversification in an
early and incomplete stage of development.
After the foregoing discussion, which
ought to have been much amplified, we
may, I think, assume that the modified
descendants of anyone species will succeed
by so much the better as they become
more diversified in structure, and are thus
enabled to encroach on places occupied by
other beings. Now let us see how this
principle of benefit being derived from
divergence of character, combined with
the principles of natural selection and of
extinction, will tend to act.
The accompanying diagram1 will aid us
in understanding this rather perplexing
subject. Let A to L represent the species
of a genus large in its own country ; these
species are supposed to resemble each
other in unequal degrees, as is so generally
the case in nature, and as is represented in
the diagram by the letters standing at
unequal distances. I have said a large
genus, because we have seen in the second
chapter that on an average more of the
species of large genera vary than of small
genera ; and the varying species of the
large genera present a greater number of
varieties. We have also seen that the
species, which are the commonest and
the most widely-diffused, vary more than
rare species with restricted ranges. Let
(A) be a common, widely-diffused, and
varying species, belonging to a genus large
in its own country. The little fan of
diverging dotted lines of unequal lengths
proceeding from (A) may represent its
varying offspring. The variations are sup
posed to be extremely slight, but of the
most diversified nature ; they are not
supposed all to appear simultaneously,
but often after long intervals of time ; nor
are they all supposed to endure for equal
periods. Only those variations which are
in some way profitable will be preserved or
naturally selected. And here the importance
of the principle of benefit being derived
from divergence of character comes in;
for this will generally lead to the most
different or divergent variations (repre
sented by the outei' dotted lines) being
1 See diagram at the commencement of volume.
53
preserved and accumulated by natural
selection. When a dotted line reaches
one of the horizontal lines, and is there
marked by a small numbered letter, a
sufficient amount of variation is supposed
to have been accumulated to have formed
a fairly well-marked variety, such as would
be thought worthy of record in a systematic
work.
The intervals between the horizontal
lines in the diagram may represent each a
thousand generations ; but it would have
been better if each had represented ten
thousand generations. After a thousand
generations, species (A) is supposed to have
produced two fairly well-marked varieties—
namely, a1 and zzz1. These two varieties
will generally continue to be exposed to the
same conditions which made their parents
variable, and the tendency to variability is
in itself hereditary; consequently they will
tend to vary, and generally to vary in nearly
the same manner as their parents varied.
Moreover, these two varieties, being only
slightly modified forms, will tend to inherit
those advantages which made their parent
(A) more numerous than most of the other
inhabitants of the same country ; they will
likewise partake of those more general
advantages which made the genus to which
the parent-species belonged a large genus
in its own country. And these circumstances
we know to be favourable to the production
of new varieties.
If, then, these two varieties be variable,
the most divergent of' their variations will
generally be preserved during the next
thousand generations. And after this inter
val variety a1 is supposed in the diagram
to have produced variety zz2, which will,
owing to the principle of divergence, differ
more from (A) than did variety a1. Variety
wz1 is supposed to have produced two varie
ties—namely, m2 and V, differing from each
other, and more considerably from their
common parent (A). We may continue the
process by similar steps for any length of
time; some of the varieties, after each
thousand generations, producing only a
single variety, but in a more and more
modified condition, some producing two or
three varieties, and some failing to produce
any. Thus the varieties or modified des
cendants, proceeding from the common
parent (A), will generally go on increasing in
number and diverging in character. In the
diagram the process is represented up to
the ten-thousandth generation, and under
a condensed and simplified form up to the
fourteen-thousandth generation.
�54
,
ON THE ORIGIN OF SPECIES
But I must here remark that I do not
suppose that the process ever goes on so
regularly as is represented in the diagram,
though in itself made somewhat irregular.
I am far from thinking that the most diver
gent varieties will invariably prevail and
multiply : a medium form may often long
endure, and may or may not produce more
than one modified descendant; for natural
selection will always act according to the
nature of the places which are either un
occupied or not perfectly occupied by other
beings ; and this will depend on infinitely
complex relations. But, as a general rule,
the more diversified in structure the descen
dants from any one species can be rendered,
the more places they will be enabled to seize
on, and the more their modified progeny
will be increased. In our diagram the line
of succession is broken at regular intervals
by small numbered letters marking the
successive forms which have become suffi
ciently distinct to be recorded as varieties.
But these breaks are imaginary, and might
have been inserted anywhere, after intervals
long enough to have allowed the accumula
tion of a considerable amount of divergent
variation.
As all the modified descendants from a
common and widely-diffused species, be
longing to a large genus, will tend to partake
of the same advantages which made their
parent successful in life, they will generally
go on multiplying in number as well as
diverging in character : this is represented
in the diagram by the several divergent
branches proceeding from (A). The modi
fied offspring from the later and more highly
improved branches in the lines of descent
will, it is probable, often take the place of,
and so destroy, the earlier and less improved
branches : this is represented in the diagram
by some of the lower branches not reaching
to the upper horizontal lines. In some cases
I do not doubt that the process of modifica
tion will be confined to a single line of
descent, and the number of the descendants
will not be increased ; although the amount
of divergent modification may have been
increased in the successive generations.
This case would be represented in the
diagram if all the lines proceeding from
(A) were removed, excepting that from aT
to <zra. In the same way, for instance, the
English race-horse and English pointer
have apparently both gone on slowly diverg
ing in character from their original stocks,
without either having given off any fresh
branches or races.
After ten thousand generations, species
(A) is supposed to have produced three
forms, a10,/10, and ot10, which, from having
diverged in charactei' during the successive
generations, will have come to differ largely,
but perhaps unequally, from each other
and from their common parent. If we
suppose the amount of change between
each horizontal line in our diagram to be
excessively small, these three forms may
still be only well-marked varieties; or they
may have arrived at the doubtful category
of sub-species ; but we have only to suppose
the steps, in the process of modification to
be more numerous or greater in amount, to
convert these three forms into well-defined
species : thus the diagram illustrates the
steps by which the small differences dis
tinguishing varieties are increased into the
larger differences distinguishing species.
By continuing the same process for a
greater number of generations (as shown in
the diagram in a condensed and simplified
manner) we get eight species, marked by
the letters between aP and z/z14, all des
cended from (A). Thus, as I believe,
species are multiplied and genera are
formed.
In a large genus it is probable that more
than one species would vary. In the dia
gram I have assumed that a second species
(I) has produced, by analogous steps, after
ten thousand generations, either two wellmarked varieties (w10 and 2'10) or two species,
according to the amount of change supposed
to be represented between the horizontal
lines. After fourteen thousand generations,
six new species, marked by the letters nP to
.s'14, are supposed to have been produced.
In each genus the species, which are
already extremely different in character,
will generally tend to produce the greatest
number of modified descendants; for these
will have the best chance of filling new
and widely different places in the polity of
nature : hence in the diagram I have chosen
the extreme species (A), and the nearly
extreme species (I), as those which have
largely varied, and have given rise to new
varieties and species. The other nine
species (marked by* capital letters) of our
original genus may for a long period con
tinue to transmit unaltered descendants ;
and this is shown in the diagram by the
dotted lines not prolonged far upwards
from want of space.
But during the process of modification,
represented in the diagram, another of our
principles, namely that of extinction, will
have played an important part. As in
each fully-stocked country natural selection
�NATURAL SELECTION
necessarily acts by the selected form having
some advantage in the struggle for life
over other forms, there will be a constant
tendency in the improved descendants of
any one species to supplant and exterminate
in each stage of descent their predecessors
and their original parent. For it should
be remembered that the competition will
generally be most severe between those
forms which are most nearly related to each
other in habits, constitution, and structure.
Hence all the intermediate forms between
the earlier and later states, that is between
the less and more improved state of a
species, as well as the original parent
species itself, will generally tend to become
extinct. So it probably will be with many
whole collateral lines of descent, which will
be conquered by later and improved lines
of descent. If, however, the modified off
spring of a species get into some distinct
country, or become quickly adapted to
some quite new station, in which child and
parent do not come into competition, both
may continue to exist.
If, then, our diagram be assumed to
represent a considerable amount of modifi
cation, species (A) and all the earlier
varieties will have become extinct, having
been replaced by eight new species (k?14 to
zzz14); and (I) will have been replaced by
six (w14 to .s’14) new species.
But we may go further than this. The
original species of our genus were supposed
to resemble each other in unequal degrees,
as is so generally the case in nature ; species
(A) being more nearly related to B, C, and
D than to the other species; and species
(I) more to G, H, K, L, than to the others.
These two species (A) and (I) were also
supposed to be very common and widely
diffused species, so that they must originally
have had some advantage over most of the
other species of the genus. Their modified
descendants, fourteen in number at the
fourteen-thousandth generation, will pro
bably have inherited some of the same
advantages : they have also been modified
and improved in a diversified manner at
each stage of descent so as to have become
adapted to many related places in the
natural economy of their country. It seems,
therefore, to me extremely probable that
they will have taken the places of, and thus
exterminated, not only their parents (A)
and (I), but likewise some of the original
species which were most nearly related to
their parents. Hence very few of the
original species will have transmitted
offspring to the fourteen-thousandth genera
55
tion. We may suppose that only one (F)
of the two species which were least closely
related to the other nine original species
has transmitted descendants to this late
stage of descent.
The new species in our diagram des
cended from the original eleven species
will now be fifteen in number. Owing to
the divergent tendency of natural selection,
the extreme amount of difference in charac
ter between species zz14 and 2-14 will be much
greater than that between the most different
of the original eleven species. The new
species, moreover, will be allied to each
other in a widely different manner. Of the
eight descendants from (A) the three
marked zz14, y14, /I4, will be nearly related
from having recently branched off from
a10; Z>14 and/'4, from having diverged at an
earlier period from a5, will be in some
degree distinct from the three first-named
species ; and, lastly, c>14, F4, and m14 will be
nearly related one to the other, but, from
having diverged at the first commencement
of the process of modification, will be widely
different from the other five species, and
may constitute a sub-genus, or even a
distinct genus.
The six descendants from (I) will form
two sub-genera, or even genera. But as
the original species (I) differed largely from
(A), standing nearly at the extreme points
of the original genus, the six descendants
from (I) will, owing to inheritance alone,
differ considerably from the eight descen
dants from (A) ; the two groups, moreover,
are supposed to have gone on diverging
in different directions. The intermediate
species, also (and this is a very important
consideration), which connected the original
species (A) and (I), have all become, except
ing (F), extinct, and have left no descendants.
Hence the six new species descended from
(I), and the eight descended from (A), will
have to be ranked as very distinct genera,
or even as distinct sub-families.
Thus it is, as I believe, that two or more
genera are produced by descent with
modification, from two or more species of
the same genus. And the two or more
parent-species are supposed to have des
cended from some one species of an earlier
genus. In our diagram this is indicated
by the broken lines beneath the capital
letters converging in sub-branches down
wards towards a single point ; this point
representing a single species, the supposed
single parent of our several new sub-genera
and genera.
It is worth while to reflect for a moment
�56
ON THE ORIGIN OF SPECIES
on the character of the new species F14,
which is supposed not to have diverged
much in character, but to have retained
the form of (F) either unaltered or altered
only in a slight degree. In this case, its
affinities to the other fourteen new species
will be of a curious and circuitous nature.
Having descended from a form which
stood between the two parent-species (A)
and (I), now supposed to be extinct and
unknown, it will be in some degree inter
mediate in character between the two
groups descended from these species. But
as these two groups have gone on diverging
in character from the type of their parents,
the new species (f14) will not be directly
intermediate between them, but rather
between types of the two groups ; and
every naturalist will be able to bring some
such case before his mind.
In the diagram each horizontal line has
hitherto been supposed to represent a
thousand generations, but each may repre
sent a million or hundred million genera
tions, and likewise a section of the succes
sive strata of the earth’s crust, including
extinct remains. We shall, when we come
to our chapter on Geology, have to refer
again to this subject, and I think we shall
then see that the diagram throws light on
the affinities of extinct beings, which,
though generally belonging to the same
orders, or families, or genera, with those
now living, yet are often, in some degree,
intermediate in character between existing
groups ; and we can understand this fact,
for the extinct species lived at very ancient
epochs when the branching lines of descent
had diverged less.
I see no reason to limit the process of
modification, as now explained, to the
formation of genera alone. If, in our
diagram, we suppose the amount of change
represented by each successive group of
diverging dotted lines to be very great, the
forms marked a14 to/I4, those marked <J14 and
/I4, and those marked <914 to z«14, will form
three very distinct genera. We shall also
have two very distinct genera descended
from (I); and as these latter two genera,
both from continued divergence of character
and from inheritance from a different parent,
will differ widely from the three genera
descended from (A), the two little groups
of genera will form two distinct families,
or even orders, according to the amount
of divergent modification supposed to be
represented in the diagram. And the two
new families, or orders, will have descended
from two species of the original genus ;
and these two species are supposed to have
descended from one species of a still more
ancient and unknown genus.
We have seen that in each country it is the
species of the larger genera which oftenest
present varieties or incipient species. This,
indeed, might have been expected ; for,
as natural selection acts through one
form having some advantage over other
forms in the struggle for existence, it
will chiefly act on those which already
have some advantage ; and the largeness
of any group shows that its species have
inherited from a common ancestor some
advantage in common. Hence, the struggle
for the production of new and modified
descendants will mainly lie between the
larger groups, which are all trying to
increase in number. One large group will
slowly conquer another large group, reduce
its numbers, and thus lessen its chance of
further variation and improvement. Within
the same large group the later and more
highly perfected sub-groups, from branching
out and seizing on many new places in the
polity of nature, will constantly tend to
supplant and destroy the earlier and less
improved sub-groups. Small and broken
groups and sub-groups will finally disappear.
Lool^jng to the future, we can predict that
the groups of organic beings which are
now large and triumphant, and which are
least broken up—that is, which as yet have
suffered least extinction—will for a long
period continue to increase. But which
groups will ultimately prevail no man can
predict; for we well know that many groups,
formerly most extensively developed, have
now become extinct. Looking still more
remotely to the future, we may predict that,
owing to the continued and steady increase
of the larger groups, a multitude of smaller
groups will become utterly extinct, and
leave no modified descendants ; and, con
sequently, that of the species living at one
period, extremely few will transmit descen
dants to a remote futurity. I shall have to
return to this subject in the chapter on
Classification, but I may add that on this
view of extremely few of the more ancient
species having transmitted descendants,
and on the view of all the descendants of
the same species making a class, we can
understand how it is that there exist but
very few classes in each main division
of the animal and vegetable kingdoms.
Although extremely few of the most ancient
species may now have living and modified
descendants, yet at the most remote geo
logical period the earth may have been as
�NATURAL SELECTION
well peopled with many species of many
genera, families, orders, and classes as at
the present day.
Summary of Chapter.— If, during the long
course of ages and under varying condi
tions of life, organic beings vary at all in
the several parts of their organisation, and
I think this cannot be disputed ; if there
be, owing to the high geometrical ratio of
increase of each species, a severe struggle
for life at some age, season, or year, and
this certainly cannot be disputed; then,
considering the infinite complexity of the
relations of all organic beings to each other
and to their conditions of existence, causing
an infinite diversity in structure, constitu
tion, and habits, to be advantageous to
them, I think it would be a most extra
ordinary fact if no variation ever had
occurred useful to each being’s own welfare,
in the same manner as so many variations
have occurred useful to man. But if varia
tions useful to any organic being do occur,
assuredly individuals thus characterised will
have the best chance of being preserved in
the struggle for life; and from the strong
principle of inheritance they will tend to
produce offspring similarly characterised.
This principle of preservation I have called,
for the sake of brevity, Natural Selection ;
and it leads to the improvement of each
creature in relation to its organic and in
organic conditions of life.
Natural selection, on the principle of
qualities being inherited at corresponding
ages, can modify the egg, seed, or young,
as easily as the adult. Among many animals
sexual selection will give its aid to ordinary
selection, by assuring to the most vigorous
and best adapted males the greatest number
of offspring. Sexual selection will also give
characters useful to the males alone in their
struggles with other males.
Whether natural selection has really thus
acted in nature, in modifying and adapting
the various forms of life to their several
conditions and stations, must be judged of
by the general tenor and balance of
evidence given in the following chapters.
But we already see how it entails extinction ;
and how largely extinction has acted in the
world’s history geology plainly declares.
Natural selection also leads to divergence
of character ; for more living beings can
be supported on the same area the more
they diverge in structure, habits, and con
stitution, of which we see proof by looking
to the inhabitants of any small spot or to
naturalised productions. Therefore, during
57
the modification of the descendants of any
one species, and during the incessant
struggle of all species to increase in num
bers, the more diversified these descendants
become, the better will be their chance of
succeeding in the battle for life. Thus the
small differences distinguishing varieties of
the same species steadily tend to increase
till they come to equal the greater differ
ences between species of the same genus,
or even of distinct genera.
We have seen that it is the common, the
widely-diffused, and widely-ranging species
belonging to the larger genera which
vary most ; and these tend to transmit to
their modified offspring that superiority
which now makes them dominant in their
own countries. Natural selection, as has
just been remarked, leads to divergence of
character and to much extinction of the
less improved and intermediate forms of
life. On these principles, I believe, the
nature of the affinities of all organic beings
may be explained. It is a truly, wonderful
fact—the wonder of which we are apt to
overlook from familiarity—that all animals
and all plants throughout all time and space
should be related to each other in group
subordinate to group in the manner which
we everywhere behold—namely, varieties
of the same species most closely related
together, species of the same genus less
closely and unequally related together,
forming sections and sub-genera, species of
distinct genera much less closely related,
and genera related in different degrees,
forming sub-families, families, orders, sub
classes, and classes. The several subor
dinate groups in any class cannot be ranked
in a single file, but seem rather to be
clustered round points, and these round
other points, and so on in almost endless
cycles. On the view that each species has
been independently created, I can see no
explanation of this great fact in the classi
fication of all organic beings ; but, to the
best of my judgment, it is explained through
inheritance and the complex action of
natural selection, entailing extinction and
divergence of character, as we have seen
illustrated in the diagram.
The affinities of all the beings of the
same class have sometimes been repre
sented by a great tree. I believe this simile
largely speaks the truth. The green and
budding twigs may represent existing
species ; and those produced during each
former year may represent the long succes
sion of extinct species. At each period of
growth all the growing twigs have tried to
�58
ON THE ORIGIN OF SPECIES
branch out on all sides, and to overtop and
kill the surrounding twigs and branches,
in the same manner as species and groups
of species have tried to overmaster other
species in the great battle for life. The
limbs divided into great branches, and
these into lesser and lesser branches, were
themselves once, when the tree was small,
budding twigs ; and this connection of the
former and present buds by ramifying
branches may well represent the classifica
tion of all extinct and living species in
groups subordinate to groups. Of the
many twigs which flourished when the tree
was a mere bush only two: or three, now
grown into great branches, yet survive and
bear all the other branches ; so with the
species which lived during long-past geolo
gical periods, very few now have living and
modified descendants. From the first
growth of the tree, many a limb and branch
has decayed and dropped off; and these
lost branches of various sizes may repre
sent those whole orders, families, and
genera which have now no living represen
tatives, and which are known to us only
from having been found in a fossil state.
As we here and there see a thin straggling
branch springing from a fork low down in
a tree, and which by some chance has been
favoured and is still alive on its summit, so
we occasionally see an animal like the
Ornithorhynchus or Lepidosiren, which in
some small degree connects by its affinities
two large branches of life, and which has
apparently been saved from fatal competi
tion by having inhabited a protected
station. As buds give rise by growth to
fresh buds, and these, if vigorous, branch
out and overtop on all sides many a feebler
branch, so by generation I believe it has
been with the great Tree of Life, which
fills with its dead and broken branches the
crust of the earth, and covers the surface
with its ever branching and beautiful rami
fications.
Chapter V.
LAWS OF VARIATION
Effects of external conditions—Use and disuse,
combined with natural selection ; organs of
flight and of vision—Acclimatisation—Correla
tion of growth—Compensation and economy
of growth—False correlations—Multiple, rudi
mentary, and lowly organised structure variable
—Parts developed in an unusual manner are
highly variable : specific characters more
variable than generic: secondary sexual cha
racters variable—Species of the same genus
vary in an analogous manner—Reversions to
long-lost characters—Summary.
I have hitherto sometimes spoken as if
the variations—-so common and multiform
in organic beings under domestication, and
in a lesser degree in those in a state of
nature—had been due to chance. This, of
course, is a wholly incorrect expression,
but it serves to acknowledge plainly our
ignorance of the cause of each particular
variation. Some authors believe it to be
as much the function of the reproductive
system to produce individual differences,
or very slight deviations of structure, as to
make the child like its parents. But the
much greater variability, as well as the
greater frequency of monstrosities under
domestication or cultivation than under
nature, leads me to believe that deviations
of structure are in some way due to the
nature of the conditions of life to which the
parents and their more remote ancestors
have been exposed during several genera
tions. I have remarked in the first chapter
—but a long catalogue of facts which
cannot be here given would be necessary
to show the truth of the remark—that the
reproductive system is eminently susceptible
to changes in the conditions of life; and
to this system being functionally disturbed
in the parents I chiefly attribute the varying
or plastic condition of the offspring. The
male and female sexual elements seem to
be affected before that union takes place
which is to form a new being. In the case
of “ sporting ” plants, the bud, which in its
earliest condition does not apparently differ
essentially from an ovule, is alone affected.
�LAWS OF VARIATION
But why, because the reproductive system
is disturbed, this or that part should vary
more or less we are profoundly ignorant.
Nevertheless, we can here and there dimly
catch a faint ray of light, and we may feel
sure that there must be some cause for
each deviation of structure, however slight.
How much direct effect difference of
climate, food, etc., produces on any being
is extremely doubtful. My impression is
that the effect is extremely small in the
case of animals, but perhaps rather more
in that of plants. We may, at least, safely
conclude that such influences cannot have
produced the many striking and complex
co-adaptations of structure between one
organic being and another which we see
everywhere throughout nature. Some little
influence may be attributed to climate, food,
etc. : thus, E. Forbes speaks confidently
that shells,at their southern limit, and when
living in shallow water, are more brightly
coloured than those of the same species
further north or from greater depths. Gould
believes that birds of the same species are
more brightly coloured under a clear atmos
phere than when living on islands or near
the coast. So with insects, Wollaston is
convinced that residence near the sea
affects their colours. Moquin-Tandon gives
a list of plants, which, when growing near
the sea-shore, have their leaves in some
degree fleshy, though not elsewhere fleshy.
Several other such cases could be given.
The fact of varieties of one species, when
they range into the zone of habitation of
other species, often acquiring in a very
slight degree some of the characters of
such species, accords with our view that
species of all kinds are only well-marked
and permanent varieties. Thus the species
of shells which are confined to tropical
and shallow seas are generally brightercoloured than those confined to cold and
deeper seas. The birds which are confined
to continents are, according to Mr. Gould,
brighter-coloured than those of islands.
The insect-species confined to sea-coasts,
as every collector knows, are often brassy
or lurid. Plants which live exclusively on
the sea-side are very apt to have fleshy
leaves. He who believes in the creation of
each species will have to say that this
shell, for instance, was created with bright
colours for a warm sea ; but that this other
shell became bright-coloured by variation
when it ranged into warmer or shallower
waters.
When a variation is of the slightest use.
to a being, we cannot tell how much of it
59
to attribute to the accumulative action of
natural selection, and how much to the
conditions of life. Thus, it is well known
to furriers that animals of the same species
have thicker and better fur the more
severe the climate is under which they have
lived ; but who can tell how much of this
difference may be due to the warmest-clad
individuals having been favoured and
preserved during many generations, and
how much to the direct action of the
severe climate ? for it would appear that
climate has some direct action on the
hair of our domestic quadrupeds.
Instances could be given of the same
variety being produced under conditions of
life as different as can well be conceived ;
and, on the other hand, of different varieties
being produced from the same species
under the- same conditions. Such facts
show how indirectly the conditions of life
act.
Again, innumerable instances are
known to every naturalist of species
keeping true, or not varying at all, although
living under the most opposite climates.
Such considerations as these incline me to
lay very little weight on the direct action
of the conditions of life. Indirectly, as
already remarked, they seem to play an
important part in affecting the reproductive
system, and in thus inducing variability ;
and natural selection will then accumulate
all profitable variations, however slight,
until they become plainly developed and
appreciable by us.
Effects of Use and Disuse.—From the
facts alluded to in the first chapter, I think
there can be little doubt that use in our
domestic animals strengthens and enlarges
certain parts, and disuse diminishes them ;
and that such modifications are inherited.
Under free nature we can have no
standard of comparison by which to judge
of the effects of long-continued use or
disuse, for we know not the parent forms ;
but many animals have structures which
can be explained by the effects of disuse.
As Professor Owen has remarked, there is
no greater anomaly in nature than, a bird
that cannot fly; yet there are several in
this state. The logger-headed duck of
South America can only flap along the
surface of the water, and has its wings in
nearly the same condition as the domestic
Aylesbury duck. As the larger ground
feeding birds seldom take flight except to
escape danger, I believe that the nearly
wingless condition of several birds which
now inhabit . or have lately inhabited
�6o
ON THE ORIGIN OF SPECIES
several oceanic islands, tenanted by no
beast of prey, has been caused by disuse.
The ostrich, indeed, inhabits continents
and is exposed to danger from which it
cannot escape by flight, but by kicking it
can defend itself from enemies, as well as
any of the smaller quadrupeds. We may
imagine that the early progenitor of the
ostrich had habits like those of a bustard,
and that, as natural selection increased in
successive generations the size and weight
of its body, its legs were used more and its
wings less, until they became incapable of
flight.
Kirby has remarked (and I have observed
the same fact) that the anterior tarsi, or
feet, of many male dung-feeding beetles
are very often broken off; he examined
seventeen specimens in his own collection,
and not one had even a relic left. In the
Onites apelies the tarsi are so habitually
lost that the insect has been described as
not having them. In some other genera
they are present, but in a rudimentary con
dition. In the Ateuchus or sacred beetle
of the Egyptians they are totally deficient.
There is not sufficient evidence to induce
me to believe that mutilations are ever in
herited ; and I should prefer explaining the
entire absence of the anterior tarsi in
Ateuchus, and their rudimentary condition
in some other genera, by the long-continued
effects of disuse in their progenitors ; for,
as the tarsi are almost always lost in many
dung-feeding beetles, they must be lost
early in life, and therefore cannot be much
used by these insects.
In some cases we might easily put down
to disuse modifications of structure which
are wholly, or mainly, due to natural selec
tion. Mr. Wollaston has discovered the
remarkable fact that 200 beetles out of the
550 species inhabiting Madeira are so far
deficient in wings that they cannot fly; and
that of the twenty-nine endemic genera
no less than.twenty-three genera have all
their species in this condition ! Several
facts—namely, that beetles in many parts of
the world are frequently blown to sea and
perish ; that the beetles in Madeira, as
observed by Mr. Wollaston, lie much con
cealed, until the wind lulls and the sun
shines; that the proportion of wingless
beetles is larger on the exposed Desertas
than in Madeira itself; and especially the
extraordinary fact, so strongly insisted on
by Mr. Wollaston, of the almost entire
absence of certain large groups of beetles,
elsewhere excessively numerous, and which
groups have habits of life almost necessi
tating frequent flight : these several con
siderations have made me believe that the
wingless condition of so many Madeira
beetles is mainly due to the action of
natural selection, but combined probably
with disuse. For during thousands of suc
cessive generations each individual beetle
which flew least, either from its wings
having been ever so little less perfectly
developed or from indolent habit, will have
had the best chance of surviving from not
being blown out to sea ; and, on the other
hand, those beetles which most readily took
to flight would oftenest have been blown
to sea, and thus have been destroyed.
The insects in Madeira which are not
ground-feeders, and which, as the flower
feeding coleoptera and lepidoptera, must ■
habitually use their wings to gain their sub
sistence, have, as Mr. Wollaston suspects,
their wings not at all reduc d, but even
enlarged. This is quite compatible with
the action of natural selection. For, when
a new insect first arrived on the island, the
tendency of natural selection to enlarge or
to reduce the wings would depend on
whether a greater number of individuals
were saved by successfully battling with the
winds, or by giving up the attempt and
rarely or never flying. As with mariners
shipwrecked near a coast, it would have
been better for the good swimmers if they
had been able to swim still further, whereas
it would have been better for the bad
swimmers if they had not been able to
swim at all, and had stuck to the wreck.
The eyes of moles and of some burrow
ing rodents are rudimentary in size, and in
some cases are quite covered up by skin
and fur. This state of the eyes is probably
due to gradual reduction from disuse, but
aided perhaps by natural selection. In
South America a burrowing rodent, the
tuco-tuco, or Ctenomys, is even more sub
terranean in its habits than the mole ; and
I was assured by a Spaniard who had often
caught them that they were frequently
blind ; one which I kept alive was certainly
in this condition, the cause, as appeared on
dissection, having been inflammation of
the nictitating membrane. As frequent in
flammation of the eyes must be injurious
to any animal, and as eyes are certainly not
indispensable to animals with subterranean
habits, a reduction in their size, with the
adhesion of the eye-lids and growth of fur
over them, might in such case be an advan*
tage; and, if so, natural selection would con
stantly aid the effects of disuse.
It is well known that several animals,
�LAWS OF VARIATION
belonging to the most different classes,
which inhabit the caves of Styria and of
Kentucky are blind. In some of the crabs
the foot-stalk for the eye remains, though
the eye is gone ; the stand for the telescope
is there, though the telescope with its
glasses has been lost. As it is difficult to
imagine that eyes, though useless, could be
in any way injurious to animals living in
darkness, I attribute their loss wholly to
disuse. In one of the blind animals—
namely, the cave-rat—the eyes are of
immense size ; and Professor Silliman
thought that it regained, after living some
days in the light, some slight power of
vision. In the same manner as in Madeira
the wings of some of the insects have been
enlarged, and the wings of others have
been reduced by natural selection aided by
use and disuse, so in the case of the cave
rat natural selection seems to have
struggled with the loss of light and to have
increased the size of the eyes ; whereas with
all the other inhabitants of the caves
disuse by itself seems to have done its
work.
It is difficult to imagine conditions of
life more similar than deep limestone
caverns under a nearly similar climate ;
so that, on the common view of the blind
animals having been separately created for
the American and European caverns, close
similarity in their organisation and affini
ties might have been expected ; but, as
Schiodte and others have remarked, this is
not the case, and the cave-insects of the
two continents are not more closely allied
than might have been anticipated from the
general resemblance of the other inhabi
tants of North America and Europe. On
my view, we must suppose that American
animals, having ordinary powers of vision,
slowly migrated by successive generations
from the outer world into the deeper and
deeper recesses of the Kentucky caves, as
did European animals into the caves of
Europe. We have some evidence of this
gradation of habit; for, as Schiodte remarks,
“animals not far remote from ordinary
forms prepare the transition from light to
darkness. Next follow those that are con
structed for twilight ; and, last of all, those
destined for total darkness.” By the time
that an animal had reached, after number
less generations, the deepest recesses,
disuse will on this view have more or less
perfectly obliterated its eyes, and natural
selection will often have effected other
changes, such as an increase in the length
of the antennae or palpi, as a compensa
61
tion for blindness. Notwithstanding such
modifications, we might expect still to see
in the cave-animals of America affinities to
the other inhabitants of that continent, and
in those of Europe to the inhabitants of
the European continent. And this is the
case with some of the American cave
animals, as I hear from Professor Dana ;
and some of the European cave-insects are
very closely allied to those of the surround
ing country. It would be most difficult to
give any rational explanation of the
affinities of the blind cave-animals to the
other inhabitants of the two continents on
the ordinary view of their independent
creation. That several of the inhabitants
of the caves of the Old and the New
Worlds should be closely related we
might expect from the well-known relation
ship of most of their other productions.
Far from feeling any surprise that some of
the cave-animals should be very anomalous,
as Agassiz has remarked in regard to the
blind fish, the Amblyopsis, and as is the
case with the blind Proteus with reference
to the reptiles of Europe, I am only
surprised that more wrecks of ancient life
have not been preserved, owing to the less
severe competition to which the inhabitants
of these dark abodes will probably have
been exposed.
Acclimatisation.—Habit is hereditary
with plants, as in the period of flowering,
in the amount of rain requisite for seeds to
germinate, in the time of sleep, etc.; and
this leads me to say a few words on
acclimatisation. As it is extremely common
for species of the same genus to inhabit
very hot and very cold countries, and as I
believe that all the species of the same
genus have descended from a single .
parent, if this view be correct, acclimati
sation must be readily effected during longcontinued descent. It is notorious that
each species is adapted to the climate of
its own home : species from an arctic, or
even from a temperate, region cannot
endure a tropical climate, or conversely.
So, again, many succulent plants cannot
endure a damp climate. But the degree
of adaptation of species to the climates
under which they live is often overrated.
We may infer this from our frequent in
ability to predict whether or not an im
ported plant will endure our climate, and
from the number of plants and animals
brought from warmer countries which here
enjoy good health. We have reason to
believe that species in a state of nature are
�62
ON THE ORIGIN OF SPECIES
limited in their ranges by the competition
of other organic beings quite as much as,
or more than, by adaptation to particular
climates. But whether or not the adapta
tion be generally very close, we have
evidence, in the case of some few plants,
of their becoming, to a certain extent,
naturally habituated to different tempera
tures, or becoming acclimatised : thus the
pines and rhododendrons, raised from seed
collected by Dr. Hooker from trees growing
at different heights on the Himalaya, were
found in this country to possess different
constitutional powers of resisting cold.
Mr. Thwaites informs me that he has
observed similar facts in Ceylon, and analo
gous observations have been made by
Mr. H. C. Watson on European species of
plants brought from the Azores to England.
In regard to animals, several authentic
cases could be given of species within
historical times having largely extended
their range from warmer to cooler latitudes,
and conversely ; but we do not positively
know that these animals were strictly
adapted to their native climate, but in all
ordinary cases we assume such to be the
case; nor do we know that they have
subsequently become acclimatised to their
new homes.
As I believe that our domestic animals
were originally chosen by uncivilised men
because they were useful and bred readily
under confinement, and not because they
were subsequently found capable of farextended transportation, I think the com
mon and extraordinary capacity in our
domestic animals of not only withstanding
the most different climates, but of being
perfectly fertile (a far severer test) under
them, may be used as an argument that a
large proportion of other animals, now in a
state of nature, could easily be brought to
bear widely different climates. We must
not, however, push the foregoing argument
too far, on account of the probable origin of
some of our domestic animals from several
wild stocks: the blood, for instance, of a
tropical and arctic wolf or wild dog may
perhaps be mingled in our domestic breeds.
The rat and mouse cannot be considered
as domestic animals, but they have been
transported by man to many parts of the
world, and now have a far wider range
than any other rodent, living free under
the cold climate of Faroe in the north and
of the Falklands in the south, and on many
islands in the torrid zones. Hence I am in
clined to look at adaptation to any special
climate as a quality readily grafted on an
innate wide flexibility of constitution, which
is common to most animals. On this view,
the capacity of enduring the most different
climates by man himself and by his domes
tic animals, and such facts as that former
species of the elephant and rhinoceros
were capable of enduring a glacial climate,
whereas the living species are now all
tropical or sub-tropical in * their habits,
ought not to be looked at as anomalies,
but merely as examples of a very common
flexibility of constitution, brought, under
peculiar circumstances, into play.
How much of the acclimatisation of
species to any peculiar climate is due to
mere habit, and how much to the natural
selection of varieties having different in
nate constitutions, and how much to both
means combined, is a very obscure ques
tion. That habit or custom has some
influence I must believe, both from analogy,
and from the incessant advice giyen in
agricultural works, even in the ancient En
cyclopaedias of China, to be very cautious in
transposing animals from one district to
another; for it is* not likely that man
should have succeeded in selecting so
many breeds and sub-breeds with consti-'
I tutions specially fitted for their own
j districts : the result must, I think, be due
i to habit. On the other hand, I can see no
reason to doubt that natural selection will
continually tend to preserve those indi
viduals which are born with constituI, tions best adapted to their native countries.
In treatises on many kinds of cultivated
plants, certain varieties are said to with
stand certain climates better than others :
this is very strikingly shown in works on
.fruit trees published in the United States,
in which certain varieties are habitually
recommended for the northern and others
for the southern States ; and, as most of
these varieties are of recent origin, they
cannot owe their constitutional differences
to habit. The case of the Jerusalem
artichoke, which is never propagated by
seed, and of which consequently new
varieties have not been produced, has even
been advanced—for it is now as tender as
ever it was—as proving that acclimatisa
tion cannot be effected ! The case, also of
the kidney-bean has been often cited for a
similar purpose, and with much greater
weight; but until some one will sow,
during a score of generations, his kidney
beans so early that a very large proportion
are destroyed by frost, and then collect
seed from the few survivors, with care to
prevent accidental crosses, and then again
�LAWS OF VARIATION
get seed from these seedlings, with the
same precautions, the experiment cannot
be said to have been even tried. Nor let
it be supposed that no differences in the
constitution of seedling kidney-beans ever
appear, for an account has been published
how much more hardy some seedlings
appeared to be than others.
On the whole, I think we may conclude
that habit, use, and disuse have, in some
cases, played a considerable part in the
modification of the constitution, and of the
structure of various organs ; but that the
effects of use and disuse have often been
largely combined with, and sometimes
overmastered by, the natural selection of
innate variations.
Correlation of Growth.—I mean by this
expression that the whole organisation is
so tied together during its growth and
development that when slight variations
in any one part occur, and are accumulated
through natural selection, other parts
become modified. This is a very impor
tant subject, most imperfectly understood.
The most obvious case is that modifications
accumulated solely for the good of the
young or larva will, it may safely be con
cluded, affect the structure of the adult;
in the same manner as any malconformation affecting the early embryo seriously
affects the whole organisation of the adult.
The several parts of the body which are
homologous, and which, at an early
embryonic period, are alike, seem liable to
vary in an allied manner : we see this in
the right and left sides of the body
varying in the same manner; in the front
and hind legs, and even in the jaws and
limbs, varying together, for the lower jaw
is believed to be homologous with the
limbs. These tendencies, I do not doubt,
may be mastered more or less completely
by natural selection : thus a family of stags
once existed with an antler only on one
side ; and if this had been of any great use
to the breed, it might probably have been
rendered permanent by natural selection.
Homologous parts, as has been remarked
by some authors, tend to cohere ; this is
often seen in monstrous plants; and
nothing is more common than the union of
homologous parts in normal structures, as
the union of the petals of the corolla into
a tube. Hard parts seem to affect the
form of adjoining soft parts ; it is believed
by some authors that the diversity in the
shape of the pelvis in birds causes the
remarkable diversity in the shape of their
kidneys. Others believe that the shape of
the pelvis in the human mother influences
by pressure the shape of the head of the
child. In snakes, according to Schlegel,
the shape of the body and the manner of
swallowing determine the position of
several of the most important viscera.
The nature of the bond of correlation is
very frequently quite obscure. M. Is.
Geoffroy St. Hilaire has forcibly remarked
that certain malconformations very fre
quently, and that others rarely, coexist,
without our being able to assign any
reason. What can be more singular than
the relation between blue eyes and deafness
in cats, and the tortoise-shell colour with
the female sex ; the feathered feet and
skin between the outer toes in pigeons, and
the presence of more or less down on the
young birds when first hatched, with the
future colour of their plumage ; or, again,
the relation between the hair and teeth in
the naked Turkish dog, though here pro
bably homology comes into play ? With
respect to this latter case of correlation, I
think it can hardly be accidental, that if we
pick out the two orders of mammalia which
are most abnormal in their dermal covering,
viz. Cetacea (whales) apd Edentata (armadilloes, scaly ant-eaters, etc.), that these are
likewise the most abnormal in their teeth.
I know of no case better adapted to show
the importance of the laws of correlation
in modifying important structures, inde
pendently of utility and, therefore, of natural
selection, than that of the difference be* tween the outer and inner flowers in some
Compositous and Umbelliferous plants.
Every one knows the difference in the ray
and central florets of, for instance, the
daisy; and this difference is often accom
panied with the abortion of parts of the
flower. But in some Compositous plants
the seeds also differ in shape and sculpture;
and even the ovary itself, with its accessory
parts, differs, as has been described by
Cassini. These differences have been at
tributed by some authors to pressure, and
the shape of the seeds in the ray-florets in
some Compositae countenances this idea;
but in the case of the corolla of the Umbelliferse it is by no means, as Dr. Hooker
informs me, in species with the densest
heads that the inner and outer flowers most
frequently differ.
It might have been
thought that the development of the ray
petals by drawing nourishment from certain
other parts of the flower had caused their
abortion ; but in some Compositae there is
I a difference in the seeds of the outer and
�64
ON THE ORIGIN OF SPECIES
inner florets without any difference in the
corolla. Possibly, these several differences
may be connected with some difference in
the flow of nutriment towards the central
and external flowers ; we know, at least,
that in irregular flowers those nearest to
the axis are oftenest subject to peloria, and
become regular. I may add, as an instance
of this and of a striking case of correlation,
that I have recently observed in some
garden pelargoniums that the central
flower of the truss often loses the patches
of darker colour in the two upper petals ;
and that when this occurs the adherent
nectary is quite aborted ; when the colour
is absent from only one of the two upper
petals, the nectary is only much shortened.With respect to the difference in the
corolla of the central and exterior flowers of
a head or umbel, I do not feel at all sure
that C. C. Sprengel’s idea, that the ray
florets serve to attract insects whose agency
is highly advantageous in the fertilisation
of plants of these two orders, is so far
fetched as it may at first appear ; and if it
be advantageous, natural selection might
have come into play. But in regard to the
differences both in the internal and external
structure of the seeds which are not always
correlated with any differences in the flowers,
it seems impossible that they can be in any
way advantageous to, the plant ; yet in the
Umbellifeme these differences are of such
apparent importance—the seeds being in
some cases, according to Tausch, orthospermous in the exterior flowers and ccelospermous in the central flowers—that the
elder De Candolle founded his main divi
sions of the order on analogous differences.
Hence we see that modifications of struc
ture, viewed by systematists as of high
value, may be wholly due to unknown laws
of correlated growth, and without being, as
far as we can see, of the slightest service
to the species.
We may often falsely attribute to cor
relation of growth structures which are
common to whole groups of species, and
which in truth are simplydue to inheritance ;
for an ancient progenitor may have ac
quired through natural selection some
one modification in structure, and, after
thousands of generations, some other and
independent modification ; and these two
modifications, having been transmitted to a
whole group of descendants with diverse
habits, would naturally be thought to be
correlated in some necessary manner. So,
again, I do not doubt that some apparent
correlations, occurring throughout whole
orders, are entirely due to the manner
alone in which natural selection can act.
For instance, Alph. De Candolle has
remarked that winged seeds are never
found in fruits which do not open : I shall
explain the rule by the fact that seeds
could not gradually become winged
through natural selection, except in fruits
which opened ; so that the individual
plants producing seeds which were a
little better fitted to be wafted further
might get an advantage over those
producing seed less fitted for dispersal ;
and this process could not possibly go on
in fruit which did not open.
The elder Geoffroy and Goethe pro
pounded, at about the same period, their
law of compensation or balancement of
growth ; or, as Goethe expressed it, “ in
order to spend on one side, nature is
forced to economise on the other side.” I
think this holds true to a certain extent
with our domestic productions : if nourish
mentflows to one part or organ in excess, it
rarely flows, at least in excess, to another
part ; thus it is difficult to get a cow to
give much milk and to fatten readily. The
same varieties of the cabbage do not yield
abundant and nutritious foliage and a
copious supply of oil-bearing seeds. When
the seeds in our fruits become atrophied,
the fruit itself gains largely in size and
quality. In our poultry a large tuft of
feathers on the head is generally accom
panied by a diminished comb, and a large
beard by diminished wattles. With species
in a state of nature it can hardly be
maintained that the law is of universal
application ; but many good observers,
more especially botanists, believe in its
truth. I will not, however, here give any
instances, for I see hardly any way of
distinguishing between the effects, on the
one hand, of a part being largely developed
through aatural selection and another and
adjoining part being reduced by this same
process or by disuse, and, on the other
hand, the actual withdrawal of nutriment
from one part owing to the excess of growth
in another and adjoining part.
I suspect, also, that some of the cases of
compensation which have been advanced,
and likewise some other facts, may be
merged under a more general principle—
namely, that natural selection is continu
ally trying to economise in every part of
the organisation. If under changed condi
tions of life a structure before useful
becomes less useful, any diminution, how
ever slight, in its development, will be
�LA WS OF VARIA TION
seized on by natural selection, for it will
profit the individual not to have its nutri
ment wasted in building up a useless
structure. I can thus only understand a
fact with which I was much struck when
examining cirripedes, and of which many
other instances could be given—namely,
that when a cirripede is parasitic within
another, and is thus protected, it loses more
or less completely its own shell or carapace.
This is the case with the male Ibla, and in
a truly extraordinary manner with the
Proteolepas ; for the carapace in all other
cirripedes consists of the three highlyimportant anterior segments of the head
enormously developed and furnished with
great nerves and muscles ; but in the
parasitic and
protected
Proteolepas
the whole anterior part of the head is
reduced to the merest rudiment attached
to the basis of the prehensile antennae.
Now, the saving of a large and complex
structure, when rendered superfluous by
the parasitic habits of the Proteolepas,
though effected by slow steps, would be a
decided advantage to each successive
individual of the species; for in the
struggle for life to which every animal is
exposed each individual Proteolepas would
have a better chance of supporting itself,
by less nutriment being wasted in develop
ing a structure now become useless.
Thus, as I believe, natural selection will
always succeed in the long run in reducing
and saving every part of the organisation,
as soon as it is rendered superfluous,
without by any means causing some other
part to be largely developed in a corre
sponding degree. And, conversely, that
natural selection may perfectly well suc
ceed in largely developing any organ,
without requiring as a necessary com
pensation the reduction of some adjoining
part.
It seems to be a rule, as remarked by
Is. Geoffroy St. Hilaire, both in varieties
and in species, that when any part or
organ is repeated many times in the struc
ture of the same individual (as the vertebrae
in snakes and the stamens in polyandrous
flowers) the number is variable ; whereas
the number of the same part or organ,
when it occurs in lesser numbers, is con
stant. The same author and some botanists
have further remarked that multiple parts
are also very liable to variation in structure.
Inasmuch as this “vegetative repetition,”
to use Professor Owen’s expression, seems
to be a sign of low organisation, the fore
going remark seems connected with the
65
very general opinion of naturalists, that
beings low in the scale of nature are more
variable than those which are higher. I
presume that lowness in this case means
that the several parts of the organisation
have been but little specialised for par
ticular functions ; and as long as the same
part has to perform diversified work, we
can perhaps see why it should remain
variable—that is, why natural selection
should have preserved or rejected each
little deviation of form less carefully than
when the part has to serve for one special
purpose alone—in the same way that a
knife which has to cut all sorts of things
may be almost any shape ; while a tool
for some particular object had better be of
some particular shape. Natural selection,
it should never be forgotten, can act on
each part of each being solely through
and for its advantage.
Rudimentary parts, it has been stated
by some authors, and I believe with truth,
are apt to be highly variable. We shall
have to recur to the general subject of
rudimentary and aborted organs ; and I
will here only add that their variability
seems to be owing to their uselessness,
and therefore to natural selection having
no power to check deviations in their
structure. Thus rudimentary parts are left
to the free play of the various laws of
growth, to the effects of long-continued
disuse, and to the tendency to reversion.
A part developed in any species in an
extraordinary degree or manner, in com
parison with the same part in allied species,
tends to be highly variable.—Several years
ago I was much struck with a .remark,
nearly to the above effect, published by
Mr. Waterhouse. I infer also from an
observation made by Professor Owen, with
respect to the length of the arms of the
ourang-outang, that he has come to a
nearly similar conclusion. It is hopeless
to attempt to convince any one of the
truth of this proposition without giving
the long array of facts which I have
collected, and which cannot possibly be
here introduced.
I can only state my
conviction that it is a rule of high gene
rality. I am aware of several causes of
error, but I hope that I have made due
allowance for them. It should be under
stood that the rule by no means applies to
any part, however unusually developed,
unless it be unusually developed in com
parison with the same part in closely-allied
species. Thus, the bat’s wing is a most
�66
ON THE ORIGIN OF SPECIES
abnormal structure in the class mammalia;
but the rule would not here apply, because
there is a whole group of bats having
wings ; it would apply only if some one
species of bat had its wings developed
in some remarkable manner in comparison
with the other species of the same genus.
The rule applies very strongly in the case
of secondary sexual characters, when dis
played in any unusual manner.
The
term, secondary sexual characters, used by
Hunter, applies to characters which are
attached to one sex, but are not directly
connected with the act of reproduction.
The rule applies to males and females ;
but as females more rarely offer remarkable
secondary sexual characters, it applies
more rarely to them. The rule being so
plainly applicable in the case of secondary
sexual characters may be due to the great
variability of these characters, whether or
not displayed in any unusual manner—ot
which fact I think there can be little doubt.
But that our rule is not confined to
secondary sexual characters is clearly
shown in the case of hermaphrodite
cirripedes ; and I may here add that I
particularly attended to Mr. Waterhouse’s
remark, while investigating this Order,
and I am fully convinced that the rule
almost invariably holds good with
cirripedes. I shall, in my future work,
give a list of the more remarkable cases ; I
will here only briefly give one, as it illus
trates the rule in its largest application.
The opercular valves of sessile cirripedes
(rock barnacles) are, in every sense of the
word, very important structures, and they
differ extremely little even in different
genera; but in the several species of one
genus, Pyrgoma, these valves present a
marvellous amount of diversification, the
homologous valves in the different species
being sometimes wholly unlike in shape ;
and the amount of variation in the indi
viduals of several of the species is so great
that it is no exaggeration to state that the
varieties differ more from each other in the
characters of these important valves than
do other species of distinct genera.
As birds within the sam.e country vary
in a remarkably small degree, I have
particularly attended to them, and the rule
seems to me certainly to hold good in this
class. I cannot make out that it applies to
plants, and this would seriously have
shaken my belief in its truth, had not the
great variability in plants made it par
ticularly difficult to compare their relative
degrees of variability.
When we see any part or organ
developed in a remarkable degree or
manner in any species, the fair presump
tion is that it is of high importance to that
species ; nevertheless, the part in this case
is eminently liable to variation. Why
should this be so ? On the view that each
species has been independently created,
with all its parts as we now see them, I can
see no explanation. But on the view that
groups of species have descended from
other species, and have been modified
through natural selection, I think we can
obtain some light. In our domestic
animals, if any part, or the whole animal,
be neglected, and no selection be applied,
that part (for instance, the comb in the
Dorking fowl) or the whole breed will
cease to have a nearly uniform character.
The breed will then be said to have
degenerated. In rudimentary organs, and
in those which have been but little
specialised for any particular purpose, and
perhaps in polymorphic groups, we see a
nearly parallel natural case ; for in such
cases natural selection either has not or
cannot come into full play, and thus the
organisation is left in a fluctuating con
dition. But what here more especially
concerns us is that in our domestic
animals those points, which at the present
time are undergoing rapid change by
continued selection, are also eminently
liable to variation. Look at the breeds of
the pigeon ; see what a prodigious amount
of difference there is in the beak of the
different tumblers, in the beak and wattle
of the different carriers, in the carriage and
tail of our fantails, etc., these being the
points now mainly attended to by English
fanciers.
Even in the sub-breeds, as
in the short-faced tumbler, it is notoriously
difficult to breed them nearly to perfection,
and frequently individuals are born which
depart widely from the standard. There
may be truly said to be a constant struggle
going on between, on the one hand, the
tendency to reversion to a less modified
state, as well as an innate tendency to
further variability of all kinds ; and, on the
other hand, the power of steady selection
to keep the breed true. In the long run
selection gains the day, and we do not
expect to fail so far as to breed a bird as
coarse as a common tumbler from a good
short-faced strain. But as long as selec
tion is rapidly going on there may always
be expected to be much variability in the
structure undergoing modification.
It
further deserves notice that these variable
�LAWS OF VARIATION
characters, produced by man’s selection,
sometimes become attached, from causes
quite unknown to us, more to one sex than
to the other, generally to the male sex, as
with the wattle of carriers and the enlarged
crop of pouters.
Now let us turn to nature. When a part
has been developed in an extraordinary
manner in any one species, compared with
the other species of the same genus, we
may conclude that this part has undergone
an extraordinary amount of modification
since the period when the species branched
off from the common progenitor of the
genus. This period will seldom be remote
in any extreme degree, as species very
rarely endure for more than one geological
period.
An extraordinary amount of
modification impliesan unusually large and
long-continued amount of variability, which
has continually been accumulated by
natural selection for the benefit of the
species. But as the variability of the
extraordinarily-developed part or organ
has been so great and long-continued
within a period not excessively remote, we
might, as a general rule, expect still to find
more variability in such parts than in
other parts of the organisation which have
remained for a much longer period nearly
constant. And this, I am convinced, is
the case.
That the struggle between
natural selection on the one hand, and the
tendency to reversion and variability on
the other hand, will, in the course of time,
cease, and that the most abnormally
developed organs may be made constant,
I can see no reason to doubt. Hence
when an organ, however abnormal it may
be, has been transmitted in approximately
the same condition to many modified
descendants, as in the case of the wing of
the bat, it must have existed, according to
my theory, for an immense period in
nearly the same state ; and thus it comes
to be no more variable than any other
structure. It is only in those cases in
which the modification has been com
paratively recent and extraordinarily great
that we ought to find the generative
variability, as it may be called, still present
in a high degree. For in this case the
variability will seldom as yet have been
fixed by the continued selection of the
individuals varying in the required manner
and degree, and by the continued rejection
of those tending to revert to a former and
less modified condition.
The principle included in these remarks
may be extended. .It is notorious that
67
specific characters are more variable than
generic. To explain by a simple example
what is meant. If some species in a large
genus of plants had blue flowers and some
had red, the colour would be only a specific
character, and no one would be surprised
at one of the blue species varying into red,
or conversely; but if all the species had
blue flowers, the colour would become a
generic character, and its variation would
be a more unusual circumstance. I have
chosen this example because an explana
tion is not in this case applicable, which
most naturalists would advance—namely,
that specific characters are more variable
than generic, because they are taken from
parts of less physiological importance than
those commonly used for classing genera.
I believe this explanation is partly, yet
only indirectly, true ; I shall, however,
have to return to this subject in our chapter
on Classification. It would be almost
superfluous to adduce evidence in support
of the above statement, that specific
characters are more variable than generic ;
but I have repeatedly noticed in works on
natural history that when an author has
remarked with surprise that some impor
tant organ or part which is generally
very constant throughout large groups of
species has differed considerably in
closely-allied species, that it has also
been variable in the individuals of some of
the species. And this fact shows that a
character’ which is generally of generic
value, when it sinks in value and becomes
only of specific value, often becomes
variable, though its physiological impor
tance may remain the same. Something
of the same kind applies to monstrosities:
at least Is. Geoffroy St. Hilaire seems to
entertain no doubt that the more an
organ normally differs -in the different
species of the same group, the more
subject it is to individual anomalies.
On the ordinary view of each species
having been independently created, why
should that part of the structure which
differs from the same part in other inde
pendently-created species of the same
genus be more variable than those parts,
which are closely alike in the several
species ? I do not see that any explanation
can be given. But on the view of species
being only strongly marked • and fixed
varieties, we might surely expect to find
them still often continuing to vary in those
parts of their structure which have varied
within a moderately recent period, and
which have thus come to differ. Or to
�68
ON THE ORIGIN OF SPECIES
state the case in another manner: The ' readily have succeeded in giving to the
species of the same group a greater
points in which all the species of a genus
amount of difference in their sexual char
resemble each other, and in which they
differ from the species of some other genus, j acters than in other parts of their structure.
It is a remarkable fact that the secondary
are called generic characters ; and these
characters in common I attribute to in sexual differences between the two sexes of
the same species are generally displayed in
heritance from a common progenitor, for it
can rarely have happened that natural | the very same parts of the organisation in
which the different species of the same
selection will have modified several species,
genus differ from each other. Of this fact
fitted to more or less widely-different
I will give in illustration two instances, the
habits, in exactly the same manner; and
first which happen to stand on my list; and
as these so-called generic characters have
as the differences in these cases are of
been inherited from a remote period—since
a very unusual nature, the relation can
that period when the species first branched
hardly be accidental. The same number
•off from their common progenitor—and
of joints in the tarsi is a character generally
subsequently have not varied or come to
common to very large groups of beetles,
differ in any degree, or only in a slight
but in the Engidae, as West wood has
degree, it is not probable that they should
remarked, the number varies greatly ; and
vary at the present day. On the other hand,
the number likewise differs in the two
the points in which species differ from
sexes of the same species. Again in fossorial
other species of the same genus are called
hymenoptera, the manner of neuration of
specific characters; and as these specific
the wings is a character of the highest
characters have varied and come to differ
within the period of the branching-off importance, because common to large
groups; but in certain genera the neuration
of the species from a common progenitor,
differs in the different species, and likewise
it is probable that they should still often be
in the two sexes of the same species.
in some degree variable—at least more
variable than those parts of the organi This relation has a clear meaning on my
view of the subject: I look at all the species
sation which have for a very long period
of the same genus as having as certainly
remained constant.
descended from the same progenitor as
In connection with the present subject, I
will make only two other remarks. I think have the two sexes of any one of the
species. Consequently, whatever part of
it will be admitted, without my entering on
the structure of the common progenitor, or
details, that secondary sexual characters
of its early descendants, became variable ;
are very variable; I think it also will
variations of this part would, it is highly
be admitted that species of the same group
probable, be taken advantage of by natural
differ from each other more widely in
and sexual selection, in order to fit the
their secondary sexual characters than in
several species to their several places in
other parts of their organisation. Compare,
the economy of nature, and likewise to fit
for instance, the amount of difference
the two sexes of the same species to each
between the males of galinaceous birds, in
other, or to fit the males and females to
which secondary sexual characters are
strongly displayed, with the amount of different habits of life, or the males to
struggle with other males for the possession
difference between their females ; and the
of the females.
truth of this proposition will be granted.
Finally, then, I conclude that the greater
The cause of the original variability of
variability of specific characters, or those
secondary sexual characters is not mani
which distinguish species from species,
fest; but we can see why these characters
should not have been rendered as constant than of generic characters, or those which
and uniform as other parts of the organi the species possess in common—that the
frequent extreme variability of any part
sation, for secondary sexual characters
which is developed in a species in an
have been accumulated by sexual selection,
extraordinary manner in comparison with
which is less rigid in its action than
the same part in its congeners ; and the
ordinary selection, as it does not entail
slight degree of variability in a part, how
death, but only gives fewer offspring to
ever extraordinarily it may be developed,
the less favoured males. Whatever the
if it be common to a whole group of
cause may be of the variability of secondary
species; that the great variability of
sexual characters, as they are highly
secondary sexual characters, and the great
variable, sexual selection will have had
amount of difference in these same
a wide scope for action, and may thus
�LA IVS OF VARIA TION
characters between closely-allied species ;
that secondary sexual and ordinary specific
differences are generally displayed in the
same parts of the organisation—are all
principles closely connected together. All
being mainly due to the species of the
same group having descended from a
common progenitor, from whom they have
inherited much in common—to parts
which have recently and largely varied
being more likely still to go on varying
than parts which have long been inherited
and have not varied—to natural selection
having more or less completely, according
to the lapse of time, overmastered the
tendency to reversion and to further
variability—to sexual selection being less
rigid than ordinary selection—and to
variations in the same parts having been
accumulated by natural and sexual selec
tion, and having been thus adapted for
secondary sexual and for ordinary specific
purposes.
Distinct species present analogous varia
tions ; and a variety of one species often
assumes some of the characters of an allied
species, or reverts to some of the characters
of an early progenitor.—These proposi
tions will be most readily understood by
looking to our domestic races. The most
distinct breeds of pigeons, in countries
most widely apart, present sub-varieties
with reversed feathers on the head and
feathers on the feet—characters not
possessed by the aboriginal rock-pigeon ;
these, then, are analogous variations in two
or more distinct races. The frequent
presence of fourteen or even sixteen tail
feathers in the pouter may be considered
as a variation representing the normal
structure of another race, the fantail. I
presume that no one will doubt that all
such analogous variations are due to the
several races of the pigeon having inherited
from a common parent the same constitutution and tendency to variation, when
acted on by similar unknown influences.
In the vegetable kingdom we have a case
of analogous variation, in the enlarged
stems, or roots as commonly called, of the
Swedish turnip and Ruta baga, plants
which several botanists rank as varieties
produced by cultivation from a common
parent : if this be not so, the case will then
be one of analogous variation in two
so-called distinct species ; and to these a
third may be added—namely, the common
turnip. According to the ordinary view of
each species having been independently
created, we should have to attribute this
similarity in the enlarged stems of these
three plants, not to the ver a causa of com
munity of descent, and a consequent ten
dency to vary in a like manner, but to three
separate yet closely related acts of creation.
With pigeons, however, we have
another case—namely, the occasional
appearance in all the breeds, of slaty-blue
birds with two black bars on the wings, a
white rump, a bar at the end of the tail,
with the outer feathers externally edged
near their bases with white. As all these
marks are characteristic of the parent
rock-pigeon, I presume that no one will
doubt that this is a case of reversion, and
not of a new yet analogous variation
appearing in the several breeds. We may,
I think, confidently come to this conclusion,
because, as we have seen, these coloured
marks are eminently liable to appear in
the crossed offspring of two distinct and
differently coloured breeds; and in this case
there is nothing in the external conditions
of life to cause the reappearance of the
slaty-blue, with the several marks, beyond
the influence of the mere act of crossing on
the laws of inheritance.
No doubt it is a very surprising fact
that characters should reappear after having
been lost for many, perhaps for hundreds
of generations. But when a breed has
been crossed only once by some other
breeds, the offspring occasionally show a
tendency to revert in character to the
foreign breed for many generations—some
say, for a dozen or even a score of
generations. After twelve generations the
proportion of blood, to use a common
expression, of any one ancestor is only
i in 2048 ; and yet, as we see, it isgenerally believed that a tendency to re
version is retained by this very small
proportion of foreign blood. In a breed
which has not been crossed, but in which «
both parents have lost some character
which their progenitor possessed, the
tendency, whether strong or weak, to
reproduce the lost character might be, as
was formerly remarked, for all that we can
see to the contrary, transmitted for almost
any number of generations.
When a
character which has been lost in a breed
reappears after a great number of genera
tions, the most probable hypothesis is,
not that the offspring suddenly takes after
an ancestor some hundred generations
distant, but that in each successive genera
tion there has been a tendency to repro
duce the character in question, which at
�7o
r»
ON THE ORIGIN OF SPECIES
last, under unknown favourable conditions,
what are new but analogous variations,
gains an ascendancy.
For instance, it
yet we ought, on my theory, sometimes to
is probable that in each generation of the
find the varying offspring of a species
barb-pigeon, which produces most rarely
assuming characters (either from reversion
-a blue and black-barred bird, there has
or from analogous variation) which already
been a tendency in each generation in the
occur in some other members of the same
plumage to assume this colour. This view
group. And this undoubtedly is the case
is hypothetical, but could be supported
in nature.
by some facts ; and I can see no more
A considerable part of the difficulty in
abstract improbability in a tendency to
recognising a variable species in our
produce any character being inherited for
systematic works is due to its varieties
an endless number of generations than in
mocking, as it were, some of the
quite useless or rudimentary organs being,
other species of the same genus. A con
as we all know them to be, thus inherited.
siderable catalogue, also, could be given of
Indeed, we may sometimes observe a mere
forms intermediate between two other
tendency to produce a rudiment inherited ;
forms, which themselves must be doubt
for instance, in the common snap-dragon
fully ranked as either varieties or species ;
(Antirrhinum) a rudiment of a fifth stamen
and this shows, unless all these forms be
so often appears that this plant must have
considered as independently created
an inherited tendency to produce it.
species, that the one in varying has
As all the species of the same genus are
assumed some of the characters of the
supposed, on my theory, to have descended
other, so as to produce the intermediate
from a common parent, it might be ex
form. But the best evidence is afforded by
pected that they would occasionally vary
parts or organs of an important and
in an analogous manner ; so that a variety
uniform nature occasionally varying so as
of one species would resemble in some
to acquire, in some degree, the character
of its characters another species; this
of the same part or organ in an allied
other species being on my view only a
species. I have collected a long list of
well-marked and permanent variety. But
such cases ; but here, as before, I lie under
characters thus gained would probably be
a great disadvantage in not being able to
• of an unimportant nature, for the presence
give them. I can only repeat that such
of all important characters will be governed
cases certainly do occur, and seem to me
by natural selection, in accordance with
very remarkable.
the diverse habits of the species, and will
I will, however, give one curious and
not be left to the mutual action of the
complex case, not indeed as affecting any
conditions of life and of a similar inherited ; important character, but from occurring in
constitution. It might further be expected i several species of the same genus, partly
that the species of the same genus would
under domestication and partly under
occasionally exhibit reversions to lost an
nature. It is a case apparently of rever
cestral characters. As", however, we never
sion. The ass not rarely has very distinct
know the exact character of the common
transverse bars on its legs, like those on
ancestor of a group, we could not dis
the legs of the zebra : it has been asserted
tinguish these two cases : if, for instance,
that these are plainest in the foal, and, from
we did not know that the rock-pigeon was
inquiries which I have made, I believe
not feather-footed or turn-crowned, we
this to be true. It has also been asserted
could not have told whether these char
that the stripe on each shoulder is some
acters in our domestic breeds were revertimes double.
The shoulder-stripe is
-sions or only analogous variations ; but
certainly very variable in length and out
we might have inferred that the blueness
line. A white ass, but not an albino, has
was a case of reversion, from the number
been described without either spinal or
of the markings, which are correlated with
shoulder stripe ; and these stripes are
the blue tint, and which it does not appear
sometimes very obscure, or actually quite
probable would all appear together from
lost, in dark-coloured asses. The koulan
simple variation.
More especially we
of Pallas is said to have been seen with a
might have inferred this, from the blue
double shoulder-stripe. The hemionus has
colour and marks so often appearing when
no shoulder-stripe ; but traces of it, as
distinct breeds of diverse colours are crossed.
stated by Mr. Blyth and others, occasion
Hence, though under nature it must gene
ally appear : and I have been informed by
rally be left doubtful what cases are rever
Colonel Poole that the foals of this species
sions to an anciently existing character, and
are generally striped on the legs, and
�LAWS OF VARIATION
faintly on the shoulder. The quagga,
though so plainly barred like a zebra over
the body, is without bars on the legs ; but
Dr. Gray has figured one specimen with
very distinct zebra-like bars on the hocks.
With respect to the horse, I have col
lected cases in England of the spinal stripe
in horses of the most distinct breeds, and
of all colours ; transverse bars on the legs
are not rare in duns, mouse-duns, and in
one instance in a chestnut : a faint
shoulder-stripe may sometimes be seen in
duns, and I have seen a trace in a bay
horse. My son made a careful examina
tion and sketch for me of a dun Belgian
cart-horse with a double stripe on each
shoulder and with leg-stripes ; and a man
whom I can implicitly trust has examined
for me a small dun Welch pony with three
short parallel stripes on each shoulder.
In the north-west part of India the
Kattywar breed of horses is so generally
striped that, as I hear from Colonel Poole,
who examined the breed for the Indian
Government, a horse without stripes is not
considered as purely-bred. The spine is
always striped; the legs are generally
barred ; and the shoulder-stripe, which is
sometimes double and sometimes treble, is
common ; the side of the face, moreover,
is sometimes striped.' The stripes are
plainest in the foal ; and sometimes quite
disappear in old horses. Colonel Poole
has seen both gray and bay Kattywar
horses striped when first foaled. I have,
also, reason to suspect, from information
given me by Mr. W. W. Edwards, that
with the English race-horse the spinal
stripe is much commoner in the foal than
in the full-grown animal. Without here
entering on further details, I may state
that I have collected cases of leg and
shoulder stripes in horses of very different
breeds, in various countries from Britain
to Eastern China; and from Norway in
the north to the Malay Archipelago in the
south. In all parts of the world these
stripes occur far oftenest in duns and
mouse-duns ; by the term dun a large
range of colour is included, from one
between brown and black to a close ap
proach to cream-colour.
I am aware that Colonel Hamilton
Smith, who has written on this subject,
believes that the several breeds of the
horse have descended from several abo
riginal species—one of which, the dun,
was striped ; and that the above-described
appearances are all due to ancient crosses
with the dun stock. But I am not at all
7i
satisfied with this theory, and should be
loth to apply it to breeds so distinct as the
heavy Belgian cart-horse, Welsh ponies,
cobs, the lanky Kattywar race, etc., in
habiting the most distant parts of the
world.
Now let us turn to the effects of crossing
the several species of the horse-genus.
Rollin asserts that the common mule from
the ass and horse is particularly apt to
have bars on its legs : according to Mr.
Gosse, in certain parts of the United States
about nine out of ten mules have striped
legs. I once saw a mule with its legs so
much striped that anyone would at first
have thought that it must have been the
product of a zebra; and Mr. W. C. Martin,
in his excellent treatise on the horse, has
given a figure of a similar mule. In four
coloured drawings, which I have seen, of
hybrids between the ass and zebra, the
legs were much more plainly barred than
the rest of the body ; and in one of them
there was a double shoulder-stripe. In
Lord Morton’s famous hybrid from a
chestnut mare and male quagga, the
hybrid, and even the pure offspring sub
sequently produced from the mare by a
black Arabian sire, were much more
plainly barred across the legs than is even
the pure quagga.
Lastly, and this is
another most remarkable case, a hybrid
has been figured by Dr. Gray (and he
informs me that he knows of a second
case) from the ass- and the hemionus;
and this hybrid, though the ass seldom
has stripes on his legs and the hemionus
has none, and has not even a shoulder
stripe, nevertheless had all four legs barred,
and had three short shoulder-stripes like
those on the dun Welsh pony, and even
had some zebra-like stripes on the sides
of its face. With respect to this last fact
I was so convinced that not even a stripe
of colour appears from what would com
monly be called an accident that I was
led, solely from the occurrence of the face
stripes on this hybrid from the ass and
hemionus, to ask Colonel Poole whether
such face-stripes 'ever occur in the emi
nently striped Kattywar breed of horses,
and was, as we have seen, answered in the
affirmative.
What now are we to say to these several
facts? We see several very distinct species
of the horse-genus becoming, by simple
variation, striped on the legs like a zebra,
or striped on the shoulders like an ass.
In the horse we see this tendency strong
whenever a dun tint appears—a tint which
�7.2
ON THE ORIGIN OF SPECIES
approaches to that of the general colouring
of the other species of the genus. The
appearance of the stripes is not accom
panied by any change of form or by any
other new character. We see this tendency
to become striped most strongly displayed
in hybrids from between several of the
most distinct species. Now observe the
case of the several breeds of pigeons :
they are descended from a pigeon (in
cluding two or three sub-species or geo
graphical races) of a bluish colour, with
certain bars and other marks ; and when
any breed assumes by simple variation
a bluish tint, these bars and other marks
invariably reappear, but without any other
change of form or character. When the
oldest and truest breeds of various colours
are crossed, we see a strong tendency for
the blue tint and bars and marks to re
appear in the mongrels. I have stated
that the most probable hypothesis to
account for the reappearance of very
ancient characters is—that there is a
tendency in the young of each successive
generation to produce the long-lost char
acter, and that this tendency, from unknown
causes, sometimes prevails. And we have
just seen that in several species of the
horse-genus the stripes are either plainer or
appear more commonly in the young than
in the old. Call the breeds of pigeons,
some of which have bred true for centuries,
species; and how exactly parallel is the case
with that of the species of the horse-genus'
For myself, I venture confidently to look
back thousands on thousands of generations,
and I see an animal striped like a zebra,
but perhaps otherwise very differently con
structed, the common parent of our domestic
horse, whether or not it be descended from
one or more wild stocks, of the ass, the
hemionus, quagga, and zebra.
He who believes that each equine species
was independently created will, I presume,
assert that each species has been created,
with a tendencyato vary, both under nature
and under domestication, in this particular
manner, so as often to become striped like
other species of the genus ; and that each
has been created with a strong tendency,
when crossed with species inhabiting dis
tant quarters of the world, to produce
hybrids resembling in their stripes, not
their own parents, but other species of the
genus. To admit this view is, as it seems
to me, to reject a real for an unreal, or at
least for an unknown, cause. It makes the
works of God a mere mockery and decep
tion ; I would almost as soon believe, with
the old and ignorant cosmogonists, that
fossil shells had never lived, but had been
created in stone so as to mock the shells
now living on the sea-shore.
Summary.—Our ignorance of the laws of
variation is profound. Not in one case out
of a hundred can we pretend to assign any
reason why this or that part differs, more or
less, from the same part in the parents.
Bnt whenever we have the means of insti
tuting a comparison the same laws appear
to have acted in producing the lesser dif
ferences between varieties of the same
species, and the greater differences between
species of the same genus. The external
conditions of life, as climate and food, etc.,
seem to have induced some slight modifica
tions. Habit in producing constitutional
differences, and use in strengthening and
disuse in weakening and diminishing organs,
seem to have been more potent in their
effects. Homologous parts tend to vary in
the same way, and homologous parts tend
to cohere. Modifications in hard parts and
in external parts sometimes affect softer and
internal parts. When one part is largely
developed, perhaps it tends to draw
nourishment from the adjoining parts ;
and every part of the structure which can
be saved without detriment to the indi
vidual will be saved. Changes of structure
at an early age will generally affect parts
subsequently developed; and there are very
many other correlations of growth, the
nature of which we are utterly unable to
understand. Multiple parts are variable in
number and in structure, perhaps arising
from such parts not having been closely
specialised to any particular function, so
that their modifications have not been
closely checked by natural selection. It is
probably from this same cause that organic
beings low in the scale of nature are more
variable than those which have their whole
organisation more specialised, and are
higher in the scale. Rudimentary organs,
from being useless, will be disregarded by
natural selection, and hence probably are
variable. Specific characters—that is, the
characters which have come to differ since
the several species of the same genus
branched off from a common parent—are
more variable than generic characters, or
those which have long been inherited, and
have not differed within this same period.
In these remarks we have referred to
special parts or organs being still variable,
because they have recently varied and
thus come to differ ; but we have also seen
�DIFFICULTIES OF THE THEORY
in the second chapter that the same
principle applies to the whole individual ;
for in a district where many species of any
genus are found—that is, where there has
been much former variation and differen
tiation, or where the manufactory of new
specific forms has been actively at work—•
there, on an average, we now find most
varieties or incipient species. Secondary
sexual characters are highly variable, and
such characters differ much in the species
of the same group. Variability in the
same parts of the organisation has gener
ally been taken advantage of in giving
secondary sexual differences to the sexes
of the same species, and specific differences
to the several species of the same genus.
Any part or organ developed to an extra
ordinary size or in an extraordinary
manner, in comparison with the same part
or organ in the allied species, must have
gone through an extraordinary amount of
modification since the genus arose; and
thus we can understand why it should
often still be variable in a much higher
degree than other parts ; for variation is
a long-continued and slow process, and
natural selection will in such cases not as
yet have had time to overcome the
tendency to further variability and to
reversion to a less modified state. But
73
when a species with any extraordinarilydeveloped organ has become the parent of
many modified descendants—which on my
view must be a very slow process, requiring
a long lapse of time—in this case natural
selection may readily have succeeded in
giving a fixed character to the organ, in
however extraordinary a manner it may be
developed. Species inheriting nearly the
same constitution from a common parent
and exposed to similar influences will
naturally tend to present analogous varia
tions, and these same species may oc
casionally revert to some of the characters
of their ancient progenitors. Although
new and important modifications may not
arise from reversion and analogous varia
tion, such modifications will add to the
beautiful and harmonious diversity of
nature.
Whatever the cause may be of each
slight difference in the offspring from their
parents—and a cause for each must exist
—it is the steady accumulation, through
natural selection, of such differences,
when beneficial to the individual, that
gives rise to all the more important
modifications of structure, by which the
innumerable beings on the face of this
earth are enabled to struggle with each
other, and the best adapted to survive.
Chapter VI.
DIFFICULTIES OF THE THEORY
Difficulties of the theory of descent with modi
fication—Transitions—Absence or rarity of
transitional varieties—Transitions in habits of
life—Diversified habits in the same species—
Species with habits widely different from those
of their allies—Organs of extreme perfection—
Means of transition—Cases of difficulty—Natura non facit saltum—Organs of small
importance—Organs not in all cases absolutely
perfect-—The law of Unity of Type and of the
Conditions of Existence embraced by the
theory of Natural Selection.
Long before having arrived at this part of
my work a crowd of difficulties will have
occurred to the reader. Some of them are
so grave that to this day I can never reflect
on them without being staggered ; but, to
the best of my judgment, the greater
number are only apparent, and those that
are real are not, I think, fatal to my
theory.
These difficulties and objections may be
classed under the following heads :—
Firstly, why, if species have descended
from other species by insensibly fine
gradations, do we not everywhere see in
numerable transitional forms ? Why is
not all nature in confusion, instead of the
species being, as we see them, well
defined ?
Secondly, is it possible that an animal
having, for instance, the structure and
�74
ON THE ORIGIN OF SPECIES
habits of a bat, could have been formed by
the modification of some animal with
wholly different habits ? Can we believe
that natural selection could produce, on
the one hand, organs of trifling importance,
such as the tail of a giraffe, which serves
as a fly-flapper, and, on the other hand,
organs of such wonderful structure as the
eye, of which we hardly as yet fully under
stand the inimitable perfection ?
Thirdly, can instincts be acquired and
modified through natural selection ? What
shall we say to so marvellous an instinct as
that which leads the bee to make cells,
which has practically anticipated the dis
coveries of profound mathematicians.
Fourthly, how can we account for species,
when crossed, being sterile and producing
sterile offspring, whereas, when varieties
are crossed, their fertility is unimpaired ?
The two first heads shall be here dis
cussed—Instinct and Hybridism in sepa
rate chapters.
On the absence or rarity of transitional
varieties.—Ns, natural selection acts solely
by the preservation of profitable modifi
cations, each new form will tend in a fullystocked country to take the place of, and
finally to exterminate, its own less improved
parent or other less favoured forms with
which it comes into competition. Thus,
extinction and natural selection will, as we
have seen, go hand-in-hand. Hence, if
we look at each species as descended from
some other unknown form, both the parent
and all the transitional varieties will gene
rally have been exterminated by the very
process of formation and perfection of the
new form.
But, as by this theory innumerable
transitional forms must have existed, why
do we not find them embedded in countless
numbers in the crust of the earth ? It will
be much more convenient to discuss the
question in th® chapter on the Imperfection
of the Geological Record; and I will here
only state that I believe the answer mainly
lies in the record being incomparably less
perfect than is generally supposed ; the
imperfection of the record being chiefly
due to organic beings not inhabiting pro
found depths of the sea, and to their
remains being embedded and preserved
to a future age only in masses of sediment
sufficiently thick and extensive to with
stand an enormous amount of future
degradation; and such' fossiliferous masses
can be accumulated only where much
sediment is deposited on the shallow bed
of the sea while it slowly subsides. These
contingencies will occur only rarely, and
after enormously long intervals. While
the bed of the sea is stationary or is rising,
or w7hen very little sediment is being
deposited, there will be blanks in our
geological history. The crust of the earth
is a vast museum; but the natural col
lections have been made only at intervals
of time immensely remote.
But it may be urged that, when several
closely-allied species inhabit the same
territory, we surely ought to find at the
present time many transitional forms. Let
us take a simple case : in travelling from
north to south over a continent we gene
rally meet at successive intervals with
closely-allied or representative species,
evidently filling nearly the same place
in the natural economy of the land.
These representative species often meet
and interlock; and, as the one becomes
rarer and rarer, the other becomes more
and more frequent, till the one replaces
the other.
But if we compare these
species where they intermingle, they are
generally as absolutely distinct from each
other in every detail of structure as are
specimens taken from the metropolis in
habited by each. By my theory these
allied species have descended from a
common parent; and during the process
of modification each has become adapted
to the conditions of life of its own region,
and has supplanted and exterminated its
original parent and all the transitional
varieties between its past and present
states. Hence we ought not to expect
at the present time to meet with numerous
transitional varieties in each region, though
they must have existed there, and may be
embedded there in a fossil condition. But
in the intermediate region, having inter
mediate conditions of life, why do wre
not now find closely-linking intermediate
varieties ? This difficulty for a long time
quite confounded me. But I think it can
be in a large part explained.
In the first place, we should be extremely
cautious in inferring, because an area is
now continuous, that it has been continuous
during a long period. Geology would lead
us to believe that almost every continent
has been broken up into islands even
during the later tertiary periods; and in such
islands distinct species might have been
separately formed without the possibility of
intermediate varieties existing in the inter
mediate zones.. By changes in the form of
the land and of climate, marine areas now
�DIFFICULTIES OF THE THEORY
continuous must often have existed within
recent times in a far less continuous and
uniform condition than at present. But I
will pass over this way of escaping from
the difficulty; for I believe that many per
fectly defined species have been formed on
strictly continuous areas, though I do not
doubt that the formerly broken condition
of areas now continuous has played an
important part in the formation of new
species, more especially with freely-crossing
and wandering animals.
In looking at species as they are now
distributed over a wide area, we generally
find them tolerably numerous over a large
territory, then becoming somewhat abruptly
rarer and rarer on the confines, and finally
disappearing. Hence the neutral territory
between two representative species is
generally narrow in comparison with the
territory proper to each. We see the same
fact in ascending mountains, and sometimes
it is quite remarkable how abruptly, as
Alph. De Candolle has observed, a common
alpine species disappears. The same fact
has been noticed by E. Forbes in sounding
the depths of the sea with the dredge. To
those who look at climate and the physical
conditions of life as the all - important
elements of distribution, these facts ought
to cause surprise, as climate and height or
depth graduate away insensibly. But when
we bear in mind that almost every species,
even in its metropolis, would increase
immensely in numbers were it not- for
other competing species ; that nearly all
either prey on or serve as prey for others ;
in short, that each organic being is either
directly or indirectly related in the most
important manner to other organic beings,
we must see that the range of the inhabi
tants of any country by no' means exclu
sively depends on insensibly changing
physical conditions, but in large part on
the presence of other species, on which it
depends, or by which it is destroyed, or with
which it comes into competition; and as
these species are already defined objects
(however they may have become so), not
blending one into another by insensible
gradations, the range of any one species,
, ■ depending as it does on the range of others,
will tend to be sharply defined. Moreover,
each species on the confines of its range,
where it exists in lessened numbers, will,
during fluctuations in the number of its
enemies or of its prey, or in the seasons, be
extremely liable to utter extermination;
and thus its geographical ra*ige will come
to be still more sharply defined.
75
If I am right in believing that allied or
representative species, when inhabiting a
continuous area, are generally so distributed
that each has a wide range, with a com
paratively narrow neutral territory between
them, in which they become rather suddenly
rarer and rarer—then, as varieties do not
essentially differ from species, the same
rule will probably apply to both; and if we
in imagination adapt a varying species to a
very large area, we shall have to adapt two
varieties to two large areas, and a third
variety to a narrow intermediate zone. The
intermediate variety, consequently, will exist
in lesser numbers from inhabiting a narrow
and lesser area ; and practically, as far as
I can make out, this rule holds good with
varieties in a state of nature. I have met
with striking instances of the rule in the
case of varieties intermediate between wellmarked varieties in the genus Balanus.
And it would appear from information
given me by Mr. Watson, Dr. Asa Gray,
and Mr. Wollaston, that generally, when
varieties intermediate between two other
forms occur, they are much rarer numeri
cally than the forms which they connect.
Now, if we may trust these facts and
inferences, and therefore conclude that
varieties linking two other varieties together
have generally existed in lesser numbers
than the forms which they connect, then, I
think, we can understand why intermediate
varieties should not endure for very long
periods—why as a general rule they should
be exterminated and disappear sooner
than the forms which they originally linked
together.
For any form existing in lesser numbers
would, as already remarked, run a greater
chance of being exterminated than one
existing in large numbers ; and in this
particular case the intermediate form
would be eminently liable to the inroads of
closely-allied forms existing on both sides
of it. But a far more important con
sideration, as I believe, is that, during the
process of further modification by which
two varieties are supposed, on my theory,
to be converted and perfected into two
distinct species, the two which exist in
larger numbers from inhabiting larger
areas will have a great advantage over the
intermediate variety which exists in smaller
numbers in a narrow and intermediate
zone. For forms existing in larger numbers
will always have a .better chance within
any given period of presenting further
favourable variations for natural selection
to seize on than will the rarer forms which
�76
ON THE ORIGIN OF SPECIES
exist in lesser numbers. Hence the more
common forms in the race for life will tend
to beat and supplant the less common
forms, for these will be more slowly
modified and improved. It is the same
principle which, as I believe, accounts for
the common species in each country as
shown in the second chapter, presenting
on an average a greater number of wellmarked varieties than do the rarer species.
I may illustrate what I mean by supposing
three varieties of sheep to be kept, one
adapted to an extensive mountainous
region ; a second to a comparatively
narrow, hilly tract ; and a third to wide
plains at the base ; and that the in
habitants are all trying with equal steadi
ness and skill to improve their stocks by
selection ; the chances in this case will be
strongly in favour of the great holders on
the mountains or on the plains improving
their breeds more quickly than the small
holders on the intermediate narrow, hilly
.tract, and consequently the improved
mountain or plain breed will soon take the
place of the less improved hill breed; and
thus the two breeds, which originally
-existed in greater numbers, will come into
close contact with each other without the
interposition of the supplanted, interme
diate hill variety.
To sum up, I believe that species come
to be tolerably well-defined objects, and do
not at any one period present an in
extricable chaos of varying and interme
diate links: firstly, because;new varieties are
very slowly formed, for variation is a very
slow process, and natural selection can do
nothing until favourable variations chance
to occur, and until a place in the natural
polity of the country can be better filled by
some modification of some one or more of
its inhabitants. And such new places will
depend on slow changes of climate, or on
the occasional immigration of new in
habitants, and, probably, in a still more
important degree, on some of the old
inhabitants becoming slowly modified,
with the new forms thus produced and the
old ones acting and re-acting on each
other. So that, in any one region and at
any time, we ought only to see a few
species presenting slight modifications of
structure in some degree permanent, and
this assuredly we do see.
Secondly, areas now continuous must
often have existed within the recent period
in isolated portions, in which many forms,
more especially among the classes which
unite for each birth and wander much, may
have separately been rendered sufficiently
distinct to rank as representative species.
In this case, intermediate varieties between
the several representative species and
their common parent must formerly have
existed in each broken portion of the
land; but these links will have been
supplanted and exterminated during the
process of natural selection, so that they
will no longer exist in a living state.
Thirdly, when two or more varieties
have been formed in different portions
of a strictly continuous area, intermediate
varieties will, it is probable, at first
have been formed in the intermediate
zones, but they will generally have had
a short duration. For these intermediate
varieties will, from reasons already as
signed (namely, from what we know of
the actual distribution of closely-allied or
representative species, and likewise of
acknowledged varieties), exist in the inter
mediate zones- in lesser numbers than the
varieties which they tend to connect. From
this cause alone the intermediate varieties
will be liable to accidental extermination;
and during the process of further modi
fication through natural selection they will
almost certainly be beaten and supplanted
by the forms which they connect; for these,
from existing in greater numbers, will, in the
aggregate, present more variation, and thus
be further improved through natural selec
tion and gain further advantages.
Lastly, looking not to any one time, but to
all times, if my theory be true, numberless
intermediate varieties, linking most closely
all the species of the same group together,
must assuredly have existed; but the very
process of natural selection constantly
tends, as has been so often remarked,
to exterminate the parent-forms and the
intermediate links. Consequently, evidence
of their former existence could be found
only among fossil remains, which are pre
served, as we shall in a future chapter
attempt to show, in an extremely imperfect
and intermittent record.
On the origin and transitions of organic
beings with peculiar habits and structure.
■—It has been asked by the opponents of
such views as I hold how, for instance,
a land carnivorous animal could have been
converted into one with aquatic habits;
for how could the animal in its transitional
state have subsisted? It would be easy to
show that within the same group carni
vorous animals exist having every inter
mediate grade between truly aquatic and
�DIFFICULTIES OF THE THEORY
strictly terrestrial habits; and, as each
exists by a struggle for life, it is clear that
each is well adapted in its habits to its
place in nature.
Look at the Mustela
vison of North America, which has webbed
feet, and which resembles an otter in its
fur, short legs, and form of tail: during
summer this animal dives for and preys
on fish, but during the long winter it leaves
the frozen waters, and preys, like other
pole-cats, on mice and land animals. If
a different case had been taken, and it had
been asked how an insectivorous quadruped
could possibly have been converted into
a flying bat, the question would have been
far more difficult, and I could have given
no answer. Yet I think such difficulties
have very little weight.
Here, as on other occasions, I lie under
a heavy disadvantage, for, out of the many
striking cases which I have collected, I
can give only one or two instances of
transitional habits and structures in closelyallied species of the same genus, and of
diversified habits, either constant or occa
sional, in the same species. And it seems
to me that nothing less than a long list of
such cases is sufficient to lessen the diffi
culty in any particular case like that of the
bat.
Look at the family of squirrels. Here we
have the finest gradation from animals
with their tails only slightly flattened, and
from others, as Sir J. Richardson has re
marked, with the posterior parts of their
bodies rather w7ide and with the skin
on their flanks rather full, to the so-called
flying squirrels ; and flying squirrels have
their limbs, and even the base of the tail,
united by a broad expanse of skin, which
serves as a parachute, and allows them
to glide through the air, to an astonishing
distance, from tree to tree. We cannot
doubt that each structure is of use to each
kind of squirrel in its own country by
enabling it to escape birds or beasts of
prey, or to collect food more quickly, or,
as there is reason to believe, by lessening
the danger from occasional falls. But it
does not follow from this fact that the
structure of each squirrel is the best that it
is possible to conceive under all natural
conditions. Let the climate and vegetation
change, let other competing rodents or
new beasts of prey immigrate, or old
ones become modified, and all analogy
would lead us to believe that some at least
of the squirrels would decrease in numbers,
or become exterminated, unless they also
became modified and improved in structure
77
in a corresponding manner. Therefore, I
can see no difficulty, more especially under
changing conditions of life, in the con
tinued preservation of individuals with
fuller and fuller flank-membranes, each
modification being useful, each being pro
pagated, until, by the accumulated effects
of this process of natural selection, a
perfect so-called flying squirrel was pro
duced.
Now, look at the Galeopithecus, or flying
lemur, which formerly was falsely ranked
among bats.
It has an extremely wide
flank-membrane, stretching from the
corners of the jaw to the tail, and including
the limbs and the elongated fingers: the
flank-membrane is also furnished with an
extensor muscle. Although no graduated
links of structure, fitted for gliding throughthe air, now connect the Galeopithecus
with the other Lemurid;:e, yet I see no
difficulty in supposing that such linksformerly existed, and that each had been
formed by the same steps as in the case of
the less perfectly gliding squirrels; and
that each grade of structure was useful to
its possessor. Nor can I see any insuper
able difficulty in further believing it.
possible that the membrane-connected
fingers and fore-arm of the Galeopithecus.
might be greatly lengthened by natural
selection, and this, as far as the organs of
flight are concerned, would convert it into
a bat.
In bats which have the wing
membrane extended from the top of the
shoulder to the tail, including the hind
legs, we perhaps see traces of an ap
paratus originally constructed for gliding
through the air rather than for flight.
If about a dozen genera of birds had
become extinct or were unknown, who
would have ventured to have surmised
that birds might have existed which used
their wings solely as flappers, like the
logger-headed duck(Micropterus of Eyton);
as fins in the water and front legs on
the land, like the penguin; as sails, like
the ostrich; and functionally for no purpose,
like the Apteryx? Yet the structure of
each of these birds is good for it under the
conditions of life to which it is exposed,
for each has to live by a struggle; but it
is not necessarily the best possible under
all possible conditions. It must not be
inferred from these remarks that any of
the grades of wing-structure here alluded
to, which perhaps may all have resulted
from disuse, indicate the natural steps by
which birds have acquired their perfect
power of flight; but they serve at least to
�78
(9/V 7775 ORIGIN OF SPECIES
show what diversified means of transition | probably often change almost simul
are possible.
taneously. Of cases of changed habits
Seeing that a few members of such
it will suffice merely to allude to that of
water-breathing classes as the Crustacea
the many British insects which now feed
and Mollusca are adapted to live on the
on exotic plants or exclusively on artificial
land ; and seeing that we have flying birds
substances. Of diversified habits innu
and mammals, flyings insects of the most
merable instances could be given: I have
diversified types, and formerly had flying
often watched a tyrant fly-catcher (Sauroreptiles, it is conceivable that flying-fish,
phagus sulphuratus) in South America
which now glide far through the air,
hovering over one spot and then pro
slightly rising and turning by the aid of
ceeding to another like a kestrel, and at
their fluttering fins, might have been
other times standing stationary on the
modified into perfectly winged animals.
margin of water and then dashing like
If this had been effected, who would have
a kingfisher at a fish. In our own country
ever imagined that in an early transitional
the larger titmouse (Parus major) may be
state they had been inhabitants of the open
seen climbing branches almost like a
ocean, and had used their incipient organs
creeper; it often, like a shrike, kills small
of flight exclusively, as far as we know, to
birds by blows on the head ; and I have
escape being devoured by other fish ?
many times seen and heard it hammering
When we see any structure highly per
the seeds of the yew on a branch, and thus
fected for any particular habit as the wings
breaking them like a nuthatch. In North
of a bird for flight, we should bear in mind
America the black bear was seen by
that animals displaying early transitional
Hearne swimming for hours with widely
grades of the structure will seldom continue
open mouth, thus catching, almost like
to exist to the present day, for they will
a whale, insects in the water.
have been supplanted by the very process
As we sometimes see individuals of a
of perfection through natural selection.
species following habits widely different
Furthermore, we may conclude that
from those of their own species and of the
transitional grades between structures
other species of the same genus, we might
fitted for very different habits of life will
expect, on my theory, that such individuals
rarely have been developed at an early
would occasionally have given rise to new
period in great numbers and under many
species, having anomalous habits, and with
subordinate forms. Thus, to return to our
their structure either slightly or con
imaginary illustration of the flying-fish, it
siderably modified from that of their
does not seem probable that fishes capable
proper type. And such instances do occur
of true flight would have been developed
in nature. Can a more striking instance
under many subordinate forms, for taking
of adaptation be given than that of a
prey of many kinds in many ways, on the
woodpecker for climbing trees, and for
land and in the water, until their organs of
seizing insects in the chinks of the bark ?
flight had come to a high stage of perfec
Yet in North America there are wood
tion, so as to have given them a decided
peckers which feed largely on fruit, and
advantage over other animals in the battle
others with elongated wings which chase
of life. Hence the chance of discovering
insects on the wing; and on the plains of
species with transitional grades of structure
La Plata, where not a tree grows, there
in a fossil condition will always be less,
is a woodpecker which, in every essential
from their having existed in lesser numbers
part of its organisation, even in its colouring,
than in the case of species with fullyin the harsh tone of its voice and unduladeveloped structures.
tory flight, told me plainly of its close blood
I will now give two or three instances of
relationship to our common species; yet it is
diversified and of changed habits in the
a woodpecker which never climbs a tree 1
individuals of the same species. When
Petrels are the most aerial and oceanic
either case occurs, it would be easy for
of birds, yet in the quiet Sounds of Tierra
natural selection to fit the animal, by some
del Fuego the Puffinuria berardi, in its
modification of its structure, for its changed
general habits, in its astonishing power
habits, or exclusively for one of its several
of diving, its manner of swimming, and
different habits. But it is difficult to tell,
of flying when unwillingly it takes flight,
and immaterial for us, whether habits
would be mistaken by anyone for an auk
generally change first and structure after
or grebe; nevertheless, it is essentially a
wards ; or whether slight modifications of
petrel, but with many parts of its organi
structure lead to changed habits ; both
sation profoundly modified. On the other
�DIFFICULTIES OF THE THEORY
79
hand, the acutest observer, by examining
be diving thrushes and petrels with the
the dead body of the water-ouzel, would
habits of auks.
never have suspected its sub-aquatic habits;
‘ yet this anomalous member of the strictly
Organs of extreme perfection and com
terrestrial thrush family wholly subsists by plication.—To suppose that the eye, with all
diving—grasping the stones with its feet
its inimitable contrivances for adjusting
and using its wings under water.
the focus to different distances, for admit
He who believes that each being has
ting different amounts of light, and for the
been created as we now see it must occa
correction of spherical and chromatic
sionally have felt surprise when he has
aberration, could have been formed by
met with an animal having habits and
natural selection, seems, I freely confess,
structure not at all in agreement. What
absurd in the highest possible degree.
can be plainer than that the webbed feet
Yet reason tells me that if numerous
of ducks and geese are formed for swim
gradations from a perfect and complex eye
ming ? Yet there are upland geese with
to one very imperfect and simple, each
webbed feet which rarely or never go near
grade being useful to its possessor, can be
the water; and no one except Audubon
shown to exist ; if, further, the eye does
has seen the frigate-bird, which has all its
vary ever so slightly and the variations be
four toes webbed, alight on the surface of
inherited, which is certainly the case, and
the sea. On the other hand, grebes and
if any variation or modification in the
coots are eminently aquatic, although their
organ be ever useful to an animal under
toes are only bordered by membrane.
changing conditions of life, then the
What seems plainer than that the long
difficulty of believing that a perfect and
toes of grallatores are formed for walking
complex eye could be formed by natural
over swamps and floating plants ; yet the
selection, though insuperable by our imagi
water-hen is nearly as aquatic as the coot,
nation, can hardly be considered real.
and the landrail nearly as terrestrial as the
How a nerve comes to be sensitive to
quail or partridge. In such cases, and
light hardly concerns us more than how
many others could be given, habits have _ life itself first originated; but I may
changed without a corresponding change ’ remark that several facts make me suspect
of structure. The webbed feet of the
that any sensitive nerve may be rendered
upland goose may be said to have become
sensitive to light, and likewise to those
rudimentary in function, though not in
coarser vibrations of the air which produce
structure. In the frigate-bird the deeplysound.
scooped membrane between the toes shows
In looking for the gradations by which
that structure has begun to change.
an organ in any species has been perfected,
He who believes in separate and in
we ought to look exclusively to its lineal
numerable acts of creation will say that in
ancestors ; but this is scarcely ever pos
these cases it has pleased the Creator to
sible, and we are forced in each case to
cause a being of one type to take the place
look to species of the same group—that is,
of one of another type ; but this seems to
to the collateral descendants from the
me only re-stating the fact in dignified
same original parent-form—in order to see
language. He who believes in the struggle
what gradations are possible, and for the
for existence and in the principle of natural
chance of some gradations having been
selection will acknowledge that every
transmitted from the earlier stages of
organic being is constantly endeavouring
descent in an unaltered or little altered
to increase in numbers ; and that if any
condition. Among existing Vertebrata we
one being vary ever so little either in
find but a small amount of gradation in the
habits or structure, and thus gain an
structure of the eye, and from fossil species
advantage over some other inhabitant of we can learn nothing on this head. In
the country, it will seize on the place of
this great class we should probably have
that inhabitant, however different it may be
to descend far beneath the lowest known
from its own place. Hence it will cause
fossiliferous stratum to discover the earlier
him no surprise that there should be geese
stages by which the eye has been perfected.
and frigate-birds with webbed feet, living
In the Articulata we can commence a
on the dry land or most rarely alighting on
series with an optic nerve merely coated
the water ; that there should be long-toed
with pigment, and without any other
corncrakes living in meadows instead of in
mechanism ; and from this low stage
swamps; that there should be woodpeckers
numerous gradations of structure, branch
where not a tree grows ; that there should
ing off in two fundamentally different lines,
�So
ON THE ORIGIN OF SPECIES
can be shown to exist, until we reach a
moderately high stage of perfection. In
certain crustaceans, for instance, there is a
double cornea, the inner one divided into
facets, within each of which there is a lens
shaped swelling. In other crustaceans the
transparent cones which are coated by
pigment, and which properly act only by
excluding lateral pencils of light, are con
vex at their upper ends, and must act by
convergence; and at their lower ends there
seems to be an imperfect vitreous sub
stance. With these facts, here far too
briefly and imperfectly given, which show
that there is much graduated diversity in
the eyes of living crustaceans, and bearing
in mind how small the number of living
animals is in proportion to those which i
have become extinct, I can see no very
great difficulty (not more than in the case
of many other structures) in believing that
natural selection has converted the simple
apparatus of an optic nerve, merely coated
with pigment and invested by transparent
membrane, into an optical instrument as
perfect as is possessed by any member
of the great Articulate class.
He who will go thus far, if he find on
finishing this treatise that large bodies
of facts, otherwise inexplicable, can be
explained by the theory of descent, ought
not to hesitate to go further, and to admit
that a structure even as perfect as the eye
of an eagle might be formed by natural
selection, although in this case he does
not know any of the transitional grades.
His reason ought to conquer his imagina
tion ; though I have felt the difficulty far
too keenly to be surprised at any degree of
hesitation in extending the principle of i
natural selection to such startling lengths.
It is scarcely possible to avoid comparing
the eye to a telescope. We know that this
instrument has been perfected by the longcontinued efforts of the highest human
intellects; and we naturally infer that the
eye has been formed by a somewhat analo
gous process. But may not this inference
be presumptuous ? Have we any right to
assume that the Creator works by intel
lectual powers like those of man ? If we
must compare the eye to an optical instru
ment, we ought in imagination to take
a thick layer of transparent tissue, with i
a nerve sensitive to light beneath, and then
suppose every part of this layer to be con
tinually changing slowly in density, so as
to separate into layers of different densities
and thicknesses, placed at different dis
tances from each other, and with the sur
faces of each layer slowly changing in
form. Further, we must suppose that
there is a power always intently watching
each slight accidental alteration in the
transparent layers, and carefully selecting
each alteration which, under varied cir
cumstances, may in any way, or in any
degree, tend to produce a distincter image.
We must suppose each new state of the
instrument to be multiplied by the million,
and each to be preserved till a better be
produced, and then the old ones to be
destroyed. In living bodies variation will
cause the slight alterations, generation will
multiply them almost infinitely, and natural
selection will pick out with unerring skill
each improvement. Let this process go
on for millions on millions of years, and
during each year on millions of individuals
of many kinds, and may we not believe
that a living optical instrument might thus
be formed as superior to one of glass as
the works of the Creator are to those of
man ?
If it could be demonstrated that any
complex organ existed which coyld not
possibly have been formed by numerous,
successive, slight modifications, my theory
would absolutely break down. But I can
find out no such case. No doubt, many
organs exist of which we do not know the
transitional grades, more especially if we
look to much isolated species, round which,
according to my theory, there has been
much extinction. Or again, if we look
to an organ common to all the members
of a large class, for in this latter case
the organ must have been first formed
at an extremely remote period, since which
all the many members of the class have
been developed; and, in order to discover
the early transitional grades through which
the organ has passed, we should have
to look to very ancient ancestral forms,
long since become extinct.
We should be extremely cautious in
concluding that an organ -could not have
been formed by transitional gradations
of some kind. Numerous cases could be
given among the lower animals of the
same organ performing at the same time
wholly distinct functions ; thus the alimen
tary canal respires, digests, and excretes
in the larva of the dragon-fly and in the
fish Cobites. In the Hydra the animal
may be turned inside out, and the exterior
surfa.ee will then digest and the stomach
respire. In such cases natural selection
might easily specialise, if any advantage
were thus gained, a part or organ, which
�81
DIFFICULTIES OF THE THEORY
branchiae might have bpen gradually
had performed two functions, for one
worked in by natural selection for some
function alone, and thus wholly change its
quite distinct purpose—in the same manner
nature by insensible steps. Two distinct
as, on the view entertained by some
organs sometimes perform simultaneously
naturalists that the branchiae and dorsal
the same function in the same individual.
scales of Annelids are homologous with
To give one instance, there are fish with
the wings and wing-covers of insects, it is
gills or branchiae that breathe the air
probable that organs which at. a very
dissolved in the water at the same time
ancient period served for respiration have
that they breathe free air in their swim
been actually converted into organs of
bladders, this latter organ having a ductus
flight.
pneumaticus for its supply, and being
In considering transitions of organs, it is
divided by highly vascular partitions. _ In
so important to bear in mind the proba
these cases one of the two organs might
bility of conversion from one function to
with ease be modified and perfected so as
another that I will give one more instance.
to perform all the work by itself, being
Pedunculated cirripedes have two minute
aided, during the process of modification,
folds of skin called by me the ovigerous
by the other organ; and then this other
frena, which serve, through the means of a
organ might be modified for some other
sticky secretion, to retain the eggs until
and quite distinct purpose, or be quite
they are hatched within the sack. These
obliterated.
cirripedes have no branchiae, the whole
The illustration of the swimbladder in
surface of the body and sack, including
fishes is a good one, because it shows us
the small frena, serving for respiration.
clearly the highly important fact that an
The Balanidae or sessile cirripedes, on the
organ originally constructed for one
other hand, have no ovigerous frena, the
purpose, namely flotation, may be con
eggs lying loose at the bottom of the sack
verted into one for a wholly different
in the well-enclosed shell ; but they have
purpose, namely respiration. The swim
large folded branchiae. Now, I think no
bladder has also been worked in as an
one will dispute that the ovigerous frena
accessory to the auditory organs of certain
in the one family are strictly homologous
fish, or, for I do not know which view is
with the branchiae of the other family ;
now generally held, a part of the auditory
indeed, they graduate into each other.
apparatus has been worked in as a com
Therefore, I do not doubt that little folds
plement to the swimbladder. All physio
of skin, which originally served as ovige
logists admit that the swimbladder is
rous frena, but which, likewise, very slightly
homologous or “ ideally similar ” in posi
aided the act of respiration, have been
tion and structure with the lungs of the
gradually converted by natural selection
higher vertebrate animals; hence there
into branchiae, simply through an increase
seems to me to be no great difficulty in
in their size and the obliteration of their
believing that natural selection has actually
adhesive glands. If all pedunculated cirri
converted a swimbladder into a lung or
pedes had become extinct, and they have
organ used exclusively for respiration.
already suffered far more extinction than
I can, indeed, hardly doubt that all
have sessile cirripedes, who would ever have
vertebrate animals having true lungs have
imagined that the branchiae in this latter
descended by ordinary generation from an
family had originally existed as organs for
ancient prototype of which we know
preventing the ova from being washed out
nothing, furnished with a floating appa
of the sack ?
ratus or swimbladder. We can thus, as
Although we must be extremely cautious
I infer from Professor Owen’s interesting
in concluding that any organ could not
; description of these parts, understand the
possibly have been produced by successive
strange fact that every particle of food and
transitional gradations, yet, undoubtedly,
drink which we swallow has to pass over
grave cases of difficulty occur, some of
. the orifice of the trachea, with some risk of
which will be discussed in my future work.
falling into the lungs, notwithstanding the
One of the gravest is that of neuter
beautiful contrivance by which the glottis
insects, which are often very differently
is closed. In the higher Vertebrata the
constructed from either the males or fertile
branchiae have wholly disappeared—the
females; but this case will be treated of in
slits on the sides of the neck and the loop
the next chapter. The electric organs of
like course of the arteries still marking in
fishes offer another case of special difficulty;
the embryo their former position. But it
it is impossible to conceive by what steps
is conceivable that the now utterly lost
G
�82
ON THE ORIGIN OF SPECIES
these wondrous organs have been pro
duced ; but, as Owen and others have
remarked, their intimate structure closely
resembles that of common muscle; and as
it has lately been shown that Rays have an
organ closely analogous to the electric
apparatus, and yet do not, as Matteucei
asserts, discharge any electricity, we must
own that we are far too ignorant to argue
that no transition of any kind is possible.
The electric organs offer another and
even more serious difficulty, for they occur
in only about a dozen fishes, of which
several are widely remote in their affinities.
Generally, when the same organ appears
in several members of the same class,
especially if in members having very dif
ferent habits of life, we may attribute its
presence to inheritance from a common
ancestor, and its absence in some of the
members to its loss through disuse or
natural selection. But, if the electric organs
had been inherited from one ancient
progenitor thus provided, we might have
expected that all electric fishes would
have been specially related to each other.
Nor does geology at all lead to the belief
that formerly most fishes had electric
organs, which most of their modified des
cendants have lost.
The presence of
luminous organs in a few insects, belonging
to different families and orders, offers a
parallel case of difficulty. Other cases
could be given: for instance, in plants
i the very curious contrivance of a mass
of pollen-grains, borne on a foot-stalk with
a sticky gland at the end, is the same
in Orchis and Asclepias—genera almost
as remote as possible among flowering
plants. In all these cases of two very
distinct species furnished with apparently
the same anomalous organ it should be
observed that, although the general ap
pearance and function of the organ may
be the same, yet some fundamental dif
ference can generally be detected. I am
inclined to believe that, in nearly the same
way as two men have sometimes indepen
dently hit on the very same invention, so
natural selection, working for the good
of each being and taking advantage of
analogous variations, has sometimes modi
fied in very nearly the same manner two
parts in two organic beings, which beings
owe but little of their structure in common
to inheritance from the same ancestor.
Although, in many cases, it is most diffi
cult to conjecture by what transitions
organs could have arrived at their present
states yet, considering that the proportion of
living and known forms to the extinct and un
known is very small, I have been astonished
how rarely an organ can be named towards
which no transitional grade is known to lead.
The truth of this remark is indeed shown by
that old, but somewhat exaggerated, canon
in natural history of “ Natura non facit
saltum.” We meet with this admission in
the writings of almost every experienced
naturalist; or, as Milne Edwards has well
expressed it, Nature is prodigal in variety,
but niggard in innovation. Why, on the
theory of Creation, should this be so?
Why should all the parts and organs of
many independent beings, each supposed
to have been separately created for its
proper place in nature, be so commonly
linked together by graduated steps ? Why
should not nature have taken a leap from
structure to structure? On the theory of
natural selection, we can clearly understand
why she should not; for natural selection
can act only by taking advantage of slight
successive variations ; she can never take
a leap, but must advance by the shortest
and slowest steps.
Organs of little apparent importance.—
As natural selection acts by life and death,
by the preservation of individuals with
any favourable variation, and by the
destruction of those with any unfavourable
deviation of structure, I have sometimes
felt much difficulty in understanding the
origin of simple parts of which the impor
tance does not seem sufficient to cause the
preservation of successively varying indi
viduals. I have sometimes felt as much
difficulty, though of a very different kind,
on this head, as in the case of an organ as
perfect and complex as the eye.
In the first place, we are much too
ignorant in regard to the whole economy
of any one organic being to say what
slight modifications would be of importance
or not. In a former chapter I have given
instances of most trifling characters, such
as the down on fruit and the colour of its
flesh, which, from determining the attacks
of insects or from being correlated with
constitutional differences, might assuredly
be acted on by natural selection. The tail
of the giraffe looks like an artificially con
structed fly-flapper; and it seems at first
incredible that this could have been
adapted for its present purpose by succes
sive slight modifications, each better and
better, for so trifling an object as driving
away flies ; yet we should pause before
being too positive even in this case, for we
�DIFFICULTIES OF THE THEORY
know that the distribution and existence of
cattle and other animals in South America
absolutely depends on their power of
resisting the attacks of insects ; so that
individuals which could by any means
defend themselves from these small enemies
would be able to range into new pastures,
and thus gain a great advantage. It is not
that the larger quadrupeds are actually
destroyed (except in some rare cases) by
flies, but they are incessantly harassed and
their strength reduced, so that they are
more subject to disease, or not so well
enabled in a coming dearth to search for
food, or to escape from beasts of prey.
Organs now of trifling importance have
probably in some cases been of high
importance to an early progenitor, and,
after having been slowly perfected at a
former period, have been transmitted in
nearly the same state, although now
become of very slight use; and any
actually injurious deviations in their struc
ture will always have been checked by
natural selection. Seeing how important
an organ of locomotion the tail is in most
aquatic animals, its general presence and
use for many purposes in so many land
animals, which in their lungs or modified
swimbladders betray their aquatic origin,
may perhaps be thus accounted for. A
well-developed tail having been formed in
an aquatic animal, it might subsequently
come to be worked in for all sorts of pur
poses, as a fly-flapper, an organ of pre
hension, or as an aid in turning, as with
the dog, though the aid must be slight, for
the hare, with hardly any tail, can double
quickly enough.
In the second place, we may sometimes
attribute importance to characters which
are really of very little importance, and
which have originated from quite secondary
causes, independently of natural selection.
We should remember that climate, food,
etc., probably have some little direct influ
ence on the organisation ; that characters
reappear from the law of reversion ; that
correlation of growth will have had a most
important influence in modifying various
structures ; and, finally, that sexual selec
tion will often have largely modified the
external characters of animals having a
will, to give one male an advantage in
fighting with another or in charming the
females. Moreover, when a modification
of structure has primarily arisen from the
above or other unknown causes, it may at
first have been of no advantage to the
species, but may subsequently have been
83
taken advantage of by the descendants of
the species under new conditions of life
and with newly-acquired habits.
To give a few instances to illustrate
these latter remarks. If green wood
peckers alone had existed, and we did not
know that there were many black arid
pied kinds, I dare say that we should have
thought that the green colour was a beauti
ful adaptation to hide this tree-frequenting
bird from its enemie§; and, consequently,
that it was a character of importance, and
might have been acquired through natural
selection. As it is, I have no doubt that
the colour is due to some quite distinct
cause, probably to sexual selection. A
trailing bamboo in the Malay archipelago
climbs the loftiest trees by the aid of
exquisitely constructed hooks clustered
around the ends of the branches, and this
contrivance, no doubt, is of the highest
service to the plant; but, as we see nearly
similar hooks on many trees which are not
climbers, the hooks on the bamboo may
have arisen from unknown laws of growth,
and have been subsequently taken advan
tage of by the plant undergoing further
modification and becoming a climber.
The naked skin on the head of a vulture is
generally looked at as a direct adapta
tion for wallowing in putridity; and so it
may be, or it may possibly be due to the
direct action of putrid matter; but we
should be very cautious in drawing any
such inference, when we see that the skin
on the head of t-he clean-feeding male
turkey is likewise naked. The sutures in
the skulls of young mammals have been
advanced as a beautiful adaptation for
aiding -parturition, and no doubt they
facilitate, or may be indispensable for this
act; but as sutures occur in the skulls of
young birds and reptiles, which have only
to escape from a broken egg, we may
infer that this structure has arisen from
the laws of growth, and has been taken
advantage of in the parturition of the
higher animals.
We - are profoundly ignorant of the
causes producing slight and unimportant
variations, and we are immediately made
conscious of this by reflecting on the
differences in the breeds of our domesti
cated animals in different countries, more
especially in the less civilised countries
where there has been but little artificial
selection. Careful observers are convinced
that a damp climate affects the growth of
the hair, and that with the hair the horns
are correlated. Mountain breeds always
�84
ON THE ORIGIN OF SPECIES
differ from lowland breeds, and a moun
tainous country would probably affect the
hind limbs from exercising them more, and
possibly even the form of the pelvis; and
then by the law of homologous variation
the front limbs, and even the head, would
probably be affected. The shape also of
the pelvis might affect by pressure the
shape of the head of the young in the
womb. The laborious breathing necessary
in high regions would, we have some
reason to believe, increase the size of the
chest, and again correlation would come
into play. Animals kept by savages in
different countries often have to struggle
for their own subsistence, and would be
exposed to a certain extent to natural
selection, and individuals with slightly
different constitutions would succeed best
under different climates ; and there is
reason to believe that constitution and
colour are correlated. A good observer
also states that in cattle susceptibility to
the attacks of flies is correlated with
colour, as is the liability to be poisoned by
certain plants; so that colour would be thus
subjected to the action of natural selection.
But we are far too ignorant to specu
late on the relative importance of the
several known and unknown laws of varia
tion ; and I have here alluded to them
only to show that, if we are unable to
account for the characteristic differences
of our domestic breeds, which nevertheless
we generally admit to have arisen through
ordinary generation, we ought not to lay
too much stress on our ignorance of the
precise cause of the slight analogous dif
ferences between species. I might have
adduced for this same purpose the differ
ences between the races of man, which
are so strongly marked. I may add that
some little light can apparently be thrown
on the origin of these differences, chiefly
through sexual selection of a particular
kind; but without here entering on copious
details my reasoning would appear frivolous.
The foregoing remarks lead me to say a
few words on the protest lately made by
some naturalists against the utilitarian
doctrine that every detail of structure has
been produced for the good of its pos
sessor.
They believe that very many
structures have been created for beauty
in the eyes of man, or for mere variety.
This doctrine, if true, would be absolutely
fatal to my theory. Yet I fully admit that
many structures are of no direct use to
their possessors. Physical conditions pro
bably have had some little effect on struc
ture, quite independently of any good thus
gained. Correlation of growth has no
doubt played a most important part, and
a useful modification of one part will often
have entailed on other parts diversified
changes of no direct use. So, again, cha
racters which formerly were useful, or which
formerly had arisen from correlation of
growth, or from other unknown cause, may
reappear from the law of reversion, though
now of no direct use. The effects of sexual
selection, when displayed in beauty to
charm the females, can be called useful
only in rather a forced sense. But by far
the most important consideration is that
the chief part of the organisation of every
being is simply due to inheritance; and
consequently, though each being assuredly
is well fitted for its place in nature, many
structures now have no direct relation to
the habits of life of each species. Thus
we can hardly believe that the webbed feet
of the upland goose or of the frigate-bird
are of special use to these birds; we
cannot believe that the small bones in the
arm of the monkey, in the fore-leg of the
horse, in the wing of the bat, and in the
flipper of the seal, are of special use to
these animals. We may safely attribute
these structures to inheritance. But to the
progenitor of the upland goose and of the
frigate-bird webbed feet no doubt were
as useful as they now are to the most
aquatic of existing birds.
So we may
believe that the progenitor of the seal had
not a flipper, but a foot with five toes fitted
for walking or grasping; and we may fur
ther venture to believe that the several
bones in the limbs of the monkey, horse,
and bat, which have been inherited from a
common progenitor, were formerly of more
special use to that progenitor, or its pro
genitors, than they now are to these
animals having such widely diversified
habits. Therefore, we may infer that these
several bones might have been acquired
through natural selection, subjected for
merly, as now, to the several laws of in
heritance, reversion, correlation of growth,
etc. Hence every detail of structure in
every living creature (making some little
allowance for the direct action of physical
conditions) may be viewed, either as havingbeen of special use to some ancestral form,
or as being now of special use to the
descendants of this form—either directly,
or indirectly through the complex laws of
growth.
Natural selection cannot possibly pro
duce any modification in any one species
�DIFFICULTIES OF THE THEORY
exclusively for the good of another species ;
though throughout nature one species in
cessantly takes advantage of, and profits
by, the structure of another. But natural
selection can and does often produce struc
tures for the direct injury of other species,
as we see in the fang of the adder, and in
the ovipositor of the ichneumon, by which
its eggs are deposited in the living bodies
of other insects. If it could be proved
that any part of the structure of any one
species had been formed for the exclusive
good of another species, it would anni
hilate my theory, for such could not have
been produced through natural selection.
Although many statements may be found
in works on natural history to this effect, I
cannot find even one which seems to me of
any weight. It is admitted that the rattle
snake has a poison-fang for its own defence
and for the destruction of its prey ; but
some authors suppose that at the same time
this snake is furnished with a rattle for its
own injury—namely, to warn its prey to
escape. I would almost as soon believe
that the cat curls the end of its tail when
preparing to spring in order to warn the
doomed mouse. But I have not space here
to enter on this and other such cases.
Natural selection will never produce in
a being anything injurious to itself, for
natural selection acts solely by and for the
good of each. No organ will be formed,
as Paley has remarked, for the purpose of
causing pain or for doing an injury to its
possessor. If a fair balance be struck
between the good and evil caused by each
part, each will be found on the whole
advantageous. After the lapse of time,
under changing conditions of life, if any
part comes to be injurious, it will be modi
fied ; or if it be not so, the being will
become extinct, as myriads have become
extinct.
Natural selection tends only to make
each organic being as perfect as, or slightly
more perfect than, the other inhabitants of
the same country with which it has to
struggle for existence. And we see that
this is the degree of perfection attained
under nature. The endemic productions
of New Zealand, for instance, are perfect
one compared with another; but they are
now rapidly yielding before the advancing
legions of plants and animals introduced
from Europe. Natural selection will not
produce absolute perfection; nor do we
always meet, as far as we can judge, with
this high standard under nature. The
correction for the aberration of light is
85
said, on high authority, not to be perfect
even in that most perfect organ, the eye.
If our reason leads us to admire with
enthusiasm a multitude of inimitable con
trivances in nature, this same reason tells
us, though we may easily err on both sides,
that some other contrivances are less
perfect. Can we consider the sting of the
wasp or of the bee as perfect, which, when
used against many attacking animals,
cannot be withdrawn, owing to the back
ward serratures, and so inevitably causes
the death of the insect by tearing out its
viscera ?
If we look at the sting of the bee, as
having originally existed in a remote pro
genitor as a boring and serrated instru
ment, like that in so many members of
the same great order, and which has been
modified, but not perfected for its present
purpose, with the poison originally adapted
to cause galls subsequently intensified, we
can perhaps understand how it is that the
use of the sting should so often cause the
insect’s own death ; for if, on the whole,
the power of stinging be useful to the
community, it will fulfil all the require
ments of natural selection, though it may
cause the death of some few members. If
we admire the truly wonderful power of
scent by which the males of many insects
find their females, can we admire the pro
duction for this single purpose of thousands
of drones, which are utterly useless to the
community for any other end, and which
are ultimately slaughtered by their indus
trious and sterile sisters? It may be
difficult, but we ought to admire the
savage instinctive hatred of the queen
bee, which urges her instantly to destroy
the young queens, her daughters, as soon
as born, or to perish herself in the combat;
for undoubtedly this is for the good of the
community; and maternal love or maternal
hatred, though the latter fortunately is
most rare, is all the same to the inexorable
principle of natural selection. If we admire
the several ingenious contrivances by
which the flowers of the orchids and of
many other plants are fertilised through
insect agency, can we consider as equally
perfect the elaboration by our fir-trees of
dense clouds of pollen, in order that a few
granules may be wafted by a chance'breeze
on to the ovules ?
Summary of Chapter.—We have in this
chapter discussed some of the difficulties
and objections which may be urged against
my theory. Many of them are very serious;
�86
ON THE ORIGIN OF SPECIES
but I think that in the discussion light has
been thrown on several facts which on the
theory of independent acts of creation are
utterly obscure. We have seen that species
at any one period are not indefinitely
variable, and are not linked together by
a multitude of intermediate gradations,
partly because the process of natural selec
tion will always be very slow, and will act,
at any one time, only on a very few forms ;
and partly because the very process of
natural selection almost implies the con
tinual supplanting and extinction of pre
ceding and intermediate gradations.
Closely-allied species, now living on a
continuous area, must often have been
formed when the area was not continuous,
and when the conditions of life did not
insensibly graduate away from one part to
another. When two varieties are formed
in two districts of a continuous area, an
intermediate variety will often be formed,
fitted for an intermediate zone ; but, from
reasons assigned, the intermediate variety
will usually exist in lesser numbers than
the two forms which it connects ; conse
quently, the two latter, during the course
of further modification, from existing in
greater numbers, will have a great advan
tage over the less numerous intermediate
variety, and will thus generally succeed in
supplanting and exterminating it.
We have seen in this chapter how
cautious we should be in concluding that
the most different habits of life could not
graduate into each other; that a bat, for
instance, could not have been formed by
natural selection from an animal which at
first could only glide through the air.
We have seen that a species may, under
new conditions of life, change its habits, or
have diversified habits, with some habits
very unlike those of its nearest congeners.
Hence we can understand, bearing in mind
that each organic being is trying to live
wherever it can. live, how it has arisen that
there are upland geese with webbed feet,
ground woodpeckers, diving thrushes, and
petrels with the habits of auks.
Although the belief, that an organ so
perfect as the eye could have been formed
by natural selection, is more than enough
to stagger anyone, yet in the case of any
organ, if we know of a long series of gra
dations in complexity, each good for its
possessor, then, under changing conditions
of life, there is no logical impossibility in
the acquirement of any conceivable degree
of perfection through natural selection.
In the cases in which we know of no inter-
♦
mediate or transitional states we should
be very cautious in concluding that none
could have existed, for the*homologies of
many organs and their intermediate states
show that wonderful metamorphoses in
function are at least possible. For in
stance, a swim-bladder has apparently
been converted into an air-breathing lung.
The same organ having performed simul
taneously very different functions, and then
having been specialised for one function;
and two very distinct organs having per
formed at the same time the same func
tion, the one having been perfected while
aided by the other, must often have largely
facilitated transitions.
We are far too ignorant, in almost every
case, to be enabled to assert that any part
or organ is so unimportant for the welfare
of a species that modifications in its
structure could not have been slowly accu
mulated by means of natural selection.
But we may confidently believe that many
modifications, wholly due to the laws of
growth, and at first in no way advan
tageous to a species, have been subse
quently taken advantage of by the still
further modified descendants of this species.
We may, also, believe that a part formerly
of high importance has often been retained
(as the tail of an aquatic animal by its
terrestrial descendants), though it has
become of such small importance that it
could not, in its present state, have been
acquired by natural selection—a poweiwhich acts solely by the preservation of
profitable variations in the struggle for life.
Natural selection will produce nothing
in one species for the exclusive good or
injury of another; though it may well
produce parts, organs, and excretions
highly useful or even indispensable, or
highly injurious to another species, but in
all cases at the same time useful to the
owner. Natural selection in each wellstocked country must act chiefly through
the competition of the inhabitants one with
another, and consequently will produce
perfection, or strength in the battle for life,
only according to the standard of that
country. Hence the inhabitants of one
country, generally the smaller one, will
often yield, as we see they do yield, to
the inhabitants of another and generally
larger country. For in the larger country7
there will have existed more individuals
and more diversified forms, and the com
petition will have been severer, and thus
the standard of perfection will have been
rendered higher. Natural selection will
�INSTINCT
not necessarily produce absolute perfec
tion ; nor, as far as we can judge by our
limited faculties, can absolute perfection
be everywhere found.
On the theory of natural selection we
can clearly understand the full meaning
of that old canon in natural history,
“ Natura non facit saltum.” This canon,
if we look only to the present inhabitants
of the world, is not strictly correct; but
if we include all those of past times, it
must by my theory be strictly true.
It is generally acknowledged that all
organic beings have been formed on two
great laws—Unity of Type, and the Con
ditions of Existence. By unity of type
is meant that fundamental agreement in
structure which we see in organic beings
of the same class, and which is quite in
87
dependent of their habits of life. On my
theory, unity of type is explained by unity
of descent. The expression of conditions
of existence, so often insisted on by the
illustrious Cuvier, is fully embraced by the
principle of natural selection. For natural
selection acts by either now adapting the
varying parts of eac-h being to its organic
and inorganic conditions of life, or by
having adapted them during long-past
periods of time; the adaptations being
aided in some cases by use and disuse,
being slightly affected by the direct action
of the external conditions of life, and being
in all cases subjected to the several laws of
growth. Hence, in fact, the law of the
Conditions of Existence is the higher law.
as it includes, through the inheritance of
former adaptations, that of Unity of Type.
Chapter VII.
INSTINCT
Instincts comparable with habits, but different I one understands what is meant when it is
in their origin—Instincts graduated—Aphides
said that instinct impels the cuckoo to
and ants—-Instincts variable—Domestic in
migrate and to lay her eggs in other birds’
stincts, their origin—Natural instincts of the
nests. An action, which we ourselves
cuckoo, ostrich, and parasitic bees—Slave
should require experience to enable us to
making ants—Hive-bee, its cell-making in
perform, when performed by an animal,
stinct—Difficulties on the theory of the Natural
more especially by a very young one,
Selection of instincts—Neuter or sterile in
without any experience, and when per
sects—S ummary.
The subject of instinct might have been
worked into the previous chapters; but I
have thought that it would be more con
venient to treat the subject separately, especiallyas so wonderful an instinct as that of
the hive-bee making its cells will probably
have occurred to many readers as a diffi
cultysufficient to overthrow my whole theory.
I must premise that I have nothing to do
with the origin of the primary mental
powers, any more than I have with that of
life itself. We are concerned only with the
diversities of instinct and of the other
mental qualities of animals within the
same class.
I will not attempt any definition of
instinct. It would be easy to show that
several distinct mental actions are com
monly embraced by this term; but every
formed by many individuals in the same
way, without their knowing for what pur
pose it is performed, is usually said to be
instinctive. But I could show that none
of these characters of instinct are universal.
A little dose, as Pierre Huber expresses it,
of judgment or reason often comes into
play even in animals very low in the scale
of nature.
Frederick Cuvier and several of the older
metaphysicians have compared instinct
with habit. This comparison gives, I think,
a remarkably accurate notion of the frame
of mind under which an instinctive action
is performed, but not of its origin. How
unconsciously many habitual actions are
performed, indeed, not rarely in direct
opposition to our conscious will, yet they
may be modified by the will or reason.
Habits easily become associated with
'
•
�88
ON THE ORIGIN OF SPECIES
other habits, and with certain periods
of time and states of the body. When
once acquired, they often remain constant
throughout life. Several other points of
resemblance between instincts and habits
could be pointed out. As in repeating a
well-known song, so in instincts, one action
follows another by a sort of rhythm; if a
person be interrupted in a song, or in
repeating anything by rote, he is generally
forced to go back to recover the habitual
train of thought: so P. Huber found it
was with a caterpillar, which makes a
very complicated hammock; for if he
took a caterpillar which had completed
its hammock up to, say, the sixth stage of
construction, and put it into a hammock
completed up only to the third stage, the
caterpillar simply re-performed the fourth,
fifth, and sixth stages of construction. If,
however, a caterpillar were taken out of a
hammock made up, for instance, to the
third stage, and were put into one finished
up to the sixth stage, so that much of its
work was already done for it, far from
feeling the benefit of this, it was much
embarrassed, and, in order to complete its
hammock, seemed forced to start from the
third stage, where it had left off, and thus
tried to complete the already finished work.
If we suppose any habitual action to
become inherited—and I think it can be
shown that this does sometimes happen—
then the resemblance between what origi
nally was a habit and an instinct becomes
so close as not to be distinguished. If
Mozart, instead of playing the pianoforte
at three years old with wonderfully little
practice, had played a tune with no practice
at all, he might truly be said to have done
so instinctively. But it would be the most
serious error to suppose that the greater
number of instincts have been acquired by
habit in one generation, and then trans
mitted by inheritance to succeeding genera
tions. It can be clearly shown that the
most wonderful instincts with which we are
acquainted—namely, those of the hive-bee
and of many ants, could not possibly have
been thus acquired.
It will be universally admitted that
instincts are as important as corporeal
structure for the welfare of each species,
under its present conditions of life. Under
changed conditions of life, it is, at least,
possible that slight modifications of instinct
might be profitable to a species ; and if it
can be shown that instincts do vary ever
so little, then I can see no difficulty in
natural selection preserving and continually
accumulating variations of instinct to any
extent that may be profitable. It is thus,
as I believe, that all the most complex
and wonderful instincts have originated.
As modifications of corporeal structure
arise from, and are increased by, use or
habit, and are diminished or lost by disuse,
so I do not doubt it has been with instincts.
But I believe that the effects of habit are
of quite subordinate importance to the
effects of the natural selection of what may
be called accidental variations of instincts
—that is, of variations produced by the
same unknown causes which produce slight
deviations of bodily structure.
No complex instinct can possibly be
produced through natural selection, except
by the slow and gradual accumulation of
numerous, slight, yet profitable, variations.
Hence, as in the case of corporeal struc
tures, we ought to find in nature, not the
actual transitional gradations by which
each complex instinct has been acquired—for these could be found only in the lineal
ancestors of each species—but we ought
to find in the collateral lines of descent
some evidence of such gradations ; or we
ought at least t-o be- able to show that
gradations of some kind are possible ; and
this we certainly can do. I have been
surprised to find, making allowance for the
instincts of animals having been but little
observed except in Europe and North
America, and for no instinct being known
among extinct species, how very generally
gradations, leading to the most complex
instincts, can be discovered. Changes of
instinct may sometimes be facilitated by
the same species having different instincts
at different periods of life or at different
seasons of the year, or when placed under
different circumstances, etc.; in which case
either one or the other instinct might be
preserved by natural selection. And such
instances of diversity of instinct in the same
species can be shown to occur in nature.
Again, as in the case of corporeal struc
ture, and conformably with my theory, the
instinct of each species is good for itself,
but has never, as far as we can judge, been
produced for the exclusive good of others.
One of the strongest instances of an animal
apparently performing an action for the
sole good of another, with* which I am
acquainted, is that of aphides voluntarily
yielding their sweet excretion to ants: that
they do so voluntarily the following facts
show. I removed all the ants from a
group of about a dozen aphides on a dock
plant, and prevented their attendance
�INSTINCT
during several hours. After this interval,
I felt sure that the aphides would want to
excrete. I watched them for some time
through a lens, but not one excreted ; I
then tickled and stroked them with a hair
in the same manner, as well as I could, as
the ants do with their antennae ; but not
one excreted. Afterwards I allowed an
ant to visit them, and it immediately
seemed, by its eager way of running about,
to be well aware what a rich flock it had
discovered; it then began to play with its
antennae on the abdomen first of one aphis
and then of another; and each aphis, as
soon as it felt the antennae, immediately
lifted up its abdomen and excreted a limpid
drop of sweet juice, which was eagerly
devoured by the ant. Even the quite young
aphides behaved in this manner, showing
that the action was instinctive, and not the
result of experience. But as the excretion
is extremely viscid, it is probably a con
venience to the aphides to have it removed;
and therefore probably the aphides do not
instinctively excrete for the sole good of the
ants. Although I do not believe that any
animal in the world performs an action for
the exclusive good of another of a distinct
species, yet each species tries to take
advantage of the instinct of others, as each
takes advantage of the weaker bodily
structure of others. So again, in some
few cases, certain instincts cannot be con
sidered as absolutely perfect; but, as
details on this and other such points are
not indispensable, they may be here passed
over.
As some degree of variation in instincts
under a state of nature, and the inheritance
of such variations, are indispensable for
the action of natural selection, as many in
stances as possible ought to be here given;
but want of space prevents me. I can only
assert that instincts certainly do vary—for
instance, the migratory instinct, both in
extent and direction, and in its total loss.
So it is with the nests of birds, which vary
partly in dependence on the situations
chosen, and on the nature and temperature
of the country inhabited, but often from
causes wholly unknown to us : Audubon
has given several remarkable cases of
differences in the nests of the same species
in the northern and southern United
States. Fear of any particular enemy is
certainly an instinctive quality, as may be
seen in nestling birds, though it is strength
ened by experience, and by the sight of
fear of the same enemy in other animals.
But fear of man is slowly acquired, as I
89
have elsewhere shown, by various animals
inhabiting desert islands; and we may see
an instance of this, even in England, in the
greater wildness of all our large birds than
of our small birds, for the large birds have
been most persecuted by man. We may
safely attribute the greater wildness of our
large birds to this cause, for in uninhabited
islands large birds are not more fearful
than small; and the magpie, so wary in
England, is tame in Norway, as is the
hooded crow in Egypt.
. That the general disposition of indi
viduals of the same species, born in a
state of nature, is extremely diversified
can be shown by a multitude of facts.
Several cases, also, could be given of
occasional and strange habits in certain
species, which might, if advantageous to
the species, give rise, through natural selec
tion, to quite new instincts.
But I am
well aware that these general statements,
without facts given in detail, can produce
but a feeble effect on the reader’s mind. I
can only repeat my assurance, that I do not
speak without good evidence.
The possibility, or even probability, of
inherited variations of instinct in a state of
nature will be strengthened by briefly con
sidering a few cases under domestication.
We shall thus also be enabled to see
the respective parts which habit and the
selection of so-called accidental variations
have played in modifying the mental
qualities of our domestic animals.
A
number of curious and authentic instances
could be given of the inheritance of all
shades of disposition and tastes, and like
wise of the oddest tricks, associated with
certain frames of mind or periods of time.
But let us look to the familiar case of the
several breeds of dogs : it cannot be
doubted that young pointers (I have my
self seen a striking instance) will some
times point and even back other dogs the
very first time that they are taken out;
retrieving is certainly in some degree in
herited by retrievers ; and a tendency to
run round, instead of at, a flock of sheep
by shepherd-dogs. I cannot see that these
actions, performed without experience by
the young, and in nearly the same manner
by each individual, performed with eager
delight by each breed, and without the end
being known—for the young pointer can
no more know that he points to aid his
master than the white butterfly knows why
she lays her eggs on the leaf of the cabbage
—I cannot see that these actions differ
essentially from true instincts. If we were
�go
ON THE ORIGIN OF SPECIES
to see one kind of wolf, when young and
without any training, as soon as it scented
its prey, stand motionless like a statue, and
then slowly crawl forward with a peculiar
gait; and another kind of wolf rushing
round, instead of at, a herd of deer, and
driving them to a distant point, we should
assuredly call these actions instinctive.
Domestic instincts, as they may be called,
are certainly far less fixed or invariable
than natural instincts ; but they have been
acted on by far less rigorous selection, and
have been transmitted for an incomparably
shorter period under less fixed conditions
of life.
How strongly these domestic instincts,
habits, and dispositions are inherited, and
. how curiously they become mingled, is well
shown when different breeds of dogs are
crossed. Thus it is known that a cross
with a bull-dog has affected for many
generations the courage and obstinacy of
greyhounds; and a cross with a greyhound
has given to a whole family of shepherd
dogs a tendency to hunt hares. These
domestic instincts, when thus tested by
crossing, resemble natural instincts, which
in a like manner become curiously blended
together, and for a long period exhibit
traces of the instincts of either parent:
for example, Le Roy describes a dog,
whose great-grandfather was a wolf,
and this dog showed a trace of its wild
parentage only in one way, by not coming
in a straight line to his master when called.
Domestic instincts are sometimes spoken
of as actions which have become inherited
solely from long-continued and compulsory
habit; but this, I think, is not true. No
one would ever have thought of teaching,
or probably could have taught, the tumbler
pigeon to tumble—an action which, as I
have witnessed, is performed by young
birds that have never seen a pigeon
tumble. We may believe that some one
pigeon showed a slight tendency to this
strange habit, and that the long-continued
selection of the best individuals in succes
sive generations made tumblers what they
now are; and near Glasgow there are
house-tumblers, as I hear from Mr. Brent,
which cannot fly eighteen inches high
without going head over heels. It may
be doubted whether anyone would have
thought of training a dog to point had not
some one dog naturally shown a tendency
in this line ; and this is known occasionally
to happen, as I once saw in a pure terrier :
the act of pointing is probably, as many
have thought, only the exaggerated pause
of an animal preparing to spring on its
prey. When the first tendency to point
was once displayed, methodical selection
and the inherited effects of compulsory
training in each successive generation
would soon complete the work; and
unconscious selection is still at work, as
each man tries to procure, without intending
to improve the breed, dogs which will stand
and hunt best. On the other hand, habit
alone in some cases has sufficed; no
animal is more difficult to tame than the
young of the wild rabbit ; scarcely any
animal is tamer than the young of the
tame rabbit; but I do not suppose that
domestic rabbits have ever been selected
for tameness ; and I presume that we must
attribute the whole of the inherited change
from extreme wildness to extreme tame
ness simply to habit and long-continued
close confinement.
Natural instincts are lost under domesti
cation : a remarkable instance of this is
seen in those breeds of fowls which very
rarely or never become “ broody ’’—that is,
never wish to sit on their eggs. Familiarity
alone prevents our seeing how universally
and largely the minds of our domestic
animals have been modified by domestica
tion. It is scarcely possible to doubt that
the love of man has become instinctive in
the dog. All wolves, foxes, jackals, and
species of the cat genus, when kept tame,
are most eager to attack poultry, sheep,
and pigs; and this tendency has been
found incurable in dogs which have been
brought home as puppies from countries
such as Tierra del Fuego and Australia,
where the savages do not keep these
domestic animals. How rarely, on the
other hand, do our civilised dogs, even
when quite young, require to be taught not
to attack poultry, sheep, and pigs 1 No
doubt they occasionally do make an attack,
and are then beaten ; and if not cured,
they are destroyed ; so that habit, with
some degree of selection, has probably
concurred in civilising by inheritance our
dogs. On the other hand, young chickens
have lost, wholly by habit, that fear of the
dog and cat, which no doubt was origi
nally instinctive in them, in the same way
as it is- so plainly instinctive in young
pheasants, though reared under a hen. It
is not that chickens have lost all fear, but
fear only of dogs and cats, for, if the hen
gives the danger-chuckle, they will run
(more especially young turkeys) from under
her, and conceal themselves in the sur
rounding grass or thickets ; and this is
�INSTINCT
evidently done for the instinctive purpose
of allowing, as we see in wild ground
birds, their mother to fly away. But this
instinct retained by our chickens has
become useless under domestication, for
the mother-hen has almost lost by disuse
the power of flight.
Hence, we may conclude that domestic
instincts have been acquired and natural
instincts have been lost partly by habit,
and partly by man selecting and accu
mulating, during successive generations,
peculiar mental habits and actions, which
at first appeared from what we must in our
ignorance call an accident. In some cases
compulsory habit alone has sufficed to
produce such inherited mental changes ;
in other cases compulsory habit has done
nothing, and all has been the result of
selection, pursued both methodically and
unconsciously; but in most cases, pro
bably, habit and selection have acted
together.
We shall, perhaps, best understand how
instincts in a state of nature have become
modified by selection by considering a few
cases. I will select only three out of the
several which I shall have to discuss in my
future work—namely, the instinct which
leads the cuckoo to lay her eggs in other
birds’ nests; the slave-making instinct of
certain ants ; and the comb-makrng power
of the hive-bee : these two latter instincts
have generally, and most justly, been
ranked by naturalists as the most wonderful
of all known instincts.
It is now commonly admitted that the
more immediate and final cause of the
cuckoo’s instinct is that she lays her eggs,
not daily, but at intervals of two or three
days ; so that, if she were to make her own
nest and sit on her own eggs, those first
laid would have to be left for some time
unincubated, or there would be eggs and
young birds of different ages in the same
nest. If this were the case, the process of
laying and hatching might be incon
veniently long, more especially as she has
to migrate at a very early period; and the
first hatched young would probably have
to be fed by the male alone. But the
American cuckoo is in this predicament ;
for she makes her own nest and has eggs
and young successively hatched, all at the
same time. It has been asserted that the
American cuckoo occasionally lays her eggs
in other birds’ nests ; but I hear on the
high authority of Dr. Brewer that this is a
mistake. Nevertheless, I could give several
instances of various birds which have been
9i
known occasionally to lay their eggs in
other birds’ nests. Now let us suppose
that the ancient progenitor of our European
cuckoo had the habits of the American
cuckoo, but that occasionally she laid an
egg in another bird’s nest. If the old bird
profited by this occasional habit, or if the
young were made more vigorous by advan
tage having been taken of the mistaken
maternal instinct of another bird than by
their own mother’s care, encumbered as
she can hardly fail to be by having eggs
and young of different ages at the same
time, then the old birds or the fostered .
young would gain an advantage. And
analogy would lead me to believe that the
young thus reared would be apt to follow
by inheritance the occasional and aberrant
habit of their mother, and in their turn
would be apt to lay their eggs in other
birds’ nests, and thus be successful in rear
ing their young. By a continued process
of this nature I believe that the strange
instinct of our cuckoo could be, and has
been, generated. I may add that, accord
ing to Dr. Gray and to some other observers,
the European cuckoo has not utterly lost
all maternal love and care for her own off
spring.
The occasional habit of birds laying their
eggs in other birds’ nests, either of the
same or of a distinct species, is not very
uncommon with the Gallinacese ; and this
perhaps explains the origin of a singular
instinct in the allied group of ostriches.
For several hen ostriches, at least in the
case of the American species, unite and lay
first a few eggs in one nest and then in
another ; and these are hatched by the
males. This instinct may probably be
accounted for by the fact of the hens laying
a large number of eggs, but, as in the case
of the cuckoo, at intervals of two or three
days.
This instinct, however, of the
American ostrich has not as yet been per
fected ; for a surprising number of eggs lie
strewed over the plains, so that in one
day’s hunting I picked up no less than
twenty lost and wasted eggs.
Many bees are parasitic, and always lay
their eggs in the nests of bees of other
kinds. This case is more remarkable than
that of the cuckoo ; for these bees have
not only their instincts but their structure
modified in accordance with their parasitic
habits ; for they do not possess the pollen
collecting apparatus which would be neces
sary if they, had to store food for their
own young. Some, species, likewise, of
Sphegidse (wasp-like insects) are parasitic
�92
ON THE ORIGIN OF SPECIES
on other species ; and M. Fabre has latelyshown good reason for believing that
although the Tachytes nigra generally
makes its own burrow and stores it with
paralysed prey for its own larvae to feed on,
yet that when this insect finds a burrow
already made and stored by another sphex,
it takes advantage of the prize, and becomes
for the occasion parasitic. In this case, as
with the supposed case of the cuckoo, I
can see no difficulty in natural selection
making an occasional habit permanent, if
of advantage to the species, and if the
insect whose nest and stored food are
thus feloniously appropriated be not thus
exterminated.
and Mr. Smith, I tried to approach the
subject in a sceptical frame of mind, as
anyone may well be excused for doubting
the truth of so extraordinary and odious
an instinct as that of making slaves.
Hence I will give the observations which
I have myself made, in some little detail.
I opened fourteen nests of F. sanguinea,
and found a few slaves in all. Males and
fertile females of the slave-species (F. fusca)
are found only in their own proper com
munities, and have never been observed in
the nests of F. sanguinea. The slaves are
black and not above half the size of their
red masters, so that the contrast in their
appearance is very great. When the nest
is slightly disturbed, the slaves occasionally
Slave-making instinct.—This remark
come out, and like their masters are much
able instinct was first discovered in the
agitated and defend the nest; when the
Formica (Polyerges) rufescens by Pierre
nest is much disturbed and the larvse and'
Huber, a better observer even than his
pupae are exposed, the slaves work ener
celebrated father. This ant is absolutely
getically with their masters in carrying
dependent on its slaves ; without their aid
them away to a place of safety. Hence it
the species would certainly become extinct
is clear that the slaves feel quite at home.
in a single year. The males and fertile
During the months of June and July, on
females do no work.
The workers or
three successive years, I have watched for
sterile females, though most energetic and
many hours several nests in Surrey and
courageous in capturing slaves, do no
Sussex, and never saw a slave either leave
other work. They are incapable of making
or enter a nest. As, during these months,
their own nests, or of feeding their own
the slaves are very few in number, I thought
larvae. When the old nest is found incon
that they might behave differently when
venient, and they have to migrate, it is the
more numerous ; but Mr. Smith informs
slaves which determine the migration, and
me that he has watched the nests at various
they actually carry their masters in their
hours during May, June, and August, both
jaws. So utterly helpless are the masters,
in Surrey and Hampshire, and has never
that when Huber shut up thirty of them
seen the slaves, though present in large
without a slave, but with plenty of the food
numbers in August, either leave or enter
which they like best and with their larvse
the nest. Hence he considers them as
and pupae to stimulate them to work, they
strictly household slaves. The masters, on
did nothing; they could not even feed
the other hand, may be constantly seen
themselves, and many perished of hunger.
bringing in materials for the nest, and food '
Huber then introduced a single slave (F.
of all kinds. During the present year,
fusca), and she instantly set to work, fed
however, in the month of July, I came
and saved the survivors; made some cells
across a community with an unusually
and tended the larvae, and put all to rights.
large stock of slaves, and I observed a few
What can be more extraordinary than these
slaves mingled with their masters leaving
well-ascertained facts? If we had not known
the nest, and marching along the same
of any other slave-making ant, it would
road to a tall Scotch fir-tree, twenty-five
have been hopeless to have speculated
yards distant, which they ascended to
how so wonderful an instinct could have
gether, probably in search of aphides or
been perfected.
cocci.
According to Huber, who had
Another species, Formica san guinea,
ample opportunities for observation, in
was likewise first discovered by P.‘Huber
Switzerland the slaves habitually work
to be a slave-making- ant. This species
with their masters in making the nest,
is found in the southern parts of England,
and they alone open and close the doors
and its habits have been attended to by
in the morning and evening; and, as
Mr. F. Smith, of the British Museum, to
Huber expressly states, their principal
whom I am much indebted for informa
office is to search for aphides. This dif
tion on this and other subjects. Although
ference in the usual habits of the masters
fully trusting to the statements of Huber
and slaves in the two countries probably
�INSTINCT
depends merely on the slaves being cap
tured in greater numbers in Switzerland
than in England.
One day I fortunately witnessed a migra
tion of F. sanguinea from one nest to
another, and it was a most interesting
spectacle to behold the masters carefully
carrying (instead of being carried by, as in
the case of F. rufescens) their slaves in their
jaws. Another day my attention was struck
by about a 'score of the slave-makers haunt
ing the same spot, and evidently not in
search of food; they approached and were
vigorously repulsed by an independent
community of the slave-species (F. fusca);
sometimes as many as three of these ants
clinging to the legs of the slave-making F.
sanguinea. The latter ruthlessly killed their
small opponents, and carried their dead
bodies as food to their nest, twenty-nine
yards distant; but they were prevented
from getting any pupae to rear as slaves. I
then dug up a small parcel of the pupae of
F. fusca from another nest, and put them
down on a bare spot near the place of
combat; they were eagerly seized, and
carried off by the tyrants, who perhaps
fancied that, after all, they had been vic
torious in their late combat.
At the same time I laid on the same
place a small parcel of the pupae of another
species, F. flava, with a few of these little
yellow ants still clinging to the fragments
of the nest. This species is sometimes,
though rarely, made into slaves, as has been
described by Mr. Smith.
Although so
small a species, it is very courageous, and
I have seen it ferociously attack other ants.
In one instance I found to my surprise an
independent community of F. flava under a
stone beneath a nest of the slave-making
F. sanguinea; and when I had accidentally
disturbed both nests, the little ants attacked
their big neighbours with surprising courage.
Now I was curious to ascertain whether F.
sanguinea could distinguish the pupae of F.
fusca, which they habitually make into
slaves, from those of the little and furious
F. flava, which they rarely capture, and it
was evident that they did at once distinguish
them ; for we have seen that they eagerly
and instantly seized the pupae of F. fusca,
whereas they were much terrified when they
came across the pupae, or even the earth
from the nest of F. flava, and quickly ran
away ; but in about a quarter of an hour,
shortly after all the little yellow ants had
crawled away, they took heart and carried
off the pupae.
One evening I visited another community
93
of F. sanguinea, and found a number of
these ants returning home and entering
their nests, carrying the dead bodies of F.
fusca (showing that it was not a migration)
and numerous pupae. I traced a long file of
ants burthened with booty, for about forty
yards, to a very thick clump of heath,
whence I saw the last individual of F. san
guinea emerge, carrying a pupa; but I was
not able to find the desolated nest in the
thick heath. The nest, however, must have
been close at hand, for two or three indi
viduals of F. fusca were rushing about in
the greatest agitation, and one was perched
motionless with its own pupa in its mouth
on the top of a spray of heath, an image of
despair over its ravaged home.
Such are the facts, though they did not
need confirmation by me, in regard to the
wonderful instinct of making slaves. Let
it be observed what a contrast the instinc
tive habits of F. sanguinea present with
those of the continental F. rufescens. The
latter does not build its own nest, does not
determine its own migrations, does not
collect food for itself or its young, and
cannot even feed itself: it is absolutely
dependent on its numerous slaves. Formica
sanguinea, on the other hand, possesses
much fewer slaves, and in the early part of
the summer extremely few: the masters
determine when and where a new nest shall
be formed, and when they migrate the
masters carry the slaves. Both in Switzer
land and England the slaves seem to have
the exclusive care of the larvae, and the
masters alone go on slave-making expe
ditions. In Switzerland the slaves and
masters work together, making and bringing
materials for the nest: both, but chiefly the
slaves, tend, and milk as it maybe called, their
aphides ; and thus both collect food for the
community. In England the masters alone
usually leave the nest to collect building
materials and food for themselves, their
slaves, and larvae. So that the masters in
this country receive much less service from
their slaves than they do in Switzerland.
By what steps the instinct of F. sanguinea
originated I will not pretend to conjecture.
But as ants, which are not slave-makers,
will, as I have seen, carry off pupae of
other species, if scattered near their nests,
it is possible that such pupae originally
stored as food might become developed ;
and the foreign ants thus unintentionally
reared would then follow their proper
instincts, and do what work they could.
If their presence proved useful to the
species which had seized them—if it were
�94
ON THE ORIGIN OF SPECIES
more advantageous to this species to ca-p. ture workers than to procreate them—the
habit of collecting pupse originally for food
might by natural selection be strengthened
and rendered permanent for the very
different purpose of raising slaves. When
the instinct was once acquired, if carried
out to a much less extent even than in our
British F. sanguinea, which, as we have
seen, is less aided by its slaves than
the same species in Switzerland, I can see
no difficulty in natural selection increasing
and modifying the instinct—always sup
posing each modification to be of use to
the species—until an ant was formed as
abjectly dependent on its slaves as is the
Formica rufescens.
Cell-making instinct of the Hive-Bee. —I
will not here enter on minute details on
this subject, but will merely give an outline
of the conclusions at which I have arrived.
He must be a dull man who can examine
the exquisite structure of a comb, so beau
tifully adapted to its end, without enthu
siastic admiration. We hear from mathe
maticians that bees have practically solved
a recondite p?oblem, and have made their
cells of the proper shape to hold the
greatest possible amount of honey, with
the least possible consumption of precious
wax in their construction. It has been
remarked that a skilful workman, with
fitting tools and measures, would find it
very difficult to make cells of wax of the
true form, though this is perfectly effected
by a crowd of bees working in a dark hive.
Grant whatever instincts you please, and it
seems at first quite inconceivable how they
can make all the necessary angles and
planes, or even perceive when they are
correctly made. But the difficulty is not
nearly so great as it at first appears :
all this beautiful work can be shown, I
think, to follow from a few very simple
instincts.
I was led to investigate this subject by
Mr. Waterhouse, who has shown that the
form of the cell stands in close relation to
the presence of adjoining cells ; and the
following view may, perhaps, be considered
only as a modification of his theory. Let
us look to the great principle of gradation,
and see whether Nature does not reveal to
us her method of work. At one end of a
short series we have humble-bees, which
use their old cocoons to hold honey, some
times adding to them short tubes of wax,
and likewise making separate and very
irregular rounded cells of wax. At the
other end of the series we have the cells
of the hive-bee, placed in a double layer:
each cell, as is well known, is an hexagonal
prism, with the basal edges of its six sides
bevelled so as to fit on to a pyramid, formed
of three rhombs. These rhombs have
certain angles, and the three which form
the pyramidal base of a single cell on one
side of the comb enter into the composi
tion of the bases of three adjoining cells
on the opposite side. In the series between
the extreme perfection of the cells of the
hive-bee and the simplicity of those of the
humble-bee we have the cells of the
Mexican Melipona domestica carefully
described and figured by Pierre Huber.
The Melipona itself is intermediate in
structure between the hive and humble
bee, but more nearly related to the latter :
it forms a nearly regular waxen comb of
cylindrical cells, in which the young are
hatched, and, in addition, some large cells
of wax for holding honey. These latter
cells are nearly spherical and of nearly
equal sizes, and are aggregated into an
irregular mass. But the important point
to notice is that these cells are always
made at that degree of nearness to each
other that they would have intersected or
broken into each other if the spheres had
been completed; but this is never per
mitted, the bees building perfectly flat
walls of wax between the spheres which
thus tend to intersect. Hence each cell
consists of an outer spherical portion and
of two, three, or more perfectly flat surfaces,
according as the cell adjoins two, three, or
more other cells. When one cell comes
into contact with three other cells, which,
from the spheres being nearly of the same
size, is very frequently and necessarily the
case, the three flat surfaces are united into
a pyramid; and this pyramid, as Huber
has remarked, is manifestly a gross imita
tion of the three-sided pyramidal bases of
the cell of the hive-bee. As in the cells of
the hive-bee, so here, the three plane sur
faces in any one cell necessarily enter into
'the construction of three adjoining cells.
It is obvious that the Melipona saves wax
by this manner of building ; for the flat
walls between the adjoining cells are not
double, but are of the' same thickness as
the outer spherical portions, and yet each
flat portion forms a part of two cells.
Reflecting on this case, it occurred to me
that if the Melipona had made its spheres
at some given distance from each other,
and had made them of equal sizes, and had
arranged them symmetrically in a double
�INSTINCT
layer, the resulting structure would pro
bably have been as perfect as the comb of
the hive-bee. Accordingly I wrote to Pro
fessor Miller, of Cambridge, and this
geometer has kindly read over the follow
ing statement, drawn up from his informa
tion, and tells me that it is strictly correct:—•
If a number of equal spheres be described
with their centres placed in two parallel
layers ; with the centre of each sphere at
the distance of radius x •$/ 2, or radius
x 1.41421 (or at some lesser distance), from
the centres of the six surrounding spheres
in the same layer; and at the same distance
from the centres of the adjoining spheres
in the other and parallel layer; then, if
planes of intersection between the several
spheres in both layers be formed, there will
result a double layer of hexagonal prisms
united together by pyramidal bases formed
of three rhombs ; and the rhombs and the
sides of the hexagonal prisms will have
every angle identically the same with the
best measurements which have been made
of the cells of the hive-bee.
Hence we may safely conclude that if
we could slightly modify the instincts
already possessed by the Melipona, and in
themselves not very wonderful, this bee
would make a structure as wonderfully
perfect as that of the hive-bee. We must
suppose the Melipona to make her cells
truly spherical, and of equal sizes ; and
this would not be very surprising, seeing
that she already does so to a certain extent,
and seeing what perfectly cylindrical
burrows in wood many insects can make,
apparently by turning round on a fixed
point. We must suppose the Melipona to
arrange her cells in level layers, as she
already does her cylindrical cells ; and we
must further suppose—and this is the
greatest difficulty—that she can somehow
judge accurately at what distance to stand
from her fellow-labourers when several are
making their spheres ; but she is already
so far enabled to judge of distance that she
always describes her spheres so as to inter
sect largely; and then she unites the points
of intersection by perfectly flat surfaces.
We have further to suppose—but this is no
difficulty—that after hexagonal prisms have
been formed by the intersection of adjoin
ing spheres in the same layer, she can
prolong the hexagon to any length requisite
to hold the stock of honey; in the same
way as the rude humble-bee adds cylinders
of wax to the circular mouths of her old
cocoons. By such modifications of instincts
in themselves not very wonderful—hardly
95
more wonderful than those which guide a
bird to make its nest—I believe that the
hive-bee has acquired, through natural
selection, her inimitable • architectural
powers.
But this theory can be tested by experi
ment. Following the example of Mr.
Tegetmeier, I separated two combs, and
put between them a long, thick, square
strip of wax : the bees instantly began to
excavate minute circular pits in it ; and as
they deepened these little pits, they made
them wider and wider, until they were con
verted into shallow basins, appearing to
the eye perfectly true or parts of a sphere,
and of about the diameter of a cell. It
was most interesting to me to observe that,
wherever several bees had begun to ex
cavate these basins near together, they had
begun their work at such a distance from
each other that by the time the basins had
acquired the above stated width (z>., about
the width of an ordinary cell), and were in
depth about one sixth of the diameter of
the sphere of which they formed a part,
the rims of the basins intersected or broke
into each other. As soon as this occurred,
the bees ceased to excavate,*and began to
build up flat walls of wax on the lines of
intersection between the basins, so that
each hexagonal prism was built upon the
scalloped edge of a smooth basin, instead
of on the straight edges of a three-sided
pyramid, as in the case of ordinary cells.
I then put into the hive, instead of a
thick, square piece of wax, a thin and
narrow, knife-edged ridge, coloured with
vermilion. The bees instantly began on
both sides to excavate little basins near
to each other, in the same way as before ;
but the ridge of wax was so thin that the
bottoms of the basins, if they had been
excavated to the same depth as in the
former experiment, would have broken into
each other from the opposite sides. The
bees, however, did not suffer this to happen,
and they stopped their excavations in due
time ; so that the basins, as soon as they
had been a little deepened, came to have
flat bottoms; and ' these flat bottoms,
formed by thin little plates of the ver
milion wax having been left ungnawed,
were situated, as far as the eye could
judge, exactly along the planes of imagi
nary intersection between the basins on
the opposite sides of the ridge of wax.
In parts only little bits, in other parts
large portions of a rhombic plate, had
been left between the opposed basins; but
the work, from the unnatural state of
�96
ON THE ORIGIN OF SPECIES
things, had not been neatly performed.
The bees must have worked at very nearly
the same rate on the opposite sides of the
ridge of vermilion wax, as they circularly
gnawed away and deepened the basins on
both sides, in order to have succeeded in
thus leaving flat plates between the basins,
by stopping work along the intermediate
planes or planes of intersection.
Considering how flexible thin wax is,
I do not see that there is any difficulty
in the bees, while at work on the two
sides of a strip of wax, perceiving when
they have gnawed the wax away to the
proper thinness, and then stopping their
work. In ordinary combs it has appeared
to me that the bees do not always succeed
in working at exactly the same rate from
the opposite sides; for I have noticed half
completed rhombs at the base of a justcommenced cell, which were slightly con
cave on one side, where I suppose that the
bees had excavated too quickly, and con
vex on the opposed side, where the bees
had worked less quickly. In one wellmarked instance I put the comb back into
the hive, and. allowed the bees to go on
working for a short time, and again ex
amined the cell •, and I found that the
rhombic plate had been completed, and
had become perfectly flat: it was absolutely
impossible, fr.om the extreme thinness of
the little rhombic plate, that they could
have effected this by gnawing away the
convex side ; and I suspect that the bees
in such cases stand in the opposed cells,
and push and bend the ductile and warm
wax (which, as I have tried, is easily done)
into its proper intermediate plane, and
thus flatten it.
From the experiment of the ridge of ver
milion wax, we can clearly see that, if the
bees were to build for themselves a thin
wall of wax, they could make their cells of
the proper shape, by standing at the proper
distance from each other, by excavating at
the same rate, and by endeavouring to
make equal spherical hollows, but never
allowing the spheres to break into each
other. Now, bees, as may be clearly seen
by examining the edge of a growing comb,
do make a rough, circumferential wall or
rim all round the comb ; and they gnaw
into this from the opposite sides, always
working circularly as they deepen each
cell. They do not make the whole threesided pyramidal base of any one cell at
the same time, but only the one rhombic
plate which stands on the extreme growing
margin, or the two plates, as the case may
be ; and they never complete the upper
edges of the rhombic plates until the
hexagonal walls are commenced. Some
of these statements differ from those made
by the justly celebrated elder Huber, but I
am convinced of their accuracy; and, if I
had space, I could show that they are con
formable with my theory.
Huber’s statement, that the very first cell
is excavated out of a little parallel-sided
wall of wax, is not, as far as I have seen,
strictly correct, the first commencement
having always been a little hood of wax;
but I will not here enter on these details.
We see how important a part excavation
plays in the construction of the cells ; but
it would be a great error to suppose that
the bees cannot build up a rough wall of
wax in the proper position—that is, along
the plane of intersection between two
adjoining spheres. I have several speci
mens showing clearly that they can do
this. Even in the rude circumferential
rim or wall of wax round a growing comb
flexures may sometimes be observed,
corresponding in position to the planes of
the rhombic basal plates of future cells.
But the rough wall of wax has in every
case to be finished off by being largely
gnawed away on both sides. The manner
in which the bees build is curious : they
always make the first rough wall from ten
to twenty times thicker than the excessively
thin finished wall of the cell, which will
ultimately be left. We shall understand
how they work by supposing masons first
to pile up a broad ridge of cement, and
then to begin cutting it away equally on
both sides near the ground till a smooth,
very thin wall is left in the middle ; the
masons always piling up the cut-away
cement, and adding fresh cement, on the
summit of the ridge. We shall thus have
a thin wall steadily growing upward, but
always crowned by a gigantic coping.
From all the cells, both those just com
menced and those completed, being thus
crowned by a strong coping of wax, the
bees can cluster and crawl over the comb
without injuring the delicate hexagonal
walls, vzhich are only about one fourhundredth of an inch in thickness, the
plates of the pyramidal basis being about
twice as thick. By this singular manner
of building strength is continually given
to the comb with the utmost ultimate
economy of wax.
It seems at first to add to the difficulty
of understanding how the cells are made
that a multitude of bees all work together;
�INSTINCT
one bee after working a short time at one
cell going to another, so that, as Huber
has stated, a score of individuals work
even at the commencement of the first
cell. I was able practically to show this
fact by covering the edges of the hexagonal
walls of a single cell, or the extreme margin
of the circumferential rim of a growing
comb, with an extremely thin layer of
melted vermilion wax ; and I invariably
found that the colour was most delicately
diffused by the bees—as delicately as a
painter could have done with his brush—
by atoms of the coloured wax having been
taken from the spot on which it had been
placed, and worked into the growing edges
of the cells all round. The work of con
struction seems to be a sort of balance
■ struck between many bees, all instinctively
standing at the same relative distance
from each other, all trying to sweep equal
spheres, and then building up, or leaving
ungnawed, the planes of intersection
between these spheres. It was really
curious to note in cases of difficulty, as
when two pieces of comb met at an angle,
how often the bees would pull down and
rebuild in different ways the same cell,
sometimes recurring to a shape which they
had at first rejected.
When bees have a place on which they
can stand in their proper positions for
working—for instance, on a slip of wood,
placed directly under the middle of a comb
growing downwards, so that the comb has
to be built over one face of the slip—in
this case the bees can lay the foundations
of one wall of a new hexagon, in its strictly
proper place, projecting beyond the other
completed cells. It suffices that the bees
should be enabled to stand at their proper
relative distances from each other and
from the walls of the last completed cells,
and then, by striking imaginary spheres,
they can build up a wall intermediate
between two adjoining spheres ; but, as far
as I have seen, they never gnaw away and
finish off the angles of a cell till a large
part both of that cell and of the adjoining
cells has been built. This capacity in bees
of laying down under certain circumstances
a rough wall in its proper place between
two just-commenced cells is important, as
it bears on a fact, which seems at first quite
subversiveof the foregoing theory—namely,
that the cells on the extreme margin of
wasp-combs are sometimes strictly hex
agonal ; but I have not space here to enter
on this subject. Nor does there seem to
me any great difficulty in a single insect
97
(as in the case of a queen wasp) making
hexagonal cells, if she work alternately on
the inside and outside of two or three cells
commenced at the same time, always
standing at the proper relative distance
from the parts of the cells just begun, sweep
ing spheres or cylinders, and building up
intermediate planes. It is even conceiv
able that an insect might, by fixing on a
point at which to commence a cell, and
then moving outside, first to one point, and
then to five other points, at the proper
relative distances from the central point
and from each other, strike the planes of
intersection, and so make an isolated
hexagon ; but I am not aware that any such
case has been observed; nor would any good
be derived from a single hexagon being
built, as in its construction more materials
would be required than for a cylinder.
As natural selection acts only by the
accumulation of slight modifications of
structure or instinct, each profitable to the
individual under its conditions of life, it
may reasonably be asked how a long and
graduated succession of modified architec
tural instincts, all tending towards the
present perfect plan of construction, could
have profited the progenitors of the hive
bee ? I think the answer is not difficult:
it is known that bees are often hard pressed
to get sufficient nectar; and I am informed
by Mr. Tegetmeier that it has been experi
mentally found that no less than from
twelve to fifteen pounds of dry sugar are
consumed by a hive of bees for the secre
tion of each pound of wax ; to that a pro
digious quantity of fluid nectar must be
collected and consumed by the bees in a
hive foi the secretion of the wax necessary
for the construction of their combs. More
over, many bees have to remain idle for
many days during the process of secretion.
A large store of honey is indispensable to
support a large stock of bees during the
winter; and the security of the hive is
known mainly to depend on a large number
of bees being supported. Hence the saving
of wax by largely saving honey must be a
most important element of success in any
family of bees. Of course, the success of
any species of bee may be dependent on
the number of its parasites or other
enemies, or on quite distinct causes, and so
be altogether independent of the quantity
of honey which the bees could collect.
But let us suppose that this latter circum
stance determined, as it probably often
does determine, the numbers of a humblebee which could exist in a country; and
�98
ON THE ORIGIN OF SPECIES
we cannot see how an instinct could pos
let us further suppose that the community
sibly have originated ; cases in which no
lived throughout the winter, and conse
quently required a store of honey : there
intermediate gradations are known to exist;
cases of instinct of apparently such trifling
can, in this case, be no doubt that it would
importance that they could hardly have
be ah advantage to our humble-bee if a
slight modification of her instinct led her to
been acted on by natural selection ; cases
make her waxen cells near together, so as
of instincts almost identically the same
in animals, so remote in the scale of nature
to intersect a little ; for a wall in common,
that we cannot account for their similarity
even to two adjoining cells, would save
by inheritance from a common parent, and
some little wax. Hence it would continu
must therefore believe that they have been
ally be more and more advantageous to our
acquired by independent acts of natural
humble-bee if she were to make her cells
selection. I will not here enter on these
more and more regular, nearer together,
several cases, but will confine myself to
and aggregated into a mass, like the cells
one special difficulty, which at first ap
of the Melipona; for in this case a large
peared to me insuperable, and actually
part of the bounding surface of each cell
fatal to my whole theory. I allude to the
would serve to bound other cells, and much
neuters or sterile females in insect-com
wax would be saved. Again, from the same
munities ; for these neuters often differ
cause, it would be advantageous to the
widely in instinct and in structure from
Melipona if she were to make her cells
both the males and fertile females, and
closer together, and more regular in every
yet, from being sterile, they cannot propa
way than at present; for then, as we have
gate their kind.
seen, the spherical surfaces would wholly
The subject well deserves to be discussed
disappear, and would all be replaced by
at great length, but I will here take only a
plane surfaces ; and the Melipona would
single case, that of working or sterile ants.
make a comb as perfect as that of the
How the workers have been rendered
hive-bee. Beyond this stage of perfection
sterile is a difficulty; but not much greater
in architecture natural selection could not
than that of any other striking modification
lead; for the comb of the hive-bee, as far
of structure ; for it can be shown that
as we can see, is absolutely perfect in
some insects' and other articulate animals
economising wax.
in a state of nature occasionally become
Thus, as I believe, the most wonderful
of all known instincts, that of the hive-bee, .sterile; and if such insects had been social,
and it had been profitable to the com
can be explained by natural selection
munity that a number should have been
having taken advantage of numerous,
annually born capable of work, but in
successive, slight modifications of simpler
capable of procreation, I can see no very
instincts : natural selection having by slow
great difficulty in this being effected by
degrees, more and more perfectly, led the
natural selection. But I must pass over
bees to sweep equal spheres at a given
this preliminary difficulty. The great diffi
distance from each other in a double layer,
culty lies in the working ants differing
and to build up and excavate the wax
widely from both the males and the fertile
along the planes of intersection.
The
females in structure, as in the shape of the
bees, of course, no more knowing that
thorax and in being destitute of wings and
they swept their spheres at one particular
sometimes of eyes, and in instinct As far
distance from each other than they know
as instinct alone is concerned, the pro
what are the several angles of the hexa
digious difference in this respect between
gonal prisms and of the basal rhombic
the workers and the perfect females would
plates. The motive power of the process
have been far better exemplified by
of natural selection having been economy
the hive-bee. If a working ant or other
of wax; that individual swarm which
neuter insect had been an animal in the
wasted least honey in the secretion of wax
ordinary state, I should have unhesitatingly
having succeeded best, and having trans
assumed that all its characters had been
mitted by inheritance its newly-acquired
slowly acquired through natural selection—
economical instinct to new swarms, which
namely, by an individual having been born
in their turn will have had the best chance
with some slight profitable modification of
of succeeding in the struggle for existence.
structure, this being inherited by its off
spring, which again varied and were again
No doubt many instincts of very diffi
selected, and so onwards. _ But with the
cult explanation could be opposed to the
working ant we have an insect differing
theory of natural selection—cases in which
�INSTINCT
greatly from its parents, yet absolutely
sterile ; so that it could never have trans
mitted successively acquired modifications
of structure or instinct to its progeny. It
may well be asked, How is it possible to
reconcile this case with the theory of
natural selection ?
First, let it be remembered that we have
innumerable instances, both in our domestic
productions and in those in a state of nature,
of all sorts of differences of structure which
have become correlated to certain ages,
and to either sex. We have differences
correlated not only to one sex, but to that
short period alone when the reproductive
system is active, as in the nuptial plumage
of many birds, and in the hooked jaws of
the male salmon. We have even slight
differences in the horns of different breeds
of cattle in relation to an artificially im
perfect state of the male sex ; for oxen of
certain breeds have longer horns than in
other breeds, in comparison with the horns
of the bulls or cows of these same breeds.
Hence I can see no real difficulty in any
character having become correlated with
the sterile condition of certain members of
insect-communities : the difficulty lies in
understanding how such correlated modi
fications of structure could have been slowly
accumulated by natural selection.
This difficulty, though appearing in
superable, is lessened, or, as I believe,
disappears, when it is remembered that
selection may be applied to the family, as
well as to the individual, and may thus gain
the desired end. Thus, a well-flavoured
vegetable is cooked, and the individual is
destroyed; but the horticulturist sows seeds
of the same stock, and confidently expects
to get nearly the same variety: breeders of
cattle wish the flesh and fat to be well
marbled together; the animal has been
slaughtered, but the breeder goes with con
fidence to the same family. I have such
faith in the powers of selection that I do
not doubt that a breed of cattle, always
yielding oxen with extraordinarily long
horns, could be slowly formed by care
fully watching which individual bulls and
cows, when matched, produced oxen with
the longest horns ; and yet no one ox
could ever have propagated its kind. Thus
I believe it has been with social insects : a
slight modification of structure, or instinct,
correlated with the sterile condition of
certain members of the community, has
been advantageous to the community: con
sequently the fertile males and females of
the same community flourished, and trans
99
mitted to their fertile offspring a tendency *
to produce sterile members having the same
modification. And I believe that this pro
cess has been repeated, until that prc^ligious
amount of difference between the fertile
and sterile females of the same species has
been produced, which we see in many
social insects.
But we have not as yet touched on the
climax of the difficulty—namely, the fact
that the neuters of several ants differ, not
only from the fertile females and males,
but from each other, sometimes to an
almost incredible degree, and are thus
divided into two or even three castes. The
castes, moreover, do not generally graduate
into each other, but are perfectly well
defined; being as distinct from each other
as are any two species of the same genus,
or rather as any two genera of the same
family. Thus in Eciton there are working
and soldier neuters, with jaws and instinctsextraordinarily different ; in Cryptocerus
the workers of one caste alone carry a
wonderful sort of shield on their heads, the
use of which is quite unknown ; in the
Mexican Myrmecocystus the workers of
one caste never leave the nest—they are
fed by the workers of another caste, an-d
they have an enormously developed
abdomen, which secretes a sort of honey,
supplying the place of that excreted by the
aphides, or the domestic cattle as they may
be called, which our European ants guard
or imprison.
It will indeed be thought that I have an.
overweening confidence in the principle of’
natural selection when I do not admit that
such wonderful and well-established factsat once annihilate my theory. I n the simpler
case of neuter insects all of one caste or of
the same kind, which have been rendered
by natural selection, as I believe to be quite
possible, different from the fertile males
and females—in this case we may safely
conclude from the analogy of ordinary
variations that each successive, slight,
profitable modification did not probably
at first appear in all the individual neuters
in the same nest, but in a few alone ; and
that by the long-continued selection of the
fertile parents which produced most neuters
with the profitable modification, all the
neuters ultimately came to have the desired
character. On this view we ought occa
sionally to find neuter-insects of the same
species, in the same nest, presenting grada
tions of structure ; and this we do find,
even often, considering how few neuter
insects out of Europe have been carefully
�IOO
ON THE ORIGIN OF SPECIES
examined. Mr. F. Smith has shown how
surprisingly the neuters of several British
ants differ from each other in size, and
sometimes in colour; and that the extreme
forms can sometimes be perfectly linked
together by individuals taken out of the
same nest: I have myself compared per
fect gradations of this kind.
It often
happens that the larger or the smaller
sized workers are the most numerous ; or
that both large and small are numerous,
with those of an intermediate size scanty
in numbers. Formica flava has larger and
smaller workers, with some of intermediate
size; and in this species, as Mr. F. Smith
has observed, the larger workers have
simple eyes (ocelli), which, though small,
can be plainly distinguished, whereas the
smaller workers have their ocelli rudi
mentary. Having carefully dissected seve
ral specimens of these workers, I can
affirm that the eyes are far more rudi
mentary in the smaller workers than can
be accounted for merely by their propor
tionally lesser size ; and- I fully believe,
though I dare not assert so positively, that
the workers of intermediate size have their
ocelli in an exactly intermediate condition.
So that we here have two bodies of sterile
workers in the same nest, differing not
only in size, but in their organs of vision,.
yet connected by some few members in an
intermediate condition. I may digress by
adding that, if the smaller workers had
been the most useful to the community,
and those males and females had been
continually selected, which produced more
and more of the smaller workers, until
all the workers had come to be in this
condition; we should then have had a
species of ant with neuters very nearly in
the same condition with those of Myrmica.
For the workers of Myrmica have not
even rudiments of ocelli, though the male
and female ants of this genus have welldeveloped ocelli.
I may give another case : so confidently
did I expect to find gradations in impor
tant points of structure between the dif
ferent castes of neuters in the same species
that I gladly availed myself of Mr. F.
Smith’s offer of numerous specimens from
the same nest of the driver ant (Anomma)
of West Africa. The reader will perhaps
best appreciate the amount of difference in
these workers by my giving not the actual
measurements, but a strictly accurate illus
tration : the difference was the same as if
we were to see a set of workmen building
a house of whom many were five feet four
inches high and many sixteen feet high ;
but we must suppose that the larger work
men had heads four instead of three times
as big as those of the smaller men, and
jaws nearly five times as big. The jaws,
moreover, of the working ants of the
several sizes differed wonderfully in shape,
and in the form and number of the teeth.
But the important fact for us is that,
though the workers can be grouped into
castes of different sizes, yet they graduate
insensibly into each other, as does the
widely-different structure of their jaws. I
speak confidently on this latter point, as
Mr. Lubbock made drawings for me with
the camera lucida of the jaws which I had
dissected from the workers of the several
sizes.
With these facts before me, I believe
that natural selection, by acting on the fertile
parents, could form a species which should
regularly produce neuters, either all of
large size with one form of jaw, or all
of small size with jaws having a widely
different structure ; or lastly, and this is
our climax of difficulty, one set of workers of
one size and structure, and simultaneously
another set of workers of a different size
and structure—a graduated series having
been first formed, as in the case of the
driver ant, and then the extreme forms,
from being the most useful to the com
munity, having been produced in greater
and greater numbers through the natural
selection of the parents which generated
them, until none with an intermediate
structure were produced.
Thus, as I believe, the wonderful fact of
two distinctly defined castes of sterile
workers existing in the same nest, both
widely different from each other and from
their parents, has originated. We can see
how useful their production may have been
to a social community of insects, on the
same principle that the division of labour
is useful to civilised man. As ants work
by inherited instincts and by inherited
organs or tools, and not by acquired know
ledge and manufactured instruments, a
perfect division of labour could be effected
with them only by the workers being sterile ;
for, had they been fertile, they would have
intercrossed, and their instincts and struc
ture would have become blended. And
nature has, as I believe, effected this admir
able division of labour in the communities
of ants by the means of natural selection.
But I am bound to confess that, with all
my faith in this principle, I should never
have anticipated that natural selection
�INSTINCT
could have been efficient in so high a
degree had not the case of these neuter
insects convinced me of the fact. I have,
therefore, discussed this case, at some little
but wholly insufficient length, in order to
show the power of natural selection, and
likewise because this is by far the most
serious special difficulty which my theory
has encountered. The case, also, is very
interesting, as it proves that with animals,
as with plants, any amount of modification
in structure can be effected by the accumu
lation of numerous, slight, and, as we must
call them, accidental variations, which are
in any manner profitable, without exercise
or habit having coming into play. For no
amount of exercise, or habit, or volition, in
the utterly sterile members of a community
could possibly affect the structure or
instincts of the fertile members, which
alone leave descendants. I am surprised
that no one has advanced this demonstra
tive case of neuter insects against the wellknown doctrine of Lamarck.
Summary.—I have endeavoured briefly
in this chapter to show that the mental
qualities of our domestic animals vary,
and that the variations are inherited. Still
more briefly I have attempted to show that
instincts vary slightly in a state of nature.
No one will dispute that instincts are of
the highest importance to each animal.
Therefore, 1 can see no difficulty, under
changing conditions of life, in natural
selection accumulating slight modifications
of instinct to any extent in any useful
direction. In some cases habit or use and
disuse have probably come into play. I
do not pretend that the facts given in this
chapter strengthen in any great degree my
theory ; but none of the cases of difficulty,
loi
to the best of my judgment, annihilate it.
On the other hand, the fact that instincts
are not always absolutely perfect, and are
liable to mistakes—that no instinct has
been produced for the exclusive good of
other animals, but that each animal takes
advantage of the instincts of others ; that
the canon in natural history, of “ Natura
non facit saltum,” is applicable to instincts
as well as to corporeal structure, and is.
plainly explicable on the foregoing views,
but is otherwise inexplicable—all tend tocorroborate the theory of natural selection.
This theory is, also, strengthened by
some few other facts in regard to instincts ;
as by that common case of closely-allied,
but certainly distinct^ species, when in
habiting distant parts of the world and
living under considerably different con
ditions of life, yet often retaining nearly
the same instincts. For instance, we can
understand, on the principle ofiinheritance,
how it is that the thrush of South America,
lines its nest with mud in the same peculiar
manner as does our British thrush ; how it
is that the male wrens (Troglodytes) of
North America build “ cock-nests ;; to roost
in, like the males of our distinct Kitty
wrens—a habit wholly unlike that of any
other known bird. Finally, it may not be
a logical deduction, but to my imagination
it is far more satisfactory to look at such
instincts as the young cuckoo ejecting its
foster-brothers—ants making slaves—the
larvae of ichneumonidae feeding within the
live bodies of caterpillars—not as specially
endowed or created instincts, but as small
consequences of one general law, leading
to the advancement of all organic beings—
namely, multiply, vary, let the strongest
live and the weakest die. •
�102
ON THE ORIGIN OF SPECIES
Chapter VIII.
HYBRIDISM
Distinction "between the sterility of first crosses
and of hybrids—Sterility various in degree,
not universal, affected by close inter-breeding,
removed by domestication—Laws governing
the sterility of hybrids—Sterility not a special
'■-endowment, but incidental on other differences
—-Causes of the sterility of first crosses and of
hybrids—Parallelism between the effects of
■ -changed conditions of life and crossing—
Fertility of varieties when crossed and of their
mongrel offspring not universal—Hybrids and
mongrels compared independently of their
fertility—Summary.
The view generally entertained by natu
ralists is that species, when intercrossed,
have been specially endowed with the
quality of sterility, in order to prevent the
confusion of all organic forms. This view
certainly seems at first probable, for species
within the same country could hardly have
kept distinct had they been capable of
crossing freely. The importance of the fact
that hybrids are very generally sterile has,
I think, been much underrated by some
late writers. On the theory of natural
selection the case is especially important,
inasmuch as the sterility of hybrids could
not possibly be of any advantage to them,
and therefore could not have been acquired
by the continued preservation of successive
profitable degrees of sterility. I hope, how
ever, to be able to show that sterility is not
a specially acquired or endowed quality,
but is incidental on other acquired differ
ences.
In treating this subjeot, two classes of
facts, to a large extent fundamentally
different, have generally been confounded
together; namely, the sterility of two species
when first crossed, and the sterility of the
hybrids produced from them.
Pure species have of course their organs
of reproduction in a perfect condition, yet
when intercrossed they produce either few
or no offspring. Hybrids, on the other
hand, have their reproductive organs func
tionally impotent, as may be clearly seen
in the state of the male element in both
plants and animals ; though the organs
themselves are perfect in structure, as far
as the microscope reveals. In the first case
the two sexual elements which go to form
the embryo are perfect; in the second case
they are either not at all developed, or are
imperfectly developed. This distinction is
important, when the cause of the sterility,
which is common to the two cases, has to
be considered. The distinction has pro
bably been slurred over, owing to the
sterility in both cases being looked on as a
special endowment, beyond the province of
our reasoning powers.
The fertility of varieties, that is of the
forms known or believed to have descended
from common parents, when intercrossed,
and likewise the fertility of their mongrel
offspring, is, on my theory, of equal im
portance with the sterility of species ; for
it seems to make a broad and clear distinc
tion between varieties and species.
First, for the sterility of species when
crossed and of their hybrid offspring. It is
impossible to study the several memoirs
and works of those two conscientious and
admirable observers, Kolreuterand Gartner,
who almost devoted their lives to this
subject, without being deeply impressed
with the high generality of some degree of
sterility. Kolreuter makes the rule uni
versal ; but then he cuts the knot, for in
ten cases in which he found two forms,
considered by most authors as distinct
species, quite fertile together, he unhesi
tatingly ranks them as varieties. Gartner,
also, makes the rule equally universal; and
he disputes the entire fertility of Kolreuter’s
ten cases. But in these and in many other
cases Gartner is obliged carefully to count
the seeds, in order to show that there is
any degree of sterility. He always com
pares the maximum number of seeds pro
duced by two species when crossed, and by
their hybrid offspring, with the average
number produced by both pure parent
species in a state of nature. But a serious
cause of error seems to me to be here intro
duced : a plant to be hybridised must be
castrated, and, what is often more impor
tant, must be secluded in order to prevent
pollen being brought to it by insects from
other plants. Nearly all the plants experimentised on by Gartner were potted,
�HYBRIDISM
and apparently were kept in a chamber in
his house. That these processes aie often
injurious to the fertility of a plant cannot
be doubted ; for Gartner gives in his table
about a score of cases of plants which he
castrated, and artificially fertilised with
their own pollen, and (excluding all cases
such as the Leguminosae, in which there is
an acknowledged difficulty in the manipula
tion) half of these twenty plants had their
fertility in some degree impaired. More
over, as Gartner during several years
repeatedly crossed the prirryose and cow
slip, which we have such good reason to
believe to be varieties, and only once or
twice succeeded in getting fertile seed ; as
he found the common red and blue pim
pernels (Anagallis arvensis and ccerulea),
which the best botanists rank as varieties,
absolutely sterile together; and as he came
to the same conclusion in several other
analogous cases, it seems to me that we
may well be permitted to doubt whether
many other species are really so sterile,
when intercrossed, as Gartner believes.
It is certain, on the one hand, that the
sterility of various species when crossed is
so different in degree, and graduates away
so insensibly, and, on the other hand, that
the fertility of pure species is so easily
affected by various circumstances, that for
all practical purposes it is most difficult to
say where perfect fertility ends and sterility
begins. I think no better evidence of this
can be required than that the two most
experienced observers who have ever lived
-—namely, Kblreuter and Gartner—should
have arrived at diametrically opposite con
clusions in regard to the very same species.
It is also most instructive to compare—
but I have not space here to enter on
details—the evidence advanced by our best
botanists on the question whether certain
doubtful forms should be ranked as species
or varieties with the evidence from fertility
adduced by different hybridisers, or by
the same author, from experiments made
during different years. It can thus be
shown that neither sterility nor fertility
affords any' clear distinction between
species and varieties; but that the evi
dence from this source graduates away,
and is doubtful in the same degree as
is the evidence derived from other con
stitutional and structural differences.
In regard to the sterility of hybrids in
successive generations; though Gartner
was enabled to rear some hybrids, care
fully guarding them from a cross with
either pure parents, for six or seven, and
103
in one case for ten generations, yet he
asserts positively that their fertility never
increased, but generally greatly decreased.
I do not doubt that this is usually the case,
and that the fertility often suddenly de
creases in the first few generations. Never
theless, I believe that in all these experi
ments the fertility has been diminished
by an independent cause—namely, from
close interbreeding. I have collected so
large a body of facts, showing that close
interbreeding lessens fertility, and, on the
other hand, that an occasional cross with a
distinct individual or variety increases fer
tility, that I cannot doubt the correctness
of this almost universal belief among
breeders. Hybrids are seldom raised by
experimentalists in great numbers ; and as
the parent-species, or other allied hybrids,
generally grow in the same garden, the
visits of insects must be carefully prevented
during the flowering season; hence hybrids
will generally be fertilised during each
generation by their own individual pollen ;
and I am convinced that this would be
injurious to their fertility, already lessened
by their hybrid origin. I am strengthened
in this conviction by a remarkable state
ment repeatedly made by Gartner—namely,
that, if even the less fertile hybrids be
artificially fertilised with hybrid pollen of
the same kind, their fertility, notwith
standing the frequent ill effects of mani
pulation, sometimes decidedly increases,
and goes on increasing. Now, in artificial
fertilisation pollen is as often taken by
chance (as I know from my own expe
rience) from the anthers of another flower
as from the anthers of the flower itself
which is to be fertilised ; so that a cross
between two flowers, though probably on
the same plant, would be thus effected.
Moreover, whenever complicated experi
ments are in progress, so careful an ob
server as Gartner would have castrated
his hybrids, and this would have insured
in each generation a cross with a
pollen from a distinct flower, either from
the same plant or from another plant of
the same hybrid nature. And thus the
strange fact of the increase of fertility
in the successive generations of artificially
fertilised hybrids may, I believe, be ac
counted for by close interbreeding having
been avoided.
Now let us turn to the results arrived at
by the third most experienced hybridiser
—namely, the Hon. and Rev. W. Herbert.
He is as emphatic in his conclusion that
some hybrids are perfectly fertile—as fertile
�104
ON THE ORIGIN OF SPECIES
as the pure parent-species—as are Kolplants in these experiments appeared per
reuter and Gartner that some degree of fectly healthy, and although both the ovules
sterility between distinct species is a uni
and pollen of the same flower were per
versal law of nature. He experimentised
fectly good with respect to other species,
on some of the very same species as did
yet, as they were functionally imperfect in
Gartner. The difference in their results
their mutual self-action, we must infer that
may, I think, be in part accounted for
the plants were in an unnatural state.
by Herbert’s great horticultural skill,
Nevertheless, these facts show on what
and by his having hothouses at his com
slight and mysterious causes the lesser or
mand. Of his many important statements
greater fertility of species when crossed,
I will here give only a single one as an
in comparison with the same species when
example—namely, that “ every ovule in a
self-fertilised, sometimes depends.
pod of Crinum capense fertilised by C.
The practical experiments of horticul
revolutum produced a plant, which (he
turists, though not made with scientific
says) I never saw to occur in a case of precision, deserve some notice.
It is
its natural fecundation.” So that we here
notorious in how complicated a manner
have perfect, or even more than commonly
the species of Pelargonium, Fuchsia, Cal
perfect, fertility in a first cross between
ceolaria, Petunia, Rhododendron, etc., have
two distinct species.
been crossed, yet many of these hybrids
This case of the Crinum leads me to
seed freely. For instance, Herbert asserts
refer to a most singular fact—namely, that
that a hybrid from Calceolaria integrifolia
there are individual plants of certain
and plantaginea, species most widely dis
species of Lobelia and of some other
similar in general habit, “reproduced itself
genera, which can be far more easily
as perfectly as if it had been a natural
fertilised by the pollen of another and
species from the mountains of Chile.” I
distinct species than by their own pollen ;
have taken some pains to ascertain the
and all the individuals of nearly all the
degree of fertility of some of the complex
species of Hippeastrum seem to be in this
crosses of Rhododendrons, and I am
predicament. For these plants have been
assured that many of them are perfectly
found to yield seed to the pollen of a
fertile. Mr. C. Noble, for instance, informs
distinct species, though quite sterile with
me that he raises stocks for grafting from
their own pollen, notwithstanding that their
a hybrid between Rhod. Ponticum and
own pollen was found to be perfectly good,
Catawbiense, and that this hybrid “seeds
as freely as it is possible to imagine.” Had
for it fertilised distinct species. So that
hybrids, when fairly treated, gone on
certain individual plants and all the indi
viduals of certain species can actually be I decreasing in fertility in each successive
generation, as Gartner believes to be the
hybridised much more readily than they
case, the fact would have been notorious
can be self-fertilised 1 For instance, a bulb
to nurserymen. Horticulturists raise large
of Hippeastrum aulicum produced four
beds of the same hybrids, and such alone
flowers; three were fertilised by Herbert
are fairly treated, for by insect agency the
with their own pollen, and the fourth was
several individuals of the same hybrid
subsequently fertilised by the pollen of a
variety are allowed to freely cross with
compound hybrid descended from three
each other, and the injurious influence
other and distinct species : the result was
of close interbreeding is thus prevented.
that “ the ovaries of the three first flowers
Anyone may readily convince himself of
soon ceased to grow, and after a few days
the efficiency of insect-agency by examining
perished entirely, whereas the pod impreg
the flowers of the more sterile kinds of
nated by the pollen of the hybrid made
hybrid rhododendrons, which produce no
vigorous growth and rapid progress to
pollen, for he will find on their stigmas
maturity, and bore good seed, which
plenty of pollen brought from other flowers.
vegetated freely.” In a letter to me, in
In regard to animals, much fewer experi
1839, Mr. Herbert told me that he had
ments have been carefully tried than with
then tried the experiment during five years,
plants. If our systematic arrangements
and he continued to try it during' several
can be trusted—that is, if the genera of
subsequent years, and always with the
animals are as distinct from each other as
same result. This result has also been
are the genera of plants—then we may
confirmed by other observers in the case
infer that animals more widely separated
of Hippeastrum with its sub-g-enera, and
in the scale of nature can be more easily
in the case of some other g-enera, as Lobelia,
crossed than in the case of plants ; but the
Passiflora, and Verbascum/ Although the
�HYBRIDISM
J05
crossed geese are kept in various parts of
hybrids themselves are, I think, more
the country ; and as they are kept for
sterile. I doubt whether any case of a
profit, where neither pure parent-species
perfectly fertile hybrid animal can be con
exists, they must certainly be highly fertile.
sidered as thoroughly well authenticated.
A doctrine which originated with Pallas
It should, however, be borne in mind that,
has been largely accepted by modern
owing to few animals breeding freely under
confinement, few experiments have been
naturalists—namely, that most of our
domestic animals have descended from two
fairly tried : for instance, the canary-bird
has been crossed with nine other finches,
or more wild species, since commingled by
intercrossing. On this view, the aboriginal
but, as not one of these nine species breeds
species must either at first have produced
freely in •confinement, we have no right to
expect that the first crosses between them I quite fertile hybrids, or the hybrids must
and the canary, or that their hybrids, should ! have become in subsequent generations
quite fertile under domestication. This
be perfectly fertile. Again, with respect to
latter alternative seems to me the most
the fertility in successive generations of the
more fertile hybrid animals, I hardly know
probable, and I am inclined to believe in
of an instance in which two families of the
its truth, although it rests on no direct
same hybrid have been raised at the same
evidence. I believe, for instance, that our
time from different parents, so as to avoid
dogs have descended from several wild
the ill effects of close interbreeding'. On
stocks ; yet, with perhaps the exception of
the contrary, brothers and sisters have
certain indigenous domestic dogs of South
usually been crossed in each successive
America, all are quite fertile together; and
generation, m opposition to the constantly
analogy makes me greatly doubt whether
repeated admonition of every breeder.
the several aboriginal species would at first
And in this case it is not at all surprising
have freely bred together and have pro
that the inherent sterility in the hybrids
duced quite fertile hybrids. So, again, there
should have gone on increasing. If we
is reason to believe that our European and
were to act thus, and pair brothers and
the humped Indian cattle are quite fertile
sisters in the case of any pure animal, which
together ; but, from facts communicated to
from any cause had the least tendency to
me by Mr. Blyth, I think they must be
sterility, the breed would assuredly be lost
considered as distinct species. On this
in a very few generations.
view of the origin of many of our domestic
Although I do not know of any thoroughly
animals, we must either give up the belief
well-authenticated cases of perfectly fertile
of the almost universal sterility of distinct
hybrid animals, I have some reason to
species of animals when crossed, or we
believe that the hybrids from Cervulus
must look at sterility, not as an indelible
vaginalis and Reevesii, and from Phasianus
characteristic, but as one capable of being
colchicus with P. torquatus and P. versi
removed by domestication.
color are perfectly fertile. There is no
Finally, looking to all the ascertained
doubt that these three pheasants—namely,
facts on the intercrossing of plants and
the common, the true ring-necked, and the
animals, it may be concluded that some
Japan — intercross, and are.- becomingdegree of sterility, both in first crosses and
blended together in the woods of several
in hybrids, is an extremely general result,
parts of England. The hybrids from the
but that it cannot, under our present state
common and Chinese geese (A. cygnoides),
of knowledge, be considered as absolutely
species, which are so different that
universal.
they are generally ranked in distinct
genera, have often bred in this country
Laws governing the Sterility of first
with either pure parent, and in one
Crosses and of Hybrids.—We will now
single instance they have bred inter se,
consider a little more in detail the circum
This was effected by Mr. Eyton, who
stances and rules governing the sterility of
raised two hybrids from the same parents,
first crosses and of hybrids. Our chief
but from different hatches ; and from
object will be to see whether or not the
these two birds he raised no less than
rules indicate that species have specially
eight hybrids (grandchildren of the pure
been endowed with this quality, in order to
geese) from one nest. In India, however,
prevent their crossing and blending to
these cross-bred geese must be far more
gether ifi utter confusion. The following
fertile, for I am assured by two eminently
rules and conclusions are chiefly drawn
capable judges—namely, Mr. Blyth and
up from Gartner’s admirable work on the
Captain Hutton—that whole flocks of these
hybridisation of plants.
I have taken
�io6
ON THE ORIGIN OF SPECIES
much pains to ascertain how far the rules
apply to animals; and, considering how
scanty our knowledge is in regard to
hybrid animals, I have been surprised to
find how generally the same rules apply to
both kingdoms.
It has been already remarked that the
degree of fertility, both of first crosses and
of hybrids, graduates from zero to perfect
fertility. It is surprising in how many
curious ways this gradation can be shown
to exist; but only the barest outline of the
facts can here be given. When pollen
from a plant of one family is placed on the
stigma of a plant of a distinct family, it exerts
no more influence than so much inorganic
dust. From this absolute zero of fertility
the pollen of different species of the same
genus, applied to the stigma of some one
species, yields a perfect gradation in the
number of seeds produced, up to nearly
complete, or even quite complete, fertility ;
and, as we have seen, in certain abnormal
cases, even to an excess of fertility beyond
, that which the plant’s own pollen will pro
duce. So in hybrids themselves there are
some which never have produced, and
probably never would produce, even with
the pollen of either pure parent, a single
fertile seed ; but in some of these cases a
first trace of fertility may be detected by
the pollen of one of the pure parent
species causing the flower of the hybrid to
wither earlier than it otherwise would have
done; and the early withering of the
flower is well known to be a sign of
incipient fertilisation. From this extreme
degree of sterility we have self-fertilised
hybrids producing a greater and greater
number of seeds up to perfect fertility.
Hybrids from two species which are
very difficult to cross, and which rarely
produce any offspring, are generally very
sterile; but the parallelism between the
difficulty of making a first cross and the
sterility of the hybrid thus produced—two
classes of facts which are generally con
founded together—is by no means strict.
There are many cases in which two pure
species can be united with unusual facility,
and produce numerous hybrid-offspring;
yet these hybrids are remarkably sterile.
On the other hand, there are species which
can be crossed very rarely, or with extreme
difficulty; but the hybrids, when at last
produced, are very fertile. Even within
the limits of the same genus—for instance,
in Dianthus—these two opposite cases
occur.
The fertility, both of first crosses and of
hybrids, is more easily affected by un
favourable conditions than is the fertility
of pure species. But the degree of fertility
is likewise innately variable ; for it is not
always the *sarne when the same two
species are crossed under the same circum
stances, but depends in part upon the con
stitution of the individuals which happen
to have been chosen for the experiment.
So it is with hybrids, for their degree of
fertility is often found to differ greatly in
the several individuals raised from seed
out of the same capsule and exposed to
exactly the same conditions.
By the term systematic affinity is meant
the resemblance between species in struc
ture and in constitution, more especially in
the structure of parts -which are of high
physiological importance, and which differ
little in the allied species. Now, the fertility
of first crosses between species, and of the
hybrids produced from them, is largely
governed by their systematic affinity. This
is clearly shown by hybrids never having
been raised between species ranked by
systematists in distinct families ; and, on
the other hand, by very closely-allied
species generally uniting with facility.
But the correspondence between syste
matic affinity and the facility of crossing
is by no means strict. A multitude of
cases could be given of very closely-allied
species which will not unite, or only with
extreme difficulty ; and, on the other hand,
of very distinct species which unite with
the utmost facility. In the same family
there may be a genus, as Dianthus, in
which very many species can most readily
be crossed; and another genus, as Silene,
in which the most persevering efforts have
failed to produce between extremely close
species a single hybrid. Even within the
limits of the same genus we meet with this
same difference ; for instance, the many
species of Nicotiana have been more largely
crossed than the species of almost any
other genus ; but Gartner found that N.
acuminata, which is not a particularly dis
tinct species, obstinately failed to fertilise,
or to be fertilised by, no less than eight
other species of Nicotiana. Very many
analogous facts could be given.
No one has been able to point out what
kind, or what amount, of difference in any
recognisable character is sufficient to pre
vent two species crossing. It can be shown
that plants most widely different in habit and
general appearance, and having strongly
marked differences in every part of the
flower, even in the pollen, in the fruit, and
�HYBRIDISM
in the cotyledons, can be crossed. Annual
and perennial plants, deciduous and ever
green trees, plants inhabiting different
stations and fitted for extremely different
climates, can often be crossed with ease.
By a reciprocal cross between two species
—-I mean the case, for instance, of a stallion
horse being first crossed with a female-ass,
and then a male-ass with a mare : these
two species may then be said to have been
reciprocally crossed. There is often the
widest possible difference in the facility of
making reciprocal crosses. Such cases are
highly important, for they prove that the
capacity in any two species to cross is
often completely independent of their
systematic affinity, or of any recognisable
difference in their whole organisation. On
the other hand, these cases clearly show
that the capacity for crossing is connected
with constitutional differences impercep
tible by us, and confined to the reproduc
tive system. This difference in the result
of reciprocal crosses between the same two
species was long ago observed by Kolreuter.
To give an instance : Mirabilis jalapa can
easily be fertilised by the pollen of M.
longiflora, and the hybrids thus produced
are sufficiently fertile ; but Kolreuter tried
more than two hundred times, during eight
following years, to fertilise reciprocally M.
longiflora with the pollen of M. jalapa,
and utterly failed. Several other equally
striking cases could be given. Thuret has
observed the same fact with certain sea
weeds or Fuci. Gartner, moreover, found
that this difference of facility in making
reciprocal crosses is extremely common in
a lesser degree. He has observed it even
between forms so closely related (as
Matthiola annua and glabra) that many
botanists rank them only as varieties. It
is also a remarkable fact that hybrids
raised from reciprocal crosses, though, of
course, compounded of the very same two
species, the one species having first been
used as the father and then as the mother,
generally differ in fertility in a small, and
occasionally in a high, degree.
Several other singular rules could be
given from Gartner: for instance, some
species have a remarkable power of crossing
with other species ; other species of the
same genus have a remarkable power of
impressing their likeness on their hybrid
offspring ; but these two powers do not at
all necessarily go together. There are
certain hybrids which, instead of having,
as is usual, an intermediate character
between their two parents, always closely
107
resemble one of them ; and such hybrids,
though externally so like one of their pure
parent-species, are with rare exceptions
extremely sterile. So again among hybrids,
which are usually intermediate in structure
between their parents, exceptional and
abnormal individuals sometimes are born,
which closely resemble one of their pure
parents; and these hybrids are almost
always utterly sterile, even when the otherhybrids raised from seed from the same
capsule have a considerable degree of
fertility. These facts show how completely
fertility in the hybrid is independent of
its external resemblance to either pure
parent.
Considering the several rules now given,
which govern the fertility of first crosses
and of hybrids, we see that when forms,„
which must be considered as good anddistinct species, are united, their fertility
graduates from zero to perfect fertility, or"
even to fertility under certain conditions in
excess. That their fertility, besides being
eminently susceptible to favourable and un
favourable conditions, is innately variable.
That it is by no means always the same in
degree in the first cross and in the hybrids
produced from this cross. That the fertility
of hybrids is not related to the degree in
which they resemble in external appearance
either parent. And, lastly, that the facility
of making a first cross between any twospecies is not always governed by their
systematic affinity or degree of resem
blance to each other. This latter state
ment is clearly proved by reciprocal,
crosses between the same two species, for,
according as the one species or the other
is used as the father or the mother, there
is generally some difference, and occa
sionally the widest possible difference, in
the facility of effecting an union. The
hybrids, moreover, produced from recip
rocal crosses often differ in fertility.
Now, do these complex and singular rules
indicate that species have been endowed
with sterility simply to prevent their be
coming confounded in nature ? I think
not. For why should the sterility be so
extremely different in degree, when various
species are crossed, all of which we must
suppose it would be equally important to
keep from blending together ? Why should
the degree of sterility be innately variable
in the individuals of the same species ?
Why should some species cross with
facility, and yet produce very sterile
hybrids; and other species cross with
extreme difficulty, and yet produce fairly
�ON THE ORIGIN OF SPECIES
fertile hybrids? Why should there often
be so great a difference in the result of a
reciprocal cross between the same two
species? Why, it may even be asked, has
the production of hybrids been permitted ?
To grant to species the special power of
producing hybrids, and then to stop their
further propagation by different degrees of
sterility, not strictly related to the facility
of the first union between their parents,
seems to be a strange arrangement
The foregoing rules and facts, on th’e
other hand, appear to me clearly to indi
cate that the sterility both of first crosses
and of hybrids is simply incidental or
dependent on unknown differences, chiefly
in the reproductive systems, of the species
which are crossed. The differences being
•of so peculiar and limited a nature that,
in reciprocal crosses between two species,
the male sexual element of the one will
•often freely act on the female sexual ele
ment of the other, but not in a reversed
direction. It will be advisable to explain a
little more fully by an example what I mean
by sterility being incidental on other differences, and not a specially endowed
quality. As the capacity of one plant to
be grafted or budded on another is so
entirely unimportant for its welfare in a
state of nature, I presume that no one will
suppose that this capacity is a specially
endowed quality, but will admit that it is
incidental on differences in the laws of
growth of the two plants. We can sometimes see the reason why one tree will not
take on another, from differences in their
rate of growth, in the hardness of their
wood, in the period of the flow or nature
of their sap, etc.; but in a multitude of
cases we can assign no reason whatever.
Great diversity in the size of two plants,
one being woody and the other herbaceous,
one being evergreen and the other de
ciduous, and adaptation to widely different
climates, does not always prevent the two
grafting together. As in hybridisation, so
with grafting, the capacity is limited by
systematic affinity, for no one has been
able to graft trees together belonging to
quite distinct families ; and, on the other
hand, closely allied species, and varieties
of the same species, can usually, but not
invariably, be grafted with ease. But this
capacity, as in hybridisation, is by no
means absolutely governed by systematic
affinity. Although many distinct genera
within the same family have been grafted
together, in other cases species of the
same genus will not take on each other.
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The pear can be grafted far more readily
on the quince, which is ranked as a distinct
genus, than on the apple, which is a
member of the same genus. Even different
varieties of the pear take with different
degrees of facility on the quince; so do
’different varieties of the apricot and peach
on certain varieties of the plum.
As Gartner found that there was some
times an innate difference in different indi
viduals of the same two species in crossing,
so Sagaret believes this to be the case
with different individuals of the same two
species in being grafted together. As, in
reciprocal crosses, the facility of effecting
an union is often very far from equal, so it
sometimes is in grafting ; the common
gooseberry, for instance, cannot be grafted
on the currant, whereas the currant will
take, though with difficulty, on the goose
berry.
We have seen that the sterility of hybrids,
which have their reproductive organs in an
imperfect condition, is a very different case
from the difficulty of uniting two pure
species, which have their reproductive
organs perfect; yet these two distinct cases
run to a certain extent parallel. Something
analogous occurs in grafting; for Thouin
found that three species of Robinia, which
seeded freely on their own roots, and which
could be grafted with no great difficulty on
another species, when thus grafted were
rendered barren. On the other hand,
certain species of Sorbus, when grafted on
other species, yielded twice as much fruit
as when on their own roots. We arc
reminded by this latter fact of the extra
ordinary case of Hippeastrum, Lobelia,
etc., which seeded much more freely when
fertilised with the pollen of distinct species
than when self-fertilised with their own
pollen.
We thus see that, although there is a
clear and fundamental difference between
the mere adhesion of grafted stocks and
the union of the male and female elements
in the act of reproduction, yet that there
is a rude degree of parallelism in the results
of grafting and of crossing distinct species.
And as we must look at the curious and
complex laws governing the facility with
which trees can be grafted on each other
as incidental or unknown differences in
their vegetative systems, so I believe that
the still more complex laws governing the
facility of first crosses are incidental on
unknown differences chiefly in their repro
ductive systems. These differences, in
both cases, follow to a certain extent, as
�HYBRIDISM
109
long as it is nourished within its mother’s
womb or within the egg or seed produced
by the mother, it may be exposed to condi
tions in some degree unsuitable, and con
sequently be liable to perish at an early
period ; more especially as all very young
beings seem eminently sensitive to injurious
or unnatural conditions of life.
In regard to the sterility of hybrids, in
which the sexual elements are imperfectly
developed, the case is very different. I
have more than once alluded to a large
body of facts, which I have collected, show
Causes of ike Sterility offirst Crosses an d ing that, when animals and plants are
of Hybrids.—We may now look a little
removed from their natural conditions, they
closer at the probable causes of the sterility
are extremely liable to have their repro
of first crosses and of hybrids. These two
ductive systems seriously affected. This,
cases are fundamentally different, for, as just in fact, is the great bar to the domestica
remarked, in the union of two pure species
tion of animals. Between the sterility thus
the male and female sexual elements are
superinduced and that of hybrids there are
perfect, whereas in hybrids they are im- j many points of similarity. In both cases
perfect. Even in first crosses the greater i the sterility is independent of general health,
or lesser difficulty in effecting a union ' and is often accompanied by excess of size
apparently depends on several distinct
or great luxuriance. In both cases the
causes. There must sometimes be a
sterility occurs in various degrees; in both’,
physical impossibility in the male element
the male element is the most liable to be
reaching the ovule, as would be the case
affected, but sometimes the female more
with a plant having a pistil too long for
than the male. In both the tendency goes,
the pollen-tubes to reach the ovarium. It
to a certain extent, with systematic affinity,
has also been observed that when pollen
for whole groups of animals and plants are
of one species is placed on the stigma of rendered impotent by the same unnatural
a distinctly allied species, though the pollen
conditions ; and whole groups of species
tubes protrude, they do not penetrate the
tend to produce sterile hybrids. On the
stigrnatic surface. Again, the male element
other hand, one species in a group will
may reach the female element, but be
sometimes resist great changes of conditions
incapable of causing an embryo to be
with unimpared fertility, and certain species
developed, as seems to have been the case
in a group will produce unusually fertile
with some of Thuret’s experiments on Fuci.
hybrids. No one can tell, till he tries,
No explanation cam be given of these facts,- whether any particular animal will breed
any more than why certain trees cannot be
under confinement or any exotic plant seed
grafted on others. Lastly, an embryo may
freely under culture; nor can he tell, till he
be developed, and then perish at an early
tries, whether any two species of a genus
period. This latter alternative has not been
will produce more or less sterile hybrids.
sufficiently attended to; but I believe, from
Lastly, when organic beings are placed
observations communicated to me by Mr.
during several generations under conditions
Hewitt, who has had great experience in
not natural to them, they are extremely
hybridising gallinaceous birds, that the
liable to vary, which is due, as I believe, to
early death of the embryo is a very frequent
their reproductive systems having been
cause of sterility in first crosses. I was at
specially affected, though in a lesser degree
first very unwilling to believe in this view,
than when sterility ensues. So it is with
as hybrids, when once born, are generally
hybrids, for hybrids in successive gene
healthy and long-lived, as we see in the
rations are eminently liable to vary, as every
case of the common mule. Hybrids, how
experimentalist has observed.
ever, are differently circumstanced before
Thus we see that when organic beings
and after birth : when born and living in a
are placed under new and unnatural con
country where their two parents can live,
ditions, and when hybrids are produced by
they are generally placed under suitable
the unnatural crossing of two species, the
conditions of life. But a hybrid partakes
reproductive system, independently of the
of only half of the nature and constitution
general state of health, is affected by sterility
of its mother, and therefore before birth, as
in a very similar manner. In the one case
might have been expected, systematic
affinity, by which every kind of resemblance
and dissimilarity between organic beings
is attempted to be expressed. The facts
by no means seem to me to indicate that
the greater or lesser difficulty of either
grafting or crossing together various species
has been a special endowment; although
in the case of crossing the difficulty is as
important for the endurance and stability
of specific forms as in the case of grafting
it is unimportant for their welfare.
�no
ON THE ORIGIN OF SPECIES
the conditions of life have been disturbed,
though often in so slight a degree as to be
inappreciable by us ; in the other case, or
that of hybrids, the external conditions have
remained the same, but the organisation
has been disturbed by two different
structures and constitutions having been
blended into one. For it is scarcely pos
sible that two organisations should be com
pounded into one without some disturbance
occurring in the development, or periodical
action, or mutual relation of the different
parts and organs one to another, or to the
conditions of life. When hybrids are able
io breed inter se, they transmit to their off
spring from generation to generation the
same compounded organisation, and hence
we need not be surprised that their sterility,
though in some degree variable, rarely
diminishes.
It must, however, be confessed that we
•cannot understand, excepting on vague
hypotheses, several facts with respect to
the sterility of hybrids; for instance, the
Unequal fertility of hybrids produced from
reciprocal crosses; or the increased
sterility in those hybrids which occa
sionally and exceptionally resemble closely
cither pure parent. Nor do I pretend that
the foregoing remarks go to the root of the
matter : no explanation is offered why an
organism, when placed under unnatural
-conditions, is rendered sterile. All that I
have attempted to show is that in two
cases, in some respects allied, sterility is
the common result—in the one case from
the conditions of life having been disturbed,
in the other case from the organisation
having been disturbed by two organisations
having been compounded into one.
It may seem fanciful, but I suspect that
a similar parallelism extends to an allied
yet very different class of facts. It is an
old and almost universal belief, founded, I
think, on a considerable body of evidence,
that slight changes in the conditions of
life are beneficial to all living things. We
see this acted on by farmers and gardeners
in their frequent exchanges of seeds, tubers,
■etc., from one soil or climate to another,
and back again. During the convalescence
of animals we plainly see that great benefit
is derived from almost any change in the
habits of life. Again, both with plants and
animals, there is abundant evidence that a
cross between very distinct individuals of
the same species—that is, between members
of different strains or sub-breeds—gives
vigour and fertility to the offspring. I
believe, indeed, from the facts alluded to in»
I our fourth chapter, that a certain amount
■ of crossing is indispensable even with her
maphrodites; and that close interbreeding
i continued during several generations be
tween the nearest relations, especially if
these be kept under the same conditions of
life, always induces weakness and sterility
• in the progeny.
Hence it seems that, on the one hand,
slight changes in the conditions of life
benefit all organic beings, and, on the other
hand, that slight crosses—that is, crosses
between the males and females of the same
species which have varied and become
slightly different—give vigour and fertility
to their offspring. But we have seen that
greater changes, or changes of a particular
nature, often render organic beings in some
degree sterile ; and that greater crosses—
that is, crosses between males and females
which have become widely or specifically
different—produce hybrids which are gene
rally sterile in some degree. I cannot
persuade myself that this parallelism is
an accident or an illusion. Both series of
facts seem to be connected together by
some common but unknown bond, which
is essentially related to the principle of life.
Fertility of Varieties when crossed, and
of their Mongrel offspring.—It may be
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urged, as a most forcible argument, that
there must be some essential distinction
between species and varieties, and that
there must be some error in all the fore
going remarks, inasmuch as varieties, how
ever much they may differ from each other
in external appearance, cross with perfect
facility, and yield perfectly fertile offspring.
I fully admit that this is almost invariably
the case. But if we look to varieties pro
duced under nature, we are immediately
involved in hopeless difficulties ; for if two
hitherto reputed varieties be found in any
degree sterile together, they are at once
ranked by most naturalists as species.
For instance, the blue and red pimpernel,
the primrose and cowslip, which are con
sidered by many of our best botanists as
varieties, are said by Gartner not to be
quite fertile when crossed, and he conse
quently ranks them as undoubted species.
If we thus argue in a circle, the fertility of
all varieties produced under nature will
assuredly have to be granted.
If we turn to varieties, produced, or
supposed to have been produced, under
domestication, we are still involved in
doubt. For when it is stated, for instance,
that the German Spitz dog unites more
�HYBRIDISM
easily than other dogs with foxes, or that
certain South American indigenous domes-,
tic dogs do not readily cross with European
dogs, the explanation which will occur to
every one, and probably the true one, is
that these dogs have descended from
severalaboriginally-distinct species. Never
theless, the perfect fertility of so many
domestic varieties, differing widely from
each other in appearance—for instance, of
the pigeon or of the cabbage—is a remark
able fact, more especially when we reflect
how many species there are which, though
resembling each other most closely, are
utterly sterile when intercrossed. Several
considerations, however, render the fertility
of domestic varieties less remarkable than
at first appears. It can, in the first place,
be clearly shown that mere external dis
similarity between two species does not
determine their greater or lesser degree of
sterility when crossed, and we may apply
the same rule to domestic varieties. In the
second place, some eminent naturalists
believe that a long course of domestication
tends to eliminate sterility in the successive
generations of hybrids which were at first
only slightly sterile ; and, if this be so, we
surely ought not to expect to find sterility
both appearing and disappearing under
nearly the same conditions of life. Lastly,
and this seems to me by far the most
important consideration, new races of
animals and plants are produced under
domestication by man’s methodical and
unconscious power of selection, for his
own use and pleasure : he neither wishes
to select, nor could select, slight differences
in the reproductive system, or other con
stitutional differences correlated with the
reproductive system. He supplies his
several varieties with the same food ; treats
them in nearly the same manner, and does
not wish to alter their general habits of
life. Nature acts uniformly and slowly
during vast periods of time on the whole
organisation, in any way which may be for
each creature’s own good ; and thus she
may, either directly or more probably
indirectly, through correlation, modify the
reproductive system in the several descen
dants from any one species. Seeing this
difference in the process of selection, as
carried on by man and nature, we need
not be surprised at some difference in the
result.
I have as yet spoken as if the varieties
of the same species were invariably fertile
when intercrossed. But it seems to me
impossible to resist the evidence of the
in
existence of a certain amount of sterility
in the few following cases, which I will
briefly abstract. The evidence is, at least,
as good as that from which we believe in
the sterility of a multitude of species.
The evidence is also derived from hostile
witnesses, who in all other cases consider
fertility and sterility as safe criterions of
specific distinction. Gartner kept, during
several years, a dwarf kind of maize with
yellow seeds, and a tall variety with red
seeds, growing near each other in his
garden; and, although these plants have
separated sexes, they never naturally
crossed. He then fertilised thirteen flowers
of the one with the pollen of the other;
but only a single head produced any seed,
and this one head produced only five
grains. Manipulation in this case could
not have been injurious, as the plants have
separated sexes. No one, I believe, has
suspected that these varieties of maize are
distinct species ; and it is important to
notice that the hybrid plants thus raised
were themselves perfectly fertile ; so that
even Gartner did not venture to consider
the two varieties as specifically distinct.
Girou de Buzareingues crossed three
varieties of gourd, which, like the maize,
has separated sexes, and he asserts that
their mutual fertilisation is by so much the
less easy as their differences are greater.
How far these experiments may be trusted
I know not; but the forms experimentised
on are ranked by Sagaret, who mainly
founds his classification by the test of
infertility, as varieties.
The following case is far more remark
able, and seems at first quite incredible;
but it is the result of an astonishing number
of experiments made during many years
on nine species of Verbascum by so good
an observer and so hostile a witness as
Gartner—namely, that yellow and white
varieties of the same species of Verbascum
when intercrossed produce less seed than
do either coloured varieties when fertilised
with pollen from their own coloured flowers.
Moreover, he asserts that, when yellow and
white varieties of one species are crossed
with yellow and white varieties of a dis
tinct species, more seed is produced by
the crosses between the similarly-coloured
flowers than between those which are dif
ferently coloured. Yet these varieties of
Verbascum present no other difference
besides the mere colour of the flower ; and
one variety can sometimes be raised from
the seed of the other.
From observations which I have made
�112
ON THE ORIGIN OF SPECIES
on certain varieties of hollyhock, I am
inclined to suspect that they present analo
gous facts.
Kolreuter, whose accuracy has been con
firmed by every subsequent observer, has
proved the remarkable fact that one variety
of the common tobacco is more fertile,
when crossed with a widely distinct species,
than are the othervarieties. He experimentised on five forms, which are commonly
reputed to be varieties, and which he tested
by the severest trial—namely, by reciprocal
crosses—and he found their mongrel off
spring perfectly fertile. But one of these
five varieties, when used either as father
or mother, and crossed with the Nicotiana
glutinosa, always yielded hybrids not so
sterile as those which were produced from
the four other varieties when crossed with
N. glutinosa.
Hence the reproductive
system of this one variety must have
been in some manner and in some degree
modified.
From these facts; from the great diffi
culty of ascertaining theinfertilityof varieties
in a state of nature, for a supposed variety,
if infertile in any degree, would generally be
ranked as species; from man selecting only
external characters in the production of the
most distinct domestic varieties, and from
not wishing or being able to produce recon
dite and functional differences in the repro
ductive system—from these several con
siderations and facts, I do not think that
the very general fertility of varieties can be
proved to be of universal occurrence, or to
form a fundamental distinction between
varieties and species. The general fertility
of varieties does not seem to me sufficient
to overthrow the view which I have taken
with respect to the very general, but not
invariable, sterility of first crosses and of
hybrids—namely, that it is not a special
endowment, but is incidental on slowlyacquired modifications, more especially in
the reproductive systems of the forms which
are crossed.
Hybrids and Mongrels compared, indepen
dently of their fertility.-—Independently of
the question of fertility, the offspring of
species when crossed and of varieties when
crossed may be compared in several other
respects. Gartner, whose strong wish was
to draw a marked line of distinction
between species and varieties, could; find
very few and, as it seems to me, quite unim
portant differences between the so-called
hybrid offspring of species and the so-called
mongrel offspring of varieties. And, on the
other hand, they agree most closely in very
many important respects.
I shall here discuss this subject with
extreme brevity. The most important dis
tinction is that in the first generation
mongrels are more variable than hybrids;
but Gartner admits that hybrids from
species which have long been cultivated
are often variable in the first generation ;
and I have myself seen striking instances
of this. fact. Gartner further admits that
hybrids between very closely-allied species
are more variable than those from very dis
tinct species; and this shows that the
difference in the degree of variability
graduates away. When mongrels and the
more fertile hybrids are propagated for
several generations, an extreme amount of
variability in their offspring is notorious ;
but some few cases both of hybrids and
mongrels long retaining uniformity of char
acter could be given.
The variability,
however, in the successive generation^ of
mongrels is, perhaps, greater than in
hybrids.
This greater variability of mongrels than
of hybrids does not seem to me at all sur
prising. For the parents of mongrels are
varieties, and mostly domestic varieties
(very few experiments having been tried on
natural varieties), and this implies in most
cases that there has been recent variability;
and therefore we might expect that such
variability would often continue and be
super-added to that arising from the mere
act of crossing. The slight degree of
variability in hybrids from the first cross or
in the first generation, in contrast with their
extreme variability in the succeeding genera
tions, is a curious fact and deserves atten
tion. For it bears on and corroborates the
view which I have taken on the cause of
ordinary variability—namely, that it is due
to the reproductive system being eminently
sensitive to any change in the conditions of
life, being thus often rendered either im
potent or at least incapable of its proper
function of producing offspring identical
with the parent-form. Now, hybrids in the
first generation are descended from species
(excluding those long cultivated) which
have not had their reproductive systems in
any way affected, and they are not vari
able ; but hybrids themselves have their
reproductive systems seriously affected, and
their descendants are highly variable.
But to return to our comparison of
mongrels and hybrids : Gartner states that
mongrels are more liable than hybrids to
revert to either parentrform ; but this, if it
�HYBRIDISM
be true, is certainly only a difference in
degree. Gartner further insists that when
any two species, although most closely
allied to each other, are crossed with a
third species, the hybrids are widely dif
ferent from each other ; whereas, if two
- very distinct varieties of one species are
crossed with another species, the hybrids
do not differ much. But this conclusion,
as far as I can make out, is founded on a
single experiment, and seems directly
opposed to the results of several experi
ments made by Kolreuter.
These alone are the unimportant differ
ences which Gartner is able to point out
between hybrid and mongrel plants. On
the other hand, the resemblance in mongrels
and in hybrids to their respective parents,
more especially in hybrids produced from
nearly-related species, follows, according to
Gartner, the same laws. When two species
are crossed, one has sometimes a pre
potent power of impressing its likeness on
the hybrid; and so I believe it to be
with varieties of plants. With animals one
variety certainly often has this prepotent
power over another variety. Hybrid plants
produced from a reciprocal cross generally
resemble each other closely ; and so it is
with mongrels from a reciprocal cross.
Both hybrids and mongrels can be reduced
to either pure parent-form by repeated
crosses in successive generations with either
parent.
These several remarks are apparently
applicable to animals ; but the subject is
here excessively complicated, partly owing
to the existence of secondary sexual char
acters, but more espec#dly owing to pre
potency in transmitting likeness running
more strongly in one sex than in the other
both when one species is crossed with
another and when one variety is crossed
with another variety. For instance, I
think those authors are right who main
tain that the ass has a prepotent power over
the horse, so that both the mule and the
hinny more resemble the ass than the
horse ; but that the prepotency runs more
strongly in the male-ass than in the female,
so that the mule, which is the offspring of j
the male-ass and mare, is more like an ass
than is the hinny, which is the offspring of
the female-ass and stallion.
■ Much stress has been laid by some
authors on the supposed fact that mongrel
animals alone are born closely like one of
their parents; but it can be shown that this
does sometimes occur with hybrids, yet, I
grant, much less frequently with hybrids
113
than with mongrels. Looking to the cases
which I have collected of cross-bred
animals closely resembling one parent, the
resemblances seem chiefly confined to
characters almost monstrous in their nature,
and which have suddenly appeared—such
as albinism, melanism, deficiency of tail or
horns, or additional fingers and toes—and
do not relate to characters which have been
slowly acquired by selection. Consequently,
sudden reversions to the perfect character
of either parent would be more likely to
occur with mongrels, which are descended
from varieties often suddenly produced and
semi-monstrous in character, than with
hybrids, which are descended from species
slowly and naturally produced. On the
whole, I entirely agree with Dr. Prosper
Lucas, who, after arranging an enormous
body of facts with respect to animals,
comes to the conclusion that the laws of
resemblance of the child to its parents
are the same, whether the two parents
differ much or little from each other—
namely, in the union of individuals of the
same variety, or of different varieties, or of
distinct species.
Laying aside the question of fertility
and sterility, in. all other respects there
seems to be a general and close similarity
in the offspring of crossed species and of
crossed varieties. If we look at species
as having been specially created, and at
varieties as having been ^produced by
secondary laws, this similarity would be
an astonishing fact. But it harmonises
perfectly with the view that there is no
essential distinction between species and
varieties.
Summary of ‘ Chapter—Yfrsk crosses
between forms sufficiently distinct to be
ranked as species, and their hybrids, are
very generally, but not universally, sterile.
The sterility is of all degrees, and is often
so slight that the two most careful experi
mentalists who have ever lived have come
to diametrically opposite conclusions in
ranking forms by this test. The sterility
is innately variable in individuals of the
same species, and is eminently susceptible
of favourable and unfavourable conditions.
The degree of sterility does not strictly
follow systematic affinity, but is governed
by several curious and complex laws. It is
generally different, and sometimes widely
different, in reciprocal crosses between the
same two species. It is not always equal
in degree in a first cross and in the hybrid
produced from this cross.
I
�114
ON THE ORIGIN OF SPECIES
In the same manner as in grafting trees
the capacity of one species or variety to
take on another is incidental on generally
unknown differences in their vegetative
systems, so, in crossing, the greater or less
facility of one species to unite with another
is incidental on unknown differences in
their reproductive systems. There is no
more reason to think that species have
been specially endowed with various de
grees of sterility to prevent them crossing
and blending in nature than to think that
trees have been specially endowed with
various and somewhat analogous degrees
of difficulty in being grafted together in
order to prevent them becoming inarched
in our forests.
The sterility of first crosses between
pure species, which have their reproductive
organs perfect, seems to depend on several
circumstances—in some cases, largely on
the early death of the embryo. The sterility
of hybrids, which have their reproductive
systems imperfect, and which have had
this system and their whole organisation
disturbed by being compounded of two
distinct species, seems closely allied to
that sterility which so frequently affects
pure species, when their natural conditions
of life have been disturbed. This view is
supported by a parallelism of another kind
—namely, that the crossing of forms only
slightly different is favourable to the vigour
and fertility of their offspring; and that
slight changes in the conditions of life are
apparently favourable to the vigour and
fertility of all organic beings. It is not
surprising that the degree of difficulty in
I uniting two species, and the degree of
sterility of their hybrid-offspring should
generally correspond, though due to dis
tinct causes, for both depend on the
amount of difference of some kind between
the species which are crossed. Nor is it
surprising that the facility of effecting a
first cross, the fertility of the hybrids pro
duced from it, and the capacity of being
grafted together—though this latter capa
city evidently depends on widely different
circumstances—should all run, to a certain
extent, parallel with the systematic affinity
of the forms which are subjected to experi
ment ; for systematic affinity attempts to
express all kinds of resemblance between
all species.
First crosses between forms known to be
varieties, or sufficiently alike to be con
■ sidered as varieties, and their mongrel
offspring, are very generally, but not quite
universally, fertile. Nor is this nearly
general and perfect fertility surprising when
we remember how liable we are to argue
in a circle with respect to varieties in a
state of nature, and when we remember
that the greater number of varieties have
been produced under domestication by the
selection of mere external differences, and
not of differences in the reproductive
system. In all other respects, excluding
| fertility, there is a close general resemblance
between hybrids and mongrels. Finally,
j then, the facts briefly given in this chapter
j do not seem to me opposed to, but even
I rather to support, the view that there is no
j fundamental distinction between species
and varieties.
Chapter IX.
ON THE IMPERFECTION OF THE GEOLOGICAL
RECORD
On the absence of intermediate varieties at
the present day—On the nature of extinct
intermediate varieties ; on their number—On
the vast lapse of time, as inferred from the
rate of deposition and of denudation—On the
poorness of our palaeontological collections—
On the intermittence of geological formations
—On the absence of intermediate varieties in
any one formation—On the sudden appear
ance of groups of species—On their sudden
appearance in the lowest known fossiliferous
strata.
In the sixth chapter I enumerated the chief
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
objections which might be justly urged
against the views maintained in this volume.
Most of them have now been discussed.
One—namely, the distinctness of specific
forms, and their not being blended together
by innumerable transitional links—is a very
obvious difficulty. I assigned reasons why
such links do not commonly occur at the
present day, under the circumstances appa
rently most favourable for their presence—
namely, on an extensive and continuous
area with graduated physical conditions.
I endeavoured to show that the life of
each species depends in a more important
manner on the presence of other already
defined organic forms than on climate;
and, therefore, that the really governing
conditions of life do not graduate away
quite insensibly, like heat or moisture. I
endeavoured also to show that intermediate
varieties, from existing in lesser numbers
than the forms which they connect, will
generally be beaten out and exterminated
during the course of further modification
and improvement. The main cause, how
ever, of innumerable intermediate links not
now occurring everywhere throughout
nature depends on the very process of
natural selection, through which new
varieties continually take the places of and
exterminate their parent-forms. But just
in proportion as this process of extermina
tion has acted on an enormous scale, so
must the number of intermediate varieties
which have formerly existed on the earth
be truly enormous. Why, then, is not every
geological formation and every stratum full
of such intermediate links ?
Geology
assuredly does not reveal any such finelygraduated organic chain ; and this, per
haps, is the most obvious and gravest
objection which can be urged against my
theory. The explanation lies, as I believe,
in the extreme imperfection of the geo
logical record.
In the first place, it should always be
borne in mind what sort of intermediate
forms must, on my theory, have formerly
existed. I have found it difficult, when
looking at any two species, to avoid pictur
ing to myself forms directly intermediate
between them. But this is a wholly false
view : we should always look for forms
intermediate between each species and a
common but unknown progenitor ; and the
progenitor will generally have differed in
some respects from all its modified descen
dants. To give a simple illustration : the
fantail and pouter pigeons have both des
cended from the rock-pigeon ; if we pos
115
sessed all the intermediate varieties which
have ever existed, we should have an
extremely close series between both and
the rock-pigeon ; but we should have no
varieties directly intermediate between the
fantail and pouter-—-none, for instance,
combining a tail somewhat expanded, with a
crop somewhat enlarged, the characteristic
features of these two breeds. These two
breeds, moreover, have become so much
modified that, if we had no historical or
indirect evidence regarding their origin, it
would not have been possible to have deter
mined, from a mere comparison of their
structure with that of the rock-pigeon,
whether they had descended from this
species or from some other allied species,
such as C. oenas.
So with natural species, if we look to
forms very distinct—for instance, to the
horse and tapir—we have no reason to
suppose that links ever existed directly
intermediate between them, but between
each and an unknown common parent.
The common parent will have had in its
whole organisation much general resem
blance to the tapir and to the horse, but
in some points of structure may have
differed considerably from both, even per
haps more than they differ from each other.
Hence, in all such cases we should be
unable to recognise the parent-form of any
two or more species, even if we closely
compared the structure of the parent with
that of its modified descendants, unless at
the same time we had a nearly perfect
chain of the intermediate links.
It is just possible, by my theory, that'one
of two living forms might have descended
from the other—for instance, a horse from
a tapir; and in this case direct intermediate
links will have existed between them. But
such a case would imply that one form had
remained for a very long period unaltered,
while its descendants had undergone a
vast amount of change ; and the principle
of competition between organism and
organism, between child and parent, will
render this a very rare event, for in all
cases the new and improved forms of life
tend to supplant the old and unimproved
forms.
By the theory of natural selection all
living species have been connected with
the parent-species of each genus, by differ
ences not greater than we see between the
varieties of the same species at the present
day; and these parent-species, now gene
rally extinct, have in their turn been similarly
connected with more ancient species; and
�' 116
ON THE ORIGIN OF SPECIES
so on backwards, always converging to the P miles any line of rocky cliff which is under
common ancestor of each great class. So
going degradation, we find that it is-only
that the number of intermediate and transi
here and there, along a short length, or
tional links, between all living and extinct
round a promontory, that the cliffs are at
species, must have been inconceivably
the present time suffering. The appear
great. But assuredly, if this theory be true,
ance of the surface and the vegetation
such have lived upon this earth.
show that elsewhere years have elapsed
since the waters washed their base.
On the lapse of Time.—Independently of
He who most closely studies the action
our not finding fossil remains of such
of the sea on our shores will, I believe, be
infinitely numerous connecting-links, it may
most deeply impressed with the slowness
be objected that time will not have sufficed
with which rocky coasts are worn away.
for so great an amount of organic change,
The observations on this head by Hugh
all changes having been effected very
Miller, and by that excellent observer, Mr.
slowly through natural selection. It is
Smith, of Jordan Hill, are most impressive.
hardly possible for me even to recall to the
With the mind thus impressed, let anyone
reader, who may not be a practical geo
examine beds of conglomerate many thou
logist, the facts leading the mind freely to
sand feet in thickness, which, though pro
comprehend the lapse of time. He who
bably formed at a quicker rate than many
can read Sir Charles Lyell’s grand work
other deposits, yet, from being formed of
on the Principles of Geology, which the
worn and rounded pebbles, each of which
future historian will recognise as having
bears the stamp of time, are good to show
produced a revolution in natural science,
how slowly the mass has been accumulated.
yet does not admit how incomprehensively i In the Cordillera I estimated one pile of
vast have been the past periods of time,
conglomerate at ten thousand feet in thick
ness. Let the observer remember Lyell’s
may at once close this volume. Not that
it suffices to study the Principles of Geology,
profound remark, that the thickness and
or to read special treatises by different
extent of sedimentary formations are the
observers on separate formations, and to
result and measure of the degradation
mark how each author attempts to give an
which the earth’s crust has elsewhere
inadequate idea of the duration of each
suffered. And what an amount of degrada
tion is implied by the sedimentary deposits
formation, or even each stratum. A man
of many countries ! Professor Ramsay has
must for years examine for himself great
given me the maximum thickness, in most
piles of superimposed strata, and watch the
cases from actual measurement, in a few
sea at work grinding down old rocks and
cases from estimate, of each formation in
making fresh sediment, before he can hope
different part of Great Britain ; and this is>
to comprehend anything of the lapse of
time, the monuments of which we see
the result :—
Feet.
around us.
Palaeozoic strata (not including
It is good to wander along lines of sea
igneous beds)...
...............
57>J54
coast, when formed of moderately hard
Secondary strata
...............
rocks, and mark the process of degradation.
Tertiary strata ...
...
...
2,240
The tides in most cases reach the cliffs
—making altogether 72,584 feet; that is,
only for a short time twice a day, and the
very nearly thirteen and three-quarters
waves eat into them only when they are
British miles. Some of the formations,
charged with sand or pebbles ; for there is
which are represented in England by thin
good evidence that pure water can effect
beds, are thousands of feet in thickness on
little or nothing in wearing away rock. At
the continent. Moreover, between each
last the base of the cliff is undermined,
successive formation we have, in the opinion
huge fragments fall down, and these,
of most geologists, enormously-long blank
remaining fixed, have to be worn away,
periods. So that the lofty pile of sedi
atom by atom, until reduced in size they
mentary rocks in Britain gives but an
can be roiled about by the waves, and
inadequate idea of the time which has
then are more quickly ground into pebbles,
elapsed during their' accumulation; yet
sand, or mud. But how often do we see
what time this must have consumed!
along the bases of retreating cliffs rounded
Good observers have estimated that sedi
boulders, all thickly clothed by marine
ment is deposited by the great Mississippi
productions, showing how little they are
river at the rate of only 600 feet in a
abraded and how seldom they are rolled
hundred thousand years. This estimate
about! Moreover, if we follow for a few
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
117
ments meet and close, one can safely
has no pretension to strict exactness ; yet,
picture to oneself the great dome of rocks
considering over what wide spaces very
which must have covered up the Weald
fine sediment is transported by the currents
within so limited a period as since the
of the sea, the process of accumulation in
latter part of the Chalk formation. The
any one area must be extremely slow.
distance from the northern to the southern
But the amount of denudation which the
Downs is about 22 miles, and the thickness
strata have in many places suffered, inde
of the several formations is on an average
pendently of the rate of accumulation of
about 1,100 feet, as I am informed by Pro
the degraded matter, probably offers the
fessor Ramsay. But if, as some geologists
best evidence of the lapse of time. I re
member having been much struck with
suppose, a range of older rocks underlies
the Weald, on the flanks of which the
the evidence of denudation, when viewing
volcanic islands, which have been worn by
overlying sedimentary deposits might have
accumulated in thinner masses than else
the waves and pared all round into perpen
dicular cliffs of one or two thousand feet in
where, the above estimate would be erro
neous ; but this source of doubt probably
height; for the gentle slope of the larva
streams, due to their former liquid state,
would not greatly affect the estimate as
showed at a glance how far the hard,
applied to the western extremity of the
rocky beds had once extended into the
district. If, then, we knew the rate at
which the sea commonly wears away a
open ocean. The same story is still more
plainly told by faults—those great cracks
line of cliff of any given height, we could
along which the strata have been upheaved
measure the time requisite to have denuded
on one side, or thrown down on the other,
the Weald. This, of course, cannot be
to the height or depth of thousands of
done ; but we may, in order to form some
feet; for, since the crust cracked, the sur
crude notion on the subject, assume that
face of the land has been so completely
the sea would eat into cliffs 500 feet in
planed down by the action of the sea that
height at the rate of one inch in a century.
no trace of these vast dislocations is ex This will at first appear much too small an
ternally visible.
allowance ; but it is the same as if we were
The Craven fault, for instance, extends
to assume a cliff one yard in height to be
for upwards of 30 miles, and along this
eaten back along a whole line of coast at
line the vertical displacement of the strata
the rate of one yard in nearly every twentyhas varied from 600 to 3,000 feet. Pro two years. I doubt whether any rock, even
fessor Ramsay has published an account
as soft as chalk, would yield at this rate
of a downthrow in Anglesea of 2,300 feet;
excepting on the most exposed coasts ;
and he informs me that he fully believes
though no doubt the degradation of a lofty
• there is one in Merionethshire of 12,000
cliff would be more rapid from the breakage
feet; yet in these cases there is nothing on
of the falling fragments. On the other
the surface to show such prodigious move hand, I do not believe that any line of*
ments, the pile of rocks on the one or
coast, ten or twenty miles in length, ever
other side having been smoothly swept • suffers degradation at the same time along
away. The consideration of these facts
its whole indented length ; and we must
impresses my mind almost in the same
remember that almost all strata contain
manner as does the vain endeavour to
harder layers or nodules, which from long
grapple with the idea of eternity.
resisting attrition form a breakwater at the
I am tempted to give one other case, the
base. We may at least confidently believe
well-known one of the denudation of the
that no rocky coast 500 feet in height
Weald. Though it must be admitted that
commonly yields at the rate of a foot per
the denudation of the Weald has been a
century; for this would be the same in
mere trifle, in comparison with that which
amount as a cliff one yard in height retreat
has removed masses of our palaeozoic
ing twelve yards in twenty-two years ; and
strata, in parts ten thousand feet in thick no one, I think, who has carefully observed
ness, as shown in Professor Ramsay’s
the shape of old fallen fragments at the
masterly memoir on this subject; yet it base of cliffs will admit any near approach
is an admirable lesson to stand on the
to such rapid wearing away. Hence,
intermediate hilly country and look on the
under ordinary circumstances, I should
one hand at the North Downs, and on the
infer that for a cliff 500 feet in height a
other hand at the South Downs ; for,
denudation of one inch per century for the
remembering that at no great distance to
whole length would be a sufficient allow
the west the northern and southern escarp ance. At this rate, on the above data, the
�ON THE ORIGIN OF SPECIES
denudation of the Weald must have
required 306,662,400 years ; or say three
hundred million years. But perhaps it
would be safer to allow two or three inches
per century, and this would reduce the
number of years to one hundred and fifty
or one hundred million years.
The action of fresh water on the gently
inclined Wealden district, when upraised,
could hardly have been great, but it would
somewhat reduce the above estimate. On
the other hand, during oscillations of level,
which we know this area has undergone,
the surface may have existed for millions of
years as land, and thus have escaped the
action of the sea : when deeply submerged
for perhaps equally long periods, it would,
likewise, have escaped the action of the
coast-waves. So that it is not improbable
that a longer period than 300 million years
has elapsed since the latter part of the
Secondary period.
I have made these few remarks because
it is highly important for us to gain some
notion, however imperfect, of the lapse of
years. During each of these years, over the
whole world, the land and the water has been
peopled by hosts of living forms. What
an infinite number of generations, which
the mind cannot grasp, must have succeeded
each other in the long roll of years ! Now
turn to our richest geological museums,
and what a paltry display we behold 1
On the poorness of our Palceontological
collections.—That our palaeontological col
lections are very imperfect is admitted by
every one. The remark of that admirable
palaeontologist, the late Edward Forbes,
should not be forgotten—namely, that
numbers of our fossil species are known
and named from single and often broken
specimens, or from a few specimens col
lected on some one spot. Only a small
portion of the surface of the earth has been
geologically explored, and no part with
sufficient care, as the important discoveries
made every year in Europe prove. No
organism wholly soft can be preserved.
Shells and bones will decay and disappear
when left on the bottom of the sea, where
sediment is not accumulating. I believe we
are continually taking a most erroneous
view when we tacitly admit to ourselves
that sediment is being deposited over
nearly the whole bed of the sea at a rate
sufficiently quick to embed and preserve
fossil remains. Throughout an enormously
large proportion of the ocean the bright
blue tint of the water bespeaks its purity.
The many cases on record of a formation
conformably covered, after an enormous
interval of time, by another and later forma
tion, without the underlying bed having
suffered in the interval any wear and tear,
seem explicable only on the view of the
bottom of the sea not rarely lying for ages
in an unaltered condition. The remains
which do become embedded, if in sand or
gravel, will, when the beds are upraised,
generally be dissolved by the percolation of
rain-water. I suspect that but few of the
very many animals which live on the beach
between high and low watermark are pre
served. For instance, the several species
of the Chthamalinae (a sub-family of sessile
cirripedes) coat the rocks all over the world
in infinite numbers : they are all strictly
littoral, with the exception of a single
Mediterranean species, which inhabits deep
water and has been found fossil in Sicily,
whereas not one other species has hitherto
been found in any tertiary formation ; yet
it is now known that the genus Chthamalus
existed during the chalk period. The molluscan genus Chiton offers a partially ana
logous case.
With respect to the terrestrial produc
tions which lived during the Secondary and
Palaeozoic periods, it is superfluous to state
that our evidence from fossil remains is
fragmentary in an extreme degree. For
instance, not a land shell is known be
longing to either of these vast periods,
with the exception of one species dis
covered by Sir C. Lyell and Dr. Dawson in
the carboniferous strata of North America,
of which shell several specimens have now *
been collected. In regard to mammiferous
remains, a single glance at the historical
table published in the Supplement to
Lyell’s Manual will bring home the truth,
how accidental and rare is their preser
vation, far better than pages of detail.
Nor is their rarity surprising when we
remember how large a proportion of the
bones of tertiary mammals have been dis
covered either in caves or in lacustrine
deposits; and that not a cave or true
lacustrine bed is known belonging to the age
of our secondary or palaeozoic formations.
But the imperfection in the geological
record mainly results from another and
more important cause than any of the
foregoing—-namely, from the several forma
tions being separated from each other by
wide intervals of time. When we see the
formations tabulated in written works, or
when we follow them in nature, it is diffi
• cult to avoid believing that they are closely
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
consecutive. But we know, for instance,
from Sir R. Murchison’s great work on
Russia, what wide gaps there are in that
country between the superimposed forma
tions ; so it is in North America, and in
many other parts of the world. The most
skilful geologist, if his attention had been
exclusively confined to these large terri
tories, would never have suspected that
during the periods which were blank and
barren in his own country great piles of
sediment, charged with new and peculiar
forms of life, had elsewhere been accumu
lated. And if in each separate territory
hardly any idea can be formed of the
length of time which has elapsed between
the consecutive formations, we may infer
that this could nowhere be ascertained.
The frequent and great changes in the
mineralogical composition of consecutive
formations, generally implying great
changes in the geography of the sur
rounding lands, whence the sediment has
been derived, accords with the belief of
vast intervals of time having elapsed
between each formation.
But we can, I think, see why the geo
logical formations of each region are
almost invariably intermittent — that is,
have not followed each other in close
sequence. Scarcely any fact struck me
more, when’ examining many hundred
miles of the South American coasts, which
have been upraised several hundred feet
within the recent period, than the absence
of any recent deposits sufficiently extensive
to last for even a short geological period.
« Along the whole west coast, which is
inhabited by a peculiar marine fauna,
tertiary beds are so poorly developed
that no record of several successive and
peculiar marine faunas will probably be
preserved to a distant age. A little reflec
tion will explain why along the rising coast
of the western side of South America no
extensive formations with recent or tertiary
remains can anywhere be found, though
the supply of sediment must for ages have
been great, from the enormous degradation
of the coast-rocks and from muddy streams
entering the sea.
The explanation, no
doubt, is that the littoral and sub-littoral
deposits are continually worn away as
soon as they are brought up by the slow
and gradual rising of the land within the
grinding action of the coast-waves.
We may, I think, safely conclude that
sediment must be accumulated in extremely
thick, solid, or extensive masses, in order
to withstand the incessant action of the
119
waves when first upraised and during
subsequent oscillations of level.
Such
thick and extensive accumulations of sedi
ment may be formed in two ways—either,
in profound depths of the sea, in which ,
case, judging from the researches of E.
Forbes, we may conclude that the bottom
will be inhabited by extremely few animals,
and the mass, when upraised, will give a
most imperfect record of the forms of life
which then existed ; or sediment may be
accumulated to any thickness and extent
over a shallow bottom, if it continue slowly
to subside. In this latter case, as long as
the rate of subsidence and supply of sedi
ment nearly balance each other, the sea
will remain shallow and favourable for life,
and thus a fossiliferous formation thick
enough, when upraised, to resist any
amount of degradation may be formed.
I am convinced that all our ancient
formations which are rich in fossils have
thus been formed during subsidence: Since
publishing my views on this subject in 1845,
I have watched the progress of Geology,
and have been surprised to note how author
after author, in treating of this or that great
formation, has come to the conclusion that
it was accumulated during subsidence. I
may add that the only ancient tertiary
formation on the west coast of South
America which has been bulky enough to
resist such degradation as it has as yet suf
fered, but which will hardly last to a distant
geological age, was certainly deposited
during a downward oscillation of level, and
thus gained considerable thickness.
All geological facts tell us plainly that
each area has undergone numerous slow
oscillations of level, and apparently these
oscillations have affected wide spaces.
Consequently, formations rich in fossils, and
sufficiently thick and extensive to resist
subsequent degradation, may have been
formed over wide spaces during periods of
subsidence, but only where the supply of
sediment was sufficient to keep the sea
shallow and to embed and preserve the
remains before they had time to decay.
On the other hand, as long as the bed of
the sea remained stationary, thick deposits
could not have been accumulated in the
shallow parts, which are the most favour
able to life. Still less could this have
happened during the alternate periods of
elevation ; or, to speak more accurately,
the beds which were then accumulated will
have been destroyed by being upraised and
brought within the limits of the coast
action.
�120
ON THE ORIGIN OF SPECIES
Thus the geological record will almost
necessarily be rendered intermittent. I
feel much confidence in the truth of these
views, for they are in strict accordance with
the general principles inculcated by Sir C.
Lyell; and E. Forbes subsequently but inde
pendently arrived at a similar conclusion.
One remark is here worth a passing
notice. During periods of elevation the
area of the land and of the adjoining shoal
parts of the sea will be increased, and new
stations will often be formed—all circum
stances most, favourable, as previously
explained, for the formation of new varieties
and species; but during such periods there
will generally be a blank in the geological
record. On the other hand, during subsi
dence the inhabited area and number of
inhabitants will decrease (excepting the
productions on the shores of a continent
when first broken up into an archipelago),
and consequently during subsidence,
though there will be much extinction, fewer
new varieties or species will be formed ;
and it is during these very periods of sub
sidence that our great deposits rich in
fossils have been accumulated. Nature
may almost be said to have guarded against
the frequent discovery of her transitional or
linking forms.
From the foregoing considerations it
cannot be doubted that the geological
record, viewed as a whole, is extremely im
perfect ; but if we confine our attention to
any one formation, it becomes more difficult
to understand why we do not therein find
closely graduated varieties between the
allied species which lived at its commence
ment and at its close. Some cases are on
record of the same species presenting
distinct varieties in the upper and lower
parts of the same formation ; but, as they
are rare, they may be here passed over.
Although each formation has indisputably
required a vast number of years for its
deposition, I can see several reasons why
each should not include a graduated series
of links between the species which then
lived; but I can by no means pretend
to assign due proportional weight to the
following considerations.
Although each formation may mark a
very long lapse of years, each perhaps is
short compared with the period requisite
to change one species into another. I am
aware that two palaeontologists, whose
opinions are worthy of much deference—
namely, Bronn and Woodward, have con
cluded that the average duration of each
formation is twice or thrice as long as the
average duration of specific forms. But
insuperable difficulties, as it seems to me,
prevent us coming to any just conclusion
on this head. When we see a species first
appearing in the middle of any formation,
it would be rash in the extreme to infer
that it had not elsewhere previously existed.
So again, when we find a species disap
pearing before the uppermost layers have
been deposited, it would be equally rash to
suppose that it then became wholly extinct.
We forget how small the area of Europe is
compared with the rest of the world ; nor
have the several stages of the same forma
tion throughout Europe been correlated
with perfect accuracy.
With marine animals of all kinds, we
may safely infer a large amount of migra
tion during climatal and other changes ;
and when we see a species first ap
pearing in any formation, the probability is
that it only then first immigrated into that
area. It is well known, for instance, that
several species appeared somewhat earlier
in the palaeozoic beds of North America
than in those of Europe; time having
apparently been required for their migra
tion from the American to the European
seas. In examining the latest'deposits of
various quarters of the world, it has every
where been noted that some few still
existing species are common in the deposit,
but have become extinct in the immediately
Surrounding sea; or, conversely, that some
are now abundant in the neighbouring sea,
but are rare or absent in this particular
deposit. It is an excellent lesson to reflect
on the ascertained amount of migration of
the inhabitants of Europe during the
Glacial period, which forms only a part of
one whole geological period ; and likewise
to reflect on the great changes of level, on
the inordinately great change of climate,
on the prodigious lapse of time, all included
within this same glacial period. Yet it
may be doubted whether in any quarter of
the world sedimentary deposits, including'
fossil remains, have gone on accumulating
within the same area during the whole of
this period. It is not, for instance, pro
bable that sediment was deposited during
the whole of the glacial period near the
mouth of the Mississippi, within that limit
of depth at which marine animals can
flourish ; for we know what vast geo
graphical changes occurred in other parts
of America during this space of time.
When such beds as were deposited in
shallow water near the mouth of the
Mississippi during some part of the glacial
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
period shall have been upraised, organic
remains will probably first appear and
disappear at different levels, owing to the
migration of species and to geographical
changes.
And in the distant future a
geologist examining these beds might be
tempted to conclude that the average
duration of life of the embedded fossils
had been less than that of the glacial
period, instead of having been really far
greater—that is, extending from before the
glacial epoch to the present day.
In order to get a perfect gradation
between two forms in the upper and lower
parts of the same formation, the deposit
must have gone on accumulating for a
very long period, in order to have given
sufficient time for the slow process of
variation; hence the deposit will generally
have to be a very thick one; and the
species undergoing modification will have
had to live on the same area throughout
this whole time. But we have seen that a
thick fossiliferous formation can only be
accumulated during a period of subsidence;
and to keep the depth approximately the
same, which is necessary in order to enable
the same species to live on the same space,
the supply of sediment must nearly have
counterbalanced the amount of subsidence.
But this same movement of subsidence
will often tend to sink the area whence the
sediment is derived, and thus diminish the
supply while the downward movement con
tinues. In fact, this nearly exact balancing
between the supply of sediment and the
amount of subsidence is probably a rare
contingency ; for it has been observed by
more than one palaeontologist that very
thick deposits are usually barren of organic
remains, except near their upper or lower
limits.
It would seem that each separate forma
tion, like the whole pile of formations in
any country, has generally been intermittent
in its accumulation. When we see, as is
so often the case, a formation composed of
beds of different mineralogical composition,
we may reasonably suspect that the process
of deposition has been much interrupted,
as a change in the currents of the sea and
a supply of sediment of a different nature
will generally have been due to geographical
changes requiring much time. Nor will
the closest inspection of a formation give
any idea of the time which its deposition
has consumed. Many instances could be
given of beds only a few feet in thickness,
representing formations, elsewhere thou
sands of feet in thickness, and which must
121
have required an enormous period for their
accumulation ; yet no one ignorant of this
fact would have suspected the vast lapse of
time represented by the thinner formation.
Many cases could be given of the lower
beds of a formation having been upraised,
denuded, submerged, and then re-covered
by the upper beds of the same formation
—facts showing what wide, yet easily over
looked, intervals have occurred in its accu
mulation. In other cases we have the
plainest evidence in great fossilised trees,
still standing upright as they grew, of many
long intervals of time and changes of level
during the process of deposition, which would
never even have been suspected had not
the trees chanced to have been preserved :
thus Messrs. Lyell and Dawson found
carboniferous beds 1,400 feet thick in Nova
Scotia, with ancientroot-b earing strata,
one above the other, at no less than sixty
eight different levels. Hence, when the
same species occur at the bottom, middle,
and top of a formation, the probability is
that they have not lived on the same spot
during the whole period of deposition, but
have disappeared and reappeared, perhaps
many times, during the same geological
period. So that, if such species were to
undergo a considerable amount of modifi
cation during any one geological period, a
section would not probably include all the
fine intermediate gradations which must,
on my theory, have existed between them,
but abrupt, though perhaps very slight,
changes of form.
It is all-important to remember that
naturalists have no golden rule by which
*to distinguish species and varieties ; they
grant some little variability to each species,
but when they meet with a somewhat
greater amount of difference between any
two forms they rank both as species, unless
they are enabled to connect them together
by close intermediate gradations. And this,
from the reasons just assigned, we can
seldom hope to effect in any one geological
section. Supposing B and C to be two
species, and a third, A, to be found in an
underlying bed ; even if A were strictly
intermediate between B and C, it would
simply be ranked as a third and distinct
species, unless at the same time it could
be most closely connected with either one
or both forms by intermediate varieties.
Nor should it be forgotten, as before
explained, that A might be the actual
progenitor of B and C, and yet might not
at all necessarily be strictly intermediate
between them in all points of structure.
�122
ON THE ORIGIN OF SPECIES
So that we might obtain the parent-species
and its several modified descendants from
the lower and upper beds of a formation,
and, unless we obtained numerous transi
tional gradations, we should not recognise
their relationship, and should consequently
be compelled to rank them all as distinct
species.
It is notorious on what excessively slight
differences many palaeontologists have
founded their species; and they do this the
more readily if the specimens come from
different sub-stages of the same formation.
Some experienced conchologists are now
sinking many of the very fine species of
D’Orbigny and others into the rank ot
varieties ; and on this view we do find the
kind of evidence of change which on my
theory we ought to find. Moreover, if we
look to rather wider intervals—namely, to
distinct but consecutive stages of the same
great formation, we find that the embedded
fossils, though almost universally ranked as
specifically different, yet are far more
closely allied to each other than are the
species found in more widely separated
formations; but to this subject I shall have
to return in the following chapter.
One other consideration is worth notice :
with animals and plants that can propagate
rapidly and are not highly locomotive, there
is reason to suspect, as we have formerly
seen, that their varieties are generally at
first local; and that such local varieties do
not spread widely and supplant their parent
forms until they have been modified and
perfected in some considerable degree.
According to this view, the chance of dis
covering in a formation in any one country
all the early stages of transition between
any two forms is small, for the successive
changes are supposed to have been local or
confined to some one spot. Most marine
animals have a wide range; and we have
seen that with plants it is those which have
the widest range that oftenest present
varieties; so that with shells and other
marine animals it is probably those which
have had the widest range, far exceeding
the limits of the known geological forma
tions of Europe, which have oftenest given
rise, first to local varieties, and ultimately to
new species ; and this again would greatly
lessen the chance of our being able to trace
the stages of transition in any one geological
formation.
It should not be forgotten that at the
present day, with perfect specimens for
examination, two forms can seldom be con
nected by intermediate varieties and thus
proved to be the same species, until many
specimens have been collected from many
places; and in the case of fossil species this
could rarely be effected by palaeontologists.
We shall, perhaps, best perceive the impro
bability of our being enabled to connect
species by numerous, fine, intermediate,
fossil links, by asking ourselves whether,
for instance, geologists at some future period
will be able to prove that our different
breeds of cattle, sheep, horses, and dogs
have descended from a single stock or from
several aboriginal stocks; or, again, whether
certain sea-shells inhabiting the shores of
North America, which are ranked by some
conchologists as distinct species from their
European representatives, and by other
conchologists as only varieties, are really
varieties, or are, as it is called, specifically
distinct. This could be effected only by
the future geologist discovering in a fossil
state numerous intermediate gradations;
and such success seems to me improbable
in the highest degree.
Geological research, though it has added
numerous species to existing and extinct
genera, and has made the intervals between
some few groups less wide than they other
wise would have been, yet has done scarcely
anything in breaking down the distinc
tion between species, by connecting them
together by numerous, fine, intermediate
varieties; and this not having been effected
is probably the gravest and most obvious of
all the many objections which may be
urged against my views. Hence it will be
worth while to sum up the foregoing
remarks, under an imaginary illustration.
The Malay Archipelago is of about the
size of Europe from the North Cape to the
Mediterranean, and from Britain to Russia;
and therefore equals all the geological
formations which have been examined with
any accuracy, excepting those of the United
States of America. I fully agree with Mr.
Godwin-Austen, that the present condition
of the Malay Archipelago, with its numerous
large islands separated by wide and shallow
seas, probably represents the former state
of Europe, whilst most of our formations
were accumulating. The Malay Archi
pelago is one of the richest regions of the
whole world in organic beings ; yet, if all
the species were to be collected which have
ever lived there, how imperfectly would they
represent the natural history of the world !
But we have every reason to believe that
the terrestrial productions of the archipelago
would be preserved in an excessively im
perfect manner in the formations which we
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
suppose to be there accumulating. I sus
pect that not many of the strictly littoral
animals, or of those which lived on naked
submarine rocks, would be embedded; and
those embedded in gravel or sand would
not endure to a distant epoch. Wherever
sediment did not accumulate on the bed of
the sea, or where it did not accumulate.at
a sufficient rate to protect organic bodies
from decay, no remains could be preserved.
I believe that fossiliferous formations
could be formed in the archipelago, of
thickness sufficient to last to an age as
distant in futurity as the secondary forma
tions lie in the past, only during periods of
subsidence. These periods of subsidence
would be separated from each other by
enormous intervals, during which the area
would be either stationary or rising; while
rising, each fossiliferous formation would
be destroyed, almost as soon as accumulated,
by the incessant coast-action, as we now
see on the shores of South America. During
the periods of subsidence there would pro
bably be much extinction of life ; during
the periods of elevation there would be
much variation; but the geological record
would then be at least perfect.
It may be doubted whether the duration
of any one great period of subsidence over
the whole or part of the archipelago,
together with a contemporaneous accu
mulation of sediment, would exceed the
average duration of the same specific forms;
and these contingencies are indispensable
for the preservation of all the transitional
gradations between any two or more species.
If such gradations were not fully preserved,
transitional varieties would merely.appear
as so many distinct species. It is,, also,
probable that each great period of subsi
dence would be interrupted, by oscillations
of level, and that slight climatal changes
would intervene during such lengthy periods;
and in these cases the inhabitants of the
archipelago would have to migrate, and no
closely consecutive record of their modi
fications could be preserved in any one
formation.
Very many of the marine inhabitants of
the archipelago now range thousands of
miles beyond its confines ; and analogy
leads me to believe that it would be chiefly
these far-ranging species which would
oftenest produce new varieties ; and the
varieties would at first generally be local or
confined to one place, but if possessed of
any decided advantage, or when further
modified and improved, they would slowly
spread and supplant their parent-forms.
123
When such varieties returned to their
ancient homes, as they would differ from
their former state, in a nearly uniform,
though perhaps extremely slight degree,
they would, according to the principles
followed by many palaeontologists, be ranked
as new and distinct species.
If, then, there be some degree of truth in
these remarks, we have no right to expect
to find in our geological formation an
infinite number of those fine transitional
forms which, on my theory, assuredly have
connected all the past and present species
of the same group into one long and branch
ing chain of life. We ought only to look
for a few links, some more closely, some
more distantly related to each other ; and
these links, let them be ever so close, if
found in different stages of the same forma
tion, would, by most palaeontologists, be
ranked as distinct species. But I do not
pretend that I should ever have suspected
how poor a record of tire mutations of life,
the best preserved geological section pre
sented, had not the difficulty of our not
discovering innumerable transitional links
between the species which appeared at the
commencement and close of each forma
tion pressed so hardly on my theory.
On the sudden appearance of whole groups
of Allied Species.—The abrupt manner in
which whole groups of species suddenly
appear in certain formations has been
urged by several palaeontologists—for
instance, by Agassiz, Pictet, and by none
more forcibly than by Professor Sedgwick
—as a fatal objection to the belief in the
transmutation of species. If numerous
species, belonging to the same genera or
families, have really started into life all at
once, the fact would be fatal to the theory
of descent with slow modification through
natural selection. For the development
of a group of forms, all of which have
descended from some one progenitor, must
have been an extremely slow process ; and
the progenitors must have lived long ages
before their modified descendants. But we
continually overrate the perfection of the
geological record, and falsely infer, because
certain genera or families have not been
found beneath a certain stage, that they
did not exist before that stage. We con
tinually forget how large the world is,
compared with the area over which our
geological formations have been carefully
examined ; we forget that groups of species
may elsewhere have long existed and have
slowly multiplied before they invaded the
�124
ON THE ORIGIN OF SPECIES
ancient archipelagoes of Europe and of
the United States. We do not make due
allowance for the enormous intervals of
time which have probably elapsed between
our consecutive formations—longer perhaps
in most cases than the time required for
the accumulation of each formation. These
intervals will have given time for the multi
plication of species from some one or some
few parent-forms; and in the succeeding
formation such species will appear as if
suddenly created.
I may here recall a remark formerly
made—namely, that it might require a
long succession of ages to adapt an organ
ism to some new and peculiar line of
life ; for instance, to fly through the air;
but that when this had been effected, and
a few species had thus acquired a great
advantage over other organisms, a com
paratively short time would be necessary
to produce many divergent forms, which
would be able to spread rapidly and widely
throughout the world.
I will now give a few examples to illus
trate these remarks, and to show how liable
we are to error in supposing that whole
groups of species have suddenly been pro
duced. I may recall the well-known fact that
in geological treatises, published not many
years ago, the great class of mammals was
always spoken of as having abruptly come
in at the commencement of the tertiary
series. And now one of the richest known
accumulations of fossil mammals,.for its
thickness, belongs to the middle of the
secondary series; and one true mammal has
been discovered in the new red sandstone
at nearly the commencement of this great
series. Cuvier used to urge that no monkey
occurred in any tertiary stratum ; but now
extinct species have been discovered in
India, South America, and in Europe even
as far back as the eocene stage. Had it
not been for the rare accident of the pre
servation of footsteps in the new red sand
stone of the United States, who would
have ventured to suppose that, besides
reptiles, no less than at least thirty kinds
of birds, some of gigantic size, existed
during that period? Not a fragment of
bone has been discovered in these beds.
Notwithstanding that the number of joints
shown in the fossil impressions correspond
with the number in the several toes of
living birds’ feet, some authors doubt
whether the animals which left the impres
sions were really birds. Until quite recently
these authors might have maintained, and
some have maintained, that the whole ciass
of birds came suddenly into existence
during an early tertiary period ; but now
we know, on the authority of Professor
Owen (as may be seen in Lyell’s Manual},
that a bird certainly lived during the deposi
tion of the upper greensand.
I may give another instance, which, from
having passed under my own eyes, has
much struck me. Ina memoir on Fossil
Sessile Cirripedes, I have stated that from
the number of existing and extinct tertiary
species ; from the extraordinary abundance
of the individuals of many species all over
the world, from-the Arctic regions to the
equator, inhabiting various zones of depths
from the upper tidal limits to 50 fathoms ;
from the perfect manner in which specimens
are preserved in the oldest tertiary beds ;
from the ease with which even a fragment
of a valve can be recognised; from all
these circumstances, I inferred that, had
sessile cirripedes existed during the secon
dary periods, they would certainly have
been preserved and discovered; and as not
one species had then been discovered in
beds of this age, I concluded that this
great group had been suddenly developed
at the commencement of the tertiary series.
This was a sore trouble to me, adding as I
thought one more instance of the abrupt
appearance of a great group of species.
But my work had hardly been published
when a skilful paleontologist, M. Bosquet,
sent me a drawing of a perfect specimen
of an unmistakable sessile cirripede, which
he had himself extracted from the chalk of
Belgium. And, as if to make the case as
striking as possible, this sessile cirripede
was a Chthamalus, a very common, large,
and ubiquitous genus, of which not one
specimen has as yet been found even in any
tertiary stratum. Hence we now positively
know that sessile cirripedes existed during
the secondary period ; and these cirripedes
might have been the progenitors of our
many tertiary and existing species.
The case most frequently insisted on by
palaeontologists, of the apparently sudden
appearance of a whole group of species, is
that of the teleostean fishes, low down in
the Chalk period. This group includes the
large majority of existing species. Lately,
Professor Pictet has carried their existence
one sub-stage further back; and some
palaeontologists believe that certain much
older fishes, of which the affinities are as
yet imperfectly known, are really teleostean.
Assuming, however, that the whole of them
did appear, as Agassiz believes, at the com
mencement of the chalk formation, the fact
�ON THE IMPERFECTION OF THE GEOLOGICAL RECORD
would certainly be highly remarkable ; but
I cannot see that it would be an insuperable
difficulty on my theory, unless it could like
wise be shown that the species of this
group appeared suddenly and simulta
neously throughout the world at this same
period. It is almost superfluous to remark
that hardly any fossil-fish are known from
south of the equator; and by running
through Pictet’s Palceontology it will be
seen that very few species are known from
several formations in Europe. Some few
families of fish now have a confined range ;
the teleostean fish might formerly have had
a similarly confined range, and, after having
been largely developed in some one sea,
might have spread widely. Nor have we
any right to suppose that the seas of the
world have always been so freely open
from south to north as they arc at present.
Even at this day, if the Malay Archipelago
were converted into land, the tropical parts
of the Indian Ocean would form a large
and perfectly enclosed basin, in which any
great group of marine animals might be
multiplied ; and here they would remain
confined until some of the species became
adapted to a cooler climate, and were
enabled to- double the southern capes of
Africa or Australia, and thus reach other
and distant seas.
From these and similar considerations,
but chiefly from our ignorance of the
geology of other countries beyond the
confines of Europe and the United States,
and from the revolution in our palaeonto
logical ideas on many points, which the
discoveries of even the last dozen years
have effected, it seems to me to be about as
rash in us to dogmatise on the succession
of organic beings throughout the world as
it would be for a naturalist to land for five
minutes on some one barren point in
Australia, and then to discuss the number
and range of its productions.
On the sudden appearance of groups of
Allied Species in the lowest known fossili
ferous strata.—There is another ami allied
difficulty which is much graver. I allude
to the manner in which numbers of species
of the same group suddenly appear in the
lowest known fossiliferous rocks. Most of
the arguments which have convinced me
that all the existing species of the same
group have descended from one progenitor
apply with nearly equal force to the earliest
known species. For instance, I cannot
doubt that all the Silurian trilobites have
descended from some one crustacean,
125
which must have lived long before the
Silurian age, and which probably differed
greatly from any known animal. Some of
the most ancient Silurian animals, as the
Nautilus, Lingula, etc., do not differ much
from living species ; and it cannot on my
theory be supposed that these old species
were the progenitors of all the species of
the orders to which they belong, for
they do not present characters in any
degree intermediate between them.
If,
moreover, they had been the progenitors
of. these orders, they would almost cer
tainly have been long ago supplanted and
exterminated by their numerous and im
proved descendants.
Consequently, if my theory be true, it is
indisputable that before the lowest Silurian
stratum was deposited, long periods elapsed,
as long as, or probably far longer than, the
whole interval from the Silurian age to the
present day ; and that during these vast,
yet quite unknown, periods of time the
world swarmed with living creatures.
To the question, why we do not find
records of these vast primordial periods, I
can give no satisfactory answer. Several
of the most eminent geologists, with Sir R.
Murchison at their head, are convinced that
we see in the organic remains of the lowest
Silurian stratum the dawn of life on this
planet. Other highly competent judges, as
Lyell and the late E. Forbes, dispute this
conclusion. We should not forget that
only a small portion of the world is known
with accuracy. M. Barrande has lately
added another and lower stage to the
Silurian system, abounding with new and
peculiar species. Traces of life have been
detected in the Longmynd beds, beneath
Barrande’s so-called primordial zone. The
presence of phosphatic nodules and bitu
minous matter in some of the lowest azoic
rocks probably indicates the former exist
ence of life at these periods. But the
difficulty of understanding the absence of
vast piles of fossiliferous strata, which on
my theory no doubt were somewhere accu
mulated before the Silurian epoch, is very
great. If these most ancient beds had been
wholly worn away by denudation, or oblite
rated by metamorphic action, we ought to
find only small remnants of the formations
next succeeding them in age, and these
ought to be very generally in a metamor
phosed condition. But the descriptions
which we now possess of the Silurian
deposits over immense territories in Russia
and in North America do not support the
viejjr, that the older a formation is, the more
�126
ON THE ORIGIN OF SPECIES
it has always suffered the extremity of
continents seem to have been formed by a
denudation and metamorphism.
preponderance, during many oscillations
The case at present must remain inex
of level, of the force of elevation ; but may
plicable; and maybe truly urged as a valid
not the areas of preponderant movement
argument against the views here enter
have changed in the lapse of ages ? At a
tained. To show that it may hereafter
period immeasurably antecedent to the
receive some explanation, I will give the
Silurian epoch continents may have existed
following hypothesis. From the nature of
where oceans are now spread out, and
the organic remains which do not appear
clear and open oceans may have existed
to have inhabited profound depths, in the
where our continents now stand. Nor
several formations of Europe and of the
should we be justified in assuming that if,
United States, and from the amount of
for instance, the bed of the Pacific Ocean
sediment, miles in thickness, of which the
were now converted into a continent, we
formations are composed, we may infer
should there find formations older than the
that from first to last large islands or tracts
Silurian strata, supposing such to have
been formerly deposited ; for it might well
of land, whence the sediment was derived,
occurred in the neighbourhood of the exist
happen that strata which had subsided
ing continents of Europe and North
some miles nearer to the centre of the
America. But we do not know what was
earth, and which had been pressed on by
the state of things in the intervals between
an enormous weight of superincumbent
the successive formations; whether Europe
water, might have undergone far more
and the United States during these intervals
metamorphic action than strata which
have always remained nearer to the sur
existed as dry land, or as a submarine
surface near land, on which sediment was
face. The immense areas in some parts of
not deposited, or as the bed of an open and
the world, for instance in South America,
of bare metamorphic rocks, which must
unfathomable sea.
Looking to the existing oceans, which
have been heated under great pressure,
are thrice as extensive as the land, we see
have always seemed to me to require some
special explanation ; and we may perhaps
them studded with many islands ; but not
believe that we see in these large areas the
one oceanic island is as yet known to afford
many formations long anterior to the Silu
even a remnant of any palaeozoic or secon
rian epoch in a completely metamorphosed
dary formation. Hence we may perhaps
condition.
infer that during the palaeozoic and secon
dary periods neither continents nor conti
The several difficulties here discussed—•
nental islands existed where our oceans now
namely, our not finding in the successive
extend ; for had they existed there, palaeo
formations infinitely numerous transitional
zoic and secondary formations would in all
links between the many species which now
probability have been accumulated from
exist or have existed ; the sudden manner
sediment derived from their wear and tear,
in which whole groups of species appear in
and would have been at least partially
our European formations; the almost entire
upheaved by the oscillations of level,
absence, as at present known, of fossiliwhich we may fairly conclude must have
ferous formations beneath the Silurian
intervened during these enormously long
strata, are all undoubtedly of the gravest
periods. If, then, we may infer anything
nature.
We see this in the plainest
from these facts, we may infer that where
manner by the fact that all the most
our oceans now extend oceans have ex
eminent palaeontologists—namely, Cuvier,
tended from the remotest period of which
Agassiz, Barrande, Falconer, E. Forbes,
we have any record ; and, on the other
etc., and all our greatest geologists, as
hand, that where continents now exist
Lyell, Murchison, Sedgwick, etc., have
large tracts of land have existed, subjected
unanimously, often vehemently, maintained
no doubt to great oscillations of level,
the immutability of species. But I have
since the earliest Silurian period. The
reason to believe that one great authority,
coloured map appended to my volume on
Sir Charles Lyell, from further reflection
Coral Reefs led me to conclude that the
entertains grave doubts on this subject.
great oceans are still mainly areas of sub
I feel how rash it is to differ from these
sidence, the great archipelagoes still areas
authorities, to whom, with others, we owe
of oscillations of level, and the continents
all our knowledge. Those who think the
areas of elevation. But have we any right
natural geological record in any degree
to assume that things have thus remained
perfect, and who do not attach much
from the beginning of this world ? Qur
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
weight to the facts and arguments of other
kinds given in this volume, will undoubt
edly at once reject my theory. For my
part, following out Lyell’s metaphor, I look
at the natural geological record as a
history of the world imperfectly kept, and
written in a changing dialect; of this
history we possess the last volume alone,
relating only to two or three countries.
Of this volume only here and there a short
chapter has been preserved ; and of each '
127
page, only here and there a few lines.
Each word of the slowly-changing lan
guage in which the history is supposed
to be written, being more or less different
in the interrupted succession of chapters,
may represent the apparently abruptlychanged forms of life, entombed in our
consecutive, but widely separated, forma
tions. On this view, the difficulties above
discussed are greatly diminished, or even
disappear.
Chapter X.
ON THE GEOLOGICAL SUCCESSION OF ORGANIC
BEINGS
On the slow and successive appearance of new
species—On their different rates of change—Species once lost do not reappear—Groups of
species follow the same general rules in their
appearance and disappearance as do single
species—On Extinction—On simultaneous
changes in the forms of life throughout the
world—On the affinities of extinct species to
each other and to living species—On the state
of development of ancient forms—On the
succession of the same types within the same
areas—Summary of preceding and present
chapters.
Let us now see whether the several facts
and rules relating to the geological succes
sion of organic beings better accord with
the common view of the immutability of
species, or with that of their slow and
gradual modification, through descent and
natural selection.
New species have appeared very slowly,
one after another, both on the land and in
the waters. Lyell has shown that it is
hardly possible to resist the evidence on
this head in the case of the several tertiary
stages ; and every year tends to fill up the
blanks between them, and to make the
percentage system of lost and new forms
more gradual. In some of the most recent
beds, though undoubtedly of high antiquity
if measured by years, only one or two
species are lost forms, and only one or two
are new forms, having here appeared for
the first time, either locally, or, as far as
we know, on the face of the earth. If we
may trust the observations of Philippi in
Sicily, the successive changes in the marine
inhabitants of that island have been many
and most gradual. The secondary forma
tions are more broken ; but, as Bronn has
remarked, neither the appearance nor dis
appearance of their many now extinct
species has been simultaneous in each
separate formation.
Species of different genera and classes
have not changed at the same rate, or in
the same degree. In the oldest tertiary
beds a few living shells may still be found
in the midst of a multitude of extinct
forms.
Falconer has given a striking
instance of a similar fact in an existing
crocodile associated with many strange
and lost mammals and reptiles in the subHimalayan deposits. The Silurian Lingula
differs but little from the living species of
this genus; whereas most of the other
Silurian Molluscs and all the Crustaceans
have changed greatly. The productions
of the land seem to change at a quicker
rate than those of the sea, of which a
striking instance has lately been observed
in Switzerland. There is some reason to
believe that organisms, considered high in
the scale of nature, change more quickly
than those that are low, though there are
exceptions to this rule. The amount of
organic change, as Pictet has remarked,
does not strictly correspond with the
�128
ON THE ORIGIN OF SPECIES
succession of our geological formations ; so
that between each two consecutive forma
tions the forms of life have seldom changed
in exactly the same degree. Yet, if we
compare any but the most closely-related
formations, all the species will be found to
have undergone some change. When a
species has once disappeared from the face
of the earth, we have reason to believe
that the same identical form never reap
pears. The strongest apparent exception
to this latter rule is that of the so-called
“ colonies ” of M. Barrande, which intrude
for a period in the midst of an older forma
tion, and then allow the pre-existing fauna
to re-appear; but Lyell’s explanation—
namely, that it is a case of temporary
migration from a distinct geographical
province—seems to me satisfactory.
These several facts accord well with my
theory.
I believe in no fixed law of
development causing all the inhabitants of
a country to change abruptly, or simul
taneously, or to an equal degree.
The
process of modification must be extremely
slow. The variability of each species is
quite independent of that of all others.
Whether such variability be taken advan
tage of by natural selection, and whether
the variations be accumulated to a greater
or lesser amount, thus causing a greater or
lesser amount of modification in the varying
species, depends on many complex contin
gencies—on the variability being of a
beneficial nature, on the power of inter
crossing, on the rate of breeding, on the
slowly changing physical conditions of the
country, and more especially on the nature
of the other inhabitants with which the
varying species comes into competition.
Hence it is by no means surprising that
one species should retain the same iden
tical form much longer than others ; or, if
changing, that it should change less. We
see. the same fact in geographical distri
bution ; for instance, in the land-shells and
coleopterous insects of Madeira having
come to differ considerably from their
nearest allies on the continent of Europe,
whereas the marine shells and birds have
remained unaltered.
We can perhaps
understand the apparently quicker rate of
change in terrestrial and in more highlyorganised productions compared with
marine and lower productions, by the
more complex relations of the higher
beings to their organic and inorganic
conditions of life, as explained in a former
chapter. When many of the inhabitants
of a country have become modified and
improved, we can understand, on the
principle of competition, and on that of the
many all-important relations of organism
to organism, that any form which does not
become in some degree modified and im
proved will be liable to be exterminated.
Hence we can see why all the species in
the same region do at last, if we look to
wide enough intervals of time, become
modified; for those which do not change
will become extinct.
In members of the same class the
average amount of change, during long
and equal periods of time, may, perhaps,
be nearly the same; but as the accumula
tion of long-enduring fossiliferous formations
depends on great masses of sediment
having been deposited on areas while
subsiding, our formations have been almost
necessarily accumulated at wide and irregu
larly intermittent intervals; consequently,
the amount of organic change exhibited by
the fossils embedded in consecutive forma
tions is not equal. Each formation, on this
view, does not mark a new and complete
act of creation, but only an occasional scene,
taken almost at hazard, in a slowly chang
ing drama.
We can clearly understand why a species
when once lost should never reappear, even
if the very same conditions of life, organic
and inorganic, should recur. For though the
offspring of one species might be adapted
(and no doubt this has occurred in innumer
able instances) to fill the exact place of
another .species in the economy of nature,
and thus supplant it, yet the two forms—
the old and the new—would not be identi
cally the same ; for both would almost
certainly inherit different characters from
their distinct progenitors. For instance, it
is just possible, if our fantail-pigeons were
all destroyed, that fanciers, by striving
during long ages for the same object, might
make a new breed hardly distinguishable
from our present fantail ; but if the parent
rock-pigeon were also destroyed, and in
nature we have every reason to believe that
the parent-form will generally be sup
planted and exterminated by its improved
offspring, it is quite incredible that a fan
tail, identical with the existing breed, could
be raised from any other species of pigeon,
or even from the other well-established
races of the domestic pigeon, for the newlyformed fantail would be almost sure to
inherit from its new progenitor some slight
characteristic differences.
Groups of species—that is, genera and
families—follow the same general rules in
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
their appearance and disappearance as do
single species, changingmoreor less quickly,
and in a greater or lesser degree. A group
does not reappear after it has once disap
peared; or its existence, as long as it lasts, is
continuous. I am aware that there are some
apparent exceptions to this rule, but the
exceptions are surprisingly few—so few that
E. Forbes, Pictet, and Woodward (though
all strongly opposed to such views as I
maintain) admit its truth ; and the rule
strictly accords with my theory. For, as all
the species of the same group have descended
from some one species, it is clear that as
long as any species of the group have
appeared in the long succession of ages, so
long must its members have continuously
existed, in order to have generated either
new and modified or the same old and un
modified forms. Species of the genus
Lingula, for instance, must have continu
ously existed by an unbroken succession of
generations, from the lowest Silurian
stratum to the present day.
We have seen in the last chapter that
the species of a group sometimes falsely
appear to have come in abruptly; and I
have attempted to give an explanation of
this fact, which, if true, would have been
fatal to my views. But such cases are
certainly exceptional, the general rule being
a gradual increase in number, till the group
reaches its maximum, and then, sooner or
later, it gradually decreases. If the number
of the species of a genus, or the number of
the genera of a family, be represented by a
vertical line of varying thickness, crossing
the successive geological formations in
which the species are found, the line will
sometimes falsely appear to begin at its
lower end, not in a sharp point, but abruptly;
it then gradually thickens upwards, some
times keeping for a space of equal thickness,
and ultimately thins out in the upper beds,
marking the decrease and final extinction
of the species. This gradual increase in
number of the species of a group is strictly
conformable with my theory, as the species
of the same genus, and the genera of the
same family, can increase only slowly and
progressively; for the process of modifica
tion and the production of a number of
allied forms must be slow and gradual—•
one species giving rise first to two or three
varieties, these being slowly converted into
species, which, in their turn, produce by
equally slow steps other species, and so on,
like the branching of a great tree from
a single stem, till the group becomes
large.
129
On Extinction.—We have as yet spoken
only incidentally of the disappearance of
species and of groups of species. On
the theory of natural selection the extinc
tion of old forms and the production of
new and improved forms are intimately
connected together. The old notion of all
the inhabitants of the earth having been
swept away at successive periods by catas
trophes is very generally given up, even
by those geologists, as Elie de Beaumont,
Murchison, Barrande, etc., whose general
views would naturally lead them to this
conclusion. On the contrary, we have
every reason to believe, from the study of
the tertiary formations, that species and
groups of species gradually disappear, one
after another, first from one spot, then from
another, and, finally, from the world. Both
single species and w’hole groups of species
last for very unequal periods ; some groups,
as we have seen, having endured from the
earliest dawn of life to the present day ;
some having disappeared before the close
of the palseozoic period. No fixed law
seems to determine the length of time
during which any single species or any
single genus endures. There is reason to
believe that the complete extinction of the
species of a group is generally a slower
process than their production : if the
appearance and disappearance of a group
of species be represented, as before, by a
vertical line of varying thickness, the line
is found to taper more gradually at its
upper end, which marks the progress of
extermination, than at its lower end, which
marks the first appearance and increase in
numbers of the species. In some cases,
however, the extermination of whole groups
of beings, as of ammonites towards the
close of the secondary period, has been
wonderfully sudden.
The whole subject of the extinction of
species has been involved in the most
gratuitous mystery. Some authors have
even supposed that as the individual has a
definite length of life, so have species a
definite duration. No one, I think, can
have marvelled more at the extinction of
species than I have done. When I found
in La Plata the tooth of a horse embedded
with the remains of Mastodon, Megatherium,
Toxodon, and other extinct monsters, which
all co-existed with still living shells at a
very late geological period, I was filled with
astonishment; for seeing that the horse,
since its introduction by the Spaniards into
South America, has run wild oyer the whole
country, and has increased in numbers at
K
�1^0
ON THE ORIGIN OF SPECIES
an unparalleled rate, I asked myself what
could so recently have exterminated the
former horse under conditions of life
apparently so favourable. But how utterly
groundless was my astonishment. Pro
fessor Owen soon perceived that the tooth,
though so like that of the existing horse,
belonged to an extinct species. Had this
horse been still living, but in some degree
rare, no naturalist would have felt the least
surprise at its rarity; for rarity is the
attribute of a vast number of species of all
classes, in all cou ltries. If we ask ourselves
why this or that species is rare, we answer
that something is unfavourable in its con
ditions of life ; but what that something is,
we can hardly ever tell. On the supposi
tion of the fossil horse still existing as a
rare species, we might have felt certain
from the analogy of all other animals, even
of the slow-breeding elephant, and from
the history of the naturalisation of the
domestic horse in South America, that
under more favourable conditions it would
in a very few years have stocked the whole
continent. But we could not have told
what the unfavourable conditions were
which checked its increase, whether some
one or several contingencies, and at what
period of the horse’s life, and in what
degree, they severally acted. If the con
ditions had gone on, however slowly,
becoming less and less favourable, we
assuredly should not have perceived the
fact, yet the fossil horse would certainly
have become rarer and rarer, and finally
extinct—its place being seized on by some
more successful competitor.
It is most difficult always to remember
that the increase of every living being is
constantly being checked by unperceived
injurious agencies, and that these same
unperceived agencies are amply sufficient
to cause rarity, and finally extinction. We
see in many cases in the more recent
tertiary formations that rarity precedes
extinction; and we know that this has
been the progress of events with those
animals which have been exterminated,
either locally or wholly, through man’s
agency. I may repeat what I published
in 1845—namely, that to admit that species
generally become rare before they become
extinct—to feel no surprise at the rarity of
a species, and yet to marvel greatly when
it ceases to exist, is much the same
as to admit that sickness in the indivi
dual is the forerunner of death—to feel
no surprise fat sickness, but when the
sick man dies, to wonder and to suspect
that he died by some unknown deed of
violence.
The theory of natural selection is
grounded on the belief that each new
variety, and ultimately each new species,
is produced and maintained by having
some advantage over those with which
it comes into competition ; and the con
sequent extinction of less favoured forms
almost inevitably follows. It is the same
with our domestic productions: when a
new and slightly improved variety has
been raised, it at first supplants the less
improved varieties in the same neigh
bourhood ; when much improved, it is
transported far and near, like our short
horn cattle, and takes the place of other
breeds in other countries. Thus the ap
pearance of new forms and the disappear
ance of old forms, both natural and
artificial, are bound together. In certain
flourishing groups the number of new
specific forms which have been produced
within a given time is probably greater
than that of the old specific forms which
have been exterminated; but we know
that the number of species has not gone on
indefinitely increasing, at least during the
later geological periods, so that, looking to
later times, we may believe that the pro
duction of new forms has caused the
extinction of about the same number of
old forms.
The competition will generally be most
severe, as formerly explained and illustrated
by examples, between the forms which are
most like each other in all respects; Hence
the improved and modified descendants of
a species will generally cause the extermi
nation of the parent-species ; and if many
new forms have been developed from any
one species, the nearest allies of that species
—z>., the species of the same genus—will be
the most liable to extermination. Thus, as
I believe, a number of new species des
cended from one species—that is, a new
genus—comes to supplant an old genus,
belonging to the same family.
But it
must often have happened that a new
species belonging to some one group will
have seized on the place occupied by a
species belonging to a distinct group, and
thus caused its extermination; and if many
allied forms be developed from the suc
cessful intruder, many will have to yield
their places; and it will generally be allied
forms which will suffer from some inherited
inferiority in common. But whether it be
species belonging to the same or to a
distinct class, which yield their places to
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
other species which have been modified or
improved, a few of the sufferers may often
long be preserved, from being fitted to
some peculiar line of life, or from in
habiting some distant and isolated station,
where they have escaped severe compe
tition. For instance, a single species of
Trigonia, a great genus of shells in the
secondary formations, survives in the Aus
tralian seas ; and a few members of the
great and almost extinct group of Ganoid
fishes still inhabit our fresh waters. There
fore, the utter extinction of a group is
generally, as we have seen, a slower pro
cess than its production.
With respect to the apparently sudden
extermination of whole families or orders,
as of Trilobites at the close of the palaeo
zoic period, and of Ammonites at the close
of the secondary period, we must remem
ber what has been already said on the
probable wide intervals of time between
our consecutive formations ; and in these
intervals there may have been much slow
extermination. Moreover, when by sudden
immigration or by unusually rapid develop
ment, many species of a new group have
taken possession of a new area, they will
have exterminated in a correspondingly
rapid manner many of the old inhabitants;
and the forms which thus yield their places
will commonly be allied, for they will par
take of some inferiority in common.
Thus, as it seems to me, the manner in
which single species and whole groups of
species become extinct accords well with
the theory of natural selection. We need
not marvel at extinction; if we must marvel,
let it be at our presumption in imagining
for a moment that we understand the many
complex contingencies on which the exist
ence of each species depends. If we forget
for an instant that each species tends to
increase inordinately, and that some check
is always in action, yet seldom perceived
by us, the whole economy of nature will be
utterly obscured. Whenever we can pre
cisely say why this species is more abundant
in individuals than that; why this species
and not another can be naturalised in a
given country ; then, and not till then, we
may justly feel surprised why we cannot
account for the extinction of this particular
species or group of species.
On the Forms of Life changing almost
simultaneously throughout the "World.—■
Scarcely any palaeontological discovery is
more striking than the fact that the forms
of life change almost simultaneously
i31
throughout the world. Thus our European
Chalk formation can be recognised in many
distant parts of the world, under the most
different climates, where not a fragment of
the mineral chalk itself can be found—
namely, in North America, in equatorial
South America, in Tierra del Fuego, at the
Cape of Good Hope, and in the peninsula
of India. For at these distant points the
organic remains in certain beds present an
unmistakeable degree of resemblance to
those of the Chalk. It is not that the same
species are met with ; for in some cases not
one species is identically the same, but
they belong to the same families, genera,
and sections of genera, and sometimes are
similarly characterised in such trifling
points as mere superficial sculpture. More
over, other forms which are not found in
the Chalk of Europe, but which occur in the
formations either above or below, are
similarly absent at these distant points of
the world.
In the several successive
palaeozoic formations of Russia, Western
Europe, and North America a similar
parallelism in the forms of life has been
observed by several authors : so it is, ac
cording to Lyell, with the several European
and North American tertiary deposits.
Even if the few fossil species which are
common to the Old and' New Worlds be
kept wholly out of view, the general parallel
ism in the successive forms of life, in the
stages of the widely-separated palaeozoic
and tertiary periods, would still be manifest,
and the several formations could be easily
correlated.
These observations, however, relate to
the marine inhabitants of distant parts of
the world : we have not sufficient data to
judge whether the productions of the land
and of fresh water change at distant points
in the same parallel manner. We may
doubt whether they have thus changed : if
the Megatherium, Mylodon, Macrauchenia,
and Toxodon had been brought to Europe
from La Plata, without any information in
regard to their geological position, no one
would have suspected that they had co
existed with still living sea-shells ; but as
these anomalous monsters co-existed with
the Mastodon and Horse, it might at least
have been inferred that they had lived
during one of the later tertiary stages.
When the marine forms of life are spoken
of as having changed simultaneously
throughout the world, it must not be sup
posed that this expression relates to the
same thousandth or hundred-thousandth
year, or even that it has a very strict
�132
ON THE ORIGIN OF SPECIES
geological sense; for if all the marine
animals which live at the present day in
Europe, and all those that lived in Europe
duri ng the pleistocene period (an enormously
remote period as measured by years, in
cluding the whole glacial epoch), were to be
compared with those now living in South
America or in Australia, the most skilful
naturalist would hardly be able to say
whether the existing or the pleistocene in
habitants of Europe resembled most closely
those of the southern hemisphere. So,
again, several highly-competent observers
believe that the existing productions
of the United States are more closely
related to those which lived in Europe
during certain later tertiary stages than to
those which now live here ; and, if this be
so, it is evident that fossiliferous beds
deposited at the present day on the shores
of North America would hereafter be
liable to be classed with somewhat older
European beds. Nevertheless, looking to
a remotely-future epoch, there can, I think,
be little doubt that all the more modern
marine formations—namely, the upper
pliocene, the pleistocene, and strictly
modern beds, of Europe, North and South
America, and Australia, from containing
fossil remains in some degree allied, and
from not including those forms which are
only found in the older underlying deposits
—would be correctly ranked as simultaneous
in a geological sense.
The fact of the forms of life changing
simultaneously in the above large sense, at
distant parts of the world, has greatly struck
those admirable observers, MM.de Verneuil
and d’Archiac. After referring to the paral
lelism of the palaeozoic forms of life in
various parts of Europe, they add : “ If,
struck by this strange sequence, we turn
our attention to North America, and there
discover a series of analogous phenomena,
it will appear certain that all these modifi
cations of species, their extinction, and the
introduction of new ones, cannot be owing
to mere changes in marine currents or
other causes more or less local and
temporary, but depend on general laws
which govern the whole animal kingdom.”
M. Barrande has made forcible remarks to
precisely the same effect. It is, indeed,
quite futile to look to changes of currents,
climate, or other physical conditions, as
the cause of these great mutations in the
forms of life throughout the world, under
the most different climates. We must, as
Barrande has remarked, look to some
special law. We shall see this more clearly
when we treat of the present distribution
of organic beings, and find how slight is
the relation between the physical conditions
of various countries and the nature of their
inhabitants.
This great fact of the parallel succes
sion of the forms of life throughout the
world is explicable on the theory of natural
selection. New species are formed by new
varieties arising which have some advan
tage over older forms ; and those forms
which are already dominant, or have some
advantage over the other forms in their
own country, would naturally oftenest give
rise to new varieties or incipient species ;
for these latter must be victorious in a still
higher degree in order to be preserved
and to survive. We have distinct evidence
on this head in the plants which are
dominant—that is, which are commonest
in their own homes, and are most widely
diffused, having produced the greatest
number of new varieties. It is also natural
that the dominant, varying, and farspreading species, which already have
invaded to a certain extent the territories
of other species, should be those which
would have the best chance of spreading
still further, and of giving rise in new
countries to new varieties and species.
The process of diffusion may often be very
slow, being dependent on climatal and
geographical changes, or on strange acci
dents ; but, in the long run, the dominant
forms will generally succeed in spreading.
The diffusion would, it is probable, be
slower with the terrestrial inhabitants of
distinct continents than with the marine
inhabitants of the continuous sea. We
might, therefore, expect to find, as we
apparently do find, a less strict degree of
parallel succession in the productions of
the land than of the sea.
Dominant species spreading from any
region might encounter still more dominant
species, and then their triumphant course^
or even their existence, would cease. We
know not at all precisely what are all the
conditions most favourable for the multi
plication of new and dominant species ;
but we can, I think, clearly see that a
number of individuals, from giving a better
chance of the appearance of favourable
variations, and that severe competition
with many already existing forms, would be
highly favourable, as would be the power
of spreading into new territories. A certain
amount of isolation, recurring at long
intervals of time, would probably be also
favourable, as before explained.
One
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
quarter of the world, may have been most
favourable for the production of new and
dominant species on the land, and another
for those in the waters of the sea. If two
great regions had been for a long period
favourably circumstanced in an equal
degree, whenever their inhabitants met
the battle would be prolonged and severe,
and some from one birthplace and some
from the ether might be victorious. But,
in the course of time, the forms dominant
in the highest degree, wherever produced,
would tend everywhere to prevail. As
they prevailed, they would cause the extinc
tion of other and inferior forms ; and as
these inferior forms would be allied in
groups by inheritance, whole groups would
tend slowly to disappear, though here and
there a single member might long be
enabled to survive.
Thus, as it seems to me, the parallel, and,
taken in a large sense, simultaneous, suc
cession of the same forms of life throughout
the world accords well with the principle
of new species having been formed by
dominant species spreading widely and
varying : the new species thus produced
being themselves dominant owing to in
heritance, and to having already had some
advantage over their parents or over other
species; these again spreading, varying,
and producing new species. The forms
which are beaten and which yield their
places to the new and victorious forms, will
generally be allied in groups, from inherit
ing some inferiority in common; and there
fore, as new and improved groups spread
throughout the world, old groups will
disappear from the world, and the succes
sion of forms in both ways will everywhere
tend to correspond.
There is one other remark connected
with this subject worth making. I have
given my reasons for believing that all our
greater fossiliferous formations were de
posited during periods of subsidence, and
that blank intervals of vast duration occur
red during the periods when the bed of the
sea was either stationary or rising, and
likewise when sediment was not thrown
down quickly enough to embed and preserve
organic remains. During these long and
blank intervals I suppose that the inhabi
tants of each region underwent a consider
able amount of modification and extinction,
and that there was much migration from
other parts of the world. As we have
reason to believe that large areas are
affected by the same movement, it is pro
bable that strictly contemporaneous forma
133
tions have often been accumulated over
very wide spaces in the same quarter of the
world ; but we are far from having any
right to conclude that this has invariably
been the case, and that large areas have
invariably been affected by the same move
ments. When two formations have been
deposited in two regions during nearly, but
not exactly, the same period, we should find
in both, from the causes explained in the
foregoing paragraphs, the same general
succession in the forms of life ; but the
species would not exactly correspond, for
there will have been a little more time in
the one region than in the other for modifi
cation, extinction, and immigration.
I suspect that cases of this nature occur
in Europe. Mr. Prestwich, in his admirable
Memoirs on the eocene deposits of England
and France, is able to draw a close general
parallelism between the successive stages
in the two countries;; but when he compares
certain stages in England with those in
France, although he finds in both a curious
accordance in the numbers of the species
belonging to the same genera, yet the
species themselves differ in a manner very
difficult to account for, considering the
proximity of the two areas—unless, indeed,
it be assumed that an isthmus separated
two seas inhabited by distinct, but con
temporaneous, faunas. Lyell has made
similar observations on some of the later
tertiary formations. Barrande also shows
that there is a striking general parallelism
in the successive Silurian deposits of
Bohemia and Scandinavia ; nevertheless,
he finds a surprising amount of difference
in the species. If the several formations
in these regions have not been deposited
during the same exact periods—a formation
in one region often corresponding with a
blank interval in the other—and if in both
regions the species have gone on slowly
changing during the accumulation of the
several formations and during the long
intervals of time between them—in this
case, the several formations in the two
regions could be arranged in the same
order, in accordance with the general
succession of the form of life, and the
order would falsely appear to be strictly
parallel; nevertheless, the species would
not all be the same in the apparently
corresponding stages in the two regions.
On the Affinities of extinct Species to each
other and to living forms.—Let us now
look to the mutual affinities of extinct and
I living species. They all fall into one grand
�134
ON THE ORIGIN OF SPECIES
natural system; and this fact is at once
explained on the principle of descent. The
more ancient any form is, the more, as a
general rule, it differs from living forms.
But, as Buckland long ago remarked, all
fossils can be classed either in still existing
groups or between them. That the extinct
forms of life help to fill up the wide intervals
between existing genera, families, and
orders cannot be disputed. For if we
confine our attention either to the living or
to the extinct alone, the series is far less
perfect than if we combine both into one
general system. With respect to the
Vertebrata, whole pages could be filled
with striking illustrations from our great
palaeontologist, Owen, showing how extinct
animals fall in between existing groups.
Cuvier ranked the Ruminants and Pachy
derms as the two most distinct orders of
mammals ; but Owen has discovered so
many fossil links that he has had to alter
the whole classification of these two orders,
and has placed certain pachyderms in
the same sub-order with ruminants : for
example, he dissolves by fine gradations
the apparently wide difference between the
pig and the camel. In regard to the
Invertebrata, Barrande (and a higher
authority could not be named) asserts that
he is every day taught that palaeozoic
animals, though belonging to the same
orders, families, or genera with those living
at the present day, were not at this early
epoch limited in such distinct groups as
they now are.
Some writers have objected to any extinct
species or group of species being considered
as intermediate between living species or
groups. If by this term it is meant that
an extinct form is directly intermediate in
all its characters between two living forms,
the objection is probably valid. But I
apprehend that in a perfectly natural classi
fication many fossil species would have to
stand between living species, and some
extinct genera between living genera, even
between genera belonging to distinct
families. The most common case, espe
cially with respect to very distinct groups,
such as fish and reptiles, seems to be that,
supposing them to be distinguished at the
present day from each other by a dozen
characters, the ancient members of the
same two groups would be distinguished
by a somewhat lesser number of characters,
so that the two groups, though formerly
quite distinct, at that period made some
small approach to each other.
ancient a form is, by so much the more it
tends to connect by some of its characters
groups now widely separated from each
other. This remark, no doubt, must be
restricted to those groups which have
undergone much change in the course of
geological ages; and it would be difficult
to prove the truth of the proposition, for
every now and then even a living animal,
as the Lepidosiren, is discovered having
affinities directed towards very distinct
groups. Yet if we compare the older
Reptiles and Batrachians, the older Fish,
the older Cephalopods, and the eocene
Mammals, with the more recent members
of the same classes, we must admit that
there is some truth in the remark.
Let us see how far these several facts
and inferences accord with the theory of
descent with modification. As the subject
is somewhat complex, I must request the
reader to turn to the diagram in the pre
liminary. We may suppose that the num
bered letters represent genera, and the
dotted lines diverging from them the
species in each genus. The diagram is
much too simple, too few genera and too
few species being given ; but this is unim
portant for us. The horizontal lines may
represent successive geological formations,
and all the forms beneath the uppermost
line may be considered as extinct. The
three existing genera, «14, y14, />r4, will form
a small family ; £14 and_/14, a closely allied
family or sub-family ; and 014, z?14, /zz'4, a
third family. These three families, together
with the many extinct genera on the several
lines of descent diverging from the parent
form (A), will form an order; for all will
have inherited something in common from
their ancient and common progenitor. On
the principle of the continued tendency
to divergence of character, which was
formerly illustrated by this diagram, the
more recent any form is, the more it will
generally differ from its ancient progenitor.
Hence we can understand the rule that the
most ancient fossils differ most from
existing forms. We must not, however,
assume that divergence of character is a
necessary contingency; it depends solely
on the descendants from a species being
thus enabled to seize on many and dif
ferent places in the economy of nature.
Therefore, it is quite possible, as we have
seen in the case of some Silurian forms,
that a species might go on being slightly
modified in relation to its slightly altered
conditions of life, and yet retain through
It is a common belief that the more
out a vast period the same general
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
characteristics. This is represented in the
diagram by the letter F14.
All the many forms, extinct and recent,
descended from (A) make, as before re
marked, one order ; and this order, from
the continued effects of extinction and
divergence of character, has become
divided into several sub-families and
families, some of which are supposed to
have perished at different periods, and
some to have endured to the present day.
By looking at the diagram we can see
that, if many of the extinct forms supposed
to be embedded in the successive forma
tions were discovered at several points
low down in the series, the three existing
families on the uppermost line would be
rendered less distinct from each other. If,
for instance, the genera a1, «3, zzI0,y8, ;/z3, z/z6,
w9, were disinterred, these three families
would be so closely linked together that
they probably would have to be united
into one great family, in nearly the same
manner as has occurred with ruminants
and pachyderms. Yet he who objected to
call the extinct genera, which thus linked
the living genera of three families together,
intermediate in character would be justi
fied, as they are intermediate, not directly,
but only by a long and circuitous course
through many widely different forms. If
many extinct forms were to be discovered
above one of the middle horizontal lines or
geological formations—for instance, above
No. VI.—but none from beneath this line,
then only the two families on the left hand
(namely, <z14, etc., and £'4, etc.) would have
to be united into one family ; and the two
other families (namely, zz'4 to /t4, now in
cluding five genera, and z>'4 to 7/z14) would
yet remain distinct. These two families,
however, would be less distinct from each
other than they were before the discovery
of the fossils. If, for instance, we suppose
the existing genera of the two families to
differ from each other by a dozen char
acters, in this case the genera, at the early
period marked VI., would differ by a lesser
number of characters ; for at this early
stage of descent they have not diverged in
character from the common progenitor of
the order nearly so much as they subse
quently diverged.
Thus it comes that
ancient and extinct genera are often in
some slight degree intermediate in char
acter between their modified descendants,
or between their collateral relations.
In nature the case will be far more com
plicated than is represented in the diagram ;
for the groups will have been more nume
135
rous, they will have endured for extremely
unequal lengths of time, and will have
been modified in various degrees. As we
possess only the last volume of the geo
logical record, and that in a very broken
condition, we have no right to expect,
except in very rare cases, to fill up wide
intervals in the natural system, and thus
unite distinct families or orders. All that
we have a right to expect is that those
groups which have within known geo
logical periods undergone much modifica
tion should in the older formations make
some slight approach to each other ; so
that the older members should differ less
from each other in some of their characters
than do the existing members of the same
groups ; and this by the concurrent evi
dence of our best palaeontologists seems
frequently to be the case.
Thus on the theory of descent with
modification the main facts with respect
to the mutual affinities of the extinct forms
of life to each other and to living forms
seem to me explained in a satisfactory
manner. And they are wholly inexplicable
on any other view.
On this same theory, it is evident that
the fauna of any great period in the earth’s
history will be intermediate in general
character between that which preceded and
that which succeeded it. Thus the species
which lived at the sixth great stage of
descent in the diagram are the modified
offspring of those which lived at the fifth
stage, and are the parents of those which
became still more modified at the seventh
stage ; hence they could hardly fail to be
nearly intermediate in character between
the forms of life above and below. We
must, however, allow for the entire extinc
tion of some preceding founs, and in any
one region for the immigration of new forms
from other regions, and for a large amount
of modification, during the long and blank
intervals between the successive formations.
Subject to these allowances, the fauna of
each geological period undoubtedly is inter
mediate in character between the preced
ing and succeeding faunas. I need give
only one instance—namely, the manner in
which the fossils of the Devonian system,
when this system was first discovered, were
at once recognised by palaeontologists as
intermediate in character between those of
the overlying carboniferous and underlying
Silurian system. But each fauna is not
necessarily exactly intermediate, as unequal
intervals of time have elapsed between con
secutive formations,
�136
ON THE ORIGIN OF SPECIES
It is no real objection to the truth of the
statement, that the fauna of each period as
a whole is nearly intermediate in character
between the preceding and succeeding
faunas, that certain genera offer exceptions
to the rule. For instance, mastodons and
elephants, when arranged by Dr. Falconer
in two series, first according to their mutual
affinities and then according to their periods
of existence, do not accord in arrangement.
The species extreme in character are not
the oldest or the most recent; nor are
those which are intermediate in character,
intermediate in age. But supposing for an
instant, in this and other such cases, that
the record of the first appearance and dis
appearance of the species was perfect, we
have no reason to believe that forms suc
cessively produced necessarily endure for
corresponding lengths of time : a very
ancient form might occasionally last much
longer than a form elsewhere subsequently
produced, especially in the case of terres
trial productions inhabiting separated dis
tricts. To compare small things with great:
if the principal living and extinct races of
the domestic pigeon were arranged as well
as they could be in serial affinity, this
arrangement would not closely accord with
the order in time of their production, and
still less with the order of their disappear
ance ; for the parent rock-pigeon now lives,
and many varieties between the rock-pigeon
and the carrier have become extinct; and
carriers which are extreme in the important
character of length of beak originated
earlier than short-beaked tumblers, which
are at the opposite end of the series in this
same respect.
Closely connected with the statement,
that the organic remains from an inter
mediate formation are in some degree
intermediate in character, is the fact, insisted
on by all palaeontologists, that fossils from
two consecutive formations are far more
closely related to each other than are the
fossils from two remote formations. Pictet
gives as a well-known instance the general
resemblance of the organic remains from
the several stages of the Chalk formation,
though the species are distinct in each
stage. This fact alone, from its generality,
seems to have shaken Professor Pictet in
his firm belief in the immutability of
species. He who is acquainted with the
distribution of existing species over the
globe will not attempt to account for the
close resemblance of the distinct species
in closely-consecutive formations by the
physical conditions of the ancient areas
having remained nearly the same. Let it
be remembered that the forms of life, at
least those inhabiting the sea, have changed
almost simultaneously throughout the world,
and therefore under the most different
climates and conditions.
Consider the
prodigious vicissitudes of climate during
the pleistocene period, which includes the
whole glacial period, and note how little
the specific forms of the inhabitants of the
sea have been affected.
On the theory of descent, the full
meaning of the fact of fossil remains from
closely-consecutive formations, though
ranked as distinct species, being closely
related is obvious. As the accumulation
of each formation has often been inter
rupted, and as long blank intervals have
intervened between successive formations,
we ought not to expect to find, as I
attempted to show in the last chapter, in
any one or two formations all the inter
mediate varieties between the species
which appeared at the commencement and
close of these periods; but we ought to find
after intervals, very long as measured by
years, but only moderately long as
measured geologically, closely-allied forms,
or, as they have been called by some
authors, representative species; and these
we assuredly do find. We find, in short,
such evidence of the slow and scarcely
sensible mutation of specific forms as we
have a just right to expect to find.
On the state of Development of Ancient
Forms.—There has been much discussion
whether recent forms are more highly
developed than ancient. I will not here
enter on this subject, for naturalists have
not as yet defined to each other’s satisfac
tion what is meant by high and low forms.
The best definition probably is that the
higher forms have their organs more dis
tinctly specialised for different functions ;
and, as such division of physiological
labour seems to be an advantage to each
being, natural selection will constantly
tend insofar to make the later and more
modified forms higher than their early
progenitors, or than the slightly modified
descendants of such progenitors. In a
more general sense, the more recent forms
must, on my theory, be higher than the
more ancient; for each new species is
formed by having had some advantage in
the struggle for life over other and pre
ceding forms. If, under a nearly similar
climate, the eocene inhabitants of one
quarter of the world were put into
�ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS
competition with the existing inhabitants of
the same or some other quarter, the eocene
fauna or flora would certainly be beaten
and exterminated, as would a secondary
fauna by an eocene and a palaeozoic fauna
by a secondary fauna. I do not doubt
that this process of improvement has
affected in a marxed and sensible manner
the organisation of the more recent and
victorious forms of life, in comparison with
the ancient and beaten forms ; but I can
see no way of testing this sort of progress.
Crustaceans, for instance, not the highest
in their own class, may have beaten the
highest molluscs. From the extraordinary
manner in which European productions
have recently spread over New Zealand,
and have seized on places which must
have been previously occupied, we may
believe, if all the animals and plants of
Great Britain were set free in New
Zealand, that in the course of time a
multitude of British forms would become
thoroughly naturalised there, and would
exterminate many of the natives. On the
other hand, from what we now see occur
ring in New Zealand, and from hardly a
single inhabitant of the southern hemi
sphere having become wild in any part of
Europe, we may doubt, if all the produc
tions of New Zealand were set free in
Great Britain, whether any considerable
number would be enabled to seize on places
now occupied by our native plants and
animals. Under this point of view, the
productions of Great Britain may be said
to be higher than those of New Zealand.
Yet the most skilful naturalist, from an
examination of the species of the two
countries, could not have foreseen this
result.
Agassiz insists that ancient animals
resemble, to a certain extent, the embryos
of recent animals of the same classes, or
that the geological succession of extinct
forms is in some degree parallel to the
embryological development of recent forms.
I must follow Pictet and Huxley in thinking
that the truth of this doctrine is very far
from proved. Yet I fully expect to see it
hereafter confirmed, at least in regard to
subordinate groups, which have branched
off from each other within comparatively
recent times. For this doctrine of Agassiz
accords well with the theory of natural
selection. In a future chapter I shall
attempt to show that the adult differs from
its embryo, owing to variations supervening
at a not early age and being inherited at
a corresponding age. This process, while
137
it leaves the embryo almost unaltered, con
tinually adds, in the course of successive
generations, more and more difference to
the adult.
Thus the embryo comes to be left as a
sort of picture, preserved by nature, of the
ancient and less modified condition of each
animal. This view may be true, and yet
it may never be capable of full proof.
Seeing, for instance, that the oldest known
mammals, reptiles, and fish strictly belong
to their own proper classes, though some
of these old forms are in a slight degree
less distinct from each other than are the
typical members of the same groups at the
present day, it would be vain to look for
animals having the common embryological
character of the Vertebrata until beds far
beneath the lowest Silurian strata are dis
covered—a discovery of which the chance
is very small.
On the Succession of the same Types
within the same areas during the later
tertiary -periods.—Mr. Clift, many years
ago, showed that the fossil mammals from
the Australian caves were closely allied to
the living marsupials of that continent.
In South America a similar relationship is
manifest, even to an uneducated eye, in
the gigantic pieces of armour like those of
the armadillo, found in several parts of La
Plata ; and Professor Owen has shown in
the most striking manner that most of the
fossil mammals, buried there in such
numbers, are related to South American
types. This relationship is even more
clearly seen in the wonderful collection of
fossil bones made by MM. Lund and
Clausen in the caves of Brazil. I was so
much impressed with these facts that I
strongly insisted, in 1839 and 1845, on this
“ law of the succession of types ”—on “ this
wonderful relationship in the same continent
between the dead and the living.” Pro
fessor Owen has subsequently extended the
same generalisation to the mammals of the
Old World. We see the same law in this
author’s restorations of the extinct and
gigantic birds of New Zealand. We see
it also in the birds of the caves of Brazil.
Mr. Woodward has shown that the same
law holds good with sea-shells; but, from
the wide distribution of most genera of
molluscs, it is not well displayed by them.
Other cases could be added, as the relation
between the extinct and living land-shells
of Madeira, and between the extinct and
living brackish-water shells of the AraloCaspian Sea.
�140
ON THE ORIGIN OF SPECIES
formations are more closely allied to each
other than are those of remote formations,
for the forms are more closely linked
together by generation: we can clearly
see why the remains of an intermediate
formation are intermediate in character.
The inhabitants of each successive period
in the world’s history have beaten their
predecessors in the race for life, and are,
insofar, higher in the scale of nature ; and
this may account for that vague, yet illdefined sentiment, felt by many palaeonto
logists, that organisation on the whole has
progressed. If it should hereafter be
proved that ancient animals resemble, to
a certain extent, the embryos of more
recent animals of the same class, the fact
will be intelligible. The succession of the
same types of structure within the same
areas during the later geological periods
ceases to be mysterious, and is simply
explained by inheritance.
If, then, the geological record be as
imperfect as I believe it to be, and it may,
at least, be asserted that the record cannot
be proved to be much more perfect, the
main objections to the theory of natural
selection are greatly diminished or dis
appear. On the other hand, all the chief
laws of palaeontology plainly proclaim, as
it seems to me, that species have been
produced by ordinary generation : old
forms having been supplanted by new and
improved forms of life, produced by the
laws of variation still acting around us,
and preserved by natural selection.
Chapter XI.
GEOGRAPHICAL DISTRIBUTION
Present distribution cannot be accounted for by
differences in physical conditions—-Importance
of barriers—Affinity of the productions of the
same continent—Centres of creation—Means
of dispersal, by changes of climate and of the
level of the land, and by occasional means—■
Dispersal during the Glacial period co-extensive with the world.
In considering the distribution of organic
beings over the face of the globe, the first
great fact which strikes us is that neither
the similarity nor the dissimilarity of the
inhabitants of various regions can be
accounted for by their climatal and other
physical conditions. Of late almost every
author who has studied the subject has
come to this conclusion. The case of
America alone would almost suffice to prove
its truth; for if we exclude the northern
parts, where the circumpolar land is almost
continuous, all authors agree that one of
the most fundamental divisions in geo
graphical distribution is that between the
New and Old Worlds; yet, if we travel
over the vast American continent, from
the central parts of the United States to its
extreme southern point, we meet with the
most diversified conditions; the most humid
districts, arid deserts, lofty mountains,
grassy plains, forests, marshes, lakes, and
great rivers, under almost every tempera
ture. There is hardly a climate or condi
tion in the Old World which cannot be
paralleled in the New—at least as closely
as the same species generally require ; for
it is a most rare case to find a group of
organisms confined to any small spot
having conditions peculiar in only a slight
degree ; for instance, small areas in the
Old World could be pointed out hotter than
any in the New World, yet these are not
inhabited by a peculiar fauna or flora.
Notwithstanding this parallelism in the
conditions of the Old and New Worlds,
how widely different are their living pro
ductions 1
In the southern hemisphere, if we com
pare large tracts of land in Australia, South
Africa, and western South America, between
latitudes 250 and 35’, we shall find parts
extremely similar in all their conditions,
yet it would not be possible to point out
three faunas and floras more utterly dis
similar. Or, again, we may compare the pro
ductions of South America south of latitude
350 with those north of 25°, which conse
quently inhabit a considerably different
�GEOGRAPHICAL DISTRIBUTION
climate, and they will be found incompar
ably more closely related to each other
than they are to the productions of Australia
or Africa under nearly the same climate.
Analogous facts could be given with respect
to the inhabitants of the sea.
A second great fact which strikes us in
our general review is that barriers of any
kind, or obstacles to free migration, are
related in a close and important manner to
the differences between the productions of
various regions. We see this in the great
difference of nearly all the terrestrial pro
ductions of the New and Old Worlds,
excepting in the northern parts, where the
land almost joins, and where, under a
slightly different climate, there might have
been free migration for the northern tem
perate forms, as there now is for the strictly
arctic productions. We see the same fact
in the great difference between the inhabi
tants of Australia, Africa, and South
America under the same latitude, for these
countries are almost as much isolated from
each other as is possible. On each conti
nent also we see the same fact; for on
the opposite sides of lofty and continuous
mountain-ranges, and of great deserts, and
sometimes even of large rivers, we find
different productions; though as mountain
chains, deserts, etc., are not as impassable,
or likely to have endured so long as the
oceans separating continents, the differ
ences are very inferior in degree to those
characteristic of distinct continents.
Turning to the sea, we find the same
law. No two marine faunas are more
distinct, with hardly a fish, shell, or crab
in common, than those of the eastern and
western shores of South and Central
America ; yet these great faunas are
separated only by the narrow, but impas
sable, isthmus of Panama. Westward of
the shores of America a wide space of
open ocean extends, with not an island as
a halting-place for emigrants ; here we
have a barrier of another kind, and, as
soon as this is passed, we meet in the
eastern islands of the Pacific with another
and totally distinct fauna. So that here
three marine faunas range far northward
and southward, in parallel lines not far
from each other, under corresponding
climates ; but from being separated from
each other by impassable barriers, either
of land or open sea, they are wholly dis
tinct. On the other hand, proceeding still
further westward from the eastern islands ■
of the tropical parts of the Pacific, we
encounter no impassable barriers, and we
141
have innumerable islands as halting-places,
or continuous coasts, until, after travelling
over a hemisphere, we come to the shores
of Africa; and over this vast space we
meet with no well-defined and distinct
marine faunas. Although hardly one shell,
crab, or fish is common to the above-named
three approximate faunas of Eastern and
Western America and the eastern Pacific
islands, yet many fish range from the
Pacific into the Indian Ocean, and many
shells are common to the eastern islands
of the Pacific and the eastern shores of
Africa, on almost exactly opposite meridians
of longitude.
A third great fact, partly included in the
foregoing statements, is the affinity of the
productions of the same continent or sea,
though the species themselves are distinct
at different points and stations. It is a
law of the widest generality, and every
continent offers innumerable instances.
Nevertheless, the naturalist, in travelling,
for instance, from north to south, never fails
to be struck by the manner in which succes
sive groups of beings, specifically distinct,
yet clearly related, replace each other.
He hears from closely-allied yet distinct
kinds of birds notes nearly similar, and
sees their nests similarly constructed, but
not quite alike, with eggs coloured in nearly
the same manner. The plains near the
Straits of Magellan are inhabited by one
species of Rhea (American ostrich), and
northward the plains of La Plata by
another species of the same genus, and
not by a true ostrich or emu, like those
found in Africa and Australia under the
same latitude. On these same plains of
La Plata we see the agouti and bizcacha,
animals having nearly the same habits as
our haresand rabbits, and.belonging to the
same order of Rodents; but they plainly
display an American type of structure.
We ascend the lofty peaks of the Cordillera,,
and we find an alpine species of bizcacha ;
we look to the waters, and we do not find
the beaver or musk-rat, but the coypu and
capybara, rodents of the American type.
Innumerable other instances could be
given. If we look to the islands off the
American shore, however much they may
differ in geological structure, the inhabitants,
though they may be all peculiar species, are
essentially American. We may look back
to past ages, as shown in the last chapter,
and we find American types then prevalent
on the American continent and in the
American seas. We see in these facts some
deep organic bond, prevailing throughout
�142
ON THE ORIGIN OF SPECIES
space and time, over the same areas of
land and water, and independent of their
physical conditions. The naturalist must
feel little curiosity who is not led to inquire
what this bond is.
This bond, on my theory, is simply
inheritance, that cause which alone, as far
as we positively know, produces organisms
quite like, or, as we see in the case of
varieties, nearly like each other. The dis
similarity of the inhabitants of different
regions may be attributed to modification
through natural selection, and in a quite
subordinate degree to the direct influence
of different physical conditions. The
degree of dissimilarity will depend on the
migration of the more dominant forms of
life from one region into another having
been effected with more or less ease, at
periods more or less remote—on the nature
and number of the former immigrants—
and on their action and reaction in their
mutual struggles for life—the relation of
organism to organism being, as I have
already often remarked, the most impor
tant of all relations.
Thus the high
importance of barriers comes into play
by checking migration ; as does time for
the slow process of modification through
natural selection. Widely-ranging species,
abounding in individuals, which have
already triumphed over many competitors
in their own widely-extended homes will
have the best chance of seizing on new
places when they spread into new coun
tries. In their new homes they will be
exposed to new conditions, and will fre
quently undergo further modification and
improvement; and thus they will become
still further victorious, and will produce
groups of modified descendants. On this
principle of inheritance with modifica
tion, we can understand how it is that
sections of genera, whole genera, and
even families, are confined to the same
areas, as is so commonly and notoriously
the case.
I believe, as was remarked in the last
chapter, in no law of necessary develop
ment. As the variability of each species
is an independent property, and will be
taken advantage of by natural selection,
only so far as it profits the individual in its
complex struggle for life, so the degree of
modification in different species will be
no uniform quantity. If, for instance, a
number of specieswhich stand in direct com
petition with each other migrate in a body
into a new and afterwards isolated country,
they will be little liable to modification ;
for neither migration nor isolation in them
selves can do anything. These principles
come into play only by bringing organisms
into new relations with each other, and in
a lesser degree with the surrounding phy
sical conditions. As we have seen in the
last chapter that some forms have retained
nearly the same character from an enor
mously remote geological period, so certain
species have migrated over vast spaces,
and have not become greatly modified.
On these views it is obvious that the
several species of the same genus, though
inhabiting the most distant quarters of the
world, must originally have proceeded from
the same source, as they have descended
from the same progenitor. In the case of
those species which have undergone during
whole geological periods but little modication, there is not much difficulty in
believing that they may have migrated
from the same region ; for during the vast
geographical and climatal changes which
will have supervened since ancient times
almost any amount of migration is pos
sible. But in many other cases in which
we have reason to believe that the species
of a genus have been produced within
comparatively recent times there is great
difficulty on this head. It is also obvious
that the individuals of the same species,
though now iuhabiting distant and isolated
regions, must have proceeded from one spot,
where their parents were first produced ;
for, as explained in the last chapter, it is
incredible that individuals identically the
same should ever have been produced
through natural selection from parents
specifically distinct.
We are thus brought to the question
which has been largely discussed by
naturalists—namely, whether species have
been created at one or more points of the
earth’s surface. Undoubtedly there are
very many cases of extreme difficulty in
understanding how the same species could
possibly have migrated from some one
point to the several distant and isolated
points where now found.
Nevertheless,
the simplicity of the view that each species
was first produced within a single region
captivates the mind. He who rejects it
rejects the vera causa of ordinary gene
ration with subsequent migration, and calls
in the agency of a miracle. It is univer
sally admitted that in most cases the area
inhabited by a species is continuous ; and
when a plant or animal inhabits two points
so distant from each other, or with an
interval of such a nature that the space
�GEOGRAPHICAL DISTRIBUTION
could not be easily passed over by migra
tion, the fact is given as something remark
able and exceptional.
The capacity of
migrating across the sea is more distinctly
limited in terrestrial mammals than perhaps
in any other organic beings ; and, accord
ingly, we find no inexplicable cases of the
same mammal inhabiting distant points of
the world. No geologist will feel any diffi
culty in such cases as Great Britain having
been formerly united to Europe, and conse
quently possessing the same quadrupeds.
But if the same species can be produced at
two separate points, why do we not find a
single mammal common to Europe and
Australia or South America ? The condi
tions of life are nearly the same, so that a
multitude of European animals and plants
have become naturalised in America and
Australia ; and some of the aboriginal
plants are identically the same as these
distant points of the northern and southern
hemispheres. The answer, as I believe,
is that mammals have not been able to
migrate, whereas some plants, from their
varied means of dispersal, have migrated
across the vast and broken interspace. The
great and striking influence which barriers
of every kind have had on distribution is
intelligible only on the view that the great
majority of species have been produced on
one side alone, and have not been able to
migrate to the other side. Some few
families, many sub families, very many
genera, and a still greater number of sec
tions of genera, are confined to a single
region; and it has been observed by several
naturalists that the most natural genera, or
those genera in which the species are most
closely related to each other, are generally
local or confined to one area. What a
strange anomaly it would be if, when
coming one step lower in the series, to the
individuals of the same species, a directly
opposite rule prevailed, and species were
not local, but had been produced in two or
more distinct areas !
Hence it seems to me, as it has to many
other naturalists, that the view of each
species having been produced in one area
alone, and having subsequently migrated
from that area as far as its powers of migra
tion and subsistence under past and present
conditions permitted, is the most probable.
Undoubtedly, many cases occur in which
we cannot explain how the same species
could have passed from one point to the
other. But the geographical and climatal
changes which have certainly occurred
within recent geological times must have
M3
interrupted or rendered discontinuous the
formerly continuous range of many species.
So that we are reduced to consider whether
the exceptions to continuity of range are so
numerous and of so grave a nature that
we ought to give up the belief, rendered
probable by general considerations, that
each species has been produced within one
area, and has migrated thence as far as it
could. It would be hopelessly tedious to
discuss all the exceptional cases of the
same species now living at distant and
separated points ; nor do I for a moment
pretend that any explanation could be
offered of many such cases. But, after some
preliminary remarks, I will discuss a few of
the most striking classes of facts—namely,
the existence of the same species on the
summits of distant mountain-ranges, and at
distant points in the arctic and antarctic
regions ; and, secondly (in the following
chapter), the wide distribution of fresh
water productions ; and, thirdly, the occur
rence of the same terrestrial species on
islands and on the mainland, though sepa
rated by hundreds of miles of open sea. If
the existence of the same species at distant
and isolated points of the earth’s surface,
can in many instances be explained on the
view of each species having migrated from
a single birthplace, then, considering our
ignorance with respect to former climatal
and geographical changes and various
occasional means of transport, the belief
that this has been the universal law seems
to me incomparably the safest.
In discussing this subject, we shall be
enabled at the same time to consider a
point equally important for us—namely,
whether the several distinct species of a
genus, which on my theory have all desscended from a common progenitor, can
have migrated (undergoing modification
during some part of their migration) from
the area inhabited by their progenitor. If
it can be shown to be almost invariably the
case that a region of which most of its
inhabitants are closely related to, or belong
to the same genera with the species of
a second region, has probably received
at some former period immigrants from
this other region, my theory will be
strengthened ; for we can clearly under
stand, on the principle of modification,
why the inhabitants of a region should be
related to those of another region whence
it has been stocked. A volcanic island,
for instance, upheaved and formed at the
distance of a few hundreds of miles from
a continent, would probably receive from
�144
ON THE ORIGIN OF SPECIES
it in the course of time a few colonists, and
their descendants, though modified, would
still be plainly related by inheritance to
the inhabitants of the continent. Cases of
this nature are common, and are, as we
shall hereafter more fully see, inexplicable
on the theory of independent creation.
This view of the relation of species in one
region to those in another does not differ
much (by substituting the word variety for
species) from that lately advanced in an
ingenious paper by Mr. Wallace, in which
he concludes that “ every species has come
into existence coincident both in space
and time with a pre-existing closely-allied
species.” And I now know from corre
spondence that this coincidence he attri
butes to generation with modification.
The previous remarks on “ single and
multiple centres of creation ” do not directly
bear on another allied question—namely,
whether all the individuals of the same
species have descended from a single pair,
or single hermaphrodite, or whether, as
some authors suppose, from many indi
viduals simultaneously created. With those
organic beings which never intercross (if
such exist), the species, on my theory,
must have descended from a succession of
improved varieties, which will never have
blended with other individuals or varieties,
but will have supplanted each other ; so
that at each successive stage of modifica
tion and improvement all the individuals
of each variety will have descended from
a single parent. But in the majority of
cases—namely, with all organisms which
habitually unite for each birth, or which
often intercross—I believe that during the
slow process of modification the individuals
of the species will have been kept nearly
uniform by intercrossing; so that many
individualswill have gone on simultaneously
changing, and the whole amount of modifi
cation will not have been due, at each
stage, to descent from a single parent.
To illustrate what I mean : Our English
race-horses differ slightly from the horses
of every other breed ; but they do not owe
their difference and superiority to descent
from any single pair, but to continued care
in selecting and training many individuals
during many generations.
Before discussing' the three classes of
facts which I have selected as presenting
the greatest amount of difficulty on the
theory of “single centres of creation,” I
must say a few words on the means of
dispersal.
Means of Dispersal.—Sir C. Lyell and
other authors have ably treated this subject.
I can give here only the briefest abstract
of the more important facts. Change of
climate must have had a powerful influence
on migration : a region when its climate
was different may have been a high road
for migration, but now be impassable. I
shall, however, presently have to discuss
this branch of the subject in some detail.
Changes of level in the land must also
have been highly influential : a narrow
isthmus now separates two marine faunas ;
submerge it, or let it formerly have been
submerged, and the two faunas will now
blend or may formerly have blended:
where the sea now extends, land may at a
former period have connected islands or
possibly even continents together, and
thus have allowed terrestrial productions
to pass from one to the other. No geologist
will dispute that great mutations of level
have occurred within the period of existing
organisms, Edward Forbes insisted that
all the islands in the Atlantic must recently
have been connected with Europe or
Africa, and Europe likewise with America.
Other authors have thus hypothetically
bridged over every ocean and have united
almost every island to some mainland. If,
indeed, the arguments used by Forbes are
to be trusted, it must be admitted that
scarcely a single island exists which has
not recently been united to some continent.
This view cuts the Gordian knot of the
dispersal of the same species to the most
distant points, and removes many a diffi
culty ; but to the best of my judgment we
are not authorised in admitting such enor
mous geographical changes within the
period of existing species. It seems to
me that we have abundant evidence of
great oscillations of level in our continents;
but not of such vast changes in their
position and extension as to have united
them within the recent period to each other
and to the several intervening oceanic
islands. I freely admit the former existence
of many islands, now buried beneath the
sea, which may have served as haltingplaces for plants and for many animals
during their migration.
In the coral
producing oceans such sunken islands are
now marked, as I believe, by rings of coral
or atolls standing over them. Whenever
it is fully admitted, as I believe it will
some day be, that each species has pro
ceeded from a single birthplace, and when
in the course of time we know something
defiilite about the means of distribution,
�GEOGRAPHICAL DISTRIBUTION
we shall be enabled to speculate with
security on the former extension of the
land. But I do not believe that it will ever
be proved that within the recent period
continents which are now quite separate
have been continuously, or almost con
tinuously, united with each other, and with
the many existing oceanic islands. Several
facts in distribution—such as the great
differences in the marine faunas on the
opposite sides of almost every continent—
the close relation of the tertiary inhabi
tants of several lands and even seas to
their present inhabitants—a ceitain degree
of relation (as we shall hereafter see)
between the distribution of mammals and
the depth of the sea—these and other such
facts seem to me opposed to the admission
of such prodigious geographical revolutions
within the recent period as are necessitated
on the view advanced by Forbes and ad
mitted by many of his followers. The
nature and relative proportions of the
inhabitants of oceanic islands likewise
seem to me opposed to the belief of their
former continuity with continents. Nor
does their almost universally volcanic com
position favour the admission that they
are the wrecks of sunken continents—if
they had originally existed as mountain
ranges on the land, some at least of the
islands would have been formed, like other
mountain summits, of granite, metamorphic
schists, old fossiliferous or other such rocks,
instead of consisting of mere piles of vol
canic matter.
I must now say a few words on what are
called accidental means, but which more
properly might be called occasional means,
of distribution. I shall here confine myself
to plants. In botanical works this or that
plant is stated to be ill adapted for wide
dissemination; but for transport across
the sea the greater or less facilities may
be said to be almost wholly unknown.
Until I tried, with Mr. Berkeley’s aid, a
few experiments, it was not even known
how far seeds could resist the injurious
action of sea-water. To my surprise, I
found that, out of 87 kinds, 64 germinated
after an immersion of 28 days, and a few
survived an immersion of 137 days. For
convenience sake, I chiefly tried small
seeds, without the capsule or fruit; and, as
all of these sank in a few days, they could
not be floated across wide spaces of the
sea, whether or not they were injured by
the salt-water. Afterwards I tried some
larger fruits, capsules, etc., and some of
these floated for a long time. It is well
145
known what a difference there is in the
buoyancy of green and seasoned timber;
and it occurred to me that floods might
wash down plants or branches, and that
these might be dried on the banks, and
then by a fresh rise in the stream be
washed into the sea. Hence I was led to
dry stems and branches of 94 plants with
ripe fruit, and to place them on sea-water.
The majority sank quickly, but some which
while green floated for a very short time,
when dried floated much longer; for
instance, ripe hazel-nuts sank immediately,
but when dried they floated for 90 days,
and afterwards when planted they ger
minated ; an asparagus plant with ripe
berries floated for 23 days, when dried it
floated for 85 days, and the seeds after
wards germinated; the ripe seeds of Helosciadium sank in 2 days, when dried they
floated for above 90 days, and afterwards
germinated. Altogether out of the 94 dried
plants, 18 floated for above 28 days, and
some of the 18 floated for a very much
longer period. So that as
seeds germi
nated after an immersion of 28 days, and
as || plants with ripe fruit (but not all the
same species as in the foregoing experi
ment) floated, after being dried, for above
28 days, as far as we may infer anything
from these scanty facts, we may conclude
that the seeds of
plants of any country
might be floated by sea-currents during
28 days, and would retain their power of
germination. In Johnston’s Physical Atlas
the average rate of the several Atlantic
currents is 33 miles per diem (some currents
running at the rate of 60 miles per diem);
on this average, the seeds of
plants
belonging to one country might be floated
across 924 miles of sea to another country;
and when stranded, if blown to a favour
able spot by an inland gale, they would
germinate.
Subsequently to my experiments, M.
Martens tried similar ones, but in a much
better manner, for he placed the seeds in a
box in the actual sea, so that they were
alternately wet and exposed to the air like
really floating plants. He tried 98 seeds,
mostly different from mine ; but he chose
many large fruits and likewise seeds from
plants which live near the sea ; and this
would have favoured the average length of
their flotation and of their resistance to the
injurious action of the salt-water. On the
other hand, he did not previously dry the
plants or branches with the fruit; and this,
as we have seen, would have caused some
of them to have floated much longer. The
L
1
�146
ON THE ORIGIN OF SPECIES
result was that |f of his seeds floated for
42 days, and were then capable of germina
tion. But I do not doubt that plants
exposed to the waves would float for a less
time than those protected from violent
movement, as in our experiments. There
fore, it would perhaps be safer to assume
that the seeds of about rVT plants of a flora,
after having been dried, could be floated
across a space of sea 900 miles in width,
and would then germinate. The fact of
the larger fruits often floating longer than
the small is interesting ; as plants with
large seeds or fruit could hardly be trans
ported by any other means ; and Alph.
de Candolle has shown that such plants
generally have restricted ranges.
But seeds may be occasionally trans
ported in another manner. Drift timber is
thrown up on most islands, even on those
in the midst of the wildest oceans ; and
the natives of the coral islands in the
Pacific procure stones for their tools solely
from the roots of drifted trees, these stones
being a valuable royal tax. I find on
examination that, when irregularly-shaped
stones are embedded in the roots of trees,
small parcels of earth are very frequently
enclosed in their interstices and behind
them—so perfectly that not a particle could
be washed away in the longest transport :
out of one small portion of earth thus com
pletely enclosed by wood in an oak about
50 years old three dicotyledonous plants
germinated. I am certain of the accuracy
of this observation. Again, I can show
that the carcasses of birds, when floating
on the sea, sometimes escape being im
mediately devoured ; and seeds of many
kinds in the crops of floating birds long
retain their vitality. Peas and vetches, for
instance, are killed by even a few days’
immersion in sea-water; but some taken
out of the crop of a pigeon which had
floated on artificial salt water for 30 days
to my surprise nearly all germinated.
Living birds can hardly fail to be highly
effective agents in the transportation of
seeds. I could give many facts showing
how frequently birds of many kinds are
blown by gales to vast distances across the
ocean. We may, I think, safely assume
that under such circumstances their rate
of flight would often be 35 miles an
hour ; and some authors have given a far
higher estimate. I have never seen an
instance of nutritious seeds passing through
the intestines of a bird; but hard seeds of
fruit pass uninjured through even the
digestive organs of a turkey.
In the
course of two months I picked up in my
garden 12 kinds of seeds out of the excre
ment of small birds, and these seemed
perfect, and some of them which I tried
germinated.
But the following fact is
more important: the crops of birds do not
secrete gastric juice, and do not in the
least injure, as I know by trial, the germi
nation of seeds. Now, after a bird has
found and devoured a large supply of food,
it is positively asserted that all the grains
dp not pass into the gizzard for twelve or even
eighteen hours. A bird in this interval might
easily be blown to the distance of 500
miles; and hawks are known to look out
for tired birds, and the contents of their
torn crops might thus readily get scattered.
Mr. Brent informs me that a friend of his
had to give up flying carrier-pigeons from
France to England, as the hawks on the
English coast destroyed so many on their
arrival. Some hawks and owls bolt their
prey whole, and after an interval of from
twelve to twenty hours disgorge pellets
which, as I know from experiments made
in the Zoological Gardens, include seeds
capable of germination. Some seeds of the
oat, wheat, millet, canary, hemp, clover,
and beet germinated after having been
from twelve to twenty-one hours in the
stomachs of different birds of prey; and
two seeds of beet grew after having been
thus retained for two days and fourteen
hours. Fresh-water fish, I find, eat seeds
of many land and water plants ; fish are
frequently devoured by birds, and thus the
seeds might be transported from place to
place. I forced many kinds of seeds into
the stomachs of dead fish, and then gave
their bodies to fishing-eagles, storks, and
pelicans ; these birds, after an interval of
many hours, either rejected the seeds in
pellets or passed them in their excrement;
and several of these seeds retained their
power of germination. Certain seeds, how
ever, were always killed by this process.
Although the beaks and feet of birds
are generally quite clean, I can show that
earth sometimes adheres to them; in one
instance I removed twenty-two grains of
argillaceous earth from one foot of a par
tridge, and in this earth there was a pebble
quite as large as the seed of a vetch. Thus
seeds might occasionally be transported to
great distances ; for many facts could be
given showing that soil almost everywhere
is charged with seeds. Reflect for a
moment on the millions of quails which
annually cross the Mediterranean; and
can we doubt that the earth adhering to
�GEOGRAPHICAL DISTRIBUTION
their feet would sometimes include a few
minute seeds ? But I shall presently have
to recur to this subject.
As icebergs are known to be some
times loaded with earth and stones, and
have even carried brushwood, bones, and
the nest of a land-bird, I can hardly doubt
that they must occasionally have trans
ported seeds from one part to another of
the arctic and antarctic regions, as sug
gested by Lyell, and, during the Glacial
period, from one part of the now temperate
regions to another. In the Azores, from
the large number of the species of plants
common to Europe, in comparison with
the plants of other oceanic islands nearer
to the mainland, and (as remarked by Mr.
H. C. Watson) from the somewhat northern
character of the flora in comparison with
the latitude, I suspected that these islands
had been partly stocked by ice-borne seeds
during the Glacial epoch. At my request,
Sir C. Lyell wrote to M. Hartung to
inquire whether he had observed erratic
boulders on these islands, and he answered
that he had found large fragments of
granite and other rocks which do not occur
in the archipelago. Hence we may safely
infer that icebergs formerly landed their
rocky burthens on the shores of these mid
ocean islands, and it is at least possible that
they may have brought thither the seeds of
northern plants.
Considering that the several above
means of transport, and that several other
means, which without doubt remain to be
discovered, have been in action year after
year, for centuries and tens of thousands
of years, it would, I think, be a marvellous
fact if many plants had not thus become
widely transported. These means of
transport are sometimes called accidental,
but this is not strictly correct: the currents
of the sea are not accidental, nor is the
direction of prevalent gales of wind. It
should be observed that scarcely any
means of transport would carry seed for
very great distances, for seeds do not retain
their vitality when exposed for a great length
of time to the action of sea-water, nor could
they be long carried in the crops or
intestines of birds. These means, how
ever, would suffice for occasional transport
across tracts of sea some hundred miles in
breadth, or from island to island, or from a
continent to a neighbouring island, but not
from one distant continent to another.
The floras of distant continents would not
by such means become mingled in any
great degree, but would remain as distinct
147
as we now see them to be. The currents,
from their course, would never bring seeds
from North America to Britain, though
they might and do bring seeds from the
West Indies to our western shores, where,
if not killed by so long an immersion in
salt water, they could not endure our
climate. Almost every year one or two
land-birds are blown across the whole
Atlantic Ocean, from North America to
the western shores of Ireland and England;
but seeds could be transported by these
wanderers only by one means—namely, in
dirt sticking to their feet, which is in itself
a rare accident. Even in this case, how
small would be the chance of a seed falling
on favourable soil, and coming to maturity 1
But it would be a great error to argue that
because a well-stocked island, like Great
Britain, has not, as far as is known (and it
would be very difficult to prove this),
received within the last few centuries,
through occasional means of transport,
immigrants from Europe or any other
continent, that a poorly-stocked island,
though standing more remote from the
mainland, would not receive colonists by
similar means. I do not doubt that out of
twenty seeds or animals transported to an
island, even if far less well stocked than
Britain, scarcely more than one would be
so well fitted to its new home as to become
naturalised. But this, as it seems to me,
is no valid argument against what would
be effected by occasional means of trans
port, during the long lapse of geological
time, while an island was being upheaved
and formed, and before it had become fully
stocked with inhabitants. On almost bare
land, with few or no destructive insects or
birds living there, nearly every seed which
chanced to arrive, if fitted for the climate,
would be sure to geiminate and survive.
Dispersal during the Glacial period.—
The identity of many plants and animals
on mountain-summits, separated from each
other by hundreds of miles of lowlands,
where the Alpine species could not possibly
exist, is one of the most striking cases
known of the same species living at distant
points, without the apparent possibility of
their having migrated from one to the
other. It is, indeed, a remarkable fact to
see so many of the same plants living on
the snowy regions of the Alps or Pyrenees
and in the extreme northern parts of
Europe; but it is far more remarkable
that the plants on the White Mountains,
in the United States of America, are all
�148
ON THE ORIGIN OF SPECIES
the same with those of Labrador, and
nearly all the same, as we hear from Asa
Gray, with those on the loftiest mountains
of Europe. Even as long ago as 1747 such
facts led Gmelin to conclude that the same
species must have been independently
created at several distinct points ; and we
might have remained in this same belief
had not Agassiz and others called vivid
attention to the Glacial period, which, as
we shall immediately see, affords a simple
explanation of these facts. We have
evidence of almost every conceivable kind,
organic and inorganic, that within a very
recent geological period central Europe
and North America suffered under an
Arctic climate. The ruins of a house by
fire do not tell their tale more plainly than
do the mountains of Scotland and Wales,
with their scored flanks, polished surfaces,
and perched boulders, of the icy streams
with which their valleys were lately filled.
So greatly has the climate of Europe
changed that in Northern Italy gigantic
moraines left by old glaciers are now
clothed by the vine and maize. Through
out a large part of the United States, erratic
boulders and rocks, scored by drifted ice
bergs and coast-ice, plainly reveal a former
cold period.
The former influence of the glacial
climate on the distribution of the inhabi
tants of Europe, as explained with remark
able clearness by Edward Forbes, is
substantially as follows. But we shall
follow the changes more readily by sup
posing a new Glacial period to come slowly
on, and then pass away, as formerly occur
red. As the cold came on, and as each
more southern zone became fitted for arctic
beings and ill-fitted for their former more
temperate inhabitants, the latter would be
supplanted, and arctic productions would
take their places. The inhabitants of the
more temperate regions would at the same
time travel southward, unless they were
stopped by barriers, in which case they
would perish. The mountains would be
come covered with snow and ice, and their
former Alpine inhabitants would descend
to the plains. By the time that the cold
had reached its maximum we should have
a uniform arctic fauna and flora covering
the central parts of Europe as far south as
the Alps and Pyrenees, and even stretching
into Spain. The now temperate regions
of the United States would likewise be
covered by arctic plants and animals, and
these would be nearly the same with those
of Europe; for the present circumpolar
inhabitants, which we suppose to have
everywhere travelled southward, are re
markably uniform round the world. We
may suppose that the Glacial period came
on a little earlier or later in North America
than in Europe, so will the southern migra
tion there have been a little earlier or later;
but this will make no difference in the final
result.
As the warmth returned, the arctic
forms would retreat northward, closely
followed up in their retreat by the produc
tions of the more temperate regions. And
as the snow melted from the bases of the
mountains, the arctic forms would seize on
the cleared and thawed ground, always
ascending higher and higher as the warmth
increased, while their brethren were pur
suing their northern journey. Hence, when
the warmth had fully returned, the same
arctic species which had lately lived in a
body together on the lowlands of the Old
and New Worlds would be left isolated
on distant mountain-summits (having been
exterminated on all lesser heights) and in
the arctic regions of both hemispheres.
Thus we can understand the identity of
many plants at points so immensely remote
as on the mountains of the United States
and of Europe. We can thus also under
stand the fact that the Alpine plants of
each mountain-range are more especially
related to the arctic forms living due north
or nearly due north of them ; for the migra
tion as the cold came on, and the re-migration on the returning warmth, will generally
have been due south and north. The
Alpine plants, for example, of Scotland, as
remarked by Mr. H. C. Watson, and those
of the Pyrenees, as remarked by Ramond,
are more especially allied to the plants of
northern Scandinavia; those of the United
States to Labrador; those of the mountains
of Siberia to the arctic regions of that
country. These views, grounded as they
are on the perfectly well-ascertained occur
rence of a former Glacial period, seem to
me to explain in so satisfactory a manner
the present distribution of the alpine and
arctic productions of Europe and America,
that, when in other regions we find the same
species on distant mountain-summits, we
may almost conclude, without other evi
dence, that a colder climate permitted their
former migration across the low intervening
tracts, since become too warm for their
existence.
If the climate, since the Glacial period,
has ever been in any degree warmer than
at present (as some geologists in the
�GEOGRAPHICAL DISTRIBUTION
United States believe to have been the
case, chiefly from the distribution of the
fossil Gnathodon), then the arctic and
temperate productions will at a very late
period have marched a little further north,
and subsequently have retreated to their
present homes; but I have met with no
satisfactory evidence with respect to this
intercalated slightly warmer period since
the Glacial period.
The arctic forms, during their long
southern migration and re-migration north
ward, will have been exposed to nearly the
same climate, and, as is especially to be
noticed, they will have kept in a body
together ; consequently, their mutual rela
tions will not have been much disturbed,
and, in accordance with the principles in
culcated in this volume, they will not have
been liable to much modification. But
with our alpine productions, left isolated
from the moment of the returning warmth,
first at the bases and ultimately on the
summits of the mountains, the case will have
been somewhat different; for it is not likely
that all the same arctic species will have been
left on mountain-ranges distant from each
other, and have survived there ever since ;
they will also, in all probability, have
become mingled with ancient alpine
species which must have existed on the
mountains before the commencement of
the Glacial epoch, and which during its
coldest period will have been temporarily
driven down to the plains ; they will also
have been exposed to somewhat different
climatal influences. Their mutual relations
will thus have been in some degree dis
turbed ; consequently, they will have been
liable to modification, and this we find
has been the case ; for, if we compare the
present alpine plants and animals of the
several great European mountain-ranges,
though very many of the species are identi
cally the same, some present varieties,
some are ranked as doubtful forms, and
some few are distinct yet closely-allied or
representative species.
In illustrating what, as I believe, actually
took place during the Glacial period, I
assumed that at its commencement the
arctic productions were as uniform round
the polar regions as they are at the present
day. But the foregoing remarks on dis
tribution apply not only to strictly arctic
forms, but also to many sub-arctic and to
some few northern temperate forms, for
some of these are the same on the lower
mountains and on the plains of North
America and Europe; and it may be
149
reasonably asked how I account for the
necessary degree of uniformity of the sub
arctic and northern temperate forms round
the world at the commencement of the
Glacial period. At the present day the
sub-arctic and northern temperate produc
tions of the Old and New Worlds are
separated from each other by the Atlantic
Ocean and by the extreme northern part of
the Pacific. During the Glacial period,
when the inhabitants of the Old and New
Worlds lived further southwards than at
present, they must have been still more
completely separated by wider spaces of
ocean. I believe the above difficulty may
be surmounted by looking to still earlier
changes of climate of an opposite nature.
We have good reason to believe that
during the newer Pliocene period, before
the Glacial epoch, and while the majority
of the inhabitants of the world were speci
fically the same as now, the climate was
warmer than at the present day. Hence
we may suppose that the organisms now
living under the climate of latitude 6o°,
during the Pliocene period lived further
north under the Polar Circle, in latitude
66°-67°; and that the strictly arctic pro
ductions then lived on the broken land
still nearer to the pole. Now, if we look
at a globe, we shall see that under the
Polar Circle there is almost continuous
land from western Europe, through Siberia,
to eastern America. And to the continuity
of the circumpolar land, and to the conse
quent freedom for intermigration under a
more favourable climate, I attribute the
necessary amount of uniformity in the sub
arctic and northern temperate productions
of the Old and New Worlds at a period
anterior to the Glacial epoch.
Believing, from reasons before alluded
to, that our continents have long remained
in nearly the same relative position, though
subjected to large, but partial, oscillations
of level, I am strongly inclined to extend
the above view, and to infer that during
some earlier and still warmer period, such
as the older Pliocene period, a large number
of the same plants and animals inhabited
the almost continuous circumpolar land ;
and that these plants and animals, both in
the Old and New Worlds, began slowly to
migrate southwards as the climate became
less warm, long before the commencement
of the Glacial period. We now see, as I
believe, their descendants, mostly in a
modified condition, in the central parts of
Europe and the United States. On this
view we can understand the relationship,
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ON THE ORIGIN OF SPECIES
with very little identity, between the pro
ductions of North America and Europe—
a relationship which is most remarkable
considering the distance of the two areas
and their separation by the Atlantic Ocean.
We can further understand the singular
fact, remarked on by several observers,
that the productions of Europe and America
during the later tertiary stages were more
closely related to each other than they are
at the present time; for during these
warmer periods the northern parts of the
Old and New Worlds will have been almost
continuously united by land, serving as a
bridge, since rendered impassable by cold,
for the intermigration of their inhabitants.
During the slowly-decreasing warmth of
the Pliocene period, as soon as the species
in common which inhabited the New and
Old Worlds migrated south of the Polar
Circle, they must have been completely
cut off from each other. This separation,
as far as the more temperate productions
are concerned, took place long ages ago.
And as the plants and animals migrated
southward, they will have become mingled
in the one great region with the native
American productions, and have had to
compete with them ; and, in the other great
region, with those of the Old World. Con
sequently, we have here everything favour
able for much modification—for far more
modification than with the Alpine produc
tions, left isolated within a much more
recent period, on the several mountain
ranges and on the arctic lands of the two
Worlds. Hence it has come that, when
we compare the now living productions of
the temperate regions of the New and Old
Worlds, we find very few identical species
(though Asa Gray has lately shown that
more plants are identical than was formerly
supposed), but we find in every great class
many forms which some naturalists rank
as geographical races and others as distinct
species, and a host of closely-allied or
representative forms which are ranked by
all naturalists as specifically distinct.
As on the land, so in the waters of the
sea, a slow southern migration of a marine
fauna, which during the Pliocene or even
a somewhat earlier period was nearly
uniform along the continuous shores of the
Polar Circle, will account, on the theory of
modification, for many closed-allied forms
now living in areas completely sundered.
Thus, I think, we can understand the
presence of many existing and tertiary
representative forms on the eastern and
western shores of temperate North America;
and the still more striking case of many
closely-allied crustaceans (as described in
Dana’s admirable work), of some fish and
other marine animals, in the Mediterranean
and in the seas of Japan—areas now sepa
rated by a continent and by nearly a hemi
sphere of equatorial ocean.
These cases of relationship, without
identity, of the inhabitants of seas now
disjoined, and likewise of the past and
present inhabitants of the temperate lands
of North America and Europe, are inexpli
cable on the theory of creation. We cannot
say that they have been created alike, in
correspondence with the nearly similar
physical conditions of the areas ; for if we
compare, for instance, certain parts of
South America with the southern continents
of the Old World, we see countries closely
corresponding in all their physical con
ditions, but with their inhabitants utterly
dissimilar.
But we must return to our more imme
diate subject, the Glacial period. I am
convinced that Forbes’s view may be largely
extended. In Europe we have the plainest
evidence of the cold period, from the
western shores of Britain to the Oural
range, and southward to the Pyrenees. We
may infer from the frozen mammals and
nature of the mountain vegetation that
Siberia was similarly affected. Along the
Himalaya, at points 900 miles apart, glaciers
have left the marks of their former low
descent; and in Sikkim Dr. Hooker saw
maize growing on giganticancient moraines.
South of the equator we have some direct
evidence of former glacial action in New
Zealand ; and the same plants, found on
widely-separated mountains in that island,
tell the same story. If one account which
has been published can be trusted, we have
direct evidence of glacial action in the south
eastern corner of Australia.
Looking to America : in the northern
half, ice-borne fragments of rock have been
observed on the eastern side as far south
as latitude 36°-37°, and on the shores of
the Pacific, where the climate is now so
different, as far south as latitude 46°; erratic
boulders have also been noticed on the
Rocky Mountains. In the Cordillera of
Equatorial South America glaciers once
extended far below their present level. In
central Chili I was astonished at the struc
ture of a vast mound of detritus, about
800 feet in height, crossing a valley of the
Andes ; and this, I now feel convinced, was
a gigantic moraine, left far below any exist
ing glacier. Further south on both sides
�GEOGRAPHICAL DISTRIBUTION
of the continent, from latitude 410 to the
southernmost extremity, we have the clearest
evidence of former glacial action in huge
boulders transported far from their parent
souice.
We do not know that the Glacial epoch
was strictly simultaneous at these several
far distant points on opposite sides of the
world. But we have good evidence in
almost every case that the epoch was in
cluded within the latest geological period.
We have also excellent evidence that it
endured for an enormous time, as measured
by years, at each point. The cold may
have come on, or have ceased, earlier at
one point of the globe than at another, but
seeing that it endured for long at each, and
that it was contemporaneous in a geological
sense, it seems to me probable that it was,
during a part at least of the period, actually
simultaneous throughout the world. With
out some distinct evidence to the contrary,
we may at least admit as probable that the
glacial action was simultaneous on the
eastern and western sides of North America,
in the Cordillera under the equator and
under the warmer temperate zones, and on
both sides of the southern extremity of the
continent. If this be admitted, it is difficult
to avoid believing that the temperature of
the whole world was at this period simul
taneously cooler. But it would suffice for
my purpose if the temperature was at the
same time lower along certain broad belts
of longitude.
On this view of the whole world, or at
least of broad longitudinal belts, having
been simultaneously colder from pole to
pole, much light can be thrown on the
present distribution of identical and allied
species.
In America Dr. Hooker has
shown that between forty and fifty of the
flowering plants of Tierra del Fuego, form
ing no inconsiderable part of its scanty
flora, are common to Europe, enormously
remote as these two points are ; and there
are many closely-allied species. On the
lofty mountains of equatorial America a
host of peculiar species belonging to
European genera occur. On the highest
mountains of Brazil some few European
genera were found by Gardner which do
not exist in the wide intervening hot
countries. So on the Silla of Caraccas the
illustrious Humboldt long ago found species
belonging to genera characteristic of the
Cordillera. On the mountains of Abyssinia
several European forms and some few re
presentatives of the peculiar flora of the
Cape of Good Hope occur. At the Cape
151
of Good Hope a very few European species,
believed not to have been introduced by
man, and on the mountains some few
representative European forms, are found
which have not been discovered in the intertropical parts of Africa. On the Himalaya
and on the isolated mountain-ranges of the
peninsula of India, on the heights of Ceylon,
and on the volcanic cones of Java, many
plants occur either identically the same or
representing each other, and at the same
time representing plants of Europe, not
found in the intervening hot lowlands. A
list of the genera collected on the loftier
peaks of Java raises a picture of a collec
tion made on a hill in Europe ! Still more
striking is the fact that southern Australian
forms are clearly represented by plants
growing on the summits of the mountains
of Borneo. Some of these Australian
forms, as I hear from Dr. Hooker, extend
along the heights of the peninsula of
Malacca, and are thinly scattered, on the
one hand, over India and, on the other, as
far north as Japan.
On the southern mountains of Australia
Dr. F. Muller has discovered several
European species ; other species, not intro
duced by man, occur on the lowlands ; and
a long list can be given, as I am informed
by Dr. Hooker, of European genera found
in Australia, but not in the intermediate
torrid regions. In the admirable Introduc
tion to the Flora of New Zealand, by Dr.
Hooker, analogous and striking facts are
given in regard to the plants of that large
island. Hence we see that throughout the
world the plants growing on the more lofty
mountains, and on the temperate lowlands
of the northern and southern hemispheres,
are sometimes identically the same; but
they are much oftener specifically distinct,
though related to each other in a most
remarkable manner.
This brief abstract applies to plants
alone : some strictly analogous facts could
be given on the distribution of terrestrial
animals. In marine productions similar
cases occur ; as an example, I may quote
a remark by the highest authority, Professor
Dana, that “ it is certainly a wonderful fact
that New Zealand should have a closer
resemblance in its Crustacea to Great
Britain, ‘its antipode, than to any other
part of the world.” Sir J. Richardson also
speaks of the reappearance on the shores
of New Zealand, Tasmania, etc., of northern
forms of fish. Dr. Hooker informs me that
twenty-five species of Algae are common to
New Zealand and to Europe, but have not
�152
ON THE ORIGIN OF SPECIES
been found in the intermediate tropical
seas.
It should be observed that the northern
species and forms found in the southern
parts of the southern hemisphere, and on
the mountain-ranges of the intertropical
regions, are not arctic, but belong to the
northern temperate zones. As Mr. H. C.
Watson has recently remarked : “In
receding from polar towards equatorial
latitudes, the alpine or mountain floras
really become less and less arctic.” Many
of the forms living on the mountains of
the warmer regions of the earth and in the
southern hemisphere are of doubtful value,
being ranked by some naturalists as speci
fically distinct, by others as varieties ; but
some are certainly identical, and many,
though closely related to northern forms,
must be ranked as distinct species.
Now, let us see what light can be thrown
on the foregoing facts on the belief, sup
ported as it is by a large body of geological
evidence, that the whole world, or a large
part of it, was, during the Glacial period,
simultaneously much colder than at present.
The Glacial period, as measured by years,
must have been very long ; and when we
remember over what vast spaces some
naturalised plants and animals have spread
within a few centuries, this period will have
been ample for any amount of migration.
As the cold came slowly on, all the tropical
plants and other productions will have
retreated from both sides towards the
equator, followed in the rear by the tem
perate productions, and these by the arctic;
but with the latter we are not now con
cerned. The tropical plants probably
suffered much extinction—how much no
one can say ; perhaps formerly the tropics
supported as many species as we see at
the present day crowded together at the
Cape of Good Hope and in parts of tem
perate Australia. As we know that many
tropical plants and animals can withstand
a considerable amount of cold, many
might have escaped extermination during
a moderate fall of temperature, more espe
cially by escaping into the lowest, most
protected, and warmest districts. But the
great fact to bear in mind is that all
tropical productions will have suffered to
a certain extent. On the other hand, the
temperate productions, after migrating
nearer to the equator, though they will
have been placed under somewhat new
conditions, will have suffered less. And it
is certain that many temperate plants, if
protected from the inroads of competitors,
can withstand a much warmer climate than
their own. Hence it seems to me possible,
bearing in mind that the tropical productions
were in a suffering state, and could not have
presented a firm front against intruders,
that a certain number of the more vigorous
and dominant temperate forms might have
penetrated the native ranks, and have
reached or even crossed the equator. The
invasion would, of course, have been
greatly favoured by high land, and perhaps
by a dry climate; for Dr. Falconer informs
me that it is the damp with the heat of the
tropics which is so destructive to perennial
plants from a temperate climate. On the
other hand, the most humid and hottest
districts will have afforded an asylum to
the tropical natives. The mountain-ranges
north-west of the Himalaya and the long
line of the Cordillera seem to have afforded
two great lines of invasion ; and it is a
striking fact, lately communicated to me
by Dr. Hooker, that all the flowering
plants, about forty-six in number, common
to Tierra del Fuego and to Europe, still
exist in North America, which must have
lain on the line of march. But I do not
doubt that some temperate productions
entered and crossed even the lowlands of
the tropics at the period when the cold
was most intense—when arctic forms had
migrated some twenty-five degrees of lati
tude from their native country and covered
the land at the foot of the Pyrenees. At
this period of extreme cold I believe that
the climate under the equator at the level
of the sea was about the same with that
now felt there at the height of six or seven
thousand feet. During this the coldest
period, I suppose that large spaces of the
tropical lowlands were clothed with a
mingled tropical and temperate vegetation,
like that now growing with strange luxu
riance at the base of the Himalaya, as
graphically described by Hooker.
Thus, as I believe, a considerable num
ber of plants, a few terrestrial animals, and
some marine productions migrated during
the Glacial period from the northern and
southern temperate zones into the inter
tropical regions, and some even crossed
the equator. As the warmth returned,
these temperate forms would naturally
ascend the higher mountains, being exter
minated on the lowlands; those which
had not reached the equator would re
migrate northward or southward towards
their former homes ; but the forms, chiefly
northern, which had crossed the equator
would travel still further from their homes
�GEOGRAPHICAL DISTRIBUTION
into the more temperate latitudes of the
opposite hemisphere. Although we have
reason to believe from geological evidence
that the whole body of arctic shells under
went scarcely any modification during their
long southern migration and re-migration
northward, the case may have been wholly
different with those intruding forms which
settled themselves on the intertropical
mountains and in the southern hemisphere.
These, being surrounded by strangers, will
have had to compete with many new forms
of life ; and it is probable that selected
modifications in their structure, habits, and
constitutions will have profited them. Thus
many of these wanderers, though still
plainly related by inheritance to their
brethren of the northern or southern hemi
spheres, now exist in their new homes as
well-marked varieties or as distinct species.
It is a remarkable fact, strongly insisted
on by Hooker in regard to America, and
by Alph. de Candolle in regard to Aus
tralia, that many more identical plants and
allied forms have apparently migrated from
the north to the south than in a reversed
direction. We see, however, a few southern
vegetable forms on the mountains of Borneo
and Abyssinia. I suspect that this prepon
derant migration from north to south js
due to the greater extent of land in the
north, and to the northern forms having
existed in their own homes in greater
numbers, and having, consequently, been
advanced through natural selection and
competition to a higher stage of perfection
or dominating power than the southern
forms. And thus, when they became com
mingled during the Glacial period, the
northern forms were enabled to beat the
less powerful southern forms. Just in the
same manner as we see at the present day
that very many European productions
cover the ground in La Plata, and in a
lesser degree in Australia, and have to a
certain extent beaten the natives ; whereas
extremely few southern forms have become
naturalised in any part of Europe, though
hides, wool, and other objects likely to
carry seeds have been largely imported into
Europe during the last two or three
centuries from La Plata, and during the
last thirty or forty years from Australia.
Something of the same kind must have
occurred on the intertropical mountains :
no doubt before the Glacial period they
were stocked with endemic Alpine forms ;
but these have almost everywhere largely
yielded to the more dominant forms, gene
rated in the larger areas and more efficient
153
workshops of the north. In many islands
the native productions are nearly equalled
or even outnumbered by the naturalised ;
and if the natives have not been actually
exterminated, their numbers have been
greatly reduced, and this is the first stage
towards extinction. A mountain is an
island on the land, and the intertropical
mountains before the Glacial period must
have been completely isolated ; and I
believe that the productions of these islands
on the land yielded to those produced
within the larger areas of the north, just in
the same way as the productions of real
islands have everywhere lately yielded to
continental forms, naturalised by man’s
agency.
I am far from supposing that all diffi
culties are removed on the view here given
in regard to the range and affinities of the
allied species which live in the northern
and southern temperate zones and on the
mountains of the intertropical regions.
Very many difficulties remain to be solved.
I do not pretend to indicate the exact lines
and means of migration, or the reason why
certain species and not others have migra
ted—why certain species have been modi
fied and have given rise to new groups of
forms, and others have remained unaltered.
We cannot hope to explain such facts,
until we can say why one species and not
another becomes naturalised by man’s
agency in a foreign land ; why one ranges
twice or thrice as far, and is twice or thrice
as common, as another species within their
own homes.
I have said that many difficulties remain
to be solved: some of the most remarkable
are stated with admirable clearness by Dr.
Hooker in his botanical works on the ant
arctic regions. These cannot be here dis
cussed. I will only say that as far as
regards the occurrence of identical species
at points soenormouslyremote as Kerguelen
Land, New Zealand, and Fuegia, I believe
that towards the close of the Glacial period
icebergs, as suggested by Lyell, have been
largely concerned in their dispersal. But
the existence of several quite distinct
species, belonging to genera exclusively
confined to the south, at these and other
distant points of the southern hemisphere,
is, on my theory of descent with modifica
tion, a far more remarkable case of diffi
culty. For some of these species are so
distinct that we cannot suppose that there
has been time since the commencement of
the Glacial period for their migration, and
for their subsequent modification to the
�154
ON THE ORIGIN OF SPECIES
necessary degree. The facts seem to ine
to indicate that peculiar and very distinct
species have migrated in radiating lines
from some common centre ; and I am
inclined to look in the southern as in the
northern hemisphere, to a former and
warmer period, before the commencement
of the Glacial period, when the antarctic
lands, now covered with ice, supported a
highly peculiar and isolated flora. I sus
pect that before this flora was exterminated
by the Glacial epoch a few forms were
widely dispersed to various points of the
southern hemisphere by occasional means
of transport, and by the aid, as haltingplaces, of existing and now sunken islands.
By these means, as I believe, the southern
shores of America, Australia, New Zealand,
have become slightly tinted by the same
peculiar forms of vegetable life.
Sir C. Lyell, in a striking passage, has
speculated, in language almost identical
with mine, on'the effects of great alterna
tions of climate on geological distribution.
I believe that the world has recently felt
one of his great cycles of change ; and
that on this view, combined with modifica
tion through natural selection, a multitude
of facts in the present distribution, both of
the same and of allied forms of life, can be
explained. The living waters may be said
to have flowed during one short period
from the north and from the south, and to
have crossed at the equator, but to have
flowed with greater force from the north, so
as to have freely inundated the south. As
the tide leaves its drift in horizontal lines,
though rising higher on the shores where
the tide rises highest, so have the living
waters left their living drift on our moun
tain-summits in a line gently rising from the
arctic lowlands to a great height under the
equator. The various beings thus left
stranded may be compared with savage
races of man, driven up and surviving in
the mountain-fastnesses of almost every
land, which serve as a record, full of
interest to us, of the former inhabitants of
the surrounding lowlands.
Chapter XII.
GEOGRAPHICAL DISTRIBUTION—Continued
Distribution of fresh-water productions—On the
inhabitants of oceanic islands—Absence of
Batrachians and of terrestrial Mammals—On
the relation of the inhabitants of islands to
those of the nearest mainland—On colonisa
tion from the nearest source with subsequent
modification — Summary of the last and
present chapters.
As lakes and river-systems are separated
from each other by barriers of land, it
might have been thought that fresh-water
productions would not have ranged widely
within the same country, and, as the sea is
apparently a still more impassable barrier,
that they never would have extended to
distant countries. But the case is exactly
the reverse. Not only have many fresh
water species, belonging to quite different
classes, an enormous range, but allied
species prevail in a remarkable manner
throughout the world. I well repierriber.
when first collecting in the fresh waters of
Brazil, feeling much surprise at the simi
larity of the fresh-water insects, shells, etc.,
and at the dissimilarity of the surrounding
terrestrial beings, compared with those of
Britain.
But this power in fresh-water productions
of ranging widely, though so unexpected,
can, I think, in most cases be explained by
their having become fitted, in a manner
highly useful to them, for short and fre
quent migrations from pond to pond, or
from stream to stream ; and liability to
wide dispersal would follow from this
capacity as an almost necessary conse
quence. We can here consider only a few
cases. In regard to fish, I believe that the
same species never occur in the fresh
waters of distant continents. But on the
same continent the species often range
widely and almost capriciously; for two
river-systems will have some fisft ip common
�GEOGRAPHICAL DISTRIBUTION
155
and some different. A few facts seem to
duck-weed from one aquarium to another,
favour the possibility of their occasional
that I have quite unintentionally stocked
transport by accidental means—like that
the one with fresh-water shells from the
of the live fish not rarely dropped by whirl
other. But another agency is perhaps more
winds in India, and the vitality of their ova
effectual : I suspended a duck’s feet, which
when removed from the water. But I am
might represent those of a bird sleeping in
inclined to attribute the dispersal of fresh
a natural pond, in an aquarium where
water fish mainly to slight changes within
many ova of fresh-water shells were hatch
the recent period in the level of the land
ing ; and I found that numbers of the
having caused rivers to flow into each
extremely minute and just-hatched shells
other. Instances also could be given of this
crawled on the feet and clung to them so
having occurred during floods, without any
firmly that, when taken out of the water,
change of level. We have evidence in the
they could not be jarred off, though at a
loess of the Rhine of considerable changes
somewhat more advanced age they would
of level in the land within a very recent
voluntarily drop off. These just-hatched
geological period, and when the surface
molluscs, though aquatic in their nature,
was peopled by existing land and fresh
survived on the duck’s feet, in damp air,
water shells. The wide difference of the
from twelve to twenty hours ; and in this
fish on opposite sides of continuous moun
length of time a duck or heron might fly at
tain-ranges, which from an early period
least six or seven hundred miles, and would
must have parted river-systems and com
be sure to alight on a pool or rivulet, if
pletely prevented their inosculation, seems
blown across sea to an oceanic island or to
to lead to this same conclusion. With
any other distant point. Sir Charles Lyell
respect to allied fresh-water fish occurring
also informs me that a Dyticus has been
at very distant points of the world, no doubt
caught with an Ancylus (a fresh-water shell
there are many cases which cannot at
like a limpet) firmly adhering to it ; and a
present be explained; but some fresh-water
water-beetle of the same family, a Colymfish belong to very ancient forms, and in
betes, once flew on board the Beagle when
such cases there will have been ample time
forty-five miles distant from the nearest
for great geographical changes, and conse
land ; how much farther it might have
quently time and means for much migra
flown with a favouring gale no one can tell.
tion. In the second place, salt-water fish
With respect to plants, it has long been
can with care be slowly accustomed to live
known what enormous ranges many fresh
in fresh water ; and, according to Valen
water and even marsh species have, both
ciennes, there is hardly a single group of over continents and to the most remote
fishes confined exclusively to fresh water, » oceanic islands. This is strikingly shown,
so that we may imagine that a marine
as remarked by Alph. de Candolle, in large
member of a fresh-water group might travel
groups of terrestrial plants which have
far along the shores of the sea, and subse
only a very few aquatic members ; for
quently become modified and adapted to
these latter seem immediately to acquire,
the fresh waters of a distant land.
as if in consequence, a very wide range.
Some species of fresh-water shells have
I think favourable means of dispersal
a very wide range, and allied species, which,
explain this fact. I have before mentioned
on my theory, are descended from a common
that earth occasionally, though rarely,
parent and must have proceeded from a
adheres in some quantity to the feet and
single source, prevail throughout the world.
beaks of birds. Wading birds, which
Their distribution at first perplexed me
frequent the muddy edges of ponds, if
much, as their ova are not likely to be
suddenly flushed, would be the most likely
transported by birds, and they are im
to have muddy feet. Birds of this order, I
mediately killed by sea-water, as are the
can show, are the greatest wanderers, and
adults. I could not even understand how
are occasionally found on the most remote
some naturalised species have rapidly
and barren islands in the open ocean ;
spread throughout the same country. But
they would not be likely to alight on the
two facts which I have observed—and no
surface of the sea, so that the dirt would
doubt many others remain to be observed
not be washed off their feet; when making
-—throw some light on this subject. When
land, they would be sure to fly to their
a duck suddenly emerges from a pond
natural fresh-water haunts. I do not believe
covered with duck-weed, I have twice seen
that botanists are aware how charged the
these little plants adhering to its back; and
mud of ponds is with seeds. I have tried
it has happened to me, in removing a little
several little experiments, but will here give
�T56
ON THE ORIGIN OF SPECIES
only the most striking case : I took, in
February, three table-spoonfuls of mud from
three different'points, beneath water, on the
edge of a little pond; this mud when dry
weighed only 6X ounces ; I kept it covered
up in my study for six months, pulling up
and counting each plant as it grew ; the
plants were of many kinds, and were
altogether 537 in number; and yet the
viscid mud was all contained in a breakfast
cup ! Considering these facts, I think it
would be an inexplicable circumstance if
water-birds did not transport the seeds of
fresh-water plants to vast distances, and if,
consequently, the range of these plants
was not very great. The same agency may
have come into play with the eggs of some
of the smaller fresh-water animals.
Other and unknown agencies probably
have also played a part. I have stated
that fresh-water fish eat some kinds of
seeds, though they reject many other kinds
after having swallowed them ; even small
fish swallow seeds of moderate size, as
of the yellow water-lily and Potamogeton.
Herons and other birds, century after
century, have gone on daily devouring
fish ; they then take flight and go to other
waters, or are blown across the sea ; and
we have seen that seeds retain their power
of germination, when rejected in pellets
or in excrement, many hours afterwards.
When I saw the great size of the seeds of
that fine water-lily, the Nelumbium, and
remembered Alph. de Candolle’s remarks
on this plant, I thought that its distribu
tion must remain quite inexplicable ; but
Audubon states that he found the seeds of
the great southern water-lily (probably,
according to Dr. Hooker, the Nelumbium
luteum) in a heron’s stomach ; although I
do not know the fact, yet analogy makes
me believe that a heron, flying to another
pond and getting a hearty meal of fish,
would probably reject from its stomach a
pellet containing the seeds of the Nelum
bium undigested, or the seeds might be
dropped by the bird while feeding its
young, in the same way as fish are known
sometimes to be dropped.
In considering these several means of
distribution, it should be remembered that
when a pond or stream is first formed, for
instance, on a rising islet, it will be unoccu
pied ; and a single seed or egg will have
a good chance of succeeding. Although
there will always be a struggle for life
between the individuals of the species,
however few, already occupying any pond,
yet as the number of kinds is small com
pared with those on the land, the competi
tion will probably be less severe between
aquatic than between terrestrial species ;
consequently, an intruder from the waters
of a foreign country would have a better
chance of seizing on a place than in the
case of terrestrial colonists. We should
also remember that some, perhaps many,
fresh-water productions are low in the scale
of nature, and that we have reason to
believe that such low beings change or
become modified less quickly than the
high ; and this will give longer time than
the average for the migration of the same
aquatic species. We should not forget
the probability of many species having
formerly ranged as continuously as fresh
water productions ever can range over
immense areas, and having subsequently
become extinct in intermediate regions.
But the wide distribution of fresh-water
plants and of the lower animals, whether
retaining the same identical form or in
some degree modified, I believe mainly
depends on the wide dispersal of their
seeds and eggs by animals, more especially
by fresh-water birds, which have large
powers of flight, and naturally travel from
one to another and often distant piece of
water. Nature, like a careful gardener,
thus takes her seeds from a bed of a par
ticular nature, and drops them in another
equally well fitted for them.
On the Inhabitants of Oceanic Islands.—
We now come to the last of the three
classes of facts which I have selected as
presenting the greatest amount of difficulty,
on the view that all the individuals both
of the same and of allied species have
descended from a single parent; and
therefore have all proceeded from a
common birth-place, notwithstanding that
in the course of time they have come to
inhabit distant points of the globe. I
have already stated that I cannot honestly
admit Forbes’s view on continental exten
sions, which, if legitimately followed out,
would lead to the belief that within the
recent period all existing islands have been
nearly or quite joined to some continent.
This view would remove many difficulties,
but it would not, I think, explain all the
facts in regard to insular productions. In
the following remarks I shall not confine
myself to the mere question of dispersal ;
but shall consider some other facts which
bear on the truth of the two theories of
independent creation and of descent with
modification.
�GEOGRAPHICAL DISTRIBUTION
The species of all kinds which inhabit
oceanic islands are few in number com
pared with those on equal continental
areas : Alph. de Candolle admits this for
plants, and Wollaston for insects. If we
look to the large size and varied stations of
New Zealand, extending over 780 miles of
latitude, and compare its flowering plants,
only 750 in number, with those on an
equal area at the Cape of Good Hope or in
Australia, we must, I think, admit that
something quite independently of any dif
ference in physical conditions has caused
so great a difference in number. Even the
uniform county of Cambridge has 847
plants, and the little island of Anglesey
764, but a few ferns and a few introduced
plants are included in these numbers, and
the comparison in some other respects is
not quite fair. We have evidence that the
barren island of Ascension aboriginally
possessed under half a dozen flowering
plants ; yet many have become naturalised
on it, as they have on New Zealand and on
every other oceanic island which can be
named. In St. Helena there is reason to
believe that the naturalised plants and
animals have nearly or quite exterminated
many native productions. He who admits
the doctrine of the creation of each sepa
rate species will have to admit that a
sufficient number of the best adapted
plants and animals have not been created
on oceanic islands ; for man has uninten
tionally stocked them from various sources
far more fully and perfectly than has
nature.
Although in oceanic islands the number
of kinds of inhabitants is scanty, the pro
portion of endemic species (z>., those found
nowhere else in the world) is often ex
tremely large. If we compare, for instance,
the number of the endemic land-shells in
Madeira, or of the endemic birds in the
Galapagos Archipelago, with the number
found on any continent, and then compare
the area of the islands with that of the
continent, we shall see that this is true.
This fact might have been expected on my
theory, for, as already explained, species
occasionally arriving after long intervals in
a new and isolated district, and having to
compete with new associates, will be
eminently liable to modification, and will
often produce groups of modified descen
dants. But it by no means follows that,
because in an island nearly all the species
of one class are peculiar, those of another
class, or of another section of the same
class, are peculiar; and this difference
157
seems to depend partly on the species
which do not become modified having
immigrated with facility and in a body, so
that their mutual relations have not been
much disturbed; and partly on the frequent
arrival of unmodified immigrants from the
mother-country, and the consequent inter
crossing with them. With respect to the
effects of this intercrossing, it should be
remembered that the offspring of such
crosses would almost certainly gain in
vigour; so that even an occasional cross
would produce more effect than might at
first have been anticipated. To give a few
examples: in the Galapagos Islands nearly
every land bird, but only two out of the
eleven marine birds, are peculiar ; and it is
obvious that marine birds could arrive at
these islands more easily than land birds.
Bermuda, on the other hand, which lies at
about the same distance from North
America as the Galapagos Islands do from
South America, and which has a very
peculiar soil, does not possess one endemic
land bird ; and we know, from Mr. J. M.
Jones’s admirable account of Bermuda, that
very many North American birds, during
their great annual migrations, visit either
periodically or occasionally this island.
Madeira does not possess one peculiar bird,
and many European and African birds are
almost every year blown there, as I am
informed by Mr. E. V. Harcourt. So that
these two islands of Bermuda and Madeira
have been stocked by birds, which for long
ages have struggled together in their former
homes, and have become mutually adapted
to each other; and when settled in their
new homes, each kind will have been kept
by the others to their proper places and
habits, and will consequently have been
little liable to modification. Any tendency
to modification will also have been
checked by intercrossing with the unmodi
fied immigrants from the mother-country.
Madeira, again, is inhabited by a wonder
ful number of peculiar land-shells, whereas
not one species of sea-shell is confined to
its shores : now, though we do not know
how sea-shells are dispersed, yet we can
see that their eggs or larvae, perhaps
attached to sea-weed or floating timber, or
to the feet of wading-birds, might be trans
ported far more easily than land-shells
across three or four hundred miles of open
sea. The different orders of insects in
Madeira apparently present analogous
facts.
Oceanic islands are sometimes deficient
in certain classes, and their places are
�i5S
ON THE ORIGIN OF SPECIES
apparently occupied by the other inhabi
tants ; in the Galapagos Islands reptiles,
and in New Zealand gigantic wingless
birds, take the place of mammals. In the
plants of the Galapagos Islands Dr.
Hooker has shown that the proportional
numbers of the different orders are very
different from what they are elsewhere.
Such cases are generally accounted for by
the physical conditions of the islands ; but
this explanation seems to me not a little
doubtful. Facility of immigration, I believe,
has been at least as important as the
nature of the conditions.
Many remarkable little facts could be given
with respect to the inhabitants of remote
islands. For instance, in certain islands
not tenanted by mammals some of the en
demic plants have beautifully hooked seeds;
yet few relations are more striking than
the adaptation of hooked seeds for trans
portal by the wool and fur of quadrupeds.
This case presents no difficulty on my view,
for a hooked seed might be transported
to an island by some other means ; and
the plant, then becoming slightly modified,
but still retaining its hooked seeds, would
form an endemic species, having as useless
an appendage as any rudimentary organ
•—for instance, as the shrivelled wings under
the soldered elytra of many insular beetles.
Again, islands often possess trees or bushes
belonging to orders which elsewhere in
clude only herbaceous species ; now trees,
as Alph. de Candolle has shown, generally
have, whatever the cause may be, confined
ranges. Hence trees would be little likely
to reach distant oceanic islands ; and an
herbaceous plant, though it would have no
chance of successfully competing in stature
with a fully developed tree, when established
on an island and having to compete with
herbaceous plants alone, might readily gain
an advantage by growing taller and taller
and overtopping the other plants. If so,
natural selection would often tend to add
to the stature of herbaceous plants when
growing on an oceanic island, to whatever
order they belonged, and thus convert
them first into bushes and ultimately into
trees.
With respect to the absence of whole
orders on oceanic islands, Bory St. Vincent
long ago remarked that Batrachians (frogs,
toads, newts) have never been found on
any of the many islands with which the
great oceans are studded. I have taken
pains. to verify this assertion, and I have
found it strictly true. I have, however,
been assured that a frog exists on the
mountains of the great island of New
Zealand ; but I suspect that this exception
(if the information be correct) may be
explained through glacial agency. This
general absence of frogs, toads, and newts
on so many oceanic islands cannot be
accounted for by their physical conditions ;
indeed, it seerris that islands are peculiarly
well fitted for these animals ; for frogs have
been introduced into Madeira, the Azores,
and Mauritius, and have multiplied so as
to become a nuisance. But as these animals
and their spawn are known to be imme
diately killed by sea-water, on my view we
can see that there would be great difficulty
in their transportal across the sea, and
therefore why they do not exist on any
oceanic island. But why, on the theory of
creation, they should not have been created
there, it would be very difficult to explain.
Mammals offer another and similar case.
I have carefully searched the oldest voyages,
but have not finished my search ; as yet I
have not found a single instance, free from
doubt, of a terrestrial mammal (excluding
domesticated animals kept by the natives)
inhabiting an island situated above 300
miles from a continent or great continental
island; and many islands situated at a
much less distance are equally barren.
The Falkland Islands, which are inhabited
by a wolf-like fox, come nearest to an
exception ; but this group cannot be con
sidered as oceanic, as it lies on a bank
connected with the mainland ; moreover,
icebergs formerly brought boulders to its
western shores, and they may have formerly
transported foxes, as so frequently now
happens in the arctic regions. Yet it
cannot be said that small islands will not
support small mammals, for they occur in
many parts of the world on very small
islands, if close to a continent; and hardly
an island can be named on which our
smaller quadrupeds have not become
naturalised and greatly multiplied. It
cannot be said, on the ordinary view of
creation, that there has not been time for
the creation of mammals ; many volcanic
islands are sufficiently ancient, as shown
by the stupendous degradation which they
have suffered and by their tertiary strata.
There has also been time for the produc
tion of endemic species belonging to other
classes ; and on continents it is thought
that mammals appear and disappear at a
quicker rate than other and lower animals.
Though terrestrial mammals do not occur
on oceanic islands, aerial mammals do
occur on almost every island. New Zealand
�GEOGRAPHICAL DISTRIBUTION
possesses two bats found nowhere else in
the world : Norfolk Island, the Viti Archi
pelago, the Bonin Islands, the Caroline and
Marianne Archipelagoes, and Mauritius—
all possess their peculiar bats. Why, it
may be asked, Has the supposed creative
force produced bats and no other mammals
on remote islands ? On my view, this ques
tion can easily be answered ; for no terres
trial mammal can be transported across
a wide space of sea, but bats can fly
across. Bats have been seen wandering
by day far over the Atlantic Ocean ; and
two North American species either regularly
or occasionally visit Bermuda, at the dis
tance of 600 miles from the mainland. I
hear from Mr. Tomes, who has specially
studied this family, that many of the same
species have enormous ranges, and are
found on continents and on far distant
islands. Hence we have only to suppose
that such wandering species have been
modified through natural selection in their
new homes in relation to their new position,
and we can understand the presence of
endemic bats on islands, with the absence
of all terrestrial mammals.
Besides the absence of terrestrial mam
mals in relation to the remoteness of islands
from continents, there is also a relation, to
a certain extent independent of distance,
between the depth of the sea separating an
island from the neighbouring mainland
and the presence in both of the same mammiferous species or of allied species in a
more or less modified condition. Mr.
Windsor Earl has made some striking
observations on this head in regard to the
great Malay Archipelago, which is traversed
near Celebes by a space of deep ocean ;
and this space separates two widely distinct
mammalian faunas. On either side the
islands are situated on moderately deep
submarine banks, and they are inhabited
by closely-allied or identical quadrupeds.
No doubt some few anomalies occur in this
great archipelago, and there is much diffi
culty in forming a judgment in some cases
owing to the probable naturalisation of
certain mammals through man’s agency ;
but we shall soon have much light thrown
on the natural history of this archipelago
by the admirable zeal and researches of
Mr. Wallace. I have not as yet had time
to follow up this subject in all other quarters
of the world ; but as far as I have gone the
relation generally holds good. We see
Britain separated by a shallow channel from
Europe, and the mammals are the same on
both sides ; we meet with analogous facts
159
on many islands separated by similar chan
nels from Australia. The West Indian
Islands stand on a deeply submerged bank,
nearly 1,000 fathoms in depth, and here we
find American forms, but the species and
even the genera are distinct. As the amount
of modification in all cases depends to a
certain degree on the lapse of time, and as
during changes of level it is obvious that
islands separated by shallow channels are
more likely to have been continuously united
within a recent period to the mainland than
islands separated by deeper channels, we
can understand the frequent relation between
the depth of the sea and the degree of affinity
of the mammalian inhabitants of islands
with those of a neighbouring continent—
an inexplicable relation on the view of
independent acts of creation.
All the foregoing remarks on the inhabi
tants of oceanic islands—namely, the
scarcity of kinds; the richness in endemic
forms in particular classes or sections of
classes; the absence of whole groups, as
of batrachians, and of terrestrial mammals,
notwithstanding the presence of aerial bats ;
the singular proportions of certain orders
of plants, herbaceous forms having been
developed into trees, etc.—seem to me to
accord better with the view of occasional
means of transport having been largely
efficient in the long course of time than
with the view of all our oceanic islands
having been formerly connected by con
tinuous land with the nearest continent ;
for on this latter view the migration would
propably have been more complete ; and
if modification be admitted, all the forms of
life would have been more equally modified,
in accordance with the paramount impor
tance of the relation of organism to organ
ism.
I do not deny that there are many and
grave difficulties in understanding how
several of the inhabitants of the more
remote islands, whether still retaining the
same specific form or modified since their
arrival, could have reached their present
homes. But the probability of many islands
having existed as halting-places, of which
not a wreck now remains, must not be over
looked. I will here give a single instance
oi one of the cases of difficulty. Almost
all oceanic islands, even the most isolated
and smallest, are inhabited by land-shells,
generally by endemic species, but sometimes
by species found elsewhere. Dr. Aug. A.
Gould has given several interesting cases
in regard to the land-shells of the islands
of the Pacific. Now, it is notorious that
�i6o
ON THE ORIGIN OF SPECIES
land-shells are very easily killed by salt;
their eggs, at least such as I have tried,
sink in sea-water and are killed by it. Yet
there must be, on my view, some unknown
but highly efficient means for their trans
portal. Would the just-hatched young
occasionally crawl on and adhere to the
feet of birds roosting on the ground, and
thus get transported? It occurred to me
that land-shells, when hibernating and
having a membranous diaphragm over the
mouth of the shell, might be floated in
chinks of drifted timber across moderately
wide arms of the sea. And I found that
several species did in this state withstand
uninjured an immersion in sea-water during
seven days : one of these shells was the
Helix pomatia, and after it had again
hibernated I put it in sea-water for twenty
days, and it perfectly recovered. As this
species has a thick calcareous operculum,
I removed it, and when it had formed a
new membranous one, I immersed it for
fourteen days in sea-water, and it recovered
and crawled away ; but more experiments
are wanted on this head.
The most striking and important fact for
us in regard to the inhabitants of islands
is their affinity to those of the nearest
mainland, without being actually the same
species. Numerous instances could be
given of this fact. I will give only one,
that of the Galapagos Archipelago, situated
under the equator, between 500 and 600
miles from the shores of South America.
Here almost every product of the land and
water bears the unmistakeable stamp of the
American continent. There are twenty-six
land-birds, and twenty-five of these are
ranked by Mr. Gould as distinct species,
supposed to have been created here; yet
the close affinity of most of these birds to
American species in every character, in
their habits, gestures, and tones of voice,
was manifest. So it is with the other
animals, and with nearly all the plants, as
shown by Dr. Hooker in his admirable
memoir on the Flora of this archipelago.
The naturalist, looking at the inhabitants
of these volcanic islands in the Pacific,
distant several hundred miles from the
continent, yet feels that he is standing on
American land. Why should this be so ?
Why should the species which are supposed
to have been created in the Galapagos
Archipelago, and nowhere else, bear so
plain a stamp of affinity to those created
in America? There is nothing in the con
ditions of life, in the geological nature of
the islands, in their height or climate, or
in the proportions in which the several
classes are associated together, which
resembles closely the conditions of the
South American coast; in fact, there is
a considerable dissimilarity in all these
respects. On the other hand, there is a
considerable degree of resemblance in the
volcanic nature of the soil, in climate,
height, and size of the islands, between
the Galapagos and Cape de Verde Archi
pelagos ; but what an entire and absolute
difference in their inhabitants! The inhabi
tants of the Cape de Verde Islands are
related to those of Africa, like those of the
Galapagos to America. I believe this
grand fact can receive no sort of explana
tion on the ordinary view of independent
creation ; whereas, on the view here main
tained, it is obvious that the Galapagos
Islands would be likely to receive colonists,
whether by occasional means of transport
or by formerly continuous land, from
America, and the Cape de Verde Islands
from Africa ; and that such colonists would
be liable to modification—the principle of
inheritance still betraying their original
birthplace.
Many analogous facts could be given ;
indeed, it is an almost universal rule that
the endemic productions of islands are
related to those of the nearest continent,
or of other near islands. The exceptions
are few, and most of them can be explained.
Thus the plants of Kerguelen Land, though
standing nearer to Africa than to America,
are related, and that very closely, as we
know from Dr. Hooker’s account, to those
of America; but on the view that this
island has been mainly stocked by seeds
brought with earth and stones on ice
bergs, drifted by the prevailing currents,
this anomaly disappears. New Zealand'in
its endemic plants is much more closely
related to Australia, the nearest mainland,
than to any other region : and this is what
might been expected ; but it is also plainly
related to South America, which, although
the next nearest continent, is so enormously
remote that the fact becomes an anomaly.
But this difficulty almost disappears on the
view that both NewZealand, South America,
and other southern lands were long ago
partially stocked from a nearly intermediate
though distant point—-namely, from the
antarctic islands-—when they were clothed
with vegetation, before the commencement
of the Glacial period. The affinity, which,
though feeble, I am assured by Dr. Hooker
is real, between the flora of the south-western
corner of Australia and of the Cape of Good
�GEOGRAPHICAL DISTRIBUTION
Hope, is a far more remarkable case, and
is at present inexplicable ; but this affinity
is confined to the plants, and will, I do not
doubt, be some day explained.
The law which causes the inhabitants of
an archipelago, though specifically distinct,
to be closely allied to those of the nearest
continent we sometimes see displayed on
a small scale, yet in a most interesting
manner, within the limits of the same
archipelago. Thus the several islands of
the Galapagos Archipelago are tenanted,
as I have elsewhere shown, in a quite mar
vellous manner, by very closely-related
species ; so that the inhabitants of each
separate island, though mostly distinct, are
related in an incomparably closer degree to
each other than to the inhabitants of any
other part of the world. And this is just
what might have been expected on my view,
for the islands are situated so near each
other that they would almost certainly
receive immigrants from the same original
source, or from each other. But this dis
similarity between the endemic inhabitants
of the islands may be used as an argument
against my views, for, it may be asked, how
has it happened in the several islands
situated within sight of each other, having
the same geological nature, the same height,
climate, etc., that many of the immigrants
should have been differently modified, though
only in a small degree ? This long appeared
to me a great difficulty, but it arises in chief
part from the deeply-seated error of con
sidering the physical conditions of a country
as the most important for its inhabitants ;
whereas it cannot, I think, be disputed that
the nature of the other inhabitants, with
which each has to compete, is at least as
important, and generally a far more impor
tant, element of success. Now, if we look
to those inhabitants of the Galapagos Archi
pelago which are found in other parts of
the world (laying on one side for the moment
the endemic species, which cannot be here
fairly included, as we are considering how
they have come to be modified since their
arrival), we find a considerable amount of
difference in the several islands. This
difference might indeed have been expected
on the view of the islands having been
stocked by occasional means of transport—a seed, for instance, of one plant having been
brought to one island, and that of another
plant to another island. Hence, when in
former times an immigrant settled on any
one or more of the islands, or when it subse
quently spread from one island to another, it
would undoubtedly be exposed to different
conditions of life in the different islands, for
it would have to compete with different sets
of organisms. A plant, for instance, would
find the best-fitted ground more perfectly
occupied by distinct plants in one island
than in another, and it would be exposed to
the attacks of somewhat different enemies.
If, then, it varied, natural selection would
probably favour different varieties in the
different islands. Some species, however,
might spread and yet retain the same
character throughout the group, just as we
see on continents some species spreading
widely and remaining the same.
The really surprising fact in this case of
the Galapagos Archipelago, and in a lesser
degree in some analogous instances, is that
the new species formed in the separate
islands have not quickly spread to the other
islands. But the islands, though in sight
of each other, are separated by deep arms
of the sea, in most cases wider than the
British Channel, and there is no reason to
suppose that they have at any former period
been continuously united. The currents of
the sea are rapid and sweep across the
archipelago, and gales of wind are extra
ordinarily rare ; so that the islands are far
more effectually separated from each other
than they appear to be on a map.
Nevertheless, a good many species, both
those found in other parts of the world
and those confined to the archipelago, are
common to the several islands, and we may
infer from certain facts that these have
probably spread from some one island to
the others. But we often take, I think, an
erroneous view of the probability of closelyallied species invading each other’s territory
when put into free intercommunication.
Undoubtedly, if one species has any advan
tage whatever over another, it will in a very
brief time wholly or in part supplant it ;
but if both are equally well fitted for their
own places in nature, both probably will
hold their own places and keep separate for
almost any length of time. Being familiar
with the fact that many species, naturalised
through man’s agency, have spread with
astonishing rapidity over new countries,
we are apt to infer that most species would
thus spread; but we should remember
that the forms which become naturalised
in new countries are not generally closely
allied to the aboriginal inhabitants, but are
very distinct species, belonging in a large
proportion of cases, as shown by Alph. de
Candolle, to distinct genera. In the Gala
pagos Archipelago many even of the birds,
though so well adapted for flying from
M
�162
ON THE ORIGIN OF SPECIES
island to island, are distinct on each ; thus
there are three closely-allied species of
mocking-thrush, each confined to its own
island. Now, let us suppose the mockingthrush of Chatham Island to be blown to
Charles Island, which has its own mockingthrush : why should it succeed in estab
lishing itself there? We may safely infer
that Charles Island is well stocked with
its own species, for annually more eggs are
laid there than can possibly be reared ;
and we may infer that the mocking-thrush
peculiar to Charles Island is, at least, as
well fitted for its home as is the species
peculiar to Chatham Island. Sir C. Lyell
and Mr. Wollaston have communicated
to me a remarkable fact bearing on this
subject—namely, that Madeira and the
adjoining islet of. Porto Santo possess
many distinct but representative land
shells, some of which live in crevices of
stone ; and although large quantities of
stone are annually transported from Porto
Santo to Madeira, yet this latter island has
not become colonised by the Porto Santo
species ; nevertheless, both islands have
been colonised by some European land
shells, which no doubt had some advantage
over the indigenous species. From these
considerations, I think we need not greatly
marvel at the endemic and representative
species, which inhabit the several islands
of the Galapagos Archipelago, not having
universally spread from island to island.
In many other instances, as in the several
districts of the same continent, pre-occupation has probably played an important
part in checking the commingling of species
under the same conditions of life. Thus
the south-east and south-west corners of
Australia have nearly the same physical
conditions, and are united by continuous
land, yet they are inhabited by a vast
number of distinct mammals, birds, and
plants.
The principle which determines the
general character of the fauna and flora
of oceanic islands—namely, that the inhabi
tants, when not identically the same, yet
are plainly related to the inhabitants of
that region whence colonists could most
readily have been derived—the_ colonists
having been subsequently modified and
better fitted to their new horpes—is of the
widest application throughout nature. We
see this on every mountain, in every lake
and marsh. For alpine species, excepting
in so far as the same forms, chiefly of plants,
have spread widely throughout the world
during the recent Glacial epoch, are related
to those of the surrounding lowlands ; thus
we have in South America alpine humming
birds, alpine rodents, alpine plants, etc., all
of strictly American forms, and it is obvious
that a mountain, as it became slowly
upheaved, would naturally be colonised
from the surrounding lowlands. So it is
with the inhabitants of lakes and marshes,
excepting in so far as great facility of trans
port has given the same general forms
to the whole world. We see this same
principle in the blind animals inhabiting
the caves of America and of Europe. Other
analogous facts could be given. And it
will, I believe, be universally found to be
true that wherever in two regions, let them
be ever so distant, many closely-allied or
representative species occur, there will like.wise be found some identical species, show
ing, in accordance with the foregoing view,
that at some former period there has been
intercommunication or migration between
the two regions. And wherever many
closely-allied species occur, there will be
found many forms which some naturalists
rank as distinct species and some as varie
ties, these doubtful forms showing us the
steps in the process of modification.
This relation between the power and
extent of migration of a species, either at
the present time or at some former period
under different physical conditions, and
the existence at remote points of the world
of other species allied to it, is shown in
another and more general way. Mr. Gould
remarked to me long ago that in those
genera of birds which range over the world
many of the species have very wide ranges.
I can hardly doubt that this rule is generally
true, though it would be difficult to prove
it. Among mammals, we see it strikingly
displayed in Bats, and in a lesser degree in
the Felidse and Canidas. We see it if we
compare the distribution of butterflies and
beetles. So it is with most fresh-water pro
ductions, in which so many genera range
over the world, and many individual species
have enormous ranges. It is not meant
that in world-ranging genera all th; species
have a wide range, or even that they have
on an average a wide range, but only that
some of the species range very widely; for
the facility with which widely-ranging
species vary and give rise to new forms
will largely determine their average range.
For instance, two varieties of the same
species inhabit America and Europe, and
the species thus has an immense range ;
but, if the variation had been a little greater,
the two varieties would have been ranked
�GEOGRAPHICAL DISTRIBUTION
as distinct species, and the common range
would have been greatly reduced. Still, less
is it meant that a species which apparently
has the capacity of crossing barriers and
ranging widely, as in the case of certain
powerfully-winged birds, will necessarily
range widely; for we should never forget
that to range widely implies, not only the
power of crossing barriers, but the more
important power of being victorious in
distant lands in the struggle for life with
foreign associates. But on the view of all
the species of a genus having descended
from a single parent, though now distributed
to the most remote points of the world, we
ought to find, and I believe as a general
rule we do find, that some at least of the
species range very widely; for it is necessary
that the unmodified parent should range
widely, undergoing modification during its
diffusion, and should place itself under
divers conditions favourable for the con
version of its offspring, firstly into new
varieties, and ultimately into new species.
In considering the wide distribution of
certain genera, we should bear in mind that
some are extremely ancient, and must have
branched off from a common parent at a
remote epoch ; so that in such cases there
will have been ample time for great climatal
and geographical changes and for accidents
of transport, and, consequently, for the
migration of some of the species into all
quarters of the world, where they may have
become slightly modified in relation to their
new conditions. There is, also, some reason
to believe, from geological evidence, that
organisms low in the scale within each
great class generally change at a slower
rate than the higher forms ; and conse
quently the lower forms will have had a
better chance of ranging widely and of still
retaining the same specific character. This
fact, together with the seeds and eggs of
many low forms being very minute and
better fitted for distant transportation, pro
bably accounts for a law which has long
been observed, and which has lately been
admirably discussed by Alph. de Candolle
in regard to plants—namely, that the lower
any group of organisms is, the more widely
it is apt to range.
The relations just discussed—namely,
low and slowly-changing organisms ranging
more widely than the high ; some of the
species of widely-ranging genera themselves
ranging widely ; such facts, as alpine,
lacustrine, and marsh productions being
related (with the exceptions before specified)
to those on the surrounding low lands and
163
dry lands, though these stations are so
different; the very close relation of the
distinct species which inhabit the islets
of the same archipelago ; and especially
the striking relation of the inhabitants of
each whole archipelago or island to those
of the nearest mainland—are, I think,
utterly inexplicable on the ordinary view of
the independent creation of each species,
but are explicable on the view of colonisa
tion from the nearest or readiest source,
together with the subsequent modification
and better adaptation of the colonists to
their new homes.
Summary of last and present Chapters.—
In these chapters I have endeavoured to
show that, if we make due allowance for out
ignorance of the full effects of all the
changes of climate and of the level of the
land which have certainly occurred within
the recent period, and of other similar
changes which may have occurred within
the same period ; if we remember how
profoundly ignorant we are with respect to
the many and curious means of occasional
transport, a subject which has hardly ever
been properly experimentised on ; if we
bear in mind how often a species may have
ranged continuously over a wide area, and
then have become extinct in the intermediate
tracts—I think the difficulties in believing
that all the individuals of the same species,
wherever located, have descended from the
same parents, are not insuperable. And
we are led to this conclusion, which has
been arrived at by many naturalists under
the designation of single centres of creation,
by some general considerations, more
especially from the importance of barriers
and from the analogical distribution of sub
genera, genera, and families.
With respect to the distinct species of
the same genus, which on my theory must
have spread from one parent-source, if we
make the same allowances as before for our
ignorance, and remember that some forms
of life change most slowly, enormous
periods of time being thus granted for
their migration, I do not think that the
difficulties are insuperable, though they
often are in this case, and in that of the
individuals of the same species, extremely
great.
As exemplifying the effects- of climatal
changes on distribution, I have attempted
to show how important has been the
influence of the modern Glacial period,
which I am fully convinced simultaneously
affected the whole world, or at least great
�164
ON THE ORIGIN OF SPECIES
meridional belts. As showing how diversi
fied are the means of occasional transport,
I have discussed at.some little length the
means of dispersal of fresh-water produc
tions.
If the difficulties be not insuperable in
admitting that in the long course of time
the individuals of the same species, and
likewise of allied species, have proceeded
from some one source, then I think all the
grand leading facts of geographical distri
bution are explicable on the theory of
migration (generally of the more dominant
forms of life), together with subsequent
modification and multiplication of new
forms. We can thus understand the high
importance of barriers whether of land or
water, which separate our several zoological
and botanical provinces. We can thus
understand the localisation of sub-genera,
genera, and families ; and how it is that
under different latitudes—for instance, in
South America—the inhabitants of the plains
and mountains, of the forests, marshes, and
deserts, are in so mysterious a manner
linked together by affinity, and are like
wise linked to the extinct beings which
formerly inhabited the same continent.
Bearing in mind that the mutual relation
of organism to organism is of the highest
importance, we can see why two areas
having nearly the same physical conditions
should often be inhabited by very different
forms of life : for according to the length
of time which has elapsed since new inhabi
tants entered one region; according to the
nature of the communication which allowed
certain forms and not others to enter, either
in greater or lesser numbers; according or
not as those which entered happened to
come in more or less direct competition
with each other and with the aborigines ;
and according as the immigrants were
capable of varying more or less rapidly—
there would ensue in different regions,
independently of their physical conditions,
infinitely diversified conditions of life;
there would be an almost endless amount
of organic action and reaction ; and we
should find, as we do find, some groups
of beings greatly and some only slightly
modified—some developed in great force,
some existing in scanty numbers—in the
different great geographical provinces of
the world.
On these same principles, we can under
stand, as I have endeavoured to show, why
oceanic islands should have few inhabitants,
but of these a great number should be
endemic or peculiar; and why, in relation
to the means of migration, one group of
beings, even within the same, class, should
have all its species endemic, and another
group should have all its species common
to other quarters of the world. We can
see why whole groups of organisms, as
batrachians and terrestrial mammals, should
be absent from oceanic islands, while the
most isolated islands possess their own
peculiar species of aerial mammals or bats.
We can see why there should be some
relation between the presence of mammals,
in a more or less modified condition, and
the depth of the sea between an island and
the mainland. We can clearly see why all
the inhabitants of an archipelago, though
specifically distinct on the several islets,
should be closely related to each other, and
likewise be related, but less closely, to those
of the nearest continent or other source,
whence immigrants were probably derived.
We can see why in two areas, however
distant from each other, there should be
a correlation, in the presence of identical
species, of varieties, of doubtful species,
and of distinct but representative species.
As the late Edward Forbes often insisted,
there is a striking parallelism in the laws
of life throughout time and space, the laws
governing the succession of forms in past
times being- nearly the same with those
governing at the present time the differences
in different areas. We see this in many
facts. The endurance of each species and
group of species is continuous in time ; for
the exceptions to the rule are so few that
they may fairly be attributed to our not
having as yet discovered in an intermediate
deposit the forms which are therein absent,
but which occur above and below ; so in
space it certainly is the general rule that
the area inhabited by a single species, or
by a group of species, is continuous; and
the exceptions, which are not rare, may, as
I have attempted to show, be accounted for
by migration at some former period under
different conditions or by occasional means
of transport, and by the species having
become extinct in the intermediate tracts.
Both in time and space species and groups
of species have their points of maximum
development. Groups of species, belonging
either to a certain period of time, or to a
certain area, are often characterised by
trifling characters in common, as of sculp
ture or colour. In looking to the long
succession of ages, as in now looking to
distant provinces throughout the world, we
find that some organisms differ little,
while others belonging to a different class,
�CLASSTFICA TION
or to a different order, or even only to a
different family of the same order, differ
greatly. In both time and space the lower
members of each class generally change
less than the higher; but there are in both
cases marked exceptions to the rule. On
my theory, these several relations through
out time and space are intelligible ; for
whether we look to the forms of life which
have changed during successive ages within
the same quarter of the world, or to those
165
which have changed after having migrated
into distant quarters, in both cases the
forms within each class have been con
nected by the same bond of ordinary gene
ration ; and the more nearly any two forms
are related in blood, the nearer they will
generally stand to each other in time and
space ; in both cases the laws of variation
have been the same, and modifications
have been accumulated by the same power
of natural selection.
Chapter XIII.
MUTUAL AFFINITIES OF ORGANIC BEINGS: MOR
PHOLOGY: EMBRYOLOGY: RUDIMENTARY
ORGANS
Classification, groups subordinate to groups
—Natural system—Rules and difficulties in
classification, explained on the theory of
descent with modification—Classification of
varieties—Descent always used in classifica
tion—Analogical or adaptive characters—Affinities, general, complex, and radiating—
Extinction separates and defines groups—■
Morphology, between members of the same
class, between parts of the same individual—•
Embryology, laws of, explained by variations
not supervening at an early age, and being
inherited at a corresponding age—Rudi
mentary organs ; their origin explained—
Summary.
From the first dawn of life all organic
beings are found to resemble each other in
descending degrees, so that they can be
classed in groups under groups. This
classification is evidently not arbitrary like
the grouping of the stars in constellations.
The existence of groups would have been
of simple signification if one group had
been exclusively fitted to inhabit the land
and another the water—one to feed on fish,
another on vegetable matter, and so on ;
but the case is widely different in nature,
for it is notorious how commonly members
of even the same sub-group have different
habits. In our second and fourth chapters,
on Variation and on Natural Selection, I
have attempted to show that it is the widely-
ranging, the much diffused and common—
that is, the dominant species belonging to
the larger genera—which vary most. The
varieties, or incipient species, thus produced
ultimately become converted, as I believe,
into new and distinct species ; and these,
on the principle of inheritance, tend to
produce other new and dominant species.
Consequently, the groups which are now
large, and which generally include many
dominant species, tend to go on increasing
indefinitely in size. I further attempted to
show that, from the varying descendants of
each species trying to occupy as many
and as different places as possible in the
economy of nature, there is a constant
tendency in their characters to diverge.
This conclusion was supported by looking
at the great diversity of the forms of life
which, in any small area, come into the
closest competition, and by looking to
certain facts in naturalisation.
I attempted also to show that there is a
constant tendency in the forms, which are
increasing in number and diverging in
character, to supplant and exterminate the
less divergent, the less improved, and pre
ceding forms. I request the reader to
turn to the diagram illustrating the action,
as formerly explained, of these several
principles ; and he will see that the inevit
able result is that the modified descendants
�i66
ON THE ORIGIN OF SPECIES
proceeding from one progenitor become
broken up into groups subordinate to
groups. In the diagram each letter on the
uppermost line may represent a genus
including several species; and all the
genera on this line form together one class,
for all have descended from one ancient
but unseen parent, and, consequently, have
inherited something in common. But the
three genera on the left hand have, on this
same principle, much in common, and form
a sub-family, distinct from that including
the next two genera on the right hand,
which diverged from a common-parent at
the fifth stage of descent. These five
genera have also much, though less, in
common ; and they form a family distinct
from that including the three genera still
further to the right hand, which diverged
at a still earlier period. And all these
genera descended from (A) form an order
distinct from the genera descended from
(I). So that we here have many species
descended from a single progenitor grouped
into genera ; and the genera are included
in, or subordinate to, sub-families, families,
and orders, all united into one class. Thus
the grand fact in natural history of the sub
ordination of group under group, which, from
its familiarity, does not always sufficiently
strike us, is in my judgment explained.
Naturalists try to arrange the species,
genera, and families in each class on what
is called the natural system. But what is
meant by this system ? Some authors look
at it merely as a scheme for arranging
together those living objects which are
most alike, and for separating those which
are most unlike ; or as an artificial means
for enunciating, as briefly as possible,
general propositions—that is, by one sen
tence to give the characters common, for
instance, to all mammals; by another, those
common to all carnivora ; by another, those
common to the dog-genus ; and then, by
adding a single sentence, a full description
is given to each kind of dog. The ingenuity'
and utility of this system are indisputable.
But many naturalists think that something
more is meant by the natural system : they
believe that it reveals the plan of the
Creator ; but unless it be specified whether
order in time or space, or what else is
meant by the plan of the Creator, it seems
to me that nothing is thus added to our
knowledge. Such expressions as that
famous one of Linneeus, and which we
often meet with in a more or less concealed
form, that the characters do not make the
genus, but that the genus gives the char
acters, seem to imply that something more
is included in our classification than mere
resemblance. I believe that something
more is included, and that propinquity of
descent—the only known cause of the
similarity of organic beings—is the bond,
hidden as it is by various degrees of modi
fication, which is partially revealed to us by
our classifications.
Let us now consider the rules followed
in classification, and the difficulties which
are encountered on the view that classifica
tion either gives some unknown plan of
creation or is simply a scheme for enun
ciating general propositions and of placing
together the forms most like each other.
It might have been thought (and was in
ancient times thought) that those parts of
the structure which determined the habits
of life and the general place of each being
in the economy of nature would be of very
high importance in classification. Nothing
can be more false. No one regards the
external similarity of a mouse to a shrew,
of a dugong to a whale, of a whale to a fish,
as of any importance. These resemblances,
though so intimately connected with the
whole life of the being, are ranked as
merely “adaptive or analogical characters”;
but to the consideration of these resem
blances we shall have to recur. It may
even be given as a general rule that, the
less any part of the organisation is con
cerned with special habits, the more impor
tant it becomes for classification. As an
instance, Owen, in speaking of the dugong,
says: “The generative organs, being those
which are most remotely related to the
habits and food of an animal, I have always
regarded as affording very clear indications
of its true affinities. We are least likely in
the modifications of these organs to mistake
a merely adaptive for an essential char
acter.” So with plants, how remarkable it
is that the organs of vegetation on which
their whole life depends are of little signifi
cation, excepting in the first main divisions ;
whereas the organs of reproduction, with
their product the seed, are of paramount
importance !
We must not, therefore, in classifying,
trust to resemblances in parts of the organi
sation, however important they may be for
the welfare of the being in relation to the
outer world. Perhaps from this cause it
has partly arisen that almost all naturalists
lay the greatest stress on resemblances in
organs of high vital or physiological impor
tance. No doubt this view of the cl^ssifi-
catory importance of organs which are
�CLASSIFICATION
important is generally, but by no means
always, true. But their importance for
classification, I believe, depends on their
greater constancy throughout large groups
of species ; and this constancy depends on
such organs having generally been subjected
to less change in the adaptation of the species
to their conditions of life. That the mere
physiological importance of an organ does
not determine its classificatory value _ is
almost shown by the one fact that in allied
groups in which the same organ, as we have
every reason to suppose, has nearly the same
physiological value its classificatory value
is widely different. No naturalist can have
worked at any group without being struck
with this fact; and it , has been fully
acknowledged in the writings of almost
every author. It will suffice to quote the
highest authority, Robert Brown, who, in
speaking of certain organs in the Proteaceae,
says their generic importance, “like that of
all their parts, not only in this but, as I
apprehend, in every natural family, is very
unequal, and in some cases seems to be
entirely lost.” Again, in another work, he
says, the genera of the Connaraceae “ differ
in having one or more ovaria, in the exist
ence or absence of albumen, in the imbri
cate or valvular aestivation. Any one of
these characters singly is frequently of
more than generic importance, though here,
even when all taken together, they appear
insufficient to separate Cnestis from Connarus.” To give an example among insects,
in one great division of the Ilymenoptera,
the antennae, as Westwood has remarked,
are most constant in structure ; in another
division they differ much, and the differences
are of quite subordinate value in classifica
tion ; yet no one probably will say that the
antennae in these two divisions of the same
order are of unequal physiological impor
tance. Any number of instances could be
given of the varying importance for classi
fication of the same important organ within
the same group of beings.
Again, no one will say that rudimentary
or atrophied organs are of high physio
logical or vital importance; yet undoubtedly
organs in this condition are often of high
value in classification. No one will dispute
that the rudimentary teeth in the upper jaws
of young ruminants and certain rudimentary
bones of the leg are highly serviceable in
exhibiting the close affinity between Rumi
nants and Pachyderms. Robert Brown has
strongly insisted on the fact that the rudi
mentary florets are of the highest impor
tance in the classification of the Grasses.
167
Numerous instances could be given of
characters derived from parts which must
be considered of very trifling physiological
importance, but which are universally
admitted as highly serviceable in the defi
nition of whole groups. For instance,
whether or not there is an open passage
from the nostrils to the mouth, the only
character, according to Owen, which abso
lutely distinguishes fishes and reptiles—the
inflection of the angle of the jaws in Mar
supials, the manner in which the wings of
insects are folded, mere colour in certain
Algae, mere pubescence on parts of the
flower in grasses, the nature of the dermal
covering, as hair or feathers, in the vertebrata. If the Ornithorhynchus had been
covered with feathers instead of hair, this
external and trifling character would, I
think, have been considered by naturalists
as important an aid in determining the
degree of affinity of this strange creature
to birds and reptiles as an approach in
structure in any one internal and important
organ.
The importance, for classification, of
trifling characters mainly depends on their
being correlated with several other charac
ters of more or less importance. The value,
indeed, of an aggregate of characters is very
evident in natural history. Hence, as has
often been remarked, a species may depart
from its allies in several characters, both
of high physiological importance and of
almost universal prevalence, and yet leave
us in no doubt where it should be ranked.
Hence, also, it has been found that a classi
fication founded on any single character,
however important that may be, has always
failed, for no part of the organisation is
universally constant. The importance of
an aggregate of characters, even when
none are important, alone explains, I think,
that saying of Linnieus, that the characters
do not give the genus, but the genus gives
the characters; for this saying seems
founded on an appreciation of many trifling
points of resemblance, too slight to be
defined. Certain plants belonging to the
Malpighiaceae bear perfect and degraded
flowers ; in the latter, as A. de Jussieu has
remarked, “ the greater number of the
characters proper to the species, to the
genus, to the family, to the class, disappear,
and thus laugh at our classification.” But
when Aspicarpa produced in France, during
several years, only degraded flowers, depart
ing so wonderfully in a number of the most
important points of structure from the
proper type of the order, yet M. Richard
�i68
ON THE ORIGIN OF SPECIES
sagaciously saw, as Jussieu observes, that
this genus should still be retained among
the Malpighiacese. This case seems to me
well to illustrate the spirit with which our
classifications are sometimes necessarily
founded.
Practically, when naturalists are at work,
they do not trouble themselves about the
physiological value of the characters which
they use in defining a group, or in allocating
any particular species. If they find a
character nearly uniform, and common to
a great number of forms, and not common
to others, they use it as one of high value ;
if common to some lesser number, they use
it as of subordinate value. This principle
has been broadly confessed by some natu
ralists to be the true one ; and by none more
clearly than by that excellent botanist, Aug.
St. Hilaire. If certain characters are always
found correlated with others, though no
apparent bond of connection can be dis
covered between them, especial value is set
on them. . As in most groups of animals,
important organs such as thosefor propelling
the blood, or for aerating it, or those for
propagating the race, are found nearly
uniform, they are considered as highly
serviceable in classification ; but in some
groups of animals all these, the most
important vital organs, are found to offer
characters of quite subordinate value.
We can see why characters derived from
the embryo should be of equal importance
with those derived from the adult, for our
classifications of course include all ages of
each species. But it is by no means obvious,
on the ordinary view, why the structure of
the embryo should be more important for
this purpose than that of the adult, which
alone plays its full part in the economy of
nature. Yet it has been strongly urged by
those great naturalists, Milne Edwards and
Agassiz, that embryonic characters are the
most important of any in the classification
of animals ; and this doctrine has very
generally been admitted as true. The same
fact holds good with flowering plants, of
which the two main divisions have been
fonnded on characters derived from the
embryo—on the number and position of
the embryonic leaves or cotyledons, and on
the mode of development of the plumule
and radicle. In our discussion on embry
ology we shall see why such characters
are so valuable, on the view of classification
tacitly including the idea of descent.
Our classifications are often plainly
influenced by chains of affinities. Nothing
can be easier than to denne a number of
characters common to all birds; but in the
case of crustaceans such definition has
hitherto been found impossible. There are
crustaceans at the opposite ends of the
series which have hardly a character in
common ; yet the species at both ends,
from being plainly allied to others, and
these to others, and so onwards, can be
recognised as unequivocally belonging to
this and to no other class of the Articulata.
Geographical distribution has often been
used, though perhaps not quite logically, in
classification, more especially in very large
groups of closely-allied forms. Temminck
insists on the utility or even necessity of
this practice in certain groups of birds;
and it has been followed by several ento
mologists and botanists.
Finally, with respect to the comparative
value of the various groups of species, such
as orders, sub-orders, families, sub-families,
and genera, they seem to be, at least at
present, almost arbitrary. Several of the
best botanists, such as Mr. Bentham and
others, have strongly insisted on their
arbitrary value. Instances could be given
among plants and insects of a group of
forms, first ranked by practised naturalists
as only a genus, and then raised to the
rank of a sub-family or family; and this
has been done, not because further research
has detected important structural differ
ences, at first overlooked, but because
numerous allied species, with slightly
different grades of difference, have been
subsequently discovered.
All the foregoing rules and aids and
difficulties in classification are explained,
if I do not greatly deceive myself, on the
view that the natural system is founded
on descent with modification : that the
characters which naturalists consider as
showing true affinity between any two or
more species are those which have been
inherited from a common parent, and in
so far all true classification is genealogical;
that community of descent is the hidden
bond which naturalists have been uncon
sciously seeking, and not some unknown
plan of creation, or the enunciation of
general propositions, and the mere putting
together and separating objects more or
less alike.
But I must explain my meaning more
fully. I believe that the arrangement of
the groups within each class, in due sub
ordination and relation to the other groups,
must be strictly genealogical in order to be
natural ; but that the amount of difference
in the several branches or groups, though
�CLASStFICA TION
169
allied in the same degree in blood to their
single genus. But this genus, though much
common progenitor, may differ greatly,
isolated, will still occupy its proper inter
being due to the different degrees of modifi
mediate position; for F originally was
cation which they have undergone ; and
intermediate in character between A and I,
this is expressed by the forms being ranked
and the several genera descended from
under different genera, families, sections,
these two genera will have inherited, to a
or orders. The reader will best understand
certain extent, their characters. This
what is meant if he will take the trouble of
natural arrangement is shown, as far as
referring to the diagram in the preliminary.
is possible on paper, in the diagram, but
We will suppose the letters A to L to
in much too simple a manner. If a
represent allied genera, which lived during
branching diagram had not been used,
the Silurian epoch, and these have des
and only the names of the groups had
cended from a species which existed at an
been written in a linear series, it would
unknown anterior period. Species of three
have been still less possible to have given
of these genera (A, F, and I) have trans
a natural arrangement; and it is notoriously
mitted modified descendants to the present
not possible to represent in a series, on a
day, represented by the fifteen genera («14
flat surface, the affinities which we discover
to .s’14) on the uppermost horizontal line.
in nature among the beings of the same
Now, all these modified descendants from a
group. Thus, on the view which I hold,
single species are represented as related in
the natural system is genealogical in its
blood or descent to the same degree ; they
arrangement, like a pedigree; but the
may metaphorically be called cousins to
degrees of modification which the different
the same millionth degree ; yet they differ
groups have undergone have to be expressed
widely and in different degrees from each
by ranking them under different so-called
other. The forms descended from A, now
genera, sub-families, families, sections,
broken up into two or three families, con
orders, and classes.
stitute a distinct order from those descended
It may be worth while to illustrate this
from I, also broken up into two families.
view of classification by taking the case of
Nor can the existing species descended
languages. If we possessed a perfect pedi
from A be ranked in the same genus with
gree of mankind, a genealogical arrange
the parent A, or those from I with the
ment of the races of man would afford the
parent I. But the existing genus F'4 may
best classification of the various languages
be supposed to have been but slightly j now spoken throughout the world ; and if all
modified, and it will then rank with the j extinct languages and all intermediate and
parent-genus F,just as some few still living
slowly-changing dialects had to be included,
organic beings belong to Silurian genera.
such an arrangement would, I think, be the
So that the amount or value of the differ
only possible one. Yet it might be that
ences between organic beings all related
some very ancient language had altered
to each other in the same degree in blood
little, and had given rise to few new
has come to be widely different. Never
languages, while others (owing to the
theless, their genealogical arrangement
spreading and subsequent isolation and
remains strictly true, not only at the present
states of civilisation of the several races,
time, but at each successive period of
descended from a common race) had altered
descent. All the modified descendants
much, and had given rise to many new
from A will have inherited something in
languages and dialects. The various degrees
common from their common parent, as will
of difference in the languages from the
all the descendants from I; so will it be
same stock would have to be expressed by
with each subordinate branch of descen
groups subordinate to groups ; but the
dants, at each successive period. If, how
proper or even only possible arrangement
ever, we choose to suppose that any of the
would still be genealogical ; and this would
descendants of A or of I have been so
be strictly natural, as it would connect
much modified as to have more or less
together all languages, extinct and modern,
completely lost traces of their parentage,
by the closest affinities, and would give the
in this case them places in a natural classi
filiation and origin of each tongue.
fication will have been more or less com
In confirmation of this view, let us glance
pletely lost—as sometimes seems to have
at the classification of varieties which are
occurred with existing organisms. All the
believed or known to have descended from
descendants of the genus F, along its whole
one species. These are grouped under
line of descent, are supposed to have been
species, with sub-varieties under varieties ;
but little modified, and they yet form a
and with our domestic productions several
�>
I^o
ON THE ORIGIN OF SPECIES
other grades of difference are requisite, as
we have seen with pigeons. The origin of
the existence of groups subordinate to
groups is the same with varieties as with
species—namely, closeness of descent with
various degrees of modification. Nearly
the same rules are followed in classifying
varieties as with species. Authors have
insisted on the necessity of classing varie
ties on a natural instead of an artificial
system ; we are cautioned, for instance,
not to class two varieties of the pine-apple
together merely because their fruit, though
the most important part, happens to be
nearly identical; no one puts the Swedish
and common turnips together, though the
esculent and thickened stems are so similar.
Whatever part is found to be most constant
is used in classing varieties : thus the great
agriculturist Marshall says the horns are
very useful for this purpose with cattle,
because they are less variable than the
shape or colour of the body, etc.; whereas
with sheep the horns are much less service
able, because less constant. In classing
varieties, I apprehend, if we had a real
pedigree, a genealogical classification would
be universally preferred, and it has been
attempted by some authors. For we might
feel sure, whether there had been more or
less modification, the principle of inheri
tance would keep the forms together which
were allied in the greatest number of points.
In tumbler pigeons, though some sub
varieties differ from the others in the
important character of having a longer
beak, yet all are kept together from having
the common habit of tumbling, but the
short-faced breed has nearlyor quite lostthis
habit; nevertheless, without any reasoning
or thinking on the subject, these tumblers
are kept in the same group, because allied
in blood and alike in some other respects.
If it could be proved that the Hottentot had
descended from the Negro, I think he would
be classed under the Negro group, however
much he might differ in colour and other
important characters from negroes.
With species in a state of nature, every
naturalist has, in fact, brought descent into
his classification, for he includes in his
lowest grade, or that of a species, the two
sexes ; and how enormously these some
times differ in the most important charac
ters is known to every naturalist : scarcely
a single fact can be predicated in common
of the males and hermaphrodites of certain
cirripedes, when adult, and yet no one
dreams of separating them. The naturalist
includes as one species the several larval
stages of the same individual, however
much they may differ from each other and
from the adult ; as he likewise includes the
so-called alternate generations of Steenstrup,
which can only in a technical sense be con
sidered as the same individual. He includes
monsters ; he includes varieties, not solely
because they closely resemble the parent
form, but because they are descended from
it. He who believes that the cowslip is
descended from the primrose, or conversely,
ranks them together as a single species,
and gives a single definition. As soon as
three Orchidean forms (Monochanthus,
Myanthus, and Catasetum), which had
previously been ranked as three distinct
genera, were known to be sometimes pro
duced on the same spike, they were imme
diately included as a single species.
As descent has universally been used in
classing together the individuals of the
same species, though the males and females
and larvae are sometimes extremely differ
ent; and as it has been used in classing
varieties which have undergone a certain
and sometimes a considerable amount of
modification, may not this same element
of descent have been unconsciously used
in grouping species under genera, and
genera under higher groups, though in
these cases the modification has been
greater in degree, and has taken a longer
time to complete ? I believe it has thus
been unconsciously used; and only thus
can I understand the several rules and
guides which have been followed by our
best systematists. We have no written
pedigrees; we have to make out community
of descent by resemblances of any kind.
Therefore, we choose those characters which,
as far as we can judge, are the least likely
to have been modified in relation to the
conditions of life to which each species
has been recently exposed. Rudimentary
structures on this view are as good as, or
even sometimes better than, other parts of
the organisation. We care not how trifling
a character may be—let it be the mere
inflection of the angle of the jaw, the
manner in which an insect’s wing is folded,
whether the skin be covered by hair or
feathers—if it prevail throughout many
and different species, especially those having
very different habits of life, it assumes high
value ; for we can account for its presence
in so many forms with such different habits
only by its inheritance from a common
parent. We may err in this respect in
regard to single points of structure, but
when several characters, let them be ever
�CLASSIFICATION
so trifling, occur together throughout a
large group of beings having different
habits, we may feel almost sure, on the
theory of descent, that these characters
have been inherited from a common
ancestor. And we know that such corre
lated or aggregated characters have especial
value in classification.
We can understand why a species or a
group of species may depart, in several of
its most important characteristics, from its
allies, and yet be safely classed with them.
This maybe safely done, and is often done,
as long as a sufficient number of characters,
let them be ever so unimportant, betrays
the hidden bond of community of descent.
Let two forms have not a single character
in common, yet, if these extreme forms are
connected together by a chain of inter
mediate groups, we may at once infer their
community of descent, and we put them
all into the same class. As we find organs
of high physiological importance—those
which serve to preserve life under the
most diverse conditions of existence—are
generally the most constant, we attach
especial value to them ; but if these same
organs, in another group or section of a
group, are found to differ much, we at once
value them less in our classification. We
shall hereafter, I think, clearly see why
embryological characters are of such high
classificatory importance.
Geographical
distribution may sometimes be brought
usefully into play in classing large and
widely-distributed genera, because all the
species of the same genus, inhabiting any
distinct and isolated region, have in all
probability descended from the same
parents.
We can understand, on these views, the
very important distinction between real
affinities and analogical or adaptive resem
blances. Lamarck first called attention to
this distinction, and he has been ably
followed by Macleay and others. The
resemblance, in the shape of the body and
in the fin-like anterior limbs, between the
dugong, which is a pachydermatous animal,
and the whale, and between both these
mammals and fishes, is analogical. Among
insects there are innumerable instances :
thus Linnaeus, misled by external appear
ances, actually classed an homopterous
insect as a moth. We see something of
the same kind even in our domestic varieties,
as in the thickened stems of the common
and Swedish turnip. The resemblance of
the greyhound and racehorse is hardly
more fanciful than the analogies which
171
have been drawn by some authors between
very distinct animals. On my view of
characters being of real importance for
classification only in so far as they reveal
descent, we can clearly understand why
analogical or adaptive character, although
of the utmost importance to the welfare of
the being, are almost valueless to the
systematist. For animals belonging to
two most distinct lines of descent may
readily become adapted to similar con
ditions, and thus assume a close external
resemblance ; but such resemblances will
not reveal—will rather tend to conceal,
their blood-relationship to their proper
lines of descent. We can also understand
the apparent paradox that the very same
characters are analogical when one class
or order is compared with another, but
give true affinities when the members of
the same class or order are compared one
with another : thus, the shape of the body
and fin-like limbs are only analogical when
whales are compared with fishes, being
adaptations in both classes for swimming
through the water; but the shape of the
body and fin-like limbs serve as characters
exhibiting true affinity between the several
members of the whale family; for these
cetaceans agree in so many characters,
great and small, that we cannot doubt that
they have inherited their general shape of
body and structure of limbs from a common
ancestor. So it is with fishes.
As members of distinct classes have
often been adapted by successive slight
modifications to live under nearly similar
circumstances—to inhabit, for instance, the
three elements of land, air, and water—we
can perhaps understand how it is that a
numerical parallelism has sometimes been
observed between the sub-groups in distinct
classes. Anaturalist, struck by a parallelism
of this nature in any one class, by arbitrarily
raising or sinking the value of the groups
in other classes (and all our experience
shows that this valuation has hitherto been
arbitrary), could easily extend theparallelism
over a wide range ; and thus the septenary,
quinary, quaternary, and ternary classifica
tions have probably arisen.
As the modified descendants of dominant
species belonging to the larger genera tend
to inherit the advantages which made the
groups to which they belong large and their
parents dominant, they are almost sure to
spread widely, and to seize on more and
more places in the economy of nature.
The larger and more dominant groups thus
tend to go on increasing in size; and they
�172
ON THE ORIGIN OF SPECIES
consequently supplant many smaller and
feebler groups. Thus we can account for
the fact that all organisms, recent and
extinct, are included under a few great
orders, under still fewer classes, and all in
one great natural system. As showing how
few the higher groups are in number, and
how widely spread they are throughout the
world, the fact is striking that the discovery
of Australia has not added a single insect
belonging to a new class ; and that in the
vegetable kingdom, as I learn from Dr.
Hooker, it has added only two or three
orders of small size.
In the chapter on Geological Succession
I attempted to show, on the principle of
each group having generally diverged much
in character during the long-continued pro
cess of modification, how it is that the more
ancient forms of life often present characters
in some slight degree intermediate between
existing groups. A few old and intermediate
parent-forms, having occasionally trans
mitted to the present day descendants but
little modified, will give to us our so-called
osculant or aberrant groups. The more
aberrant any form is, the greater must be
the number of connecting forms which, on
my theory, have been exterminated and
utterly lost. And we have some evidence
of aberrant forms having suffered severely
from extinction, for they are generally repre
sented by extremely few species ; and such
species as do occur are generally very
distinct from each other, which, again,
implies extinction. The genera Ornithorhynchus and Lepidosiren, for example,
would not have been less aberrant had
each been represented by a dozen species
instead of by a single one ; but such rich
ness in species, as I find after some investi
gation, does not commonly fall to the lot
of aberrant genera. We can, I think,
account for this fact only by looking at
aberrant forms as failing groups con
quered by more successful competitors
with a few members preserved by some
unusual coincidence of favourable circum
stances.
Mr. Waterhouse has remarked that, when
a member belongingto one group of animals
exhibits an affinity to a quite distinct group,
this affinity in most cases is general and
not special: thus, according to Mr. Water
house, of all Rodents, the bizcacha is most
nearly related to Marsupials ; but in the
points in which it approaches this order its
relations are general, and not to any one
marsupial species more than to another.
As the points of affinity of the bizcacha to
Marsupials are believed to be real and not
merely adaptive, they are due, on my
theory, to inheritance in common. There
fore, we must suppose either that all
Rodents, including the bizcacha, branched
off from some very ancient Marsupial, which
will have had a character in some degree
intermediate with respect to all existing
Marsupials; or that both Rodents and
Marsupials branched off from a common
progenitor, and that both groups have since
undergone much modification in divergent
directions. On-either view we may suppose
that the bizcacha has retained, by inherit
ance, more of the character of its ancient
progenitor than have other Rodents ; and
therefore it will not be specially related to
any one existing Marsupial, but indirectly
to all, or nearly all, Marsupials, from having
partially retained the character of their
common progenitor, or of an early member
of the group. On the other hand, of all Mar
supials, as Mr. Waterhouse has remarked,
the phascolomys resembles most nearly, not
any one species, but the general order of
Rodents. In this case, however, it may be
strongly suspected that the resemblance is
only analogical, owing to the phascolomys
having become adapted to habits like those
of a Rodent. The elder De Candolle has
made nearly similar observations on the
general nature of the affinities of distinct
orders of plants.
On the principle of the multiplication and
gradual divergence in character of the
species descended from a common parent,
together with their retention, by inheritance,
of some characters in common, we can
understand the excessively complex and
radiating affinities by which all the members
of the same family or higher group are
connected together. For the common
parent of a whole family of species, now
broken up by extinction into distinct groups
and sub-groups, will have transmitted some
of its characters, modified in various ways
and degrees, to all; and the several species
will consequently be related to each other
by circuitous lines of affinity of various
lengths (as may be seen in the diagram so
often referred to), mounting up through
many predecessors. As it is difficult to show
the blood-relationsh ip between the numerous
kindred of any ancient and noble family,
even by the aid of a genealogical tree, and
almost impossible to do this without this aid,
we can understand the extraordinary diffi
culty which naturalists have experienced in
describing, without the aid of a diagram,
the various affinities which they perceive
�CLASSIFICATION
between the many living and extinct
members of the same great natural class.
Extinction, as we have seen in the fourth
chapter, has played an important part in
defining and widening the intervals between
the several groups in each class. We may
thus account even for the distinctness of
whole classes from each other—for instance,
of birds from all other vertebrate animals—
by the belief that many ancient forms of life
have been utterly lost, through which the
early progenitors of birds were formerly
connected with the early progenitors of the
other vertebrate classes. There has been
less entire extinction of the forms of life
which once connected fishes with batrachians. There has been still less in some
other classes, as in that of the Crustacea,
for here the most wonderfully diverse forms
are still tied together by a long, but broken,
chain of affinities. Extinction has only
separated groups : it has by no means made
them; for if every form which has ever lived
on this earth were suddenly to reappear,
though it would be quite impossible to give
definitions by which each group could be
distinguished from other groups, as all
would blend together by steps as fine as
those between the finest existing varieties,
nevertheless a natural classification, or at
least a natural arrangement, would be
possible. We shall see this by turning to
the diagram : the letters A to L may
represent eleven Silurian genera, some of
which have produced large groups of modi
fied descendants. Every intermediate link
between these eleven genera and their
primordial parent, and every intermediate
link in each branch and sub-branch of their
descendants, may be supposed to be still
alive, and the links to be as fine as those
between the finest varieties. In this case it
would be quite impossible to give any
definition by which the several members cf
the several groups could be distinguished
from their more immediate parents ; or
these parents from their ancient and un
knownprogenitor. Yet the natural arrange
ment in the diagram would still hold good ;
and, on the principle of inheritance, all the
forms descended from A, or from I, would
have something in common. In a tree we
can specify this or that branch, though at
the actual fork the two unite and blend
together. We could not, as I have said,
define the several groups ; but we could
pick out types, or forms, representing most
of the characters of each group, whether
large or small, and thus give a general idea
of the value of the differences between them.
173
This is what we should be driven to if we
were ever to succeed in collecting all the
forms in any class which have lived through
out all time and space. We shall certainly
never succeed in making so perfect a collec
tion ; nevertheless, in certain classes, we
are tending in this direction; and Milne
Edwards has lately insisted, in an able
paper, on the high importance of looking to
types, whether or not we can separate and
define the groups to which such types
belong.
Finally, we have seen that natural selec
tion, which results from the struggle for
existence, and which almost inevitably
induces extinction and divergence of char
acter in many descendants from one
dominant parent-species, explains that great
and universal feature in the affinities of all
organic beings—namely, their subordina
tion in group under group. We use the
element of descent in classing the indi
viduals of both sexes and of all ages,
although having few characters in common,
under one species; we use descent in
classing acknowledged varieties, however
different they may be from their parent;
and I believe this element of descent is
the hidden bond of connection which
naturalists have sought under the term of
the Natural System. On this idea of the
natural system being, in so far as it has
been perfected, genealogical in its arrange
ment, with the grades of difference between
the descendants from a common parent,
expressed by the terms genera, families,
order, etc., we can understand the rules
which we are compelled to follow in our
classification. We can understand why
we value certain resemblances far more
than others ; why we are permitted to use
rudimentary and useless organs, or others
of trifling physiological importance ; why,
in comparing one group with a distinct
group, we summarily reject analogical or
adaptive characters, and yet use these same
characters within the limits of the same
group. We can clearly see how it is that
all living and extinct forms can be grouped
together in one great system ; and how the
several members of each class are con
nected together by the most complex and
radiating lines of affinities. We shall
never, probably, disentangle the inextric
able web of affinities between the members
of any one class ; but when we have a
distinct object in view, and do not look to
some unknown plan of creation, we may
hope to make sure but slow progress.
�174
ON THE ORIGIN OF SPECIES
Morphology.—We have seen that the
members of the same class, independently
of their habits of life, resemble each other
in the general plan of their organisation.
The resemblance is often expressed by the
term “unity of type,” or by saying that
the several parts and organs in the different
species of the class are homologous. The
whole subject is included under the general
name of morphology. This is the most inte
resting department of natural history, and
may be said to be its very soul. What can
be more curious than that the hand of a
man, formed for grasping, that of a mole
for digging, the leg of the horse, the paddle
of the porpoise, and the wing of the bat,
should all be constructed on the same
pattern, and should include similar bones,
m the same relative positions ? Geoffroy
St. Hilaire has insisted strongly on the high
importance of relative connection in homo
logous organs : the parts may change to
almost any extent in form and size, and yet
they always remain connected together in
the same order. We never find, for instance,
the bones of the arm and forearm, or of the
thigh and leg, transposed. Hence the same
names can be given to the homologous
bones in widely different animals. We see
the same great law in the construction of
the mouths of insects : what can be more
different than the immensely long spiral
proboscis of a sphinx-moth, the curious
folded one of a bee or bug, and the great
jaws of a beetle?—yet all these organs,
serving for such different purposes, are
formed by infinitely numerous modifications
of an upper lip, mandibles, and two pairs
of maxillae. Analogous laws govern the
construction of the mouths and limbs of
crustaceans. So it is with the flowers of
plants.
Nothing can be more hopeless than to
attempt to explain this similarity of pattern
in members of the same class, by utility or
by the doctrine of final causes. The hope
lessness of the attempt has been expressly
admitted by Owen in his most interesting
work on The Nature of Limbs. On the
ordinary view of the independent creation
of each being, we can only say that so it is—that it has so pleased the Creator to con
struct each animal and plant.
The explanation is manifest on the theory
of the natural selection of successive slight
modifications—each modification being
profitable in some way to the modified form,
but often affecting by correlation of growth
other parts of the organisation. I n changes
of this nature there will be little or no
tendency to modify the original pattern, or
to transpose parts. The bones of a limb
might be shortened and widened to any
extent, and become gradually enveloped in
thick membrane, so as to serve as a fin; or
a webbed foot might have all its bones, or
certain bones, lengthened to any extent, and
the membrane connecting them increased
to any extent, so as to serve as a wing; yet
in all this great amount of modification
there will be no tendency to alter the frame
work of bones or the relative connection of
the several parts. If we suppose that the
ancient progenitor—the archetype, as it may
be called—of all mammals had its limbs
constructed on the existing general pattern,
for whatever purpose they served, we can
at once perceive the plain signification of
the homologous construction of the limbs
throughout the whole class. So with the
mouths of insects, we have only to suppose
that their common progenitor had an upper
lip, mandibles, and two pairs of maxillae,
these parts being perhaps very simple in
form; and then natural selection, acting on
some originally created form, will account
for the infinite diversity in structure and
function of the mouths of insects. Never
theless, it is conceivable that the general
pattern of an organ might become so much
obscured as to be finally lost, by the atrophy
and ultimately by the complete abortion of
certain parts, by the soldering together of
other parts, and by the doubling or multi
plication of others—variations which we
know to be within the limits of possibility.
In the paddles of the extinct gigantic sea
lizards, and in the mouths of certain suctorial
crustaceans, the general pattern seems to
have been thus to a certain extent obscured.
There is another and equally curious
branch of the present subject—namely, the
comparison, not of the same part in different
members of a class, but of the different
parts or organs in the same individual.
Most physiologists believe that the bones
of the skull are homologous with—that is,
correspond in number and in relative con
nection with—the elemental parts of a cer
tain number of vertebrae. The anterior
and posterior limbs in each member of the
vertebrate and articulate classes are plainly
homologous. We see the same law in
comparing the wonderful complex jaws and
legs in crustaceans. It is familiar to almost
every one that in a flowei- the relative
position of the sepals, petals, stamens, and
pistils, as well as their intimate structure,
are intelligible on the view that they consist
of metamorphosed leaves, arranged in a
�MORPHOLOGY
spire. In monstrous plants we often get
direct evidence of the possibility of one
organ being transformed into another; and
we can actually see in embryonic crus
taceans and in many other animals, and in
flowers, that organs which, when mature,
become extremely different are at an early
stage of growth exactly alike.
How inexplicable are these facts on the
ordinary view of creation! Why should
the brain be enclosed in a box composed
of such numerous and such extraordinary
shaped pieces of bone ? As Owen has
remarked, the benefit derived from the
yielding of the separate pieces in the act of
parturition of mammals will by no means
explain the same construction in the skulls
of birds. Why should similar bones have
been created in the formation of the wing
and leg of a bat, used as they are for such
totally different purposes ? Why should
one crustacean which has an extremely
complex mouth formed of many parts con
sequently always have fewer legs ; or, con
versely, those with many legs have simpler
mouths ? Why should the sepals, petals,
stamens, and pistils in any individual flower,
though fitted for such widely different
purposes, be all constructed on the same
pattern ?
On the theory of natural selection, we
can satisfactorily answer these questions.
In the vertebrata we see a series of internal
vertebrae bearing certain processes and
appendages ; in the articulata we see the
body divided into a series of segments
bearing external appendages; and in flower
ing plants we see a series of successive
spiral whorls of leaves. An indefinite repe
tition of the same part or organ is the
common characteristic (as Owen has
observed) of all low or little modified
forms ; therefore, we may readily believe
that the unknown progenitor of the verte-,
brata possessed many vertebrae; the un
known progenitor of the articulata, many
segments ; and the unknown progenitor of
flowering plants, many spiral whorls of
leaves. We have formerly seen that parts
many times repeated are eminently liable
to vary in number and structure; conse
quently, it is quite probable that natural
selection, during a long-continued course
of modification, should have seized on a
certain number of the primordially similar
elements, many times repeated, and have
adapted them to the most diverse purposes.
And as the whole amount of modification
will have been effected by slight successive
steps, we need, not wonder at discovering
175
in such parts or organs a certain degree of
fundamental resemblance, retained by the
strong principle of inheritance.
In the great class of molluscs, though we
can homologise the parts of one species
with those of other and distinct species, we
can indicate but few serial homologies;
that is, we are seldom enabled to say that
one part or organ is homologous with
another in the same individual. And we
can understand this fact; for in molluscs,
even in the lowest members of the class,
we do not find nearly so much indefinite
repetition of any one part as we find in the
other great classes of the animal and vege
table kingdoms.
Naturalists frequently speak of the skull
as formed of metamorphosed vertebrae ; the
jaws of crabs as metamorphosed legs ; the
stamens and pistils of flowers as metamor
phosed leaves ; but it would in these cases
probably be more correct, as Professor
Huxley has remarked, to speak of both
skull and vertebrae, both jaws and legs,
etc., as having been metamorphosed, not
one from the other, but from some common
element. Naturalists, however, use such
language only in a metaphorical sense :
they are far from meaning that, during a
long course of descent, primordial organs
of any kind—vertebrae in the one case
and legs in the other—have actually been
modified into skulls or jaws. Yet so strong
is the appearance of a modification of this
nature having occurred that naturalists can
hardly avoid employing language having
this plain signification. On my view these
terms may be used literally; and the
wonderful fact of the jaws, for instance, of
a crab retaining numerous characters, which
they would probably have retained through
inheritance if they had really been meta
morphosed during a long course of descent
from true legs, or from some simple appen
dage, is explained.
Embryology.—It has already been cas
ually remarked that certain organs in the
individual which, when mature, become
widely different, and serve for different
purposes, are in the embryo exactly alike.
The embryos, also, of distinct animals
within the same class are often strikingly
similar: a better proof of this cannot be
given than a circumstance mentioned by
Agassiz—namely, that, having forgotten to
ticket the embryo of some vertebrate animal,
he cannot now tell whether it be that of a
mammal, bird, or reptile. The vermiform
larvae of moths, flies, beetles, etc., resemble
�176
ON THE ORIGIN OF SPECIES
each other much more closely than do the
mature insects ; but in the case of larvae
the embryos are active, and have been
adapted for special lines of life. A trace
of the law of embryonic resemblance some
times lasts till a rather late age : thus birds
of the same genus and of closely-allied
genera often resemble each other in their
first and second plumage ; as we see in the
spotted feathers in the thrush group. In
the cat tribe most of the species are
striped or spotted in lines, and stripes can
be plainly distinguished in the whelp of
the lion. We occasionally, though rarely,
see something of this kind in plants : thus
the embryonic leaves of the ulex or furze
and the first leaves of the phyllodineous
acaceas are pinnate or divided like the
ordinary leaves of the leguminosae.
The points of structure in which the
embryos of widely-different animals of the
same class resemble each other often have
no direct relation to their conditions of
existence. We cannot,for instance, suppose
that in the embryos of the vertebrata the
peculiar loop-like course of the arteries
near the branchial slits are related to
similar conditions—in the young mammal
which is nourished in the womb of its
mother, in the egg of the bird which is
hatched in a nest, and in the spawn of a
frog under water. We have no more
reason to believe in such a relation than
we have to believe that the same bones in
the hand of a man, wing of a bat, and fin
of a porpoise are related to similar con
ditions of life. No one will suppose that
the stripes on the whelp of a lion, or the
spots on the young blackbird, are of any
use to these animals, or are related to the
conditions to which they are exposed.
The case, however, is different when an
animal during any part of its embryonic
career is active, and has to provide for
itself. The period of activity may come
on earlier or later in life ; but, whenever it
comes on, the adaptation of the larva to
its conditions of life is just as perfect and
as beautiful as in the adult animal. From
such special adaptations the similarity of
the larvae or active embryos of allied
animals is sometimes much obscured ; and
cases could be given of the larvae of two
species, or of two groups of species, differing
quite as much, or even more, from each
other than do their adult parents. In most
cases, however, the larvae, though active,
still obey, more or less closely, the law of
common embryonic resemblance. Cirripedes afford a good instance of this : even
the illustrious Cuvier did not perceive that
a barnacle was, as it certainly is, a crusta
cean ; but a glance at the larva shows this
to be the case in an unmistakeable manner.
So, again, the two main divisions of cirri
pedes, the pedunculated and sessile, which
differ widely in external appearance, have
larvae in all their stages barely distinguish
able.
The embryo in the course of develop
ment generally rises in organisation. I use
this expression, though I am aware that it
is hardly possible to define clearly what is
meant by the organisation being higher or
lower. But no one probably will dispute
that the butterfly is higher than the cater
pillar. In some cases, however, the mature
animal is generally considered as lower in
the scale than the larva, as with certain
parasitic crustaceans. To refer once again
to cirripedes : the larvae in the first stage
have three pairs of legs, a very simple
single eye, and a probosciformed mouth,
with which they feed largely, for they
increase much in size. In the second
stage, answering to the chrysalis stage of
butterflies, they have six pairs of beauti
fully constructed natatory legs, a pair of
magnificent compound eyes, and extremely
complex antennae ; but they have a closed
and imperfect mouth, aud cannot feed:
their function at this stage is to search by
their well-developed organs of sense, and
to reach by their active powers of swimming
a proper place on which to become attached
and to undergo their final metamorphosis.
When this is completed they are fixed for
life : their legs are now converted into
prehensile organs; they again obtain a
well-constructed mouth ; but they have no
antennae, and their two eyes are now recon
verted into a minute, single, and very simple
eye-spot. In this last and complete state
cirripedes may be considered as either
more highly or more lowly organised than
they were in the larval condition. But in
some genera the larvae become developed
either into hermaphrodites having the
ordinary structure, or into what I have
called complemental males; and in the
latter the development has assuredly been
retrograde, for the male is a mere sack,
which lives for a short time, and is destitute
of mouth, stomach, or other organ of im
portance, excepting for reproduction.
We are so much accustomed to see dif
ferences in structure between the embryo
and the adult, and likewise a close similarity
in the embryos of widely-different animals
within the same class, that we might be led
�EMBRYOLOGY
177
will be tall or short, or what its precise
to look at these facts as necessarily continfeatures will be. The question is not at
gent in some manner on growth. But there
what period of life any variation has been
is no obvious reason why, for instance, the
caused, but at what period it is fully dis
wing of a bat, or the fin of a porpoise,
played. The cause may have acted, and I
ghchlld not have been sketched out with all
believe generally has acted, even before the
the parts in proper proportion as soon as
embryo is formed; and the variation may
any structure became visible in the embryo.
be due to the male and female sexual
And ill some whole groups of animals and
elements having been affected by the con
in certain members of other groups the
ditions to which either parent or their
embryo does not at any period differ widely
ancestors have been exposed. Neverthe
from the adult. Thus Owen has remarked
less, an effect thus caused at a very early
in regard to cuttle-fish: “There is no meta
period, even before the formation of the
morphosis ; the cephalopodic character is
embryo, may appear late in life; as when
manifested long before the parts of the
an hereditary disease, which appears in old
embryo are completed”; and again in
age alone, has been communicated to the
spiders: “There is nothing worthy to be
called a metamorphosis.” The larvae of offspring from the reproductive element of
one parent. Or, again, as when the horns
insects, whether adapted to the most diverse
of cross-bred cattle have been affected by
and active habits, or quite inactive, being
the shape of the horns of either parent.
fed by their parents or placed in the midst
For the welfare of a very young animal, as
of proper nutriment, yet nearly all pass
through a similar worm-like stage of de
long as it remains in its mother’s womb, or
velopment ; but in some few cases, as in
in the egg, or as long as it is nourished and
that of Aphis, if we look to the admirable
protected by its parent, it must be quite
drawings by Professor Huxley of the de
unimportant whether most of its characters
velopment of this insect, we see no trace of are fully acquired a little earlier or later in
life. It would not signify, for instance, to a
the vermiform stage.
How, then, can we explain these several
bird which obtained its food best by having
a long beak whether or not it assumed a
facts in embryology—-namely, the very
beak of this particular length, as long as it
general, but not universal, difference in
structure between the embryo and the
was fed by its parents. Hence, I conclude
that it is quite possible that each of the
adult; of parts in the same individual
many successive modifications by which
embryo, which ultimately became very un
each species has acquired its present
like and serve for diverse purposes, being
at this early period of growth alike; of i structure may have supervened at a not
very early period of life; and some direct
embryos of different species within the
evidence fromourdomesticanimals supports
same class generally, but not universally,
resembling each other; of the structure of this view. But in other cases it is quite
the embryo not being closely related to its
possible that each successive modification,
conditions of existence, except when the or most of them, may have appeared at an
embryo becomes at any period of life active
extremely early period.
and has to provide for itself; of the embryo
I have stated in the first chapter that
apparently having sometimes a higher
there is some evidence to render it probable
organisation than the mature animal into
that, at whatever age any variation first
which it is developed ? I believe that all
appears in the parent, it tends to reappear
these facts can be explained, as follows, on
at a corresponding age in the offspring.
the view of descent with modification.
Certain variations can only appear at cor
It is commonly assumed, perhaps from
responding ages—for instance, peculiarities
monstrosities often affecting the embryos
in the caterpillar, cocoon, or imago states
at a very early period, that slight variations
of the silk-moth; or, again, in the horns of
necessarily appear at an equally early
almost full-grown cattle. But, further than
period. But we have little evidence on
this, variations which, for all that we can
filis head—indeed, the evidence rather
see, might have appeared earlier in life
points the other way; for it is notorious that
tend to appear at a corresponding age in
breeders of cattle, horses, and various fancy
the offspring and parent. I am far from
animals cannot positively tell, until some
meaning that this is invariably the case ;
fee after the animal has been born, what
and I could give a good many cases of
its merits or form will ultimately turn out.
variations (taking the word in the largest
We see this plainly in our own children :
sense) which have supervened at an earlier
W cannot always tell whether the child
age in the child than in the parent.
N
�i78
ON THE ORIGIN OF SPECIES
These two principles, if their truth be
admitted, will, I believe, explain all the
above specified leading facts in embryology.
But first let us look at a few analogous
cases in domestic varieties. Some authors
who have written on Dogs maintain that
the greyhound and bull-dog, though appear
ing so different, are really varieties most
closely allied, and have probably descended
from the same wild stock ; hence, I was
curious to see how far their puppies differed
from each other: I was told by breeders
that they differed just as much as their
parents, and this, judging by the eye,
seemed almost to be the case; but, on
actually measuring the old dogs and their
six-days old puppies, I found that the
puppies had not nearly acquired their full
amount of proportional difference. So,
again, I was told that the foals of cart
and race horses differed as much as the
full-grown animals ; and this surprised me
greatly, as I think it probable that the
difference between these two breeds has
been wholly caused by selection under
domestication; but, having had careful
measurements made of the dam and of a
three-days old colt of a race and heavy
cart-horse, I find that the colts have by no
means acquired their full amount of pro
portional difference.
As the evidence appears to me conclusive
that the several domestic breeds of Pigeon
have descended from one wild species, I
compared young pigeons of various breeds
within twelve hours after being hatched; I
carefully measured the proportions (but
will not here give details) of the beak,
width of mouth, length of nostril and of
eyelid, size of feet and length of leg, in the
wild stock, in pouters, fantails, runts, barbs,
dragons, carriers, and tumblers. Now, some
of these birds, when mature, differ so extra
ordinarily in length and form of beak that
they would, I cannot doubt, be ranked in
distinct genera had they been natural pro
ductions. But when the nestling birds of
these several breeds were placed in a row,
though most of them could be distinguished
from each other, yet their proportional
differences in the above specified several
points were incomparably less than in the
full-grown birds.
Some characteristic
points of difference—for instance, that of
the width of mouth — could hardly be
detected in the young. But there was one
remarkable exception to this rule, for the
young of the short-faced tumbler differed
from the young of the wild rock-pigeon and
of the other breeds, in all its proportions,
almost exactly as much as in the adult
state.
The two principles above given seem to
me to explain these facts in regard to the
latter _ embryonic stages of our domestic
varieties. Fanciers select their horses, dogs,
and pigeons, for breeding, when they are
nearly grown up : they are indifferent
whether the desired qualities and structures
have been acquired earlier or later in life
if the full-grown animal possess them. And
the cases just given, more especially that of
pigeons, seem to show that the character
istic differences which give value to each
breed, and which have been accumulated
by man’s selection, have not generally first
appeared at an early period of life, and have
been inherited by the offspring at a corres
ponding not early period. But the case of
the short-faced tumbler, which, when twelve
hours old, had acquired its proper propor
tions, proves that this is not the universal
rule ; for here the characteristic differences
must either have appeared at an earlier
period than usual, or, if not so, the diffe
rences must have been inherited, not at the
corresponding, but at an earlier age.
Now, let us apply these facts, and the
above two principles—which latter, though
not proved true, can be shown to be in
some degree probable—to species in a state
of nature. Let us take a genus of birds,
descended on my theory from some one
parent-species, and of which the several
new species have become modified through
natural selection in accordance with their
diverse habits. Then, from the many slight
successive steps of variation having super
vened at a rather late age, and having been
inherited at a corresponding age, the young
of the new species of our supposed genus
will manifestly tend to resemble each other
much more closely than do the adults, just
as we have seen in the case of pigeons.
We may extend this view to whole families,
or even classes. The fore-limbs, for instance,
which served as legs in the parent-species
may have become, by a long course of
modification, adapted in one descendant to
act as hands, in another as paddles, in
another as wings ; and on the above two
principles—namely, of each successive modi
fication supervening at a rather late age, and
being inherited at a corresponding late age—
the fore-limbs in the embryos of the several
descendants of the parent-species will still
resemble each other closely, for they will
not have been modified. But in each of
our new species the embryonic fore-limbs
will differ greatly from the fore-limbs in the
�EMBRYOLOGY
mature animal; the limbs in the latter
having undergone much modification at a
rather late period of life, and having thus
been converted into hands, or paddles, or
wings. Whatever influence long-continued
exercise or use on the one hand, and disuse
on the other, may have in modifying an
organ, such influence will mainly affect the
mature animal, which has come to its full
powers of activity and has to gain its own
living ; and the effects thus produced will
be inherited at a corresponding mature age.
Whereas the young will remain unmodified,
or be modified in a lesser degree, by the
effects of use and disuse.
In certain cases the successive steps of
variation might supervene, from causes of
which we are wholly ignorant, at a very
early period of life, or each step might be
inherited at an earlier period than that at
which it first appeared. In either case (as
with the short-faced tumbler) the young or
embryo would closely resemble the mature
parent-form. We have seen that this is the
rule of development in certain whole groups
of animals, as with cuttle-fish and spiders,
and with a few members of the great class
of insects, as with Aphis. With respect to
the final cause of the young in these cases
not undergoing any metamorphosis, or
closely resembling their parents from their
earliest age, we can see that this would
result from the two following contingencies :
firstly, from the young, during a course of
modification carried on for many genera
tions, having to provide for their own wants
at a very early stage of development; and,
secondly, from their following exactly the
same habits of life with their parents, for
in this case, it would be indispensable, for
the existence of the species, that the child
should be modified at a very early age in
the same manner with its parents, in accor
dance with their similar habits.
Some
further explanation, however, of the embryo
not undergoing any metamorphosis is
perhaps requisite. If, on the other hand,
it profited the young to follow habits of life
in any degree different from those of their
parent, and consequently to be constructed
in a slightly different manner, then, on the
principle of inheritance at corresponding
ages, the active young or larvae might easily
be rendered by natural selection different
to any conceivable extent from their parents.
Such differences might also become cor
related with successive stages of develop
ment ; so that the larvae, in the first stage,
might differ greatly from the larvae in the
second stage, as we have seen to be the case
179
with cirripedes. The adult might become
fitted for sites or habits in which organs of
locomotion or of the senses, etc., would be
useless ; and in this case the final metamor
phosis would be said to be retrograde.
As all the organic beings, extinct and
recent, which have ever lived on this earth
have to be classed together, and as all have
been connected by the finest gradations,
the best, or indeed, if our collections were
nearly perfect, the only possible, arrange
ment would be genealogical: descent
being on my view the hidden bond of con
nection which naturalists have been seeking
under the term of the natural system. On
this view we can understand how it is that,
in the eyes of most naturalists, the structure
of the embryo is even more important for
classification than that of the adult. For
the embryo is the animal in its less modified
state, and in so far it reveals the structure
of its progenitor. In two groups of animals,
however much they may at present differ
from each other in structure and habits, if
they pass through the same or similar
embryonic stages, we may feel assured that
they have both descended from the same
or nearly similar parents, and are therefore
in that degree closely related. Thus com
munity in embryonic structure reveals com
munity of descent.
It will reveal this
community of descent, however much the
structure of the adult may have been modi
fied and obscured. We have seen, for
instance, that cirripedes can at once be
recognised by their larvae as belonging to
the great class of crustaceans. As the
embryonic state of each species and group
of species partially shows us the structure
of their less modified ancient progenitors,
we can scarcely see why ancient and extinct
forms of life should resemble the embryos
of their descendants—our existing species.
Agassiz believes this to be a law of nature;
but I am bound to confess that I only hope
to see the law hereafter proved true. It
can be proved true in those cases alone in
which the ancient state, now supposed to
be represented in existing embryos, has not
been obliterated, either by the successive
variations in a long course of modification
having supervened at a very early age, or
by the variations having been inherited at
an earlier period than that at which they
first appeared. It should also be borne in
mind that the supposed law of resemblance
of ancient forms of life to the embryonic
stages of recent forms may be true, but yet,
owing to the geological record not extend
ing far enough back in time, may remain
�i8o
ON THE ORIGIN OF SPECIES
for a long period, or for ever, incapable of
demonstration.
Thus, as it seems to me, the leading
facts in embryology, which are second in
importance to none in natural history, are
explained on the principle of slight modifi
cations not appearing, in the many descen
dants from one ancient progenitor, at a very
early period in the life of each, though per
haps caused at the earliest, and being in
herited at a corresponding not early period.
Embryology rises greatly in interest when
we thus look at the embryo as a picture,
more or less obscured, of the common
parent-form of each great class of animals.
Rudimentary, atrophied, or aborted
Organs.—Organs or parts in this strange
condition, bearing the stamp of inutility,
are extremely common throughout nature.
For instance, rudimentary mamma: are
very general in the males of mammals : I
presume that the “ bastard-wing ” in birds
may be safely considered as a digit in a
rudimentary state: in very many snakes one
lobe of the lungs is rudimentary ; in other
snakes there are rudiments of the pelvis
and hind limbs. Some of the cases of
rudimentary organs are extremely curious ;
for instance, the presence of teeth in fcetal
whales, which, when grown up, have not a
tooth in their heads ; and the presence of
teeth, which never cut through the gums,
in the upper jaws of our unborn calves.
It has even been stated on good authority
that rudiments of teeth can be detected
in the beaks of certain embryonic birds.
Nothing can be plainer than that wings are
formed for flight, yet in how many insects
do we see wings so reduced in size as to
be utterly incapable of flight, and not rarely
lying under wing-cases, firmly soldered
together 1
The meaning of rudimentary organs is
often quite unmistakeable ; for instance,
there are beetles of the same genus (and
even of the same species) resembling each
other most closely in all respects, one of
which will have full-sized wings, and
another mere rudiments of membrane ;
and here it is impossible to doubt that the
rudiments represent wings. Rudimentary
organs sometimes retain their potentiality,
and are merely not developed : this seems
to be the case with the mammae of male
mammals, for many instances are on record
of these organs having become well
developed in full-grown fnales, and having
secreted milk. So, again, there are normally
four developed and two rudimentary teats
in the udders of the genus Bos, but in our
domestic cows the two sometimes become
developed and give milk. In plants of the
same species the petals sometimes occur
as mere rudiments, and sometimes in a
well-developed state. In plants with sepa
rated sexes the male flowers often have a
rudiment of a pistil; and Kolreuter found
that, by crossing such male plants with an
hermaphrodite species, the rudiment of the
pistil in the hybrid offspring was much
increased in size ; and this shows that the
rudiment and the perfect pistil are essen
tially alike in nature.
An organ serving for two purposes may
become rudimentary or utterly aborted for
one, even the more important purpose, and
remain perfectly efficient for the other.
Thus in plants the office of the pistil is to
allow the pollen-tubes to reach the ovules
protected in the ovarium at its base. The
pistil consists of a stigma supported on the
style ; but in some Compositas the male
florets, which, of course, cannot be fecun
dated, have a pistil which is in a rudi
mentary state, for it is not crowned with
a stigma ; but the style remains well
developed, and is clothed with hairs as in
other Composite, for the purpose of brushing
the pollen out of the surrounding anthers.
Again, an organ may become rudimentary
for its proper purpose, and be used for a
distinct object: in certain fish the swim
bladder seems to be nearly rudimentary for
its proper function of giving buoyancy,
but has become converted into a nascent
breathing organ or lung. Other similar
instances could be given.
Organs, however little developed, if of
use, should not be called rudimentary; they
cannot properly be said to be in an atro
phied condition; they may be called
nascent, and may hereafter be developed
to any extent by natural selection. Rudi
mentary organs, on the other hand, are
essentially useless, as teeth which never cut
through the gums; in a still less developed
condition, they would be of still less use.
They cannot, therefore, under their present
condition, have been formed by natural
selection, which acts solely by the preserva
tion of useful modifications; they have been
retained, as we shall see, by inheritance,
and relate to a former condition of their
possessor. It is difficult to know what are
nascent organs ; looking to the future, we
cannot of course tell how any part will be
developed, and whether it is now nascent;
looking to the past, creatures with an organ
in a nascent condition will generally have
�RUDIMENTARY ORGANS
been supplanted and exterminated by their
successors with the organ in a more perfect
and developed condition. The wing of the
penguin is of high service, and acts as a fin;
it may, therefore, represent the nascent
state of the wings of birds ; not that I
believe this to be the case—it is more prob
ably a reduced organ, modified for a new
function: the wing of the Apteryx is useless,
and is truly rudimentary. The mammary
glands of the Ornithorhynchus may, per
haps, be considered, in comparison with
the udder of a cow, as in a nascent state.
The ovigerous frena of certain cirripedes,
which are only slightly developed and which
have ceased to give attachment to the ova,
are nascent branchiae.
Rudimentary organs in the individuals of
the same species are very liable to vary in
degree of development and in other respects.
Moreover, in closely-allied species the
degree to which the same organ has been
rendered rudimentary occasionally differs
much. This latter fact is well exemplified
in the state of the wings of the female
moths in certain groups. Rudimentary
* organs may be utterly aborted ; and this
implies that we find in an animal or plant
no trace of an organ which analogy would
lead us to expect to find, and which is
occasionally found in monstrous individuals
of the species. Thus in the snapdragon
(antirrhinum) we generally do not find a
rudiment of a fifth stamen ; but this may
sometimes be seen. In tracing the homo
logies of the same part in different members
of a class, nothing is more common or more
necessary than the use and discovery of
rudiments. This is well shown in the
drawings given by Owen of the bones of
the leg of the horse, ox, and rhinoceros.
It is an important fact that rudimentary
organs, such as teeth in the upper jaws of
whales and ruminants, can often be detected
in the embryo, but afterwards wholly dis
appear. It is also, I believe, a universal
rule that a rudimentary part or organ is of
greater size relatively to the adjoining parts
in the embryo than in the adult ; so that
the organ at this early age is less rudi
mentary, or even cannot be said to be in
any degree rudimentary. Hence, also, a
rudimentary organ in the adult is often
said to have retained its embryonic con
dition.
I have now given the leading facts with
respect to rudimentary organs. In reflect
ing on them, everyone must be struck with
astonishment; forthe same reasoning power
which tells us plainly that most parts a>nd
181
organs are exquisitely adapted for certain
purposes, tells us with equal plainness
that these rudimentary or atrophied organs
are imperfect and useless. In works on
natural history rudimentary organs are
generally said to have been created “ for
the sake of symmetry,” or in order “ to
complete the scheme of nature”; but this
seems to me no explanation—merely a re
statement of the fact. Would it be thought
sufficient to say that, because planets
revolve in elliptic courses round the sun,
satellites follow the same course round the
planets, for the sake of symmetry, and to
complete the scheme of nature ? An
eminent physiologist accounts for the pre
sence of rudimentary organs by supposing
that they serve to excrete matter in excess,
or injurious to the system ; but can we
suppose that the minute papilla, which often
represents the pistil in male flowers, and
which is formed merely of cellular tissue,
can thus act ? Can we suppose that the
formation of rudimentary teeth, which are
subsequently absorbed, can be of any service
to the rapidly-growing embryonic calf by
the excretion of precious phosphate of lime?
When a man’s fingers have been amputated,
imperfect nails sometimes appear on the
stumps : I could as soon believe that these
vestiges of nails have appeared, not from
unknown laws of growth, but in order to
excrete horny matter, as that the rudimen
tary nails on the fin of the manatee were
formed for this purpose.
On my view of descent with modification,
the origin of rudimentary organs is simple.
We have plenty of cases of rudimentary
organs in our domestic productions—as the
stump of a tail in tailless breeds, the vestige
of an ear in earless breeds, the reappear
ance of minute dangling horns in hornless
breeds of cattle (more especially, according
to Youatt, in young animals), and the state
of the whole flower in the cauliflower. We
often see rudiments of various parts in
monsters. But I doubt whether any of
these cases throw light on the origin of
rudimentary organs in a state of nature
further than by showing that rudiments can
be produced; for I doubt whether species
under nature ever undergo abrupt changes.
I believe that disuse has been the main
agency; that it has led in successive
generations to the gradual reduction of
various organs until they have become
rudimentary—as in the case of the eyes of
animals inhabiting dark caverns, and of
the wings of birds inhabiting oceanic
islands, which have seldom been forced to
�182
ON THE ORIGIN OF SPECIES
take flight, and have ultimately lost the
power of flying. Again, an organ useful
under certain conditions might become
injurious under others, as with the wings
of beetles living on small and exposed
islands; and in this case natural selection
would continue slowly to reduce the organ
until it was rendered harmless and rudi
mentary.
Any change in function which can be
effected by insensibly smali steps is within
the power of natural selection ; so that an
organ rendered, during changed habits of
life, useless or injurious for one purpose
might be modified and used for another
purpose. Or an organ might be retained
for one alone of its former functions. An
organ, when rendered useless, may well
be variable, for its variations cannot be
checked by natural selection. At whatever
period of life disuse or selection reduces an
organ, and this will generally be when the
being has come to maturity and to its full
powers of action, the principle of inherit
ance at corresponding ages will reproduce
the organ in its reduced state at the same
age, and, consequently, will seldom affect
or reduce it in the embryo. Thus we can
understand the greater relative size of
rudimentary organs in the embryo and
their lesser relative size in the adult. But
if each step of the process of reduction were
to be inherited, not at the corresponding
age, but at an extremely early period of
life (as we have good reason to believe to
be possible), the rudimentary part would
tend to be wholly lost, and we should have
a case of complete abortion. The prin
ciple also of economy, explained in a
former chapter, by which the materials
forming any part or structure, if not useful
to the possessor, will be saved as far as is
possible, will probably often come into
play ; and this will tend to cause the entire
obliteration of a rudimentary organ.
As the presence of rudimentary organs
is thus due to the tendency in every part of
the organisation, which has long existed,
to be inherited, we can understand, on the
genealogical view of classification, how it
is that systematists have found rudimentary
parts as useful as, or even sometimes more
useful than, parts of high physiological
importance. Rudimentary organs may be
compared with the letters in a word, still
retained in the.spelling, but become useless
in the pronunciation, but which serve as a
clue in seeking for its derivation. On the
view of descent with modification, we may
conclude that the existence of organs in a
rudimentary, imperfect, and useless con
dition, or quite aborted, far from presenting
a strange difficulty, as they assuredly do
on the ordinary doctrine of creation, might
even have been anticipated, and can be
accounted for by the laws of inheritance.
Summary.—In this chapter I have
attempted to show that the subordination
of group to group in all organisms through
out all time; that the nature of the rela
tionship by which all living and extinct
beings are united by complex, radiating,
and circuitous lines of affinities into one
grand system; the rules followed and the
difficulties encountered by naturalists in
their classifications ; the value set upon
characters, if constant and prevalent,
whether of high vital importance or of
the most trifling importance, or, as in rudi
mentary organs, of no importance ; the
wide opposition in value between analogical
or adaptive characters and characters of
true affinity ; and other such rules—all
naturally follow on the view of the common
parentage of those forms which are con
sidered by naturalists as allied, together*
with their modification through natural
selection, with its contingencies of extinc
tion and divergence of character. In con
sidering this view of classification, it should
be borne in mind that the element of
descent has been universally used in ranking
together the sexes, ages, and acknowledged
varieties of the same species, however
different they may be in structure. If we
extend the use of this element of descent
-—the only certainly known cause of simi
larity in organic beings—we shall under
stand what is meant by the natural system :
it is genealogical in its attempted arrange
ment, with the grades of acquired difference
marked by the terms varieties, species,
genera, families, orders, and classes.
On this same view of descent with modi
fication, all the great facts in Morphology
become intelligible—whether we look to the
same pattern displayed in the homologous
organs, to whatever purpose applied, of the
different species of a class, or to the homo
logous parts constructed on the same
pattern in each individual animal and
plant.
On the principle of successive slight
variations, not necessarily or generally
supervening at a very early period of life,
and being inherited at a corresponding
period, we can understand the great leading
facts in Embryology ; namely, the resem
blance in an individual embryo of the
�RECAPITULATION AND CONCLUSION
homologous parts, which, when matured,
will become widely different from each
other in structure and function ; and the
resemblance in different species of a class
of the homologous parts or organs, though
fitted in the adult members for purposes, as
different as possible. Larva; are active
embryos, which have become specially
modified in relation to their habits of life,
through the principle of modifications being
specially inherited at corresponding ages.
On this same principle—and bearing, in
mind that, when organs are reduced in size,
either from disuse or selection, it will
generally be at that period of life when the
being has to provide for its own wants, and
bearing in mind how strong is the principle
of inheritance—the occurrence of rudimen
tary organs and their final abortion present
183
to us no inexplicable difficulties ; on the
contrary, their presence might have been
even anticipated. The importance of em
bryological characters and of rudimentary
organs in classification is intelligible, on the
view that an arrangement is only so far
natural as it is genealogical.
Finally, the several classes of facts which
have been considered in this chapter seem
to me to proclaim so plainly that the innu
merable species, genera, and families «of
organic beings with which this world is
peopled, have all descended, each within
its own class or group, from common
parents, and have all been modified in the
course of descent, that I should without
hesitation adopt this view, even if it were
unsupported by other facts or arguments.
Chapter XIV.
RECAPITULATION AND CONCLUSION
Recapitulation of the difficulties on the theory of
Natural Selection — Recapitulation of the
general and special circumstances in its favour
—Causes of the general belief in the immut
ability of species—-How far the theory of
natural selection may be extended—Effects of
its adoption on the study of natural history—
Concluding remarks.
As this whole volume is one long argument,
it may be convenient to the reader to have
the leading facts and inferences briefly re
capitulated.
That many and serious objections may be
advanced against the theory of descent with
modification through natural selection I do
not deny. I have endeavoured to give them
their full force. Nothing at first can appear
more difficult to believe than that the more
complex organs and instincts should have
been perfected, not by means superior to,
though analogous with, human reason, but
by the accumulation of innumerable slight
variations, each good for the individual
possessor.
Nevertheless, this difficulty,
though appearing to our imagination in
superably great, cannot be considered real
if we admit the following propositions—
namely, that gradations in the perfection
of any organ or instinct which we may con
sider either do now exist or could have
existed, each good of its kind; that all
organs and instincts are, in ever so slight
a degree, variable; and, lastly, that there is
a struggle for existence leading to the pre
servation of each profitable deviation of
structure or instinct. The truth of these
propositions cannot, I think, be disputed.
It is, no doubt, extremely difficult even to
conjecture by what gradations many struc
tures have been perfected, more especially
among broken and failing groups of
organic beings; but we see so many strange
gradations in nature that we ought to be
extremely cautious in saying that any organ
or instinct, or any whole being, could not
have arrived at its present state by many
graduated steps. There are, it must be
admitted, cases of special difficulty on the
theory of natural selection; and one of the
most curious of these is the existence of two
or three defined castes of workers or sterile
females in the same community of ants ;
but I have attempted to show how this diffi
culty can be mastered.
With respect to the almost universal
sterility of species when first crossed, which
�184
ON THE ORIGIN OF SPECIES
forms so remarkable a contrast with the
almost universal fertility of varieties when
crossed, I must refer the reader to the re
capitulation of the facts given at the end of
the eighth chapter, which seem to me con
clusively to show that this sterility is no
more a special endowment than is the in
capacity of two trees to be grafted together;
but that it is incidental on constitutional
differences in the reproductive systems of
the intercrossed species. We see the truth
of this conclusion in the vast difference in
the result, when the same two species are
crossed reciprocally—that is, when one
species is first used as the father and then
as the mother.
The fertility of varieties when intercrossed
and of their mongrel offspring cannot be
considered as universal; nor is their very
general fertility surprising when we re
member that it is not likely that either their
constitutions or their reproductive systems
should have been profoundly modified.
Moreover, most of the varieties which have
been experimentised on have been pro
duced under domestication ;■ and as domesti
cation (I do not mean mere confinement)
apparently tends to eliminate sterility, we
ought not to expect it also to produce
sterility.
The sterility of hybrids is a very different
case from that of first crosses, for their repro
ductive organs are more or less functionally
impotent; whereas in first crosses the organs
on both sides are in a perfect condition.
As we continually see that organisms of all
kinds are rendered in some degree sterile
from their constitutions having been dis
turbed by slightly different and new con
ditions of life, we need not feel surprised at
hybrids being in some degree sterile, for
their constitutions can hardly fail to have
been disturbed from being compounded of
two distinct organisations. This parallelism
is supported by another parallel, but directly
opposite, class of facts—-namely, that the
vigour and fertility of all organic beings
are increased by slight changes in their
conditions of life, and that the offspring of
slightly modified forms or varieties acquire,
from being crossed, increased vigour and
fertility. So that, on the one hand, con
siderable changes in the conditions of life
and crosses between greatly modified
forms lessen fertility; and, on the other
hand, lesser changes in the conditions of
life and crosses between less modified
forms increase fertility.
Turning to geographical distribution, the
difficulties encountered on the theory of
descent with modification are grave enough.
All the individuals of the same species,
and all the species of the same genus, or
even higher group, must have descended
from common parents; and therefore, in
however distant and isolated parts of the
world they are now found, they must, in
the course of successive generations, have
passed from some one part to the others.
We are often wholly unable even to con
jecture how this could have been effected.
Yet, as we have reason to believe that some
species have retained the same specific
form for very long periods, enormously
long as measured by years, too much stress
ought not to be laid on the occasional wide
diffusion of the same species; for during
very long periods of time there will always
have been a good chance for wide migration
by many means. A broken or interrupted
range may often be accounted for by the
extinction of the species in the intermediate
regions. It cannot be denied that we are
as yet very ignorant of the full extent of the
various climatal and geographical changes
which have affected the earth during modern
periods ; and such changes will obviously
have greatly facilitated migration. As an
example, I have attempted to show how
potent has been the influence of the Glacial
period on the distribution both of the same
and of representative species throughout the
world. We are as yet profoundly ignorant
of the many occasional means of transport.
With respect to distinct species of the same
genus inhabiting very distant and isolated
regions, as the process of modification has
necessarily been slow, all the means of
migration will have been possible during a
very long period ; and, consequently, the
difficulty of the wide diffusion of species *
of the same genus is in some degree
lessened.
As on the theory of natural selection an
interminable number of intermediate forms
must have existed, linking together all the
species in each group by gradations as fine
as our present varieties, it maybe asked,
Why do we not see these linking forms all
around us ? Why are not all organic beings
blended together in an inextricable chaos ?
With respect to existing forms, we should
remember that we have no right to expect
(excepting in rare cases) to discover directly
connecting-links between them, but only
between each and some extinct and sup
planted form. Even on a wide area, which
has during’ a long period remained con
tinuous, and of which the climate and other
conditions of life change insensibly in going
�RECAPITULATION AND CONCLUSION
from a district occupied by one species into
another district occupied by a closely-allied
species, we have no just right to expect
often to find intermediate varieties in the
intermediate zone. For we have reason to
believe that only a few species are under
going change at any one period; and all
changes are slowly effected. I have also
shown that the intermediate varieties which
will at first probably exist in the inter
mediate zones will be liable to be supplanted
by the allied forms on either hand ; and
the latter, from existing in greater numbers,
will generally be modified and improved at
aquickerrate than the intermediate varieties,
which exist in lesser numbers ; so that the
intermediate varieties will, i i the long run,
be supplanted and exterminated.
On this doctrine of the extermination of
an infinitude of connecting-links between
the living and extinct inhabitants of the
world, and at each successive period between
the extinct and still older species, why is
not every geological formation charg'ed
with such links? Why does not every collec
tion of fossil remains afford plain evidence
of the gradation and mutation of the forms
of life? We meet with no such evidence,
and this is the most obvious and forcible of
the many objections which may be urged
against my theory. Why, again, do whole
groups of allied species appear, though
certainly they often falsely appear, to have
come in suddenly on the several geological
stages ? Why do we not find great piles of
strata beneath the Silurian system stored
with the remains of the progenitors of the
Silurian groups of fossils? For certainly,
on my theory,'inch strata must somewhere
have been deposited at these ancient and
utterly unknown epochs in the world’s
history.
I can answer these questions and grave
objections only on the supposition that the
geological record is far more imperfect
than most geologists believe. It cannot be
objected that there has not been time suffi
cient for any amount of organic change,
for the lapse of time has been so great as to
be utterly inappreciable by the human
intellect. The number of specimens in all
our museums is absolutely as nothing com
pared with the countless generations of
countless species which certainly have
existed. We should not be able to recog
nise a species as the parent of any one or
more species, if we were to examine them
ever so closely, unless we likewise pos
sessed many of the intermediate links
between their past or parent and present
!85
states; and these many links we could
hardly ever expect to discover, owing to
the imperfection of the geological record.
Numerous existing doubtful forms could be
named which are probably varieties ; but
who will pretend that in future ages so
many fossil links will be discovered that
naturalists will be able to decide, on the
common view, whether or not these doubt
ful forms are varieties ? As long as most of
the links between any two species are un
known, if any one link or intermediate
variety be discovered, it will simply be
classed as another and distinct species.
Only a small portion of the world has been
geologically explored. Only organic beings
of certain classes can be preserved in a
fossil condition, at least in any great number.
Widely ranging species vary most, and
varieties are often at first local —- both
causes rendering the discovery of inter
mediate links less likely. Local varie
ties will not spread into other and distant
regions until they are considerably modified
and improved; and when they do spread,
if discovered in a geological formation, they
will appear as if suddenly created there, and
will be simply classed as new species.
Most formations have been intermittent in
their accumulation ; and their duration, I
am inclined to believe, has been shorter
than the average duration of specific forms.
Successive formations are separated from
each other by enormous blank intervals of
time; for fossiliferous formations, thick
enough to resist future degradation, can be
accumulated only where much sediment is
deposited on the subsiding bed of the sea.
During the alternate periods of elevation
and of stationary level the record will be
blank. During these latter periods there
will probably be more variability in the
forms of life; during periods of subsidence,
more extinction.
With respect to the absence of fossili
ferous formations beneath the lowest
Silurian strata, I can only recur to the
hypothesis given in the ninth chapter.
That the geological record is imperfect all
will admit; but that it is imperfect to the
degree which I require few will be inclined
to admit. If we look to long enough inter
vals of time, geology plainly declares that
all species have changed; and they have
changed in the manner which my theory
requires, for they have changed slowly and
in a graduated manner. We clearly see
this in the fossil remains from consecutive
formations invariably being much more
closely related to each other than are the
�186
ON THE ORIGIN OF SPECIES
fossils from formations distant from each
other in time.
Such is the sum of the several chief
objections and difficulties which may justly
be' urged against my theory; and I have
now briefly recapitulated the answers and
explanations which can be given to them.
I have felt these difficulties far too heavily
duri: g many years to doubt their weight.
But it deserves especial notice that the more
important objections relate to questions on
which we are confessedly ignorant; nor do
we know how ignorant we are. We do not
know all the possible transitional gradations
between the simplest and the most perfect
organs ; it cannot be pretended that we
know all the varied means of Distribution
during the long lapse of years, or that we
know how imperfect the Geological Record
is. Grave as these several difficulties are,
in my judgment they do not overthrow the
theory of descent from a few created forms
with subsequent modification.
Now, let us turn to the other side of the
argument. Under domestication we see
much variability. This seems to be mainly
due to the reproductive system being
eminently susceptible to changes in the
conditions of life; so that this system, when
not rendered impotent, fails to reproduce
offspring exactly like the parent-form.
Variability is governed by many complex
laws—by correlation of growth, by use and
disuse, and by the direct action of the
physical conditions of life. There is much
difficulty in ascertaining how much modifi
cation our domestic productions have under
gone ; but we may safely infer that the
amount has been large, and that modifi
cations can be inherited for long periods.
As long as the conditions of life remain the
same, we have reason to believe that a
modification which has already been in
herited for many generations may continue
to be inherited for an almost infinite number
of generations. On the other hand, we have
evidence that variability, when it has once
come into play, does not wholly cease ; for
new varieties are still occasionally pro
duced by our most anciently domesticated
productions.
Man does not actually produce vari
ability ; he only unintentionally exposes
organic beings to new conditions of life,
and then nature acts on the organisation,
and causes variability. But man can and
does select the variations given to him by
nature, and thus accumulate them in any
desired manner. He thus adapts animals
and plants for his own benefit or pleasure.
He may do this methodically, or he may
do it unconsciously by preserving the in
dividuals most useful to him at the time,
without any thought of altering the breed.
It is certain that he can largely influence
the character of a breed by selecting, in
each successive generation, individual dif
ferences so slight as to be quite inappreci
able by an uneducated eye. This process
of selection has been the great agency in
the production of the most distinct and
useful domestic breeds. That many of the
breeds produced by man have to a large
extent the character of natural species is
shown by the inextricable doubts whether
very many of them are varieties or aboriginal
species.
There is no obvious reason why the
principles which have acted so efficiently
under domestication should not have acted
under nature.
In the preservation of
favoured individuals and races, during the
constantly-recurrent Struggle for Existence,
we see the most powerful and ever-acting
means of selection. The struggle for exist
ence inevitably follows from the high geo
metrical ratio of increase which is common
to all organic beings. This high rate of
increase is proved by calculation—by the
rapid increase of many animals and plants
during a succession of peculiar seasons, or
when naturalised in a new country. More
individuals are born than can possibly
survive. A grain in the balance will deter
mine which individual shall live and which
shall die—which variety or species shall
increase in number, and which shall
decrease, or finally become extinct. As
the individuals of the same species come
in all respects into the closest competition
with each other, the struggle will generally
be most severe between them ; it will be
almost equally severe between the varieties
of the same species, and next in severity
between the species of the same genus.
But the struggle will often be very severe
between beings most remote in the scale of
nature. The slightest advantage in one
being, at any age or during any season,
over those with which it comes into com
petition, or better adaptation in however
slight a degree to the surrounding physical
conditions, will turn the balance.
With animals having separated sexes
there will in most cases be a struggle
between the males for possession of the
females. The most vigorous individuals,
or those which have most successfully
struggled with their conditions of life, will
�RECAPITULA TION AND CONCL USION
generally leave most progeny. But success
will often depend on having special weapons
or means of defence, or on the charms of
the males ; and the slightest advantage will
lead to victory.
As geology plainly proclaims that each
land has undergone great physical changes,
we might have expected that organic beings
would have varied under nature, in the
same way as they generally have varied
under the changed conditions of domesti
cation. And if there be any variability
under nature, it would be an unaccountable
fact if natural selection had not come into
play. It has often been asserted, but the
assertion is quite incapable of proof, that
the amount of variation under nature is a
strictly limited quantity. Man, though
acting on external characters alone and
often capriciously, can produce within a
short period a great result by adding up
mere individual differences in his domestic
productions; and everyone admits that
there are, at least, individual differences in
species under nature. But, besides such
differences, all naturalists have admitted
the existence of varieties, which they think
sufficiently distinct to be worthy of record
in systematic works. No one can draw
any clear distinction between individual
differences and slight varieties, or between
more plainly-marked varieties and sub
species and species. Let it be observed
how naturalists differ in the rank which
they assign to the many representative
forms in Europe and North America.
If, then, we have under nature variability
and a powerful agent always ready to act
and select, why should we doubt that varia
tions in any way useful to beings, under
their excessively complex relations of life,
would be preserved, accumulated, and
inherited ? Why, if man can by patience
select variations most useful to himself,
should nature fail in selecting variations
useful, under changing conditions of life,
to her living products ? What limit can be
put to this power, acting during long ages
and rigidly scrutinising the whole constitu
tion, structure, and habits of each creature
—favouring the good and rejecting the bad ?
I can see no limit to this power in slowly
and beautifully adapting each form to the
most complex relations of life. The theory
of natural selection, even if we looked no
further than this, seems to me to be in itself
probable. 1 have already recapitulated, as
fairly as I could, the opposed difficulties and
objections ; now let us turn to the special
facts and arguments in favour of the theory.
187
On the view that species are only strongly
marked and permanent varieties, and that
each species first existed as a variety, we
can see why it is that no line of demarca
tion can be drawn between species com
monly supposed to have been produced by
special acts of creation and varieties which
are acknowledged to have been produced
by secondary laws. On this same view, .we
can understand how it is that in each region
where many species of a genus have been
produced, and where they now flourish,
these same species should present many
varieties; for where the manufactory of
species has been active we might expect,
as a general rule, to find it still in action ;
and this is the case if varieties be incipient
species. Moreover, the species of the larger
genera which afford the greater number of
varieties or incipient species retain to a
certain degree the character of varieties;
for they differ from each other by a less
amount of difference than do the species of
smaller genera. The closely-allied species
also of the larger genera apparently have
restricted ranges, and in their affinities they
are clustered in little groups round other
species—in which respects they resemble
varieties. These are strange relations on
the view of each species having been in
dependently created, but are intelligible if
all species first existed as varieties.
As each species tends by its geometrical
ratio of reproduction to increase inordinately
in number; and as the modified descen
dants of each species will be enabled to
increase by so much the more as they
become diversified in habits and structure,
so as to be enabled to seize on many and
widely-different places in the economy of
nature, there will be a constant tendency
in natural selection to preserve the most
divergent offspring of any one species.
Hence, during a long-continued course of
modification, the slight differences, charac
teristic of varieties of the same species,
tend to be augmented into the greater
differences characteristic of species of the
same genus. New and improved varieties
will inevitably supplant and exterminate
the older, less improved, and intermediate
varieties ; and thus species are rendered to
a large extent defined and distinct objects.
Dominant species belonging to the larger
groups tend to give birth to new and
dominant forms ; so that each large group
tends to become still larger, and at the
same time more divergent in character.
But as all groups cannot thus succeed in
increasing in size, for the world would not
�188
ON THE ORIGIN OF SPECIES
hold them, the more dominant groups beat
the less dominant. This tendency in the
large groups to go on increasing in size and
diverging in character, together with the
almost inevitable contingency of much
extinction, explains the arrangement of all
the forms of life, in groups subordinate to
groups, all within a few great classes, which
we now see everywhere around us, and
which has prevailed throughout all time.
This grand fact of the grouping of all
organic beings seems to me utterly in
explicable on the theory of creation.
As natural selection acts solely by ac
cumulating slight, successive, favourable
variations, it can produce no great or sudden
modification ; it can act only by very short
and slow steps. Hence the canon of Natura
nonfacit saltum,which every fresh addition
to our knowledge tends to make truer, is, on
this theory simply intelligible. We can
plainly see why nature is prodigal in variety,
though niggard in innovation. But why
this should be a law of nature if each species
has been independently created, no man can
explain.
Many other facts are, as it seems to me,
explicable on this theory. How strange it
is that a bird, under the form of wood
pecker, should have been created to prey
on insects on the ground; that upland
geese, which never or rarely swim, should
have been created with webbed feet; that
a thrush should have been created to dive
and feed on sub-aquatic insects; and that
a petrel should have been created with
habits and structure fitting it for the life of
an auk or grebe; and so on in endless other
cases. But on the view of each species
constantly trying to increase in number,
with natural selection always ready to adapt
the slowly varying descendants of each to
any unoccupied or ill-occupied place in
nature, these facts cease to be strange, or
perhaps might even have been anticipated.
As natural selection acts by competition,
it adapts the inhabitants of each country
only in relation to the degree of perfection
of their associates; so that we need feel
no surprise at the inhabitants of any one
country, although on the ordinary view sup
posed to have been specially created and
adapted for that country, being beaten and
supplanted by the naturalised productions
from another land. Nor ought we to marvel
if all the contrivances in nature be not, as
far as we can judge, absolutely perfect,
and if some of them be abhorrent to our
ideas of fitness. We need not marvel at
the sting of the bee causing the bee’s own
death ; at drones being produced in such
vast numbers for one single act, with the
great majority slaughtered by their sterile’
sisters ; at the astonishing waste of pollen
by our fir-trees ; at the instinctive hatred
of the queen bee for her own fertile
daughters; at ichneumonidae feeding within
the live bodies of caterpillars ; and at other
such cases. The wonder, indeed, is, on the
theory of natural selection, that more cases
of the want of absolute perfection have not
been observed.
The complex and little-known laws
governing variation are the same, as far
• as we can see, with the laws which have
governed the production of so-called specific
forms. In both cases physical conditions
seem to have produced but little direct
effect; yet when varieties enter any zone
they occasionally assume some of the
characters of the species proper to that
zone. In both varieties and species use
and disuse seem to have produced some
effect; for it is difficult to resist this con
clusion when we look, for instance, at the
logger-headed duck, which has wings incap
able of flight, in nearly the same condition
as in the domestic duck ; or when wre look
at the burrowing tucutucu, which is occa
sionally blind, and then at certain moles,
which are habitually blind and have their
eyes covered with skin ; or when we look
at the blind animals inhabiting the dark
caves of America and Europe. In both
varieties and species correlation of growth
seems to have played a most important
part, so that, when one part has been modi
fied, other parts are necessarily modified.
In both varieties and species reversions to
long-lost characters occur. How inexplic
able, on the theory of creation, is the occa
sional appearance of stripes on the s'houlder
and legs of the several species of the horse
genus and in their hybrids ! How simply
is this fact explained if we believe that these
species have descended from a striped pro
genitor, in the same manner as the several
domestic breeds of pigeon have descended
from the blue and barred rock-pigeon 1
On the ordinary view of each species
having been independently created, why
should the specific characters, or those by
which the species of the same genus differ
from each other, be more variable than the
generic characters in which they all agree?
Why, for instance, should the colour of a
flower be more likely to vary in any one
species of a genus if the other species,
supposed to have been created inde
pendently, have differently coloured flowers,
�RECAPITULATION AND CONCLUSION
than if all the species of the genus have
the same coloured flowers ? If species are
only well-marked varieties, of which the
characters have become in a high degree
permanent, we can understand this fact;
for they have already varied since they
branched off from a common progenitor in
certain characters, by which they have
come to be specifically distinct from each
other; and, therefore, these same char
acters would be more likely still to be
variable than the generic characters which
have been inherited without change for an
enormous period. It is inexplicable, on the
theory of creation, why a part developed
in a very unusual manner in any one
species of a genus, and therefore, as we
may naturally infer, of great importance to
the species, should be eminently liable to
variation ; but, on my view, this part has
undergone, since the several species
branched off from a common progenitor,
an unusual amount of variability and modi
fication, and, therefore, we might expect
this part generally to be still variable.
But a part may be developed in the most
unusual manner, like the wing of a bat,
and yet not be more variable than any
other structure, if the part be common to
many subordinate forms—that is, if it has
been inherited for a very long period ; for
in this case it will have been rendered con
stant by long-continued natural selection.
Glancing at instincts, marvellous as some
are, they offer no greater difficulty than does
corporeal structure on the theory of the
natural selection of successive,slight, but pro
fitable modifications. We can thus under
stand why nature moves by graduated steps
in endowing different animals of the same
class with their several instincts. I have
attempted to show how much light the
principle of gradation throws on the admir
able architectural powers of the hive-bee.
Habit, no doubt, sometimes comes into
play in modifying instincts ; but it certainly
is not indispensable, as we see, in the case
of neuter insects, which leave no progeny
to inherit the effects of long-continued
habit. On the view of all the species of
the same genus having descended from a
common parent, and having inherited much
in common, we can understand how it is
that allied species, when placed under con
siderably different conditions of life, yet
should follow nearly the same instincts ;
why the thrush of South America, for
instance, lines her nest with mud like our
British species. On the view of instincts
having been slowly acquired through natural
189
selection, we need not marvel at some
instincts being apparently not perfect and
liable to mistakes, and at many instincts
causing other animals to suffer.
If species be only well-marked and per
manent varieties, we can at once see why
their crossed offspring should follow the
same complex laws in their degrees and
kinds of resemblance to their parents—in
being absorbed into each other by succes
sive crosses, and in other such points—as
do the crossed offspring of acknowledged
varieties. On the other hand, these would
be strange facts if species have been inde
pendently created and varieties have been
produced by secondary laws.
If we admit that the geological record is
imperfect in an extreme degree, then such
facts as the record gives support the theory
of descent with modification. New species
have come on the stage slowly and at
successive intervals ; and the amount of
change, after equal intervals of time, is
widely different in different groups. The
extinction of species and of whole groups
of species, which has played so conspicuous
a part in the history of the organic world,
almost inevitably follows on the principle
of natural selection ; for old forms will be
supplanted by new and improved forms.
Neither single species nor groups of species
reappear when the chain of ordinary genera
tion has once been broken. The gradual
diffusion of dominant forms, with the slow
modification of their descendants, causes
the forms of life, after long intervals of
time, to appear as if they had changed
simultaneously throughout the world. The
fact of the fossil remains of each formation
being in some degree intermediate in char
acter between the fossils in the formations
above and below is simply explained by
their intermediate position in the chain of
descent. The grand fact that all extinct
organic beings belong to the same system
with recent beings, falling either into the
same or into intermediate groups, follows
from the living and the extinct being the
offspring of common parents. As the
groups which have descended from an
ancient progenitor have generally diverged
in character, the progenitor with its early
descendants will often be intermediate in
character in comparison with its later
descendants ; and thus we can see why
the more ancient a fossil is, the oftener it
stands in some degree intermediate between
existing and allied groups. Recent forms
are generally looked at as being, in some
vague sense, higher than ancient and
�190
ON THE ORIGIN OF SPECIES
extinct forms; and they are in so far
higher as the later and more improved
forms have conquered the older and less
improved organic beings in the struggle
for life. Lastly, the law of the long endur
ance of allied forms on the same continent
—of marsupials in Australia, of edentata
in America, and other such cases—is intel
ligible, for within a confined country the
recent and the extinct will naturally be
allied by descent.
Looking to geographical distribution, if
we admit that there has been during the
long course of ages much migration from
one part of the world to another, owing to
former climatal and geographical changes
and to the many occasional and unknown
means of dispersal, then we can understand,
on the theory of descent with modification,
most of the great leading facts in Distribu
tion. We can see why there should be so
striking a parallelism in the distribution of
organic beings throughout space, and in
their geological succession throughout time;
for in both cases the beings have been con
nected by the bond of ordinary generation,
and the means of modification have been
the same. We see the full meaning of the
wonderful fact, which must have struck
every traveller—namely, that on the same
continent, under the most diverse condi
tions, under heat and cold, on mountain
and lowland, on deserts and marshes, most
of the inhabitants within each great class
are plainly related ; for they will generally
be descendants of the same progenitors and
early colonists. On this same principle of
former migration, combined in most cases
with modification, we can understand, by
the aid of the Glacial period, the identity
of some few plants, and the close alliance
of many others, on the most distant moun
tains, under the most different climates ;
and likewise the close alliance of some of
the inhabitants of the sea in the northern
and southern temperate zones, though
separated by the whole intertropical ocean.
Although two areas may present the same
physical conditions of life, we need feel no
surprise at their inhabitants being widely
different, if they have. been for a long
period completely separated from each
other; for as the relation of organism to
organism is the most important of all rela
tions, and as the two areas will have
received colonists from some third source
or from each other, at various periods and
in different proportions, the course of modi
fication in the two areas will inevitably be
different.
On this view of migration, with subse
quent modification, we can see why oceanic
islands should be inhabited by few species,
but of these that many should be peculiar;
We can see clearly why those animals
which cannot cross wide spaces of ocean,
as frogs and terrestrial mammals, should
not inhabit oceanic islands ; and why, on
the other hand, new and peculiar species of
bats which can traverse the ocean should
so often be found on islands far distant
from any continent. Such facts as the
presence of peculiar species of bats, and
the absence of all other mammals, on
oceanic islands, are utterly inexplicable on
the theory of independent acts of creation.
The existence of closely-allied or repre
sentative species in any two areas implies,
on the theory of descent with modification,
that the same parents formerly inhabited
both areas ; and we almost invariably find
that, wherever many closely-allied species
inhabit two areas, some identical species
common to both still exist. Wherever many
closely-allied yet distinct species occur,
many doubtful forms and varieties of the
same species likewise occur. It is a rule of
high generality that the inhabitants of each
area are related to the inhabitants of the
nearest source whence immigrants might
have been derived. We see this in nearly
all the plants and animals of the Galapagos
Archipelago, of Juan Fernandez, and of the
other American islands being related in the
most striking manner to the plants and
animals of the neighbouring American
mainland; and those of the Cape de Verde
Archipelago and other African islands to
the African mainland. It must be admitted
that these facts receive no explanation on
the theory of creation.
The fact, as we have seen, that all past
and present organic beings constitute one
grand natural system, with group sub
ordinate to group, and with extinct groups
often falling in between recent groups, is
intelligible on the theory of natural selec
tion with its contingencies of extinction and
divergence of character. On these same
principles we see how it is that the mutual
affinities of the species and genera within
each class are so complex and circuitous.
We see why certain characters are far
more serviceable than others for classifi
cation—why adaptive characters, though of
paramount importance to the being, are of
hardly any importance in classification ;
why characters derived from rudimentary
parts, though of no service to the being,
are often of high classificatory value ; and
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RECAPITULATION AND CONCLUSION
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at corresponding ages, have been inherited
why embryological characters are the most
from a remote period to the present day.
valuable of all. The real affinities of all
On the view of each organic being and
organic beings are due to inheritance or
each separate organ having been specially
community of descent. The natural system
created, how utterly inexplicable it is that
is a genealogical arrangement, in which we
parts, like the teeth in the embryonic calf
have to discover the lines of descent by the
or like the shrivelled wings under the
most permanent characters, however slight
soldered wing-covers of some beetles, should
their vital importance may be.
thus so frequently bear the plain stamp of
The framework of bones being the same
inutility! Nature may be said to have
in the hand of a man, wing of a bat, fin of
taken pains to reveal, by rudimentary organs
the porpoise, and leg of the horse; the
and by homologous structure, her scheme
same number of vertebrae forming the neck
of modification, which it seems that we
of the giraffe and of the elephant; and
wilfully will not understand.
innumerable other such facts, at once
explain themselves on the theory of descept
I have now recapitulated the chief facts
with slow and slight successive modifraB
and considerations which have thoroughly
tions. The similarity of pattern in the wing
convinced me that species have been modi
and leg of a bat, though used for such
fied, during a long course of descent, by
different purpose—in the jaws and legs of
the preservation or the natural selection of
a crab, in the petals, stamens, and pistils
many successive slight favourable varia
of a flower—is likewise intelligible on t^e
tions. I cannot believe that a false theory
view of the gradual modification of parts or
would explain, as it seems to me that the
organs, which were alike in the early pro
theory of natural selection does explain,
genitor of each class. On the principle of
the several large classes of facts above
successive variations not always super
specified. I see no good reason why the
vening at an early age, and being inherited
views given in this volume should shock
at a corresponding not early period of life,
the religious feelings of any one. A cele
we can clearly see why the embryos of
brated author and divine has written to me
mammals, birds, reptiles, and fishes should
that “ he has gradually learnt to see that it
be so closely alike, and should be so unlike
is just as noble a conception of the Deity
the adult forms. We may cease marvelling
at the embryo of an air-breathing mammal ' to believe that He created a few original
forms capable of self-development into other
or bird having branchial slits and arteries
and needful forms as to believe that He re
running in loops, like those in a fish which
quired a fresh act of creation to supply the
has to breathe the air dissolved in water
voids caused by the action of His laws.”
by the aid of well-developed branchiae.
Why, it may be asked, have all the most
. Disuse, aided sometimes by natural selec
eminent living naturalists and geologists
tion, will often tend to reduce an organ
rejected this view of the mutability of
when, it has become useless by changed
species ? It cannot be asserted that organic
habits or under changed conditions of life ;
beings in a state of nature are subject to
and we can clearly understand on this view
no variation ; it cannot be proved that the
the meaning of rudimentary organs. But
amount of variation in the course of long
disuse and selection will generally act on
ages is a limited quantity ; no clear dis
each creature when it has come to maturity
tinction has been, or can be, drawn between
and has to play its full part in the struggle for
species and well-marked varieties. ‘It can
existence, and will thus have little power of
not be maintained that species when inter
acting on an organ during early life; hence
crossed are invariably sterile and varieties
the organ will not be much reduced or ren
invariably fertile; or that sterility is a
dered rudimentary at this early age. The
special endowment and sign of creation.
calf, for instance, has inherited teeth, which
The belief that species were immutable
never cut through the gums of the upper
productions was almost unavoidable as long
jaw, from an early progenitor having wellas the history of the world was thought to
developed teeth ; and we may believe that
be of short duration; and now that we have
the teeth in the mature animal were reduced,
acquired some idea of the lapse of time, we
during successive generations, by disuse or
are too apt to assume, without proof, that
by the tongue and palate having been better
the geological record is so perfect that it
fitted by natural selection to browse without
would have afforded us plain evidence of
their aid ; whereas in the calf the teeth
the mutation of species, if they had under
have been left untouched by selection or
gone mutation.
disuse, and, on the principle of inheritance
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�192
ON THE ORIGIN OF SPECIES
But the chief cause of our natural unwil
lingness to admit that one species has given
birth to other and distinct species is that
we are always slow in admitting any great
change of which we do not see the inter
mediate steps. The difficulty is the same
as that felt by so many geologists when
Lyell first insisted that long lines of inland
cliffs had been formed and great valleys
excavated by the slow action of the coast
waves. The mind cannot possibly grasp
the full meaning of the term of a hundred
million years ; it cannot add up and per
ceive the full effects of many slight varia
tions, accumulated during an almost infinite
number of generations.
Although I am fully convinced of the
truth of the views given in this volume
under the form of an abstract, I by no
means expect to convince experienced
naturalists whose minds are stocked with
a multitude of facts all viewed, during a
long course of years, from a point of view
directly opposite to mine. It is so easy to
hide our ignorance under such expressions
as the “ plan of creation,” “ unity of design,”
etc., and to think that we give an explana
tion when we only restate a fact. Anyone
whose disposition leads him to attach more
weight to unexplained difficulties than to
the explanation of a certain number of facts
will certainly reject my theory. A few
naturalists, endowed with much flexibility
of mind, and who have already begun to
doubt on the immutability of species, may
be influenced by this .volume ; but I look
with confidence to the future, to young and
rising naturalists, who will be able to view
both sides of the question with impartiality.
Whoever is led to believe that species are
mutable will do good service by conscien
tiously expressing his conviction ; for only
thus can the load of prejudice by which this
subject is overwhelmed be removed.
Several eminent naturalists have of late
published their belief that a multitude of
reputed species in each genus are not real
species, but that' other species are real—that is, have been independently created.
This seems to me a strange conclusion to
arrive at. They admit that a multitude of
forms which till lately they themselves
thought were special creations, and which
are still thus looked at by the majority of
naturalists, and which consequently have
every external characteristic feature of true
species—they admit that these have been
produced by variation, but they refuse to
extend the same view to other and very
slightly different forms. Nevertheless they
do not pretend that they can define, or even
conjecture, which are the created forms of
life, and which are those produced by
secondary laws. They admit variation as
a vera causa in one case, they arbitrarily
reject it in another, without assigning any
distinction in the two cases. The day will
come when this will be given as a curious
illustration of the blindness of preconceived
opinion. These authors seem no more
startled at a miraculous act of creation than
at an ordinary birth. But do they really
believe that at innumerable periods in the
earth’s history certain elemental atoms have
been commanded suddenly to flash into
living tissues? Do they believe that at
each supposed act of creation one individual
or many were produced? Were all the
infinitely numerous kinds of animals and
plants created as eggs or seed, or as fullgrown ? and in the case of mammals, were
they created bearing the false marks of
nourishment from the mother’s womb?
Although naturalists very properly demand
a full explanation of every difficulty from
those who believe in the mutability of
species, on their own side they ignore the
whole subject of the first appearance of
species in what they consider reverent
silence.
It may be asked how far I extend the
doctrine of the modification of species.
The question is difficult to answer, because
the more distinct the forms are which we
may consider, by so much the arguments
fall away in force. But some arguments of
the greatest weight extend very far. All
the members of whole classes can be con
nected together by chains of affinities, and
all can be classified on the same principle,
in groups subordinate to groups. Fossil
remains sometimes tend to fill up very wide
intervals between existing orders. Organs
in a rudimentary condition plainly show
that an early progenitor had the organ in
a fully developed state ; and this, in some
instances, necessarily implies an enormous
amount of modification in the descendants.
Throughout whole classes various struc
tures are formed on the same pattern, and
at an embryonic age the species closely
resemble each other. Therefore, I cannot
doubt that the theory of descent with modi
fication embraces all the members of'the
same class. I believe that animals have
descended from at most only four or five
progenitors, and plants from an equal or
lesser number.
Analogy would lead me one step further
—namely, to the belief that all animals and
�RECAPITULATION AND CONCLUSION
plants have descended from some one pro
totype. But analogy may be a deceitful
•guide. Nevertheless, all living things have
much in common, in their chemical compo
sition, their germinal vesicles, their cellular
Structure, and their laws of growth and re
production. We see this even in so trifling
a circumstance as that the same poison
often similarly affects plants and animals ;
or that the poison secreted by the gall-fly
produces monstrous growths on the wild
rose or oak-tree. Therefore, I should infer
from analogy that probably all the organic
beings which have ever lived on this earth
have descended from some one primordial
form, into which life was first breathed by
the Creator.
When the views advanced by me in this
volume, and by Mr. Wallace in the Linnean
Journal, or when analogous views on the
origin of species are generally admitted, we
can dimly foresee that there will be a
considerable revolution in natural history.
Systematists will be able to pursue their
labours as at present; but they will not be
incessantly haunted by the shadowy doubt
whether this or that form be in essence a
species. This I feel sure, and I speak after
experience, will be no slight relief. The
endless disputes whether or not some fifty
Species of British brambles are true species
will cease. Systematists will have only to
decide (not that this will be easy) whether
any form be sufficiently constant and dis
tinct from other forms to be capable of
definition ; and, if definable, whether the
differences be sufficiently important to
deserve a specific name. This latter point
will become a far more essential considera
tion than it is at present; for differences,
however slight, between any two forms, if
not blended by intermediate gradations, are
looked at by most naturalists as sufficient
to raise both forms to the rank of species.
’Hereafter we shall be compelled to acknow
ledge that the only distinction between
species and well-marked varieties is that
the latter are known, or believed, to be con
nected at the present day by intermediate
gradations, whereas species were formerly
thus connected. Hence, without rejecting
the consideration of the present existence
of intermediate gradations between any
WO forms, we shall be led to weigh more
carefully and to value higher the actual
amount of difference between them. It
is quite possible that forms now generally
acknowledged to be merely varieties may
hereafter be thought worthy of specific
193
names, as with the primrose and cowslip ;
and in this case scientific and common
language will come into accordance. In
short, we shall have to treat species in the
same manner as those naturalists treat
genera who admit that genera are merely
artificial combinations made for conveni
ence. This may not be a cheering pro
spect ; but we shall at least be freed from
the vain search for the undiscovered and
undiscoverable essence of the term species.
The other and more general departments
of natural history will rise greatly in interest.
The terms used by naturalists of affinity,
relationship, community of type, paternity,
morphology, adaptive characters, rudimen
tary and aborted organs, etc., will cease
to be metaphorical, and will have a plain
signification. When we no longer look at
an organic being as a savage looks at a
ship, as at something wholly beyond his
comprehension ; when we regard every
production of nature as one which has had
a history; when we contemplate every
complex structure and instinct as the sum
ming-up of many contrivances, each useful
to the possessor, nearly in the same way
as when we look at any great mechanical
invention as the summing-up of the labour,
the experience, the reason, and even the
blunders of numerous workmen ; when we
thus view each organic being, how far more
interesting—-I speak from experience—
will the study of natural history become !
A grand and almost untrodden field of
inquiry will be opened on the causes and
laws of variation, on correlation of growth,
on the effects of use and disuse, on the
direct action of external conditions, and so
forth. The study of domestic productions
will rise immensely in value. A new variety
raised by man will be a more important
and interesting subject for study than one
more species added to the infinitude of
already recorded species. Our classifica
tions will come to be, as far as they can be
so made, genealogies, and will then truly
give what may be called the plan of crea
tion. The rules for classifying will, no
doubt, become simpler when we have a
definite object in view. We possess no
pedigrees or armorial bearings ; and we
have to discover and trace the many diverg
ing lines of descent in our natural gene
alogies by characters of any kind which
have long been inherited. Rudimentary
organs will speak infallibly with respect to
the nature of long-lost structures. Species
and groups of species which are called
aberrant, and which may fancifully be
O
�194
ON THE ORIGIN OF SPECIES
called living fossils, will aid us in forming i remain for a long period unchanged, while
a picture of the ancient forms of life. ' . within this same period several of these
Embryology will reveal to us the structure,
species, by migrating into new countries
in some degree obscured, of the prototypes
and coming into competition with foreign
of each great class.
associates, might become modified; so that
When we can feel assured that all the
we must not overrate the accuracy of
individuals of the same species, and all the
organic change as a measure of time.
closely-allied species of most genera, have
During early periods of the earth’s history,
within a not very remote period descended
when the forms of life were probably fewer
from one parent, and have migrated from
and simpler, the rate of change was probsome one birth-place ; and when we better ! ably slower; and at the first dawn of life,
know the many means of migration, then, i when very few forms of the simplest strucby the light which geology now throws, j ture existed, the rate of change may have
and will continue to throw, on former ■ been slow in an extreme degree. The whole
changes of climate and of the level of the
history of the world, as at present known,
land, we shall surely be enabled to trace
although of a length quite incomprehensible
in an admirable manner the former migra
by us, will hereafter be recognised as a mere
tions of the inhabitants of the whole world.
fragment of time, compared with the ages
which have elapsed since the first creature,
Even at present, by comparing the dif
the progenitor of innumerable extinct and
ferences of the inhabitants of the sea on
living descendants, was created.
the opposite sides of a continent, and the
In the distant future I see open fields for
nature of the various inhabitants of that
far more important researches. Psychology
continent in relation to their apparent
will be based on a new foundation, that of
means of immigration, some light can be
the necessary acquirement of each mental
thrown on ancient geography.
power and capacity by gradation. Light
The noble science of geology loses glory
will be thrown on the origin of man and
from the extreme imperfection of the record.
his history.
The crust of the earth, with its embedded
Authors of the highest eminence seem to
remains, must not be looked at as a well- i
be fully satisfied with the view that each
filled museum, but as a poor collection
species has been independently created.
made at hazard and at rare intervals. The
To my mind, it accords better with what we
accumulation of each great fossiliferous
know of the laws impressed on matter by
formation will be recognised as having
the Creator that the production and extinc
depended on an unusual concurrence of
tion of the past and present inhabitants of
circumstances, and the blank intervals
the world should have been due to secondary
between the successive stages as having
causes, like those determining the birth and
been of vast duration. But we shall be
death of the individual. When I view all
able to gauge with some security the
beings not as special creations, but as the
duration of these intervals by a com
lineal descendants of some few beings
parison of- the preceding and succeeding
which lived long before the first bed of the
organic forms. We must be cautious in
Silurian system was deposited, they seem
attempting to correlate as strictly contem
to me to become ennobled. Judging from
poraneous two formations, which include
the past, we may safely infer that not one
few identical species, by the general suc
living species will transmit its unaltered
cession of their forms of life. As species
likeness to a distant futurity. And of the
are produced and exterminated by slowly
species now living very few will transmit
acting and still existing causes, and not by
progeny of any kind to a far distant futurity;
miraculous acts of creation and by catastro
for the manner in which all organic beings
phes; and as themost important of all causes
are grouped shows that the greater number
of organic change is one which is almost
of species of each genus, and all the species
independent of altered, and perhaps sud
of many genera, have left no descendants,
denly altered, physical conditions—namely,
but have become utterly extinct. We can
the mutual relation of organism to organism,
the improvement of one being entailing I so far take a prophetic glance into futurity
the improvement or the extermination of ; as to foretell that it will be the common
others—it follows that the amount of organic I and widely-spread species, belonging to
change in the fossils of consecutive forma ‘ the larger and dominant groups, which will
tions probably serves as a fair measure of I ultimately prevail and procreate new and
the lapse of actual time. A number of j dominant species. As all the living forms
of life are the lineal descendants of those
species, however, keeping in a body might
�RECAPITULATION AND CONCLUSION
195
which lived long before the Silurian epoch, | with Reproduction ; Inheritance, which is
ralmost implied by reproduction; Variability,
)■ s we may feel certain that the ordinary suc
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cession by generation has never once been
broken, and that no cataclysm has desolated
the whole world. Hence we may look with
some confidence to a secure future of
equally inappreciable length. And as
natural selection works solely by and for
the good of each being, all corporeal and
mental endowments will tend to progress
towards perfection.
It is interesting to contemplate an en
tangled bank, clothed with many plants of
many kinds, with birds singing on the
bushes, with various insects flitting about,
and with worms crawling through the damp
earth, and to reflect that these elaborately
constructed forms, so different from each
other, and dependent on each other in so
complex a manner, have all been produced
by laws acting around us. These laws,
taken in the largest sense, being Growth
from the indirect and direct action of the
external conditions of life, and from use and
disuse ; a Ratio of Increase so high as to
lead to a Struggle for Life, and as a con
sequence to Natural Selection, entailing
Divergence of Character and the Extinction
of less-improved forms. Thus, from the
war of nature, from famine and death, the
most exalted object which we are capable
of conceiving—namely, the production of
the higher animals—directly follows. There
is grandeur in this view of life, with its
several powers, having been originally
breathed by the Creator into a few forms
or into one ; and that, while this planet has
gone cycling on according to the fixed law
of gravity, from so simple a beginning end
less forms most beautiful and most wonder
ful have been, and are being, evolved.
�INDEX
Aberrant groups, 172
Abyssinia, plants of, 151
Acclimatisation, 61
Affinities of extinct species, 133
’------ of organic beings, 165
Agassiz on Amblyopsis, 61
------ on groups of species suddenly appearing,
123-4
------ on embryological succession, 137
•----- on the glacial period, 148
----- - on embryological characters, 168
------ on the embryos of vertebrata, 175
------ on parallelism of embryological develop
ment and geological succession, 180
Algae of New Zealand, 151
Alligators, males, fighting, 42
Amblyopsis, blind fish, 61
America, North, productions allied to those of
Europe, 150
------- ---- - boulders and glaciers of, 150
------ South, no modern formations on west
coast, 119
Ammonites, sudden extinction of, 131
Anagallis, sterility of, 103
Analogy of variations, 69
Ancylus, 155
Animals, not domesticated from being variable, 15
------ domestic, descended from several stocks, 15
------ acclimatisation of, 62
------ of Australia, 52-3
----- - with thicker fur in cold climates, 59
------blind, in caves, 60
------ extinct, of Australia, 137
Anomma, 100
Antarctic islands, ancient flora of, 160
Antirrhinum, 70
Ants attending aphides, 88
------ slave-making instinct, 92
------ neuter, structure of, 98
Aphides, attended by ants, 88
Aphis, development of, 177
Apteryx, 77
Arab horses, 22
Aralo-Caspian Sea, 137
Archiac, M. de, on the succession of species, 132
Artichoke, Jerusalem, 62
Ascension, plants of, 157
Asclepias, pollen of, 82
Asparagus, 145
Aspicarpa, 167
Asses, striped, 70
Ateuchus, 60
Audubon on habits of frigate-bird, 79
Audubon on variation in birds’-nests, 89
------ on heron eating seeds, 156
Australia, animals of, 52-3
------ dogs of, 90
------ extinct animals of, 137
------ European plants in, 151
Azara on flies destroying cattle, 36
Azores, flora of, 147
Babington, Mr., on British plants, 27
Balancement of growth, 64
Bamboo with hooks, 83
Barberry, flowers of, 46
Barrande, M., on Silurian colonies, 128
------ on the succession of species, 132
------ on parallelism of palaeozoic formations, 133
------on affinities of ancient species, 134
Barriers, importance of, 141
Batrachians on islands, 158
Bats, how structure acquired, 77
------ distribution of, 159
Bear catching water-insects, 78
Bee, sting of, 85
------queen, killing rivals, 85
Bees fertilising flowers, 37
------hive, not sucking the red clover, 44
------ hive, cell-making instinct, 94
------ humble, cells of, 94
------parasitic, 91
Beetles, wingless, in Madeira, 60
------ with deficient tarsi, 60
Bentham, Mr., on British plants, 27
------ on classification, 168
Berkeley, Mr., on seeds in salt-water, 145
Bermuda, birds of, 157
Birds acquiring fear, 89
------annually cross the Atlantic, 147
------ colour of, on continents, 59
—— footsteps and remains of, in secondary
rocks, 124
—— fossil, in caves of Brazil, 137
------ of Madeira, Bermuda, and Galapagos, 157
------ song of males, 42
------ transporting seeds, 146
----- - waders, 155
------wingless, 59, 77
•----- - with traces of embryonic teeth, 180
Bizcacha, 141
------ affinities of, 172
Bladder for swimming in fish, 81
Blindness of cave animals, 60
Blyth, Mr., on distinctness of Indian cattle, 15
------ on striped Hemionus, 70
�INDEX
Bly th, Mr., on crossed geese, 105
Boar, shoulder-pad of, 42
Borrow, Mr., on the Spanish pointer, 22
Bory St. Vincent on Batrachians, 158
Bosquet, M,t on fossil Chthamalus, 124
Boulders, erratic, on the Azores, 147
Bran chi®, 81
Brent, Mr., on house-tumblers, 90
----- on hawks killing pigeons, 146
Brewer, Dr., on American cuckoo, 91
Britain, mammals of, 159
Bronn on duration of specific forms, 120
Brown, Robert, on classification, 167
Buckman on variation in plants, 12
Buzareingues on sterility of varieties, ill
Cabbag®, varieties of, crossed, 46
Calceolaria, 104
Canary-birds, sterility of hybrids, 105
Cape de Verde Islands, 160
Cape of Good Hope, plants of, 50, 151
Carrier-pigeons killed by hawks, 146
Cassini on flowers of composite, 63
Catasetum, 170
Cats, with blue eyes, deaf, 13
----- variation in habits of, 43
------curling tail when-going to spring, 85
Cattle destroying fir-trees, 36
------destroyed by flies in Paraguay, 36
------breeds of, locally extinct, 50
------ fertility of Indian and European breeds, 105
Cave, inhabitants of, blind, 60
Centres of creation, 142
Cephalopoda:, development of, 177
Cervulus, 105
Cetacea, teeth and hair, 63
Ceylon, plants of, 151
Chalk formation, 131
Characters, divergence of, 51
------ sexual, variable, 73
------ adaptive or analogical, 171
Charlock, 38
Checks to increase, 34
------ mutual, 36
Chickens, instinctive tameness of, 90
Chthamalinae, 118
Chthamalus, cretacean species of, 124
Circumstances favourable to selection of domestic
products, 24
----- to natural selection, 47
Cirripedes capable of crossing, 47
carapace aborted, 65
their ovigerous frena, 81
fossil, 124
------larvae of, 176
Classification, 165
Clift, Mr., on the succession of types, 137
Climate, effects of, in checking increase of beings,
35
.
.
------ adaptation of, to organisms, 01
Cobites, intestine of, 80
Cockroach, 38
Collections, palaeontological, poor, 118
Colour, influenced by climate, 59
in relation to attacks by flies, 84
i
197
Columba livia, parent of domestic pigeons, 17
Colymbetes, 155
Compensation of growth, 64
Composite, outer and inner florets of, 63
------ male flowers of, 180
Conclusion, general, 191
Conditions, slight changes in, favourable to
fertility, no
Coot, 79
Coral-islands, seeds drifted to, 146
------ reefs, indicating movements of earth, 126
Corn-crake, 79
Correlation of growth in domestic productions,
12-13
■------of growth, 63, 84
Cowslip, 27
Creation, single centres of, 142
Crinum, 104
Crosses, reciprocal, 107
Crossing of domestic animals, importance in
altering breeds, 15-16
------ advantages of, 45
Crustacea of New Zealand, 151
Crustacean, blind, 61
Cryptocerus, 99
Ctenomys, blind, 60
Cuckoo, instinct of, 91
Currants, grafts of, 108
Currents of sea, rate of, 145
Cuvier on conditions of existence, 87
------ on fossil monkeys, 124
------ Fred., on instinct, 87
Dana, Prof., on blind cave-animals, 61
------ on relations of crustaceans of Japan, 150
------ on crustaceans of New Zealand, 151
De Candolle on struggle for existence, 32
------ on umbelliferae, 64
------ on general affinities, 172
------ Alph., on low plants, widely dispersed, 163
------ on widely ranging plants being variable, 29
------ on naturalisation, 52
------on winged seeds, 64
------on Alpine species suddenly becoming rare,75
------ on distribution of plants with large seeds, 146
----- - on vegetation of Australia, 153
------ on fresh-water plants, 155
------ on insular plants, 157
Degradation of coast-rocks, 116
Denudation, rate of, 117
------ of oldest rocks, 125
Development of ancient forms, 136
Devonian system, 135
Dianthus, fertility of crosses, 106
Dirt on feet of birds, 146
Dispersal, means of, 144
------ during glacial periods, 147
Distribution, geographical, 140
----- means of, 144
Disuse, effects of, under nature, 59
Divergence of character, 51
Division, physiological, of labour, 52
Dogs, hairless, with imperfect teeth, 1
------ descended from several wild stocks, 15
------ domestic instincts of, 90
i
%
Jg5c*i
i
w
£
�j 98
INDEX
Dogs, inherited civilisation of, 90
------ fertility of breeds together, 105
------of crosses, 110-11
------ proportions of, when young, 178
Domestication, variation under, 11
Downing, Mr., on fruit trees in America, 41
Downs, North and South, 117
Dragon-flies, intestines of, 80
Drift timber, 146
Driver-ant, 100
Drones killed by other bees, 85
Duck, domestic, wings of, reduced, 12
------ logger-headed, 77
Duckweed, 155
Dugong, affinities of, 166
Dung-beetles with deficient tarsi, 60
Dyticus, 155
Earl, Mr. W., on the Malay Archipelago, 159
Ears, drooping, in domestic animals, 12
------ rudimentary, 181
Earth, seeds in roots of trees, 146
Eciton, 99
Economy of organisation, 64
.Edentata, teeth and hair, 63
------ fossil species of, 138
Edwards, Milne, on physiological divisions of
labour, 52
------ on gradations of structure, 82
------ on embryological characters, 168
Eggs, young birds escaping from. 42
Electric organs, 82
•Elephant, rate of increase, 33
------ of glacial period, 62
Embryology, 175
Existence, struggle for, 31
------ conditions of, 87
Extinction, as bearing on natural selection, 50
------ of domestic, varieties, 51
—— 129
Eye, structure of, 79
------ correction for aberration, 85
Eyes reduced in moles, 60
Fishes, ganoid, now confined to fresh water, 49
• ----- electric organs of, 82
------ ganoid, living in fresh water, 131
------of southern hemisphere, 151
Flight, powers of, how acquired, 78
Flowers, structure of, in relation to crossing, 43
—— of composite and umbelliferae, 63
Forbes, E., on colours of shells, 58
----- - on abrupt range of shells in depth, 75
----- - on poorness of palceontological collections
118
------on continuous succession of genera, 129
------ on continental extensions, 144
------ on distribution during glacial period, 148
------ on parallelism in time and space, 164
Forests, changes in, in America, 37
Formation, Devonian, 135
Formations, thickness of, in Britain, 116
----- - intermittent, 123
Formica rufescens, 92
----- -sanguinea, 92
------ flava, neuter of, ioo
Frena, ovigerous, of cirripedes, 81
Fresh-water productions, dispersal of, 154
Fries on species in large genera being closely
allied to other speoies, 30
Frigate-bird, 79
Frogs on islands, 158
Fruit-trees, gradual improvement of, 22
------ in United States, 41
------varieties of, acclimatised in United States, 62
Fuci, crossed, 107
Fur, thicker in cold climates, 59
Furze, 176
Galapagos Archipelago, birds of, 157
------productions of, 160-1
Galeopithecus, 77
Game, increase of, checked by vermin, 34.-5
Gartner on sterility of hybrids, 102-3
------ on reciprocal crosses, 107
------ on crossed maize and verbascum, hi
• ----- on comparison of hybrids and mongrels, 112
Geese, fertility when crossed, 105
Fabre, M., on parasitic sphex, 92
------upland, 79
Falconer, Dr., on naturalisation of plants in
Genealogy important in classification, 168
India, 33
Geoffroy St. Hilaire on balancement, 64
------ on fossil crocodile, 127
■----- on homologous organs, 174
------ on elephantsand mastodons, 136
------Isidore, on variability of repeated parts, 65
•---- - and Cautley on mammals of sub-Himalavan I ------ on correlation in monstrosities, 12-13
beds, 138
.
------on correlation, 63
Falkland Island, wolf of, 158
------ on variable parts being often monstrous, 67
Geographical distribution, 140
Faults, 117
Faunas, marine, 141
Geography, ancient, 194
Fear, instinctive, in birds, 89
Geology, future progress of, 194
Feet of birds, young molluscs adhering to, 155
------imperfection of the record, 114
Fertility of hybrids, 103
Giraffe, tail of, 82
----- from slight changes in conditions, no
Glacial period, 147
------ of crossed varieties, no
Gmelin on distribution, 148
Fir-trees destroyed by cattle, 36
Gnathod on, fossil, 149
------pollen of, 85
Godwin-Austen, Mr., on the Malay Archi
Fish, flying, 78
pelago, 122
------ teleostean, sudden appearance of, 124
Goethe on compensation of growth, 64
■----- eating seeds, 146, 156
Gooseberry, grafts of, 108
------ fresh-water, distribution of, 154
Gould, Dr. A., on land-shells, 159
�INDEX
Gould, Mr., on colours of birds, 59
------ on birds of the Galapagos, 160
------ on distribution of genera of birds, 162
Gourds, crossed, in
Grafts, capacity of, 108
Grasses, varieties of, 51-2
Gray, Dr. Asa, on trees of United States, 46
:----- on naturalised plants in the United States, 52
— on rarity of intermediate varieties, 75
—— on Alpine plants, 148
—- Dr. J. E., on striped mule, 71
Grebe, 79
Groups, aberrant, 172
Grouse, colours of, 41
—— red, a doubtful species, 27
Growth, compensation of, 64
------ correlation of, in domestic products, 12-13
------ correlation of, 63
Habit, effect of, under domestication, 12
------ effect of, under nature, 59
------ diversified, of same species, 78
Hair and teeth, correlated, 63
Harcourt, Mr. E. V., on the birds of Madeira, 157
Hartung, M., on boulders in the Azores, 147
Hazel-nuts, 145
Hearne on habits of bears, 78
Heath, changes in vegetation, 36
Heer, O., on plants of Madeira, 49
Helix pomatia, 160
Helosciadium, 145
Hemionus, striped, 71
Herbert, W., on struggle for existence, 32
—— on sterility of hybrids, 103
Hermaphrodites crossing, 45
Heron eating seed, 156
Heron, Sir R., on peacocks, 42
Heusinger on white animals not poisoned by
certain plants, 13
Hewitt, Mr., on sterility of first crosses, 109
Himalaya, glaciers of, 150
------ plants of, 151
Hippeastrum, 104
Holly-trees, sexes of, 44
Hollyhock, varieties of, crossed, 111-2
Hooker, Dr., on trees of New Zealand, 46
—*— on-acclimatisation of Himalayan trees, 62
■ ----- on flowers of umbelliferce, 63
-—- on glaciers of Himalaya, 150
■ ----- on alga; of New Zealand, 151
---- - on vegetation atthebaseof the Himalaya, 152.
■—— on plants of Tierra del Fuego, 131-2
------ on Australian plants, 151, 160
----- - on relations of flora of South America, 152-3
—on flora of the Antarctic lands, 153, 160
------ on the plants of the Galapagos, 158, 160
Hooks on bamboos, 83
------ to seeds on islands, 158
Horner, Mr., on the antiquity of Egyptians, 15
Horns, rudimentary, 181
Horse, fossil, in La Plata, 129
Horses destroyed by flies in Paraguay, 36
——striped, 71
------ proportions of, when young, 178
Horticulturists, selection applied by, 20-1
199
Huber on cells of bees, 96
------P., on reason blended with instinct, 88 '
------ on habitual nature of instincts, 88
------ on slave-making ants, 92
----- - on Melipona domestica, 94
Humble-bees, cells of, 94
Hunter, J., on secondary sexual characters, 66
Hutton, Captain, on crossed geese, 105
Huxley, Prof., on structure ofhermaphrodites,'47
------ on embryological succession, 137
----- - on homologous organs, 175
------ on the development of aphis, 177
Hybrids and mongrels compared, 112
Hybridism, 112
Hydra, structure of, 80
Ibla, 65
Icebergs transporting seeds, 147
Increase, rate of, 33
Individuals, numbers favourable to selection, 47
• ----- many, whether simultaneously created, 144
Inheritance, laws of, 13
------at corresponding ages, 13, 41 _
Insects, colour of, fitted for habitations, 41
----- sea-side, colours of, 59
------ blind in caves, 61
------luminous, 82
• ----- neuter, 98
Instinct, 87
Instincts, domestic, 90
Intercrossing, advantages of, 45
Islands, oceanic, 156
Isolation favourable to selection, 48
Japan, productions of, 150
Java, plants of, 151
Jones, Mr. J. M., on the birds of Bermuda, 157
Jussieu on classification, 167
•
Kentucky, caves of, 60-1
ICerguelen-land, flora of, 153s *6o
Kidney-bean, acclimatisation of, 62
Kidneys of birds, 63
Kirby on tarsi deficient in beetles, 60
Knight, Andrew, on cause of variation, 11
Kolreuter on the barberry, 46
------ on sterility of hybrids, 102
------on reciprocal crosses, 107
------ on crossed varieties of nicotiana, 112
------on crossing male and hermaphrodite flowers,
180
Lamarck, on adaptive characters, 171
Land-shells, distribution of, 159
------ of Madeira, naturalised, 162
Languages, classification of, 169
Lapse, great, of time, 116
Larvte, 175
Laurel, nectar secreted by the leaves, 43
Laws of variation, 58
Leech, varieties of, 37
Leguminosm, nectar secreted by glands, 43
Lepidosiren, 49, 134
Life, struggle for, 31
Lingula, Silurian, 125
�200
INDEX
Linnaeus, aphorism of, 167
Lion, mane of, 42
------ young of, striped, 176
Lobelia fulgens, 36
Lobelia, sterility of crosses, 104
Loess of the Rhine, 155
Lowness ofstructure connected with variability, 65
Lowness, related to wide distribution, 163
Lubbock, Mr., on the nerves of coccus, 26
Lucas, Dr. P., on inheritance, 13
------ on resemblance of child to parent, 113
Lund and Clausen on fossils of Brazil, 137
Lyell, Sir C., on the struggle for existence, 32
------ on modern changes of the earth, 45
----- - on measure of denudation, 116
------- on a carboniferous land-shell, 118
------ on strata beneath Silurian system, 125
• ---- - on the imperfection of the geological record,
>•
126
------ on the appearance of species, 127
------ on Barrande’s colonies, 128
------ on tertiary formations of Europe and North
America, 131
------ on parallelism of tertiary formations, 133
------on transport of seeds by icebergs, 147
------- on great alternations of climate, 154
------ on the distribution of fresh-water shells, i55
• ----- on land-shells of Madeira, 162
Lyell and Dawson on fossilised trees in Nova
Scotia, 121
MACLEAY on analogical characters, 171
Madeira, plants of, 49
------ beetles of, wingless, 60
----- - fossil land-shells of, 137
------ birds of, 157
Magpie tame in Norway, 89
Maize, crossed, ill
Malay Archipelago compared with Europe, 122
------ mammals of, 159
Malpighiaceae, 167
Mammie, rudimentary, 180
Mammals, fossil, in secondary formation, 124
------ insular, 158
Man, origin of races of, 84
Manatee, rudimentary nails of, 181
Marsupials of Australia, 52-3
----- - fossil species of, 138
Martens, M., experiment on seeds, 145
Martin, Mr. W. C., on striped mules, 71
Matteucci, on the electric organs of rays, 81
Matthiola, reciprocal crosses of, 107
Means of dispersal, 144
Melipona domestica, 94
Metamorphism of oldest rocks, 125
Mice destroying bees, 37
------ acclimatisation of, 62
Migration, bears on first appearance of fossils, 122
Miller, Prof., on the cells of bees, 95
Mirabilis, crosses of, 107
Missel-thrush, 38
Mistletoe, complex relations of, 8
Mississippi, rate of deposition at mouth, 116
Mocking thrush of the Galapagos, 162
Modification of species, how far applicable, 192
Moles, blind, 60
Mongrels, fertility and sterility of, no
------ and hybrids compared, 112
Monkeys, fossil, 124
Monochan thus, 170
Mons, Van, on the origin of fruit-trees, 19
Moquin-Tandon on sea-side plants, 59
Morphology, 157
Mozart, musical powers of, 88
Mud, seeds in, 155-6
Mules, striped, 71
Muller, Dr. F., on Alpine Australian plants, 151
Murchison, Sir R., on the formations of Russia, 119
----- - on azoic formations, 125
----- - on extinction, 129
Mustela vision, 77
Myanthus, 170
Myrmecocystus, 99
Myrmica, eyes of, 100
Nails, rudimentary, 181
Natural history, future progress of, 193
------ selection, 39
----- - system, 166
Naturalisation of forms distinct from the indi
genous species, 52
----- - in New Zealand, 85
Nautilus, Silurian, 125
Nectar of plants, 43
Nectaries, how formed, 43
Nelumbium luteum, 156
Nests, variation in, 89
Neuter insects, 98
Newman, Mr., on humble bees, 37
New Zealand, productions of, not perfect, 85
------ naturalised products of, 137
------ fossil birds of, 137
------ glacial action in, 150
------ crustaceans of, 151
----- - algce of, 151
------ number of plants of, 157
------ flora of, 160
Nicotiana, crossed varieties of, 112
----- - certain species very sterile, 106
Noble, Mr., on fertility of rhododendron, 104
Nodules, phosphatic, in azoic rocks, 125
Oak, varieties of, 28
Onites apelles, 60
Orchis, pollen of, 82
Organs of extreme perfection, 79
----- electric, of fishes, 82
----- - of little importance, 82
----- homologous, 174
------rudiments of, and nascent, i3o
Ornithorhynchus, 49, 167
Ostrich not capable of flight, 60
----- habit of laying eggs together, 91
------American, two species of, 141
Otter, habits of, how acquired, 77
Ouzel, water, 79
Owen, Prof., on birds not flying, 59
------ on vegetative repetition, 65
------ on variable length of arms in ourang-outang,
65
�INDEX
Owen, Prof., on the swim-bladder of fishes, 81
— on electric organs, 82
—-— on fossil horse of La Plata, 129
—— on relations of ruminants and pachyderms,
134
------on fossil birds of New Zealand, 137
------ on succession of types, 137
------ on affinities of the dugong, 166
------ on homologous organs, 174
------ on the metamorphosis of cephalopods and
spiders, 177
Pacific Ocean, faunas of, 141
Paley on no organ formed to give pain, 85
Pallas on the fertility of the wild stocks of
domestic animals, 105
Paraguay, cattle destroyed by flies, 36
Parasites, 91
Partridge, dirt on feet, 146
Parts greatly developed, variable, 65
——~ degrees of utility of, 85
Pares major, 78
Passiflora, 104
Peaches in United.States, 41
Pear, grafts of, 108
Pelargonium, flowers of, 64
------ sterility of, 104
Pelvis of women, 63
Peloria, 64
Period, glacial, 147
Petrels, habits of, 78
Phasianus, fertility of hybrids, 105
Pheasant, young, wild, 90
Philippi on tertiary species in Sicily, 127
Pictet, Prof., on groups of species suddenly
appearing, 123-4
------on rate of organic change, 127
----- - on continuous succession of genera, 129
----- - on close alliance of fossils in consecutive
formations, 136
—- on embryological succession,' 137
Pierce, Mr., on varieties of wolves, 43
Pigeons with feathered feet and skin between
toes, 13
— breeds described, and origin of, 16-17
------ breeds of, how produced, 23-4
—— tumbler, not being able to get out of egg, 42
reverting to blue colour, 69
—— instinct of tumbling, 90
. carriers, killed by hawks, 146
------ young of, 178
Pistil, rudimentary, 180
Plants, poisonous, not affecting certain coloured
animals, 13
—— selection applied to, 21
----- - gradual improvement of, 22
------not improved in barbarous countries, 23
----- - destroyed by insects, 34
----- - in midst of range, have to struggle with
other plants, 38
------ nectar of, 43
------fleshy, on sea-shores, 59
——- fresh-water, distribution of, 155
— low in scale, widely distributed, 163
Plumage, laws of change in sexes of birds, 42
201
Plums in the United States, 41
Pointer dog, origin of, 22
------ habits of, 90
Poison not affecting certain coloured animals, 13
----- - similar effects of, on animals and plants, 193
Pollen of fir-trees, 85
Poole, Col., on striped hemionus, 71
Potamogeton, 156
Prestwich, Mr., on English and French eocene
formations, 133
Primrose, 27
------ sterility of, 103
Primula, varieties of, 27
Proteolepas, 65
Proteus, 61
Psychology, future progress of, 194
Quagga, striped, 71
Quince, grafts of, 108
Rabbit, disposition of young, 90
Races, domestic, characters of, 14-16
Race-horses, Arab, 22
----- - English, 144
Ramond on plants of Pyrenees, 148
Ramsay, Prof., on thickness of the British for
mations, 116
------ on faults, 117
Ratio of increase, 33
Rats, supplanting each other, 38
------ acclimatisation of, 62
------ blind, in cave, 61
Rattle-snake, 85
Reason and instinct, 87
Recapitulation, general, 183
Reciprocity of crosses, 107
Record, geological, imperfect, 114
Rengger on flies destroying cattle, 36
Reproduction, rate of, 33
Resemblance to parents in mongrels and hybrids,
112
Reversion, law of inheritance, 13-14
------ in pigeons to blue colour, 69
Rhododendron, sterility of, 104
Richard, Prof., on Aspicarpa, 167
Richardson, Sir J., on structure of squirrels, 77
------ on fishes of the southern hemisphere, 151
Robinia, grafts of, 108
Rodents, blind, 60
Rudimentary organs, 180
Rudiments important for classification, 167
Sagaret on grafts, 108
Salmon, males fighting, and hooked jaws of, 42
Salt-water, how far injurious to seeds, 145
Saurophagus sulphuratus, 78
Schiodte on blind insects, 61
Schlegel on snakes, 63
Sea-water, how far injurious to seeds, 145
Sebright, Sir J., on crossed animals, 16
------ on selection of pigeons, 20
Sedgwick, Prof., on groups of species suddenly
appearing, 123
Seedlings destroyed by insects, 34
Seeds, nutriment in, 38
------winged, 64
�202
INDEX
Seeds, power of, resisting salt-water, 145
Strata, thickness of, in Britain, 116
------ in crops and intestines of birds, 146
Stripes on horses, 71
------ eaten by fish, 146, 156
Structure, degrees of utility of, 85
------ in mud, 155
Struggle for existence, 32
,------ hooked, on islands, 158
Succession, geological, 127
Selection of domestic products, 19
Succession of types in same areas, 137
------principle not of recent origin, 21
Swallow, one species supplanting another, 38
------ unconscious, 21
Swim-bladder, 81
------ natural, 39
System, natural, 166
------sexual, 42
------ natural circumstances favourable to, 47
Tail of giraffe, 82
Sexes, relations of, 42
• ----- - of aquatic animals, 83
Sexual characters variable, 6S
------ rudimentary, 181
------- selection, 42
Tarsi deficient, 60
Sheep, merino, their selection, 20
Tausch on umbelliferous flowers, 64
----- - two sub-breeds, unintentionally produced,
Teeth and hair correlated, 63
22
- ---- - embryonic, traces of, in birds, 180
------ mountain, varieties of, 37
• ------ rudimentary, in embryonic calf, 180, 191
Shells, colours of, 59
Tegetmeier, Mr., on cells of bees, 95, 97
------ littoral, seldom embedded, 118
Temminck on distribution aiding classification,
------- fresh-water, dispersal of, 154
168
------ of Madeira, 157
Thouin on grafts, 108
----- - land, distribution of, 159
Thrush, aquatic species of, 79
Silene, fertility of crosses, 106
------ mocking, of the Galapagos, 162
Silliman, Prof., on blind rat, 61
------ young of, spotted, 176
Skulls of young mammals, 83
------ nest of, 101
Slave-making instinct, 92
Thuret, M., on crossed fucT7io7
Smith, Col. Hamilton, on striped horses, 71
Thwaites, Mr., on acclimatisation, 62
------ Mr. Fred., on slave-making ants, 92
Tierra del Fuego, dogs of, 90
------- on neuter ants, 100
1 -------plants of, 152-3
------- Mr., of Jordan Hill, on the degradation of
Timber-drift, 146
coast-rocks, 116
Time, lapse of, 116
Snap-dragon, 70
Titmouse, 78
Somerville, Lord, on selection of sheep, 20
Toads on islands, 158
Sorbus, grafts of, 108
Tobacco, crossed varieties of, 112
Spaniel, King Charles’s breed, 22
Tomes, Mr., on the distribution of bats, 159
Species, polymorphic, 26
Transitions in varieties rare, 74
------ common, variable, 29
Trees on islands belong to peculiar orders, 158
----- - in large genera variable, 29
------ - with separated sexes, 46
------ groups of, suddenly appearing, 123, 125
Trifolium pratense, 37, 44
■----- - incarnatum, 44
------ beneath Silurian formations, 125
------ successively appearing, 127
Trigonia, 131
’
------ changing simultaneously throughout the
Trilobites, 125
world, 131
• ----- - sudden extinction of, 131
Spencer, Lord, on increase in size of cattle, 22
Troglodytes, 101
Sphex, parasitic, 91-2
Tucutucu, blind, 60
Tumbler pigeons, habits of, hereditary, 90
Spiders, development of, 177
Spitz-dog crossed with fox, 110-11
------ young of, 178
. Turkey-cock, brush of hair on breast, 43
Sports in plants, 12
Turkey, naked skin on head, 83
Sprengel, C. C., on crossing, 46
------ young, wild, 90
• ---- - on ray-florets, 64
Turnip and cabbage, analogous variations of,
Squirrels, gradations in structure, 77
69
Staffordshire heath, changes in, 36
Type, unity of, 87
Stag-beetles, fighting, 42
Types, succession of, in same areas, 137
Sterility from changed conditions of life, 12
------ of hybrids, 102
Udders enlarged by use, 12
------laws of, 105
------ rudimentary, 180
• ----- causes of, 109
Ulex, young leaves of, 176
------from unfavourable conditions, 109
Umbelliferae, outer and inner florets of, 63
----- - of certain varieties, III
St. Helena, productions of, 157
Unity of type, 87
St. Hilaire, Aug., on classification, 167
Use, effects of, under domestication, 12
St.John, Mr. , on habits of cats, 43
------ effects of, in a state of nature, 59
Sting of bees, 85
Utility, how far important in the construction of
Stocks, aboriginal, of domestic animals, 15
each part, 84
�INDEX
Valenciennes on fresh-water fish, 155
Variability of mongrels and hybrids, 112
Variation under domestication, 11
------ caused by reproductive system being affected
by conditions of life, 11
------ under nature, 25
----- - laws of, 58
Variations appear at corresponding ages, 13, 42
------ analogous in distinct species, 69
Varieties natural, 25
----- - struggle between, 37
—— domestic, extinction of, 51
•----- - transitional, rarity of, 74
----- - when crossed, fertile, no
------ when crossed, sterile, ill
------ classification of, 169
Verbascum, sterility of, 104
—— varieties of, crossed, in
Verneuil, M. de, on the succession of species,
132
Viola tricolor, 37
Volcanic islands, denudation of, 117
Vulture, naked skin on head, 83
Wading-birds, 155
Wallace, Mr., on origin of species, 7
—■ — on law of geographical distribution, 144
------ on the Malay Archipelago, 159
Wasp, sting of, 85
Water, fresh, productions of, 154
Water-hen, 79
Waterhouse, Mr., on Australian marsupials, 53
------ on greatly developed parts being variable,
65
------ on the cells of bees, 94
------ on general affinities, 172
Water-ouzel, 79
Watson, Mr. H. C., on range of varieties of
British plants, 27
------on acclimatisation, 62
----- - on rarity of intermediate varieties, 75
203
Watson, Mr. H. C., on flora of Azores, 147
—— on Alpine plants, 148, 152
Weald, denudation of, 117
Web of feet in water-birds, 79
West Indian islands, mammals of, 159
Westwood on species in large genera being
closely allied to others, 30
•—— on the tarsi of Engidce, 68
------- on the antennae of hymenopterous insects,
l67
Wheat, varieties of, 51-2
White Mountains, flora of, 147
Wings, reduction of size, 59-60
Wings of insects homologous with branchile, 81
------ rudimentary, in insects, 180
Wolf crossed with dog, 90
------ of Falkland Isles, 158
Wollaston, Mr., on varieties of insects, 27
----- - on fossil varieties of land-shells in Madeira,
28
------ on colours of insects on sea-shore, 59
------ on wingless beetles, 60
------ on rariety of intermediate varieties, 75
------ on insular insects, 157
------ on land-shells of Madeira, naturalised, 162
Wolves, varieties of, 43
Woodpecker, habits of, 79
----- - green colour of, 83
Woodward, Mr., on the duration of specific
forms, 120
—— on the continuous succession of genera, 129
----- - on the succession of types, 137
World, species changing simultaneously through
out; 131
Wrens, nest of, 101
Youatt, Mr., on selection, 20
—-— on sub-breeds of sheep, 22
•----- - on rudimentary horns in young cattle, 181
Zebra, stripes on, 71
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Dublin Core
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Victorian Blogging
Description
An account of the resource
A collection of digitised nineteenth-century pamphlets from Conway Hall Library & Archives. This includes the Conway Tracts, Moncure Conway's personal pamphlet library; the Morris Tracts, donated to the library by Miss Morris in 1904; the National Secular Society's pamphlet library and others. The Conway Tracts were bound with additional ephemera, such as lecture programmes and handwritten notes.<br /><br />Please note that these digitised pamphlets have been edited to maximise the accuracy of the OCR, ensuring they are text searchable. If you would like to view un-edited, full-colour versions of any of our pamphlets, please email librarian@conwayhall.org.uk.<br /><br /><span><img src="http://www.heritagefund.org.uk/sites/default/files/media/attachments/TNLHLF_Colour_Logo_English_RGB_0_0.jpg" width="238" height="91" alt="TNLHLF_Colour_Logo_English_RGB_0_0.jpg" /></span>
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Conway Hall Library & Archives
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2018
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Conway Hall Ethical Society
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On the origin of species by means of natural selection, or: The preservation of favoured races in the struggle for life
Creator
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Darwin, Charles [1809-1882]
Description
An account of the resource
Place of publication: London
Collation: 208 p. ; 22 cm.
Series title: R.P.A. Cheap Reprints
Series number: No. 11
Notes: Part of the NSS pamphlet collection. Includes index. First published 1859-60. Reprint of 1st ed. "Mr John Murray, the original publisher, is now issuing the final edition in cloth binding...Students and all admirers of Darwin should compare the first and last editions...in order to fully understand the development of the doctrine of Evolution."--Publishers' note. Publisher's advertisements (RPA, Longmans, Grant Richards) at the end (p. 204-208). Printed in double columns.
Publisher
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Watts & Co.
Date
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1903
Identifier
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N186
Subject
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Evolution
Science
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<a href="http://creativecommons.org/publicdomain/mark/1.0/"><img src="http://i.creativecommons.org/p/mark/1.0/88x31.png" alt="Public Domain Mark" /></a><span> </span><br /><span>This work (On the origin of species by means of natural selection, or: The preservation of favoured races in the struggle for life), identified by </span><a href="https://conwayhallcollections.omeka.net/items/show/www.conwayhall.org.uk"><span>Humanist Library and Archives</span></a><span>, is free of known copyright restrictions.</span>
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application/pdf
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Text
Language
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English
Evolution
Evolution (Biology)
Natural Selection
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Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
A name given to the resource
Victorian Blogging
Description
An account of the resource
A collection of digitised nineteenth-century pamphlets from Conway Hall Library & Archives. This includes the Conway Tracts, Moncure Conway's personal pamphlet library; the Morris Tracts, donated to the library by Miss Morris in 1904; the National Secular Society's pamphlet library and others. The Conway Tracts were bound with additional ephemera, such as lecture programmes and handwritten notes.<br /><br />Please note that these digitised pamphlets have been edited to maximise the accuracy of the OCR, ensuring they are text searchable. If you would like to view un-edited, full-colour versions of any of our pamphlets, please email librarian@conwayhall.org.uk.<br /><br /><span><img src="http://www.heritagefund.org.uk/sites/default/files/media/attachments/TNLHLF_Colour_Logo_English_RGB_0_0.jpg" width="238" height="91" alt="TNLHLF_Colour_Logo_English_RGB_0_0.jpg" /></span>
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Conway Hall Library & Archives
Date
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2018
Publisher
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Conway Hall Ethical Society
Text
A resource consisting primarily of words for reading. Examples include books, letters, dissertations, poems, newspapers, articles, archives of mailing lists. Note that facsimiles or images of texts are still of the genre Text.
Original Format
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Pamphlet
Dublin Core
The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/.
Title
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Design and natural selection
Creator
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Moss, Arthur B.
Description
An account of the resource
Place of publication: London
Collation: 16 p. ; 19 cm.
Notes: Titles by the same author listed on back cover. Date of publication from KVK (OCLC, WorldCat). Underlining on pages 8 & 10.
Publisher
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Watts & Co.
Date
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[1885]
Identifier
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G5783
Subject
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Creationism
Evolution
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<a href="http://creativecommons.org/publicdomain/mark/1.0/"><img src="http://i.creativecommons.org/p/mark/1.0/88x31.png" alt="Public Domain Mark" /></a><span> </span><br /><span>This work (Design and natural selection), identified by </span><a href="https://conwayhallcollections.omeka.net/items/show/www.conwayhall.org.uk"><span>Humanist Library and Archives</span></a><span>, is free of known copyright restrictions.</span>
Format
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application/pdf
Type
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Text
Language
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English
Creation
Natural Selection