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Full text of "On the origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life"

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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 

BY 

CHARLES DARWIN, M.A. 




HENRY FROWDE 

OXFORD UNIVERSITY PRESS 

LONDON, NEW YORK AND TORONTO 



First impression January 1902 

Second impression Jzuie 1902 

Third impression January 1904 

Fourth impression November 1907 



Printed by R. & R. Clark, Limited, Edinburgh. 



A NOTE 
ON 'THE ORIGIN OF SPECIES ' 



Charles Darwin, the author of this volume, was horn at 
Shrewsbury in 1809 ; he died at Bromley, Kent, in 1832, 
aged 73. His years of active work thus covered ap- 
proximately the five midmost decades of the Nineteenth 
Century, from 1830 to 1880. He was a naturalist of the 
very highest rank, and the discoverer of the famous theory 
of Natural Selection. The great treatise in which that 
theory was promulgated, however, — f The Origin of 
Species' — did not appear till 1859, when Darwin v>as 
over fifty. It completely revolution? zed the sciences of 
Botany and Zoology, and made the doctrine of Organic 
Evolution, till then admitted only by a few advanced 
philosophical biologists, the universal creed of men of 
science. By that famous book, and by its equally 
admirable companion volume l The Descent of Man,' 
Darwin will always be most remembered. He was not 
indeed the first to set forth the now accepted idea that all 
species of plants or animals, including man, are derived by 
descent, with various modifications, from a single original 
ancestor ; but he was the first to give that idea general 
currency and to secure its acceptance by means of his 
luminous conception of Natural Selection. Organic Evolu- 
tion triumphed through Darwin. 

GRANT ALLEN. 



CONTENTS 



CHAP. 

Introduction 

1. Variation under Domestication 

2. Variation under Nature . 

3. Struggle for Existence 

4. Natural Selection 

5. Laws of Variation 

6. Difficulties on Theory 

7. Instinct .... 

8. Hybridism .... 

9. On the Imperfection of the 

Record .... 



Geological 



10. On the Geological Succession of Organic 

Beings .... 

11. Geographical Distribution 

12. Geographical Distribution — Continued 

13. Mutual Affinities of Organic Beings 

Morphology: Embryology: Rudimentary 
Organs ..... 

14. Recapitulation and Conclusion 
Index ...... 



PAGE 

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02 






ON THE OEIGIN OF SPECIES 



INTRODUCTION 

When on board H.M.S. Beagle, as 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 accumulating 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 
this ^Abstract. 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 conclusions that I 
have on the origin of species. Last year he sent me a 

B 



1 ON THE ORIGIN OF SPECIES 

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 
rolume 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 advisable to publish, with Mr. Wallace's 
excellent memoir, some brief extracts from my manu- 
scripts. 

This Abstract, which I now publish, must neces- 
sarily 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 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 discussed 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 arguments on both sides of each question ; and 
this cannot possibly be here done. 

I much regret that want of space prevents my having 
the satisfaction of acknowledging the generous assist- 
ance 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 con- 
ceivable that a naturalist, reflecting on the mutual 
affinities of organic beings, on their embryological 



INTRODUCTION 3 

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 struc- 
ture and coadaptation which most justly excites our 
admiration. Naturalists continually refer to external 
conditions, such as climate, food, etc., as the only pos- 
sible cause of variation. In one very limited sense, as 
we shall hereafter see, this maybe true; but it is pre- 
posterous to attribute to mere external conditions the 
structure, for instance, of the woodpecker, 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 importance to gain a 
clear insight into the means of modification and co- 
adaptation. At the commencement of my observations 
it seemed to me probable that a careful study of domes- 
ticated animals and of cultivated plants would offer the 



4 ON THE ORIGIN OF SPECIES 

best chance of making out this obscure problem. Nor 
have 1 been disappointed ; in this and in all other 
perplexing cases I have invariably found that our 
knowledge, 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 Domestica- 
tion. We shall thus see that a large amount of 
hereditary modification is at least possible ; 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 en- 
abled to discuss what circumstances are most favourable 
to variation. In the next chapter the Struggle for 
Existence amongst all organic beings throughout the 
world, which inevitably follows from the high geo- 
metrical ratio of their increase, will be treated of. 
This is the doctrine of Malthus, applied to the whole 
animal and vegetable kingdoms. As many more 
individuals of each species are born than can possibly 
survive ; and as, consequently, there is a frequently 
recurring struggle for existence, it follows that any 
being, if it vary however slightly in any manner profit- 
able to itself, under the complex and sometimes 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 in- 
evitably causes much Extinction of the less improved 
forms of life, and leads to what I have called Divergence 



INTRODUCTION 6 

of Character. In the next chapter I shall discuss the 
complex and little known laws of variation and of 
correlation 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 in- 
fertility of species and the fertility of varieties when 
intercrossed ; 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 space ; in the thirteenth, their 
classification or mutual affinities, both when mature 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 relations 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 modification 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 geological 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 which most 
naturalists entertain, and which I formerly entertained 
— namely, that each species has been independently 
created — is erroneous. I am fully convinced that 



6 ON THE ORIGIN OF SPECIES 

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 acknowledged varieties of any one species 
are the descendants of that species. Furthermore, 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 — Correlation of Growth- 
Inheritance— Character of Domestic Varieties— Difficulty of dis- 
tinguishing 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 conclude that this great variability is simply due to 
our domestic productions having been raised under con- 
ditions 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 propounded 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 generallv continues to varv 

7 



8 ON THE ORIGIN OF SPECIES 

for many generations. No case is on record of a vari- 
able 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 reproductive 
elements having been affected prior to the act of con- 
ception. 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 repro- 
ductive 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 
confinement, 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 con- 
finement 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 
onter 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 



VARIATION UNDER DOMESTICATION 9 

the plantigrades or bear family ; whereas carnivoious 
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 one hand, we see domesticated animals 
and plants, though often weak and sickly, yet breeding 
quite freely under confinement ; and when, on the other 
hand, we see individuals, though taken young from a 
state of nature, perfectly tamed, long-lived, and healthy 
(of which I could give numerous instances), yet having 
their reproductive system so seriously affected by un- 
perceived causes as to fail in acting, we need not be 
surprised at this system, when it does act under con- 
finement, acting not quite regularly, and producing off- 
spring 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 produces sterility ; and variability is the source 
of all the choicest productions of the garden. I may 
add, that as some organisms will breed freely under 
the most unnatural conditions (for instance, the rabbit 
and ferret kept in hutches), showing that their repro- 
ductive system has not been thus affected ; so will some 
animals and plants withstand domestication or cultiva- 
tion, 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 f sports' are extremely 
rare under nature, 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 attri- 
buted to the ovules or pollen, or to both, having been 



10 ON THE ORIGIN OF SPECIES 

affected by the treatment of the parent prior to the act 
of conception. These cases anyhow show that variation 
is not necessarily connected, as some authors have sup- 
posed, 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 unim- 
portant the direct effects of the conditions of life are 
in comparison 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 attributed to the 
direct action of the conditions of life — as, in some cases, 
increased size from amount of food, colour from par- 
ticular 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. 



VARIATION UNDER DOMESTICATION 11 

The great and inherited development of the udders in 
eows 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 variation, 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 be- 
tween quite distinct parts are very curious ; and many 
instances are given in Isidore GeofFroy 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 amongst animals and 
plants. From the facts collected by Heusinger, it ap- 
pears 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 animals 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 unconsciously 
modify other parts of the structure, owing to the 
mysterious laws of the correlation 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 



12 ON THE ORIGIN OF SPECIES 

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 structure, 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 amongst individuals, apparently exposed to 
the same conditions, any very rare deviation, due to 
some extraordinary combination of circumstances, 
appears in the parent — say, once amongst several million 
individuals — and it reappears in the child, the mere 
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 grandmother or other more remote 



VARIATION UNDER DOMESTICATION 13 

ancestor ; why a peculiarity is often transmitted from 
one sex to both sexes, or to one sex alone, more com- 
monly but not exclusively to the like sex. It is a fact 
of some little importance to us, that peculiarities appear- 
ing- in the males of our domestic breeds are often trans- 
mitted 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 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 silkworm are known to appear at 
the corresponding 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 apparent 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 reversion, I may 
here refer to a statement often 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 



14 ON THE ORIGIN OF SPECIES 

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 inter- 
crossing, that only a single variety should be turned 
loose in its new home. Nevertheless, as our varieties 
certainly 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 experi- 
ment 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 char- 
acters, whilst kept under the same conditions, and whilst 
kept in a considerable body, so that free intercrossing 
might check, by blending together, any slight devia- 
tions 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, varia- 
tions and reversions of character probably 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 or races of 
our domestic animals and plants, and compare them 



VARIATION UNDER DOMESTICATION 15 

with closely-allied species, we generally perceive in 
each domestic race, as already remarked, less uni- 
formity 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 
differing from 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 
amongst animals or plants, which have not been 
ranked by competent judges as mere varieties, and by 
other competent judges as the descendants of aborigin- 
ally distinct species. If any marked distinction ex- 
isted between domestic races and species, this source of 
doubt could not so perpetually 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 
naturalists 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 struc- 
tural 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, 



16 ON THE ORIGIN OF SPECIES 

terrier, spaniel, and bull-dog, which we all know pro- 
pagate their kind so truly, 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 we shall presently see, that 
the whole amount of difference between the several 
breeds of the dog has been produced under domestica- 
tion ; I 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 evidence, 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 extra- 
ordinary 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 productions ; but how could a savage 
possibly know, when he first tamed an animal, whether 
it would vary in succeeding generations, and whether 
it would endure other climates ? Has the little varia- 
bility 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 
domestication, they would vary on an average as largely 
as the parent species of our existing domesticated pro- 
ductions have varied. 

In the case of most of our anciently domesticated 
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 



VARIATION UNDER DOMESTICATION 17 

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 
sufficiently 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 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 con- 
siderations, 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 throughout 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, 1 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 any one, thinks 
that all the breeds of poultry have proceeded from the 
common wild Indian fowl (Gallus bankiva). In regard 

c 



18 ON THE ORIGIN OF SPECIES 

to ducks and rabbits, the breeds of which differ con- 
siderably 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, j 
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 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 de- 
scended from several wild species, I cannot doubt that 
there has been an immense amount of inherited varia- 
tion. 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, bloodhound, bull-dog, etc., 
in the wild state. Moreover, the possibility of making 
distinct races by crossing has been greatly exaggerated. 






VARIATION UNDER DOMESTICATION 19 

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 ex- 
pressly 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 difficulty, 
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 permanent race having 
been thus formed. 

On the Breeds of the Domestic Pigeon. — Believing 
that it is always best to study some special group, J 
have, after deliberation, 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 
antiquity. 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 



20 ON THE ORIGIN OF SPECIES 

gape of mouth. The short-faced tumbler has a beak J 
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, j 
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 singularly 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 I 
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 J 
it has the habit of continually 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 J 
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 develop- | 
ment of the bones of the face in length and breadth and 
curvature differs enormously. The shape, as well as 1 
the breadth and length of the ramus of the lower jaw, 
varies in a highly remarkable manner. The number 
of the caudal and 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 J 
the degree of divergence and relative size of the two I 
arms of the furcula. The proportional width of the J 
gape of mouth, the proportional length of the eyelids, ] 



VARIATION UNDER DOMESTICATION 21 

o* 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 development 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 development 
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 ornithologist 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 de- 
scended from the rock-pigeon (Columba livia), including 
under this term several geographical races or sub- 
species, which differ from each other in the most trifling 
respects. As several of the reasons which have led me 
to this belief are in some degree applicable 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 im- 
possible to make the present domestic breeds by the 



22 ON THE ORIGIN OF SPECIES 

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 enor- 
mous crop? The supposed aboriginal stocks must 
all have been rock-pigeons, that is, not breeding 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, con- 
sidering their size, habits, and remarkable characters, 
seems very improbable ; or they must have become 
extinct in the wild state. But birds breeding on preci- 
pices, 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 exter- 
minated 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 above-named 
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 con- 
stitution, habits, voice, colouring, and in most parts of 



VARIATION UNDER DOMESTICATION 23 

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 Columbidae 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 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 intention- 
ally or by chance picked out extraordinarily abnormal 
species ; and further, that these very species have since 
all become extinct or unknown. So many strange con- 
tingencies 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, beside 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 perfectly 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 understand these facts, on the well-known principle 



24 ON THE ORIGIN OF SPECIES 

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, although 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 counten- 
ancing the belief that the child ever reverts to some 
one ancestor, removed by a greater number of genera- 
tions. 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 genera- 
tion 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 char- 
acter, which has been lost during some former 
generation, this tendency, for all that we can see to 
the contrary, may be transmitted undiminished 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 difficult, 
perhaps impossible, to bring forward one case of the 
hybrid offspring of two animals clearly distinct being 
themselves 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 ex- 
tend the hypothesis so far as to suppose that species, 



VARIATION UNDER DOMESTICATION 25 

aboriginally as distinct as carriers, tumblers, pouters, 
and fantails now are, should yield offspring perfectly 
fertile, inter $e, 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 domestica- 
tion ; these supposed species being quite unknown in 
a wild state, and their becoming nowhere feral ; these 
species having very abnormal characters in certain re- 
spects, as compared with all other Columbidse, though so 
like in most other respects to the rock-pigeon ; the blue 
colour and various marks occasionally 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 found capable of 
domestication in Europe and in India ; and that it 
agrees in habits and in a great number of points of 
structure with all the domestic breeds. Secondly, 
although an English carrier or short-faced tumbler 
differs immensely in certain characters from the rock- 
pigeon, yet by comparing the several sub -breeds of 
these varieties, more especially those brought from 
distant countries, we can make an almost perfect series 
between the extremes of structure. Thirdly, those 
characters which are mainly distinctive of each breed, 
for instance the wattle and length of beak of the 
carrier, the shortness of that of the tumbler, and the 
number of tail-feathers in the fantail, are in each breed 
eminently variable ; and the explanation of this fact 
will be obvious when we come to treat of selection. 
Fourthly, pigeons have been watched, and tended with 
the utmost care, and loved by many people. They 
have been domesticated for thousands of years in 
several quarters of the world ; the earliest known 
record of pigeons is in the fifth Egyptian dynasty, about 
3000 B.C., as was pointed out to me by Professor 



26 ON THE ORIGIN OF SPECIES 

Lepsius ; but Mr. Birch informs me that pigeons are 
given in a bill of fare in the previous dynasty. In the 
time of the Romans, as we hear from Pliny, immense 
prices were given for pigeons ; ' nay, they are come to 
this pass, that they can reckon up their pedigree and 
race.' Pigeons were much valued by Akber Khan in 
India, about the year 1600 ; never less than 20,000 
pigeons were taken with the court. f The monarchs 
of Iran and Turan sent him some very rare birds'; 
and, continues the courtly historian, f His Majesty 
by crossing the breeds, which method was never 
practised before, has improved them astonishingly.' 
About this same period the Dutch were as eager about 
pigeons as were the old Romans. The paramount 
importance of these considerations in explaining the 
immense amount of variation which pigeons have 
undergone, will be obvious when we treat of Selection. 
We shall then, also, see how it is that the breeds so 
often have a somewhat monstrous character. It is 
also a most favourable circumstance for the production 
of distinct breeds, that male and female pigeons can 
be easily mated for life ; and thus different breeds can 
be kept together in the same aviary. 

I have discussed the probable origin of domestic 
pigeons at some, yet quite insufficient, length ; because 
when I first kept pigeons and watched the several 
kinds, knowing well how true they bred, I felt fully 
as much difficulty in believing that they could have 
descended from a common parent, as any naturalist 
could in coming to a similar conclusion in regard to 
the many species of finches, or other large groups of 
birds, in nature. One circumstance has struck me 
much ; namely, that all the breeders of the various 
domestic animals and the cultivators of plants, with 
whom I have ever conversed, or whose treatises I have 
read, are firmly convinced that the several breeds to 
which each has attended, are descended from so many 
aboriginally distinct species. Ask, as I have asked, a 
celebrated raiser of Hereford cattle, whether his cattle 
might not have descended from long-horns, and he will 



VARIATION UNDER DOMESTICATION 27 

iaugh you to scorn. I have never met a pigeon, or 
poultry, or duck, or rabbit fancier, who was not fully 
convinced that each main breed was descended from a 
distinct species. Van Mons, in his treatise on pears 
and apples, shows how utterly he disbelieves that the 
several sorts, for instance a Ribston-pippin or Codlin- 
apple, could ever have proceeded from the seeds of the 
same tree. Innumerable other examples could be 
given. The explanation, I think, is simple : from long- 
continued study they are strongly impressed with the 
differences between the several races ; and though 
they well know that each race varies slightly, for they 
win their prizes by selecting such slight differences, yet 
they ignore all general arguments, and refuse to sum 
up in their minds slight differences accumulated during 
many successive generations. May not those natural- 
ists who, knowing far less of the laws of inheritance 
than does the breeder, and knowing no more than he 
does of the intermediate links in the long lines of 
descent, yet admit that many of our domestic races 
have descended from the same parents — may they not 
learn a lesson of caution, when they deride the idea of 
species in a state of nature being lineal descendants of 
other species ? 

Selection. — Let us now briefly consider the steps by 
which domestic races have been produced, either from 
one or from several allied species. Some little effect 
may, perhaps, be attributed to the direct action of the 
external conditions of life, and some little to habit ; but 
he would be a bold man who would account by such 
agencies for the differences of a dray and a race horse, 
a greyhound and bloodhound, a carrier and tumbler 
pigeon. One of the most remarkable features in our 
domesticated races is that we see in them adaptation, 
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 



28 ON THE ORIGIN OF SPECIES 

Dipsacus ; and this amount of change may have sucL 
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 dromedary 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 ' ever- 
lasting layers ' which never desire to sit, and with 
the bantam so small and elegant ; when we compare 
the host of agricultural, culinary, orchard, and flower- 
garden 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 com- 
petent authorities. Youatt, who was probably better 
acquainted with the works of agriculturists than 
almost any other individual, and who was himself a 



VARIATION UNDER DOMESTICATION 29 

very good judge of an animal, speaks of the principle of 
selection as ' that which enables the agriculturist, not 
only to modify the character 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 Somerville, 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 amongst closely allied sub- 
breeds. And when a cross has been made, the closest 
selection is far more indispensable even than in ordi- 
nary cases. If selection consisted merely in separating 
some very distinct variety, and breeding from it, the 
principle would be so obvious as hardly to be worth 
notice ; but its importance consists in the great effect 
produced by the accumulation in one direction, during 
successive generations, of differences absolutely in- 
appreciable 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 judgment 
sufficient to become an eminent breeder. If gifted 
with these qualities, and he studies his subject for 



30 ON THE ORIGIN OF SPECIES 

years, and devotes his lifetime to it with indomitable 
perseverance, he will succeed, and may make gTeat 
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 be- 
come even a skilful pigeon-fancier. 

The same principles are followed by horticulturists ; 
but the variations are here often more abrupt. No one 
supposes that our 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- increasing size of 
the common gooseberry may be quoted. We see an 
astonishing improvement 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 any one is so careless as 
to allow his worst animals to breed. 

In regard to plants, there is another means of ob- 
serving 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 com- 
parison 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 hairi- 
ness, and yet the flowers present very slight differences. 
It is not that the varieties which differ largely in some 



VARIATION UNDER DOMESTICATION 31 

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 three-quarters 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 corresponding degree, rapid and important. But 
it is very far from true that the principle is a modern 
discovery. I could give several references to the full 
acknowledgment 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 may be compared to the ' roguing ' of plants 
by nurserymen. The principle of selection I find dis- 
tinctly 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. Livingstone 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 



32 ON THE ORIGIN OF SPECIES 

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 Unconscious, and 
which results from every one trying to possess and 
breed from the best individual animals, is more im- 
portant. Thus, a man who intends keeping pointers 
naturally tries to get as good dogs as he can, and after- 
wards breeds from his own best dogs, but he has no 
wish or expectation of permanently altering the breed. 
Nevertheless I cannot doubt that this process, con- 
tinued 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 
methodically, 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 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 dis- 
tricts, 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 
ns 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. 



VARIATION UNDER DOMESTICATION 33 

By a similar process of selection, and by careful train- 
ing, the whole body of English racehorses 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 un- 
consciously followed, in so far that the breeders could 
never have expected or even have wished to have pro- 
duced 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 re- 
marks, ' 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 use- 
ful 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 

D 



34 ON THE ORIGIN OF SPECIES 

old women, in times of dearth, as of less value thau 
their dog's. 

In plants the same gradual process of improvement, 
through the occasional preservation of the best indi- 
viduals, whether or not sufficiently distinct to be ranked 
at their first appearance as distinct varieties, and whethei 
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 de- 
scription, 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 cultivated 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 chosen and preserved the best varieties they 
could anywhere find. 

A large amount of change in our cultivated 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 



VARIATION UNDER DOMESTICATION 3S 

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 can 
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 abori- 
ginal 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 overlooked 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 all-important part 
which selection by man has played, it becomes at once 
obvious how it is that our domestic races show adapta- 
tion in their structure or in their habits to man's wants 
or fancies. We can, I think, further understand the 
frequently abnormal character of our domestic races, 
and likewise their differences being so great in external 
characters and relatively so slight in internal 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, ex- 
cepting on variations which are first given to him in 
some slight degree by nature. No man would ever try 



36 ON THE ORIGIN OF SPECIES 

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 some- 
what expanded, like the present Java fantail, or like 
individuals 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, however slight, in 
one's own possession. Nor must the value which would 
formerly be set on any slight differences in the indi- 
viduals 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 differ- 
ences might, and indeed do now, arise amongst 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 some- 
times been noticed — namely, that we know nothing 
about the origin or history of any of our domestic 



VARIATION UNDER DOMESTICATION 37 

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 have a distinct name, and from being 
only slightly valued, their history will be disregarded. 
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 b6 
a slow process. As soon as the points of value of the 
new sub-breed are once fully acknowledged, the prin- 
ciple, 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. 

I 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 



38 ON THE ORIGIN OF SPECIES 

belong 1 to poor people, and are mostly in small lots t 
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 conditions of life, so as to breed freely 
in that country. When the individuals of any species 
are scanty, all the individuals, whatever 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 straw- 
berry 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 new 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 convenience to the 
fancier, for thus many races may be kept true, though 
mingled in the same aviary ; and this circumstance 



VARIATION UNDER DOMESTICATION 39 

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 im- 
ported 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 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 variability. 
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 cor- 
relation of growth. Something may be attributed to 
the direct action of the conditions of life. Something 
must be attributed to use and disuse. The final result 
is thus rendered infinitely complex. In some cases, I 
do not doubt that the intercrossing of species, aborigin- 
ally distinct, has played an important part in the origin 
of our domestic productions. When in any country 
several domestic breeds have once been established, 



40 ON THE ORIGIN OF SPECIES 

their occasional intercrossing, 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 importance 
to us, for their endurance is only temporary. Over all 
these causes of Change I am convinced that the 
accumulative action of Selection, whether applied 
methodically and more quickly, or unconsciously and 
more slowly, but more efficiently, is by far the pre- 
dominant Power. 



CHAPTER II 

VARIATION UNDER NATl/RE 

Variability— 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 f 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 
implying a modification directly due to the physical 
conditions of life ; and ' variations ' in this sense are 
supposed not to be inherited : but who can say that the 

41 



42 ON THE ORIGIN OF SPECIES 

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. 

Again, we have many slight differences which may 
be called individual differences, such as are known 
frequently to appear in the offspring from the 
same parents, or which may be presumed to have thus 
arisen, from being frequently observed in the indivi- 
duals of the same species inhabiting the same confined 
locality. No one supposes that all the individuals 
of the same species are cast in the very same mould. 
These individual differences are highly important for 
us, as they afford materials for natural selection to 
accumulate, in the same manner as man can accumu- 
late in any given direction individual differences in his 
domesticated productions. These individual differences 
generally affect what naturalists consider unimportant 
parts ; but I could show by a long catalogue of facts, 
that parts which must be called important, whether 
viewed under a physiological or classificatory point of 
view, sometimes vary in the individuals of the same 
species. I am convinced that the most experienced 
naturalist would be surprised at the number of the cases 
of variability, even in important parts of structure, which 
he could collect on good authority, as I have collected, 
during a course of years. It should be remembered 
that systematists are far from pleased at finding varia- 
bility in important characters, and that there are not 
many men who will laboriously examine internal and 
important organs, and compare them in many speci- 
mens of the same species. I should never have expected 
that the branching of the main nerves close to the great 
central ganglion of an insect would have been variable 
in the same species ; I should have expected that 
changes of this nature could have been effected only 
by slow degrees : yet quite recently Mr. Lubbock has 
shown a degree of variability in these main nerves 



VARIATION UNDER NATURE 43 

in Coccus, which may almost be compared to the 
irregular branching of the stem of a tree. This 
philosophical naturalist, I may add, has also quite 
recently shown that the muscles in the larvaB of certain 
insects are very far from uniform. Authors sometimes 
argue in a circle when they state that important organs 
never vary ; for these same authors practically rank 
that character as important (as some few naturalists 
have honestly confessed) which does not vary ; and, 
under this point of view, no instance of an important 
part varying will ever be found : but under any other 
point of view many instances assuredly can be given. 

There is one point connected with individual differ- 
ences which seems to me extremely perplexing : I refer 
to those genera which have sometimes been called 
' protean ' or ' polymorphic,' in which the species 
present an inordinate amount of variation ; and hardly 
two naturalists can agree which forms to rank as 
species and which as varieties. We may instance 
Rubus, Rosa, and Hieracium amongst plants, several 
genera of insects, and several genera of Brachiopod 
shells. In most polymorphic genera some of the 
species have fixed and definite characters. Genera 
which are polymorphic in one country seem to be, with 
some few exceptions, polymorphic in other countries, 
and likewise, judging from Brachiopod shells, at former 
periods of time. These facts seem to be very per- 
plexing, for they seem to show that this kind of varia- 
bility is independent of the conditions of life. I am 
inclined to suspect that we see in these polymorphic 
genera variations in points of structure which are of no 
service or disservice to the species, and which con- 
sequently have not been seized on and rendered 
definite by natural selection, as hereafter will be 
explained. 

Those forms which possess in some considerable 
degree the character of species, but which are so 
closely similar to some other forms, or are so closely 
linked to them by intermediate gradations, that 
naturalists do not like to rank them as distinct species, 



44 ON THE ORIGIN OF SPECIES 

are in several respects the most important for us. We 
have every reason to believe that many of these 
doubtful and closely-allied forms have permanently 
retained their characters in their own country for a 
long time ; for as long, as far as we know, as have 
good and true species. Practically, when a naturalist 
can unite two forms together by others having inter- 
mediate characters, he treats the one as a variety of 
the other, ranking the most common, but sometimes 
the one first described, as the species, and the other as 
the variety. But cases of great difficulty, which I will 
not here enumerate, sometimes occur in deciding 
whether or not to rank one form as a variety of 
another, even when they are closely connected by 
intermediate links ; nor will the commonly-assumed 
hybrid nature of the intermediate links always remove 
the difficulty. In very many cases, however, one form 
is ranked as a variety of another, not because the 
intermediate links have actually been found, but 
because analogy leads the observer to suppose either 
that they do now somewhere 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 natural- 
ists 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 well-known varieties can be named which 
have not been ranked as species by at least some com- 
petent judges. 

That varieties of this doubtful nature are far from 
uncommon cannot be disputed. 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 



VARIATION UNDER NATURE 45 

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, including the most polymorphic forms, 
Mr. Babington gives 251 species, whereas Mr. Ben- 
tham gives only 112, — a difference of 139 doubtful 
forms ! Amongst 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. Wol- 
laston's admirable work, but which it cannot be doubted 
would be ranked as distinct species by many entomo- 
logists. Even Ireland has a few animals, now generally 
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 ef two doubtful forms leads many naturalists 
to rank both as distinct species ; but what distance, it has 
been well asked, will suffice? 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, 



46 ON THE ORIGIN OF SPECIES 

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 dis- 
tribution, 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 con- 
siderably 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 natural- 
ists to an agreement how to rank doubtful forms. Yet 
it must be confessed that it is in the best- known 
countries 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 



VARIATION UNDER NATURE 47 

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 considered 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 perplexed 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 impres- 
sions. 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 admission will often 
be disputed by other naturalists. When, moreover, Jh.e 
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 



48 ON THE ORIGIN OF SPECIES 

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 im- 
presses 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 hereafter be more fully explained) differences 
of structure in certain definite directions. Hence I 
believe a well-marked variety may be called an in- 
cipient 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 whilst 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 exterminate the parent species ; or both 
might co-exist, and both rank as independent species. 
But we shall hereafter have to return to this subject. 



VARIATION UNDER NATURE 49 

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 
applied arbitrarily, and for mere convenience' 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 difficulties, 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 pro- 
portional numbers of the varying species. Dr. Hooker 
permits me to add, that after having carefully read my 
manuscript, 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 exist- 
ence,' ' divergence of character,' and other questions, 
hereafter 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), 



50 ON THE ORIGIN OF SPECIES 

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 modi- 
fied, still inherit those advantages 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 some- 
what larger number of the very common and much 
diffused or dominant species will be found 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, conse- 
quently, 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 



VARIATION UNDER NATURE 51 

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. 

l'rom looking at species as only strongly-marked 
and well-defined varieties, I was led to anticipate that 
the species of the larger genera in each country would 
oftener present varieties, than the species of the smaller 
genera ; for wherever many closely-related species (i.e. 
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, circum- 
stances have been favourable for variation ; and hence 
we might expect that the circumstances 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. 

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 pro- 
portion 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 
signification 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 generally to find 



52 ON THE ORIGIN OF SPECIES 

the manufactory still in action, more especially as we 
have every reason to believe the process of manufactur- 
ing 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 well- 
marked varieties ; and in those cases in which inter- 
mediate links have not been found between doubtful 
forms, naturalists are compelled to come to a deter- 
mination 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 
3pecies 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 deliberation, they concur in this view. In 
this respect, therefore, the species of the larger generm 



VARIATION UNDER NATURE 53 

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 manufacturing, 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 natur- 
alist 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 varieties but groups of forms, unequally 
related to each other, and clustered round certain 
forms — that is, round their parent-species ? Undoubt- 
edly there is one most important point of difference 
between varieties and species ; namely, that the amount 
of difference between varieties, when compared 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 differ- 
ences 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 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. 
W atson has marked for me in the well-sifted London 
Catalogue of plants (4th edition) 63 plants which are 



54 ON THE ORIGIN OF SPECIES 

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 acknow- 
ledged 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 acknow- 
ledged 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 cannot 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- 
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 independently 
created. 

We have, also, seen that it is the most flourishing 



VARIATION UNDER NATURE 55 

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 
■pedes. 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 subordinate 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 — Com- 
petition 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 relations. 

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 amongst organic 
beings in a state of nature there is some individual vari- 
ability : 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 existence 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 perfected ? We see these beauti- 
ful co-adaptations most plainly in the woodpecker and 

56 



STRUGGLE FOR EXISTENCE 57 

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 beauti- 
ful adaptations everywhere 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 con- 
verted 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, and from whatever 
cause proceeding, if it be in any degree profitable to an 
individual of any species, in its infinitely complex rela- 
tions 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 off- 
spring, also, will thus have a better chance of surviving, 
for, of the many individuals of any species which are 
periodically born, but a small number can survive. 
1 have called this principle, by which each slight vari- 
ation, if useful, is preserved, by the term of Natural 
Selection, in order to mark its relation to man's power 
of selection. 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. 



68 ON THE ORIGIN OF SPECIES 

The elder de Candolle and Lyell have largely and philo- 
sophically shown that all organic beings are exposed 
to severe competition. In regard to plants, no one has 
treated this subject with more spirit and ability than 
W. Herbert, Dean of Manchester, 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 constantly 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 metaphorical sense, including 
dependence of one being on another, and including 
(which is more important) not only the life of the indi- 
vidual, 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 dependent 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 mistletoe is dependent on the apple and a few other 
trees, but can only in a far-fetched sense be said to 
struggle with these trees, for if too many of these para- 
sites grow on the same tree, it will languish and dia. 



STRUGGLE FOR EXISTENCE 59 

But several seedling mistletoes, growing- close together 
on the same branch, may more truly be said to struggle 
with each other. As the mistletoe is disseminated by 
birds, its existence depends on birds ; and it may meta- 
phorically be said to struggle with other fruit-bearing 
plants, in order to tempt birds to devour and thus 
disseminate its seeds rather than those of other plants. 
In these several senses, which pass into each other, I 
use for convenience' sake the general term of struggle 
for existence. 

A struggle for existence inevitably follows from the 
high rate at which all organic beings tend to increase. 
Every being, which during its natural lifetime produces 
several eggs or seeds, must suffer destruction during 
some period of its life, and during some season or occa- 
sional year, otherwise, on the principle of geometrical 
increase, its numbers would quickly become so in- 
ordinately great that no country could support the 
product. Hence, as more individuals are produced 
than can possibly survive, there must in every case 
be a struggle for existence, either one individual with 
another of the same species, or with the individuals of 
distinct species, or with the physical conditions of life. 
It is the doctrine of Malthus applied with manifold 
force to the whole animal and vegetable kingdoms ; for 
in this case there can be no artificial increase of food, 
and no prudential restraint from marriage. Although 
some species may be now increasing, more or less 
rapidly, in numbers, all cannot do so, for the world 
would not hold them. 

There is no exception to the rule that every organic 
being naturally increases at so high a rate, that if not 
destroyed, the earth would soon be covered by the 
progeny of a single pair. Even slow-breeding man has 
doubled in twenty-five years, and at this rate, in a few 
thousand years, there would literally not be standing 
room for his progeny. Linnaeus has calculated that if 
an annual plant produced only two seeds — and there is 
no plant so unproductive as this — and their seedlings 
next year produced two, and so on, then in twenty 



60 ON THE ORIGIN OF SPECIES 

years there would be a million plants. The elephant is 
reckoned the slowest breeder of all known animals, 
and I have taken some pains to estimate its probable 
minimum rate of natural increase : it will be under the 
mark to assume that it breeds when thirty years old, 
and goes on breeding till ninety years old, bringing 
forth three pair of young in this interval ; if this be so, 
at the end of the fifth century there would be alive 
fifteen million elephants, descended from the first pair. 
But we have better evidence on this subject than 
mere theoretical calculations, namely, the numerous 
recorded cases of the astonishingly rapid increase of 
various animals in a state of nature, when circumstances 
have been favourable to them during two or three 
following seasons. Still more striking is the evidence 
from our domestic animals of many kinds which have 
run wild in several parts of the world : if the statements 
of the rate of increase of slow-breeding cattle and 
horses in South America, and latterly in Australia, had 
not been well authenticated, they would have been 
incredible. So it is with plants : cases could be given 
of introduced plants which have become common 
throughout whole islands in a period of less than ten 
years. Several of the plants, such as the cardoon and 
a tall thistle, now most numerous over the wide plains 
of La Plata, clothing square leagues of surface almost 
to the exclusion of all other plants, have been intro- 
duced from Europe ; and there are plants which now 
range in India, as I hear from Dr. Falconer, from Cape 
Comorin to the Himalaya, which have been imported 
from America since its discovery. In such cases, and 
endless instances could be given, no one supposes that 
the fertility of these animals or plants has been suddenly 
and temporarily increased in any sensible degree. The 
obvious explanation is that the conditions of life have 
been very favourable, and that there has consequently 
been less destruction of the old and young, and that 
nearly all the young have been enabled to breed. In 
such cases the geometrical ratio of increase, the 
result of which never fails to be surprising, simply 



STRUGGLE FOR EXISTENCE 61 

explains the extraordinarily rapid increase and wide 
diffusion of naturalised productions in their new homes. 

In a state of nature almost every plant produces seed, 
and amongst animals there are very few which do not 
annually pair. Hence we may confidently assert, that 
all plants and animals are tending to increase at a 
geometrical ratio, that all would most rapidly stock 
every station in which they could anyhow exist, and 
that the geometrical tendency to increase must be 
checked by destruction at some period of life. Our 
familiarity with the larger domestic animals tends, 
I think, to mislead us : we see no great destruction 
falling on them, and we forget that thousands are 
annually slaughtered for food, and that in a state of 
nature an equal number would have somehow to be 
disposed of. 

The only difference between organisms which annually 
produce eggs or seeds by the thousand, and those which 
produce extremely few, is, that the slow-breeders would 
require a few more years to people, under favourable 
conditions, a whole. district, let it be ever so large. 
The condor lays a couple of eggs and the ostrich a score, 
and yet in the same country the condor may be the 
more numerous of the two : the Fulmar petrel lays 
but one egg, yet it is believed to be the most numerous 
bird in the world. One fly deposits hundreds of eggs, 
and another, like the hippobosca, a single one ; but 
this difference does not determine how many indi- 
viduals of the two species can be supported in a district. 
A large number of eggs is of some importance to those 
species which depend on a rapidly fluctuating amount 
of food, for it allows them rapidly to increase in 
number. But the real importance of a large number 
of eggs or seeds is to make up for much destruction 
at some period of life ; and this period in the great 
majority of cases is an early one. If an animal can in 
any way protect its own eggs or young, a small number 
may be produced, and yet the average stock be fully 
kept up; but if many eggs or young are destroyed, many 
must be produced, or the species will become extinct 



62 ON THE ORIGIN OF SPECIES 

It would suffice to keep up the full number of a tree, 
which lived on an average for a thousand years, if a 
single seed were produced once in a thousand years, 
supposing that this seed were never destroyed, and 
could be ensured to germinate in a fitting place. 
So that in all cases, the average number of any animal 
or plant depends only indirectly on the number of its 
eggs or seeds. 

In looking at Nature, it is most necessary to keep 
the foregoing considerations always in mind — never to 
forget that every single organic being around us may 
be said to be striving to the utmost to increase in 
numbers ; that each lives by a struggle at some period 
of its life ; that heavy destruction inevitably falls 
either on the young or old, during each generation 
or at recurrent intervals. Lighten any check, mitigate 
the destruction ever so little, and the number of the 
species will almost instantaneously increase to any 
amount. 

The causes which check the natural tendency of each 
species to increase in number are most obscure. Look 
at the most vigorous species ; by as much as it swarms 
in numbers, by so much will its tendency to increase 
be still further increased. We know not exactly what 
the checks are in even one single instance. Nor will 
this surprise any one who reflects how ignorant we are 
on this head, even in regard to mankind, so incompar- 
ably better known than any other animal. This subject 
has been ably treated by several authors, and I shall, 
in my future work, discuss some of the checks at con- 
siderable length, more especially in regard to the feral 
animals of South America. Here I will make only a 
few remarks, just to recall to the reader's mind some 
of the chief points. Eggs or very young animals seem 
generally to suffer most, but this is not invariably the 
case. With plants there is a vast destruction of seeds, 
but, from some observations which I have made, I 
believe that it is the seedlings which suffer most from 
germinating in ground already thickly stocked with 
other plants. Seedlings, also, are destroyed in vagi 



STRUGGLE FOR EXISTENCE 63 

numbers by various enemies ; for instance, on a piece 
of ground three feet long- and two wide, dug and 
cleared, and where there could be no choking from 
other plants, 1 marked all the seedlings of our native 
weeds as they came up, and out of the 857 no less than 
295 were destroyed, chiefly by slugs and insects. If 
turf which has long been mown, and the case would be 
the same with turf closely browsed by quadrupeds, be 
let to grow, the more vigorous plants gradually kill the 
less vigorous, though fully grown, plants : thus out of 
twenty species growing on a little plot of turf (three 
feet by four) nine species perished from the other species 
being allowed to grow up freely. 

The amount of food for each species of course gives 
the extreme limit to which each can increase ; but very 
frequently it is not the obtaining food, but the serving 
as prey to other animals, which determines the average 
numbers of a species. Thus, there seems to be little 
doubt that the stock of partridges, grouse, and hares on 
any large estate depends chiefly on the destruction of 
vermin. If not one head of game were shot during 
the next twenty years in England, and, at the same 
time, if no vermin were destroyed, there would, in all 
probability, be less game than at present, 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 iD India most rarely 
dares to attack a young elephant protected by its dam. 

Climate plays an important part in determining 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 
1854r-55 destroyed four-fifths of the birds in my own 
grounds ; and this is a tremendous 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 existence ; but in so far as climate 
chiefly acts in reducing food, it brings on the most 



64 ON THE ORIGIN OF SPECIES 

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 advanc- 
ing 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 disappearing ; 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 de- 
struction 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 decreas- 
ing 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 somewhat lesser degree, for the number of 
species of all kinds, and therefore of competitors, 
decreases northwards ; hence in going northward, or 
in ascending a mountain, we far oftener meet with 
stunted forms, due to the directly injurious action of 
climate, than we do in proceeding southwards or in 
descending a mountain. When we reach the Arctic 
regions, or snow-capped summits, or absolute desert-?, 
the struggle for life is almost exclusively with the 
elements. 

That climate acts in main part indirectly by favour- 
ing 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 favourable circum- 



STRUGGLE FOR EXISTENCE 65 

stances, increases inordinately in numbers in a small 
tract, epidemics — at least, this seems generally to occur 
with our game animals — often ensue : and 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 from 
some cause, possibly in part through facility of diffusion 
amongst the crowded animals, been disproportionably 
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 num- 
bers of its enemies, is absolutely necessary for its pre- 
servation. Thus we can easily raise plenty of corn and 
rape-seed, etc., in our 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 this one season, increase in 
number proportionally to the supply of seed, as their 
numbers are checked during winter : but any one who 
has tried, knows how troublesome 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 some- 
times extremely abundant in the few spots where they 
do occur ; and that of some social plants 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 con- 
ditions 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 inter- 
breeding, probably come into play in some of these cases; 
but on this intricate subject I will not here enlarge. 

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 

F 



66 ON THE ORIGIN OF SPECIES 

country. I will give only a single instance, which, 
though a simple one, has interested me. In Stafford- 
shire, on the estate of a relation, where I had ample 
means of investigation, 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 proportional numbers of the heath-plants were 
wholly changed, but twelve species of plants (not 
counting grasses and carices) flourished in the planta- 
tions, which could not be found on the heath. The 
effect on the insects must have been still greater, for 
six insectivorous birds were very common in the planta- 
tions, 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 



STRUGGLE FOR EXISTENCE 67 

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 be- 
came 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 closely and effectually searched it for food. 

Here we see that cattle absolutely determine the 
existence of the Scotch fir ; but in several parts of 
the world insects determine 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 prob- 
ably 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. Nevertheless 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 



68 ON THE ORIGIN OF SPECIES 

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 structure, 
never can set a seed. Many of our orchidaceous plants 
absolutely require the visits of moths to remove their 
pollen-masses and thus to fertilise them. 1 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 J 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 humble-bees became extinct or very 
rare in England, the heartsease and red clover would 
become very rare, or wholly disappear. 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. Newman, 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 every one 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 in 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 



STRUGGLE FOR EXISTENCE 69 

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 
surrounding virgin forests. WTiat a struggle between 
the several kinds of trees must here have gone on 
during long centuries, each annually scattering it* 
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 their 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 propor- 
tional 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 exposed to the same 
dangers. In the case of varieties of the same species, 



70 ON THE ORIGIN OF 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 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 con- 
stitution, that the original proportions of a mixed 
stock could be kept up for half-a-dozen generations, if 
they were allowed to struggle together, like beings in a 
state of 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 be 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 frequently we hear 
of one species of rat taking the place of another species 
under the most different climates ! In Russia the 
■mall Asiatic cockroach has everywhere driven before it 
its great congener. One species of charlock will tup- 



STRUGGLE FOR EXISTENCE 71 

plant another, and so in other cases. We can dimlj 
see why the competition should be most severe betweei: 
allied forms, which fill nearly the same place in the- 
economy of nature ; but probably in no one case could 
we precisely say why one species has been victorious 
over another in the great battle of life. 

A corollary of the highest importance may be de- 
duced 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 residence, 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 advantage 
of plumed seeds no doubt stands in the closest re- 
lation 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 compete 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, whilst strug- 
gling 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 



72 ON THE ORIGIN OF SPECIES 

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 confines 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 
competition cease. The land may be 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 amongst 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 competitors 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 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 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 inter- 
crosses between individuals of the same species — Circumstance? 
favourable and unfavourable to Natural Selection, namely, inter- 
crossing, isolation, number of individuals — Slow action — Extinc- 
tion caused by Natural Selection — Divergence of Character, 
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 Grouping of all organic beings. 

How will the struggle for existence, discussed 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 ? 1 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 productions, 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 com- 
plex battle of life, should sometimes occur in the course 
of thousands of generations ? If such do occur, can we 

73 



74 ON THE ORIGIN OF SPECIES 

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 hanc^ 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 under- 
going some physical change, for instance, of climate. 
The proportional 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 to- 
gether, 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 introduced 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, 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 pre- 



NATURAL SELECTION 75 

served ; 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 conditions 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 selection, 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 incom- 
parably 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, extremely slight 
modifications in the structure or habits of one in- 
habitant 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 everywhere beaten some of the natives, we may 
safely conclude that the natives might have been modi- 
fied 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 



76 ON THE ORIGIN OF SPECIES 

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 long-backed 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 half-monstrous form ; or at least by some modifi- 
cation 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 nicely- 
balanced scale in the struggle for life, and so be pre- 
served. How fleeting are the wishes and efforts of man ] 
how short his time! and consequently how poor will 
his products be, compared with those accumulated 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 condi- 
tions 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 
opportunity offers, at the improvement of each organic 



NATURAL SELECTION 



being in relation to its organic and inorganic condi- 
tions 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 are apt to consider as of very trifling import- 
ance, may thus be acted on. W"hen 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 selec- 
tion 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 considered 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 differences make 



78 ON THE ORIGIN OF SPECIES 

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 effectually settle which 
variety, whether a smooth or downy, a yellow or purple 
fleshed fruit, should succeed. 

In looking at many small points of difference be- 
tween 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 
organisation is modified through variation, and the 
modifications are accumulated by natural selection for 
the good of the being, will cause other modifications, 
often of the most unexpected nature. 

As we see that those variations which under domesti- 
cation appear at any particular period of life, tend to 
reappear in the offspring at the same period ; — for in- 
stance, 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 inheritance at a corresponding age. If it profit a 
plant to have its seeds more and more widely dissemi- 
nated 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 
structure of the adult; and probably in the case of those 
insects which live only for a few hours, and which never 



NATURAL SELECTION 79 

feed, a large part of their structure is merely the cor- 
related result of successive changes in the structure of 
their larvae. So, conversely, modifications 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 structure of one species, without giving it any advan- 
tage, for the good of another species ; and though state- 
ments to this effect may be found in works of natural 
history, I cannot find one case which will bear investi- 
gation. A structure used only once in an animal's whole 
life, if of high importance to it, might be modified to 
any extent by 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 peculiarities often 
appear under domestication in one sex and become 



80 ON THE ORIGIN OF SPECIES 

hereditarily attached to that sex, the same fact prob- 
ably occurs under nature, and if so, natural selection 
will be able to modify one sex in its functional rela- 
tions 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 existence, 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 allow- 
ing 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 careful 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 pro- 
vided 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. 

Amongst birds, the contest is often of a more peaceful 
character. All those who have attended to the subject, 



NATURAL SELECTION 81 

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, congregate ; 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 appar- 
ently weak means : I cannot here enter on the details 
necessary to support this 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 melodious or beau- 
tiful 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 comparison 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 corre- 
sponding 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 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 attri- 
bute all such sexual differences to this agency : for we 

o 



82 ON THE ORIGIN OF SPECIES 

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 selec- 
tion 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 can under 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 im- 
prove 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 proportional 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 im- 
probable ; for we often observe great differences in the 
natural tendencies of our domestic animals ; one cat, j 
for instance, taking to catch rats, another mice ; one ; 



NATURAL SELECTION 83 

cat, according to Mr. St. John, bringing home cringed 
game, another hares or rabbits, and another hunting on 
marshy ground and almost nightly catching woodcocks 
or snipes. The tendency to catch rats rather than 
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 coexist with 
the parent form of wolf. Or, again, the wolves in- 
habiting 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, apparently for the sake of 
eliminating something inj urious from their sap : this is 
effected by glands at the base of the stipules in some 
Leguminos*, 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 frilly 



34 ON THE ORIGIN OF SPECIES 

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 
or 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, 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 flowers 
for the sake of collecting pollen instead of nectar ; and 
as pollen is formed for the sole object of fertilisation, 
its destruction 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 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 illustrating 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 



NATURAL SELECTION 85 

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 favour- 
able to bees, nevertheless 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 produce 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 sometimes 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 separa- 
tion of the sexes of our plant would be advantageous 
on the principle of the division of labour, individuals 
with this tendency more and more increased, would be 
continually favoured or selected, until at last a com- 
plete 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 part on 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 



86 ON THE ORIGIN OF SPECIES 

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 
appreciated 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 descend- 
ants 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 experiment that the fertility of clover 
depends on bees visiting and moving parts of the 
corolla, so as to push the pollen on to the stigmatic 
surface. Hence, again, if humble-bees 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 corolla, 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 pre- 
servation of individuals presenting mutual and slightly 
favourable deviations of structure. 

I am well aware that this doctrine of natural selec- 
tion, exemplified in the above imaginary instances, is 
open to the same objections which were at first urged 
against Sir Charles Ly ell'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. 






NATURAL SELECTION 87 

when applied to the excavation of gigantic valleys 01 
to the formation of the longest lines of inland cliffs. 
Natural selection can act only by the preservation and 
accumulation 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 well-understood cases of par- 
thenogenesis) unite for each birth ; but in the case of 
hermaphrodites this is far from obvious. Nevertheless 
I am strongly inclined to believe that with all herma- 
phrodites two individuals, either occasionally or habitu- 
ally, 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 prepared for an ample discussion. All 
vertebrate animals, all insects, and some other large 
groups of animals, pair for each birth. Modern re- 
search has much diminished the number of supposed 
hermaphrodites, and 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 are hermaphrodites. What reason, it may 
be asked, is there for supposing in these cases that 
two individuals ever concur in reproduction ? 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 



88 ON THE ORIGIN OF SPECIES 

facts, showing-, in accordance 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 generations ; but that 
a cross with another individual 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 inex- 
plicable. Every hybridizer knows how unfavourable 
exposure to wet is to the fertilisation of a flower, yet 
what a multitude of flowers have their anthers and 
stigmas fully exposed to the weather ! but if an occa- 
sional 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 enclosed, as in the great papilio- 
naceous or pea-family ; but in several, perhaps in all, 
such flowers, there is a very curious adaptation 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 not carry pollen from 
one to the other, to the great good, as I believe, of the 
plant. Bees will act like a camel-hair pencil, and it is 
quite sufficient just to touch the anthers of one flower 



NATURAL SELECTION 89 

and then the stigma of another with the same brush 
to ensure fertilisation ; but it must not be supposed 
that bees would thus produce a multitude of hybrids 
between distinct species ; for if you bring on the same 
brush a plant's own pollen and pollen from another 
species, the former will have such a prepotent effect, 
that it will invariably and completely destroy, as has 
been shown by Gartner, any influence from the foreign 
pollen. 

When the stamens of a flower suddenly spring 
towards the pistil, or slowly move one after the other 
towards it, the contrivance seems adapted solely to 
ensure self-fertilisation ; and no doubt it is useful for 
this end : but, the agency of insects is often required 
to cause the stamens to spring forward, as Kolreuter 
has shown to be the case with the barberry ; and in 
this very genus, which seems to have a special contri- 
vance for self - fertilisation, it is well known that if 
closely-allied forms or varieties are planted near each 
other, it is hardly possible to raise pure seedlings, so 
largely do they naturally cross. In many other cases, 
far from there being any aids for self- fertilisation, 
there are special contrivances, as I could show from 
the writings of C. C. Sprengel and from my own 
observations, which effectually prevent the stigma 
receiving pollen from its own flower : for instance, 
in Lobelia fulgens, there is a really beautiful and 
elaborate contrivance by which every one of the infin- 
itely numerous pollen -granules are swept out of the 
conjoined anthers of each flower, before the stigma of 
that individual flower is ready to receive them ; and as 
this flower is never visited, at least in my garden, by 
insects, it never sets a seed, though by placing pollen 
from one flower on the stigma of another, I raised 
plenty of seedlings ; and whilst another species of 
Lobelia growing close by, which is visited by bees, 
seeds freely. In very many other cases, though there 
be no special mechanical contrivance to prevent the 
stigma of a flower receiving its own pollen, yet, as 
C. C. Sprengel has shown, and as I can confirm, either 



90 ON THE ORIGIN OF SPECIES 

the anthers burst before the stigma is ready for fertil- 
isation, or the stigma is ready before the pollen of 
that flower is ready, so that these plants have in fact 
separated sexes, and must habitually be crossed. How 
strange are these facts ! How strange that the pollen 
and stigmatic surface of the same flower, though placed 
so close together, as if for the very purpose of self- 
fertilisation, should in so many cases be mutually 
useless to each other ! How simply are these facts 
explained on the view of an occasional cross with a 
distinct individual being advantageous or indispen- 
sable ! 

If several varieties of the cabbage, radish, onion, and 
of some other plants, be allowed to seed near each 
other, a large majority, as I have found, of the seedlings 
thus raised will turn out mongrels : for instance, I 
raised 233 seedling cabbages from some plants of 
different varieties growing near each other, and of 
these only 78 were true to their kind, and some even 
of these were not perfectly true. Yet the pistil of each 
cabbage-flower is surrounded not only by its own six 
stamens, but by those of the many other flowers on the 
same plant. How, then, comes it that such a vast 
number of the seedlings are mongrelized ? I suspect 
that it must arise from the pollen of a distinct variety 
having a prepotent effect over a flower's own pollen ; 
and that this is part of the general law of good being 
derived from the intercrossing of distinct individuals 
of the same species. When distinct species are crossed 
the cas« is directly the reverse, for a plant's own pollen 
is always prepotent over foreign pollen ; but to this 
subject we shall return in a future chapter. 

In the case of a gigantic tree covered with innumer- 
able flowers, it may be objected that pollen could 
seldom be carried from tree to tree, and at most only 
from flower to flower on the same tree, and that 
flowers on the same tree can be considered as distinct 
individuals only in a limited sense. I believe this 
objection to be valid, but that nature has largely pro- 
vided against it by giving to trees a strong tendency 



NATURAL SELECTION 91 

to bear flowers with separated sexes. When the sexes 
are separated, although the male and female flowers 
may be produced on the same tree, we can see that 
pollen must be regularly carried from flower to flower ; 
and this will give a better chance of pollen being 
occasionally carried from tree to tree. That trees 
belonging to all Orders have their sexes more often 
separated than other plants, I find to be the case in 
this country ; and at my request Dr. Hooker tabulated 
the trees of New Zealand, and Dr. Asa Gray those of 
the United States, and the result was as I anticipated. 
On the other hand, Dr. Hooker has recently informed 
me that he finds 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 some 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. We 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 
terrestrial 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 concurrence of two 
individuals. Of aquatic animals, there are many 
self-fertilising hermaphrodites ; but here currents in 
the water offer an obvious means for an occasional 
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 ; 



92 ON THE ORIGIN OF SPECIES 

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 herma- 
phrodites 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 king- 
doms, an occasional intercross with a distinct individual 
is a law of nature. I am well 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 individuals, 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 individual, 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 



NATURAL SELECTION 93 

of nature, if any one species does not become modified 
and improved in a corresponding degree with its com- 
petitors, 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 intend- 
ing 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 direction, 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 inter- 
crossing 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 same manner 
to the conditions of each ; for in a continuous area, the 
physical conditions at least will generally graduate 
away insensibly from one district to another. The 
intercrossing will most affect those animals which unite 
for each birth, which wander much, and which do not 
breed at a very quick rate. Hence in animals of this 
nature, for instance in birds, varieties will generally 
be confined to separated countries ; and this I believe 
to be the case. In hermaphrodite organisms which 
cross only occasionally, and likewise in animals which 
unite for each birth, but which wander little and which 
can increase at a very rapid rate, a new and improved 
variety might be quickly formed on any one spot, and 
might there maintain itself in a body, so that whatever 



94 ON THE ORIGIN OF SPECIES 

intercrossing took place would be chiefly between the 
individuals of the same new variety. A local variety 
when once thus formed might subsequently slowly 
spread to other districts. On the above principle, 
nurserymen always prefer getting seed from a large 
body of plants of the same variety, as the chance of 
intercrossing with other varieties is thus lessened. 

Even in the case of slow-breeding animals, which 
unite for each birth, we must not overrate the effects 
of intercrosses in retarding natural selection ; for I 
can bring a considerable catalogue of facts, showing 
that within the same area, varieties of the same animal 
can long remain distinct, from haunting different 
stations, from breeding at slightly different seasons, or 
from varieties of the same kind preferring to pair 
together. 

Intercrossing plays a very important part in nature 
in keeping the individuals of the same species, or of 
the same variety, true and uniform in character. It 
will obviously thus act far more efficiently with those 
animals which unite for each birth ; but I have already 
attempted to show that we have reason to believe that 
occasional intercrosses take place with all animals and 
with all plants. Even if these take place only at long 
intervals, I am convinced that the young thus pro- 
duced will gain so much in vigour and fertility over 
the offspring from long-continued self-fertilisation, 
that they will have a better chance of surviving and 
propagating their kind ; and thus, in the long run, the 
influence of intercrosses, even at rare intervals, will 
be great. If there exist organic beings which never 
intercross, uniformity of character can be retained 
amongst them, as long as their conditions of life 
remain the same, only through the principle of inherit- 
ance, and through natural selection destroying any 
which depart from the proper type ; but if their 
conditions of life change and they undergo modification, 
uniformity of character can be given to their modified 
offspring, solely by natural selection preserving the 
lame favourable variations. 



NATURAL SELECTION 95 

Isolation, also, is an important element in the process 
of natural selection. In a confined or isolated area, if" 
not very large, the organic and inorganic conditions of 
life will generally be in a great degree uniform ; so 
that natural selection will tend to modify all the 
individuals of a varying species throughout the area in 
the same manner in relation to the same conditions. 
Intercrosses, also, with the individuals of the same 
species, which otherwise would have inhabited the 
surrounding and differently circumstanced districts, 
will be prevented. But isolation probably acts more 
efficiently in checking the immigration of better 
adapted organisms, after any physical change, such as 
of climate or elevation of the land, etc. ; and thus new 
places in the natural economy of the country are left 
open for the old inhabitants to struggle for, and 
become adapted to, through modifications in their 
structure and constitution. Lastly, isolation, by 
checking immigration and consequently competition, 
will give time for any new variety to be slowly im- 
proved ; and this may sometimes be of importance in 
the production of new species. If, however, an 
isolated area be very small, either from being sur- 
rounded by barriers, or from having very peculiar 
physical conditions, the total number of the individuals 
supported on it will necessarily be very small ; and 
fewness of individuals will greatly retard the produc- 
tion of new species through natural selection, by 
decreasing the chance of the appearance of favourable 
variations. 

If we turn to nature to test the truth of these re- 
marks, and look at any small isolated area, such as an 
oceanic island, although the total number of the species 
inhabiting it, will be found to be small, as we shall see 
in our chapter on geographical distribution ; yet of 
these species a very large proportion are endemic, — 
that is, have been produced there, and nowhere else. 
Hence an oceanic island at first sight seems to have 
been highly favourable for the production of new 
species. But we may thus greatly deceive ourselves, 



96 ON THE ORIGIN OF SPECIES 

for to ascertain whether a small isolated area, or a 
large open area like a continent, has been most favour- 
able for the production of new organic forms, we ought 
to make the comparison within equal times ; and this 
we are incapable of doing. 

Although I do not doubt that isolation is of consider- 
able importance in the production of new species, on 
the whole I am inclined to believe that largeness of 
area is of more importance, 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 im- 
proved, will be able to spread over the open and con- 
tinuous 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, to 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, understand some 



NATURAL SELECTION 97 

facta 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 Europaeo-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 
there will have been less modification and less exter- 
mination. 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 com- 

ftetition between fresh-water productions will have been 
ess severe than elsewhere ; new forms will have been 
more slowly formed, and old forms more slowly ex- 
terminated. And it is in fresh water that we find seven 
genera of Ganoid fishes, remnants of a once pre- 
ponderant 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 un- 
favourable 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 
continental area, which will probably undergo many 
oscillations of level, and which consequently 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 long 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. Wheo 

H 



98 ON THE ORIGIN OF SPECIES 

converted by subsidence 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 shall be re- 
converted 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 continent will again be changed ; and again 
there will be a fair field for natural selection to im- 
prove still further the inhabitants, 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 immigration 
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 disturbed. Nothing can be 
eifected, unless favourable variations occur, and varia- 
tion itself is apparently always a very slow process. 
The process will often be greatly retarded by free inter- 
crossing. 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 selection always acts 
very slowly, often only at long intervals of time, and 
generally on only a very few of the inhabitants of the 



NATURAL SELECTION 99 

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 at 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 coadaptations 
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 selec- 
tion. Natural selection acts solely through the pre- 
servation 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 repre- 
sented by few individuals will, during fluctuations in 
the seasons or in the number of its enemies, run 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 in- 
definitely increasing, 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 ha\*e 
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 SDecies. Probably no region is as yet 



100 ON THE ORIGIN OF SPECIES 

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 descendants of the commoner 
species. 

From these several considerations I think it in- 
evitably 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 under- 
going modification and improvement, will naturally 
suffer most. And we have seen in the chapter on the 
Struggle for Existence that it is the most closely-allied 
forms, — varieties of the same species, and species of 
the same genus or of related genera, — which, from 
having nearly the same structure, constitution, and 
habits, generally come into the severest competition 
with each other. Consequently, each new variety or 
species, during the progress of its formation, will gener- 
ally press hardest on its nearest kindred, and tend to 
exterminate them. We see the same process of ex- 
termination amongst our domesticated productions, 
through the selection of improved forms by man. Many 
curious instances could be given showing how quickly 
new breeds of cattle, sheep, and other animals, and 
varieties 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 ' 



NATURAL SELECTION 101 

(I quote the words of an agricultural writer) { as if by 
some murderous 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 strongly- 
marked 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. Never- 
theless, 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 differ- 
ences ; whereas varieties, the supposed prototypes and 
parents oTTuture well-marked species, present slight 
and ill-defined differences. Mere chance, as we may 
call it, might cause one variety to differ in some char- 
acter 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 differ- 
ence 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 something 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 



102 ON THE ORIGIN OF SPECIES 

stronger and more bulky horses. The early 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 inter- 
mediate characters, being neither very swift nor very 
strong, will have been neglected, and will have tended 
to disappear. Here, then, we see in man's productions 
the action of what may be called the principle of diver- 
gence, causing differences, at first barely appreciable, 
steadily to increase, and the breeds to diverge in char- 
acter both from each other and from their common 
parent. 

But how, it may be asked, can any analogous prin- 
ciple 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 diversified 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 quadru- 
ped, 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 increasing (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 carnivorous. 
The more diversified in habits and structure tha 
descendants of our carnivorous animal became, the 
more places they would be enabled to occupy. What 



NATURAL SELECTION 103 

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 
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 in- 
creasing 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 extremely 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 con- 
ditions, 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. 



104 ON THE ORIGIN OF SPECIES 

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 com- 
petition with each other, the advantages of diversifica- 
tion of structure, 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 naturalisation 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, proportionally 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 indi- 
genous, and thus a large proportional addition is made 
to the genera of these States. 



NATURAL SELECTION 105 

By considering the nature of the plants or animals 
which have struggled successfully 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, amount- 
ing to new generic differences, 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 physiologist 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 
perfectly diversified in structure. It may be doubted, 
for instance, whether the Australian 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 successfully compete with these 
well-pronounced 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 any one 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 selec- 
tion and of extinction, will tend to act. 



106 ON THE ORIGIN OF SPECIES 

The accompanying- diagram will aid us in under- 
standing 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 vary- 
ing 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 supposed 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 (represented 
by the outer dotted lines) being preserved and accumu- 
lated 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 genera- 
tions, species (A) is supposed to have produced two 
See diagram at the commencement of volume. 



NATURAL SELECTION 107 

fairly well-marked varieties, namely, a 1 and m 1 . 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 modi- 
fied 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 like- 
wise 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 circum- 
stances 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 
interval, variety a 1 is supposed in the diagram to have 
produced variety a 2 , which will, owing to the principle 
of divergence, differ more from (A) than did variety a 1 . 
Variety m 1 is supposed to have produced two varieties, 
namely ra a and s 2 , 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 gener- 
ations, 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 descendants, 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. 

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 
divergent varieties will invariably prevail and multiply : 



108 ON THE ORIGIN OF SPECIES 

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 unoccupied 
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 
descendants 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 suc- 
cessive forms which have become sufficiently distinct to 
be recorded as varieties. But these breaks are imagi- 
nary, and might have been inserted anywhere, after 
intervals long enough to have allowed the accumulation 
of a considerable amount of divergent variaticu. 

As all the modified descendants from a common and 
widely-diffused species, belonging 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 char- 
acter : 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 dia- 
gram by some of the lower branches not reaching to the 
upper horizontal lines. In some cases I do not doubt 
that the process of modification will be confined to a 
single line of descent, and the number of the de- 
scendants will not be increased ; although the amount 
of divergent modification may have been increased in 
the successive generations. This case would be repre- 
sented in the diagram, if all the lines proceeding 
from (A) were removed, excepting that from a 1 to a 10 . 
In the same way, for instance, the English race-horse 
and English pointer have apparently both gone on 
slowly diverging in character from their original 



NATURAL SELECTION 109 

stocks, without either having given off any fresh 
branches or races. 

After ten thousand generations, species (A) is sup- 
posed to have produced three forms, a 10 ,/ 10 , and m™, 
which, from having diverged in character 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 
distinguishing 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 a 14 and m 14 , all descended 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 diagram I have assumed 
that a second species (I) has produced, by analogous 
steps, after ten thousand generations, either two well- 
marked varieties (w 10 and z 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 ra 14 
to z u , are supposed to have been produced. In each 
genus, the species, which are already extremely dif- 
ferent 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 



110 ON THE ORIGIN OF SPECIES 

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 continue 
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 neces- 
sarily 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 com- 
petition 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 offspring 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 con- 
siderable amount of modification, species (A) and all 
the earlier varieties will have become extinct, having 
been replaced by eight new species (a 14 to m 14 ) ; and 
(I) will have been replaced by six (n u to # 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, 



NATURAL SELECTION 111 

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 
probably 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 trans- 
mitted offspring to the fourteen -thousandth genera- 
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 descended 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 character between 
species a 14 and z 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 a 14 , q u , 
p H , will be nearly related from having recently 
branched off from a 10 ; b u and/ 14 , from having diverged 
at an earlier period from a 6 , will be in some degree dis- 
tinct from the three first-named species ; and lastly, 
o 14 , e u , and m 14 , 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-genua 
or even a distinct genus. 



112 ON THE ORIGIN OF SPECIES 

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 de- 
scendants from (I) will, owing to inheritance alone, 
differ considerably from the eight descendants from 
(A) ; the two groups, moreover, are supposed to have 
gone on diverging in different directions. The inter- 
mediate species, also (and this is a very important 
consideration), which connected the original species 
(A) and (I), have all become, excepting (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 descended 
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 on the 
character of the new species f 14 , 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 intermediate 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 (f 14 ) will 
not be directly intermediate between them, but rather 
between types of the two groups ; and every naturalist 



NATURAL SELECTION 113 

will be able to bring some such case before bis 
mind. 

In the diagram, each horizontal line has hitherto 
been supposed to represent a thousand generations, but 
each may represent a million or hundred million 
generations, and likewise a section of the successive 
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 a 14 to 
p M , those marked b 14 and f 1 *, and those marked o u to 
m 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 

I 



114 ON THE ORIGIN OF SPECIES 

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. Looking 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 in- 
crease of the larger groups, a multitude of smaller 
groups will become utterly extinct, and leave no 
modified descendants ; and consequently that of the 
species living at any one period, extremely few will 
transmit descendants 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 vege- 
table kingdoms. Although extremely few of the most 
ancient species may now have living and modified 



NATURAL SELECTION 115 

descendants, yet at the most remote geological period, 
the earth may have been as 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 conditions of life, organic 
beings vary at all in the several parts of their organisa- 
tion, 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, 
constitution, and habits, to be advantageous to them, 
I think it would be a most extraordinary 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 variations 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 inorganic 
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. Amongst 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 



116 ON THE ORIGIN OF SPECIES 

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 de- 
clares. 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 constitution, of which we see proof by 
looking to the inhabitants of any small spot or to 
naturalised productions. Therefore during the modifica- 
tion of the descendants of any one species, and during 
the incessant struggle of all species to increase in 
numbers, 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 
differences 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 coun- 
tries. 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 



NATURAL SELECTION 117 

classes. The several subordinate 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 classification 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 represented 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 succession of extinct species. At each period of 
growth all the growing twigs have tried to 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 
classification of all extinct and living species in groups 
subordinate to groups. Of the many twigs which flou- 
rished 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 geological periods, very few now 
have living and modified descendants. From the first 
growth of the tree, many a limb and branch have decayed 
and dropped off; and these lost branches of various 
size* may represent those whole orders, families, and 
genera which have now no living representatives, and 
which are known to us only from having been found in 
a fossil state. As we here and there see a thin strag- 
gling branch springing from a fork low down in a tree, 



118 ON THE ORIGIN OF SPECIES 

and which hy 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 competition by having 1 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 ramifications. 



CHAPTER V 



LAWS OF VARIATION 



Effects of external conditions — Use and disuse, combined with 
natural selection ; organs of flight and of vision— Acclimatisa- 
tion — Correlation of growth — Compensation and economy of 
growth— False correlations— Multiple, rudimentary, and lowly 
organised structures variable— Parts developed in an unusual 
manner are highly variable: specific characters more variable 
than generic : secondary sexual characters 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 acknow- 
ledge plainly our ignorance of the cause of each par- 
ticular 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 generations. 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 

119 



120 ON THE ORIGIN OF SPECIES 

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. 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 attri- 
buted 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 atmosphere, 
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. 



LAWS OF VARIATION 121 

Thus the species of shells which are confined to tropical 
and shallow seas are generally brighter-coloured 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 to attribute to the accu- 
mulative action of natural selection, and how much to 
the conditions of life. Thus, it is well known to fur- 
riers 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 ; 



122 ON THE ORIGIN OF SPECIES 

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 en- 
larges 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 condi- 
tion of several birds, which now inhabit or have lately 
inhabited 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 quad- 
rupeds. 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 genera- 
tions 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 
apelles the tarsi are so habitually lost, that the insect 
has been described as not having them. In some 



LAWS OF VARIATION 123 

other genera they are present, but in a rudimentary 
condition. In the Ateuchus or sacred beetle of the 
Egyptians, they are totally deficient. There is not 
sufficient evidence to induce me to believe that mutila- 
tions are ever inherited ; and I should prefer explain- 
ing 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 pro- 
genitors ; 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 selection. 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 
concealed, 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 
necessitating frequent flight ; — these several considera- 
tions 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 dis- 
use. For during thousands of successive generations 
each individual beetle which flew least, either from its 
wings having been ever so little less perfectly de- 
veloped 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 



124 ON THE ORIGIN OF SPECIES 

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 lepi- 
doptera, must habitually use their wings to gain their 
subsistence, have, as Mr. Wollaston suspects, their 
wings not at all reduced, 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 burrowing 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 subterranean 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 inflammation 
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 advantage ; and if so, 
natural selection would constantly aid the effects of 
disuse. 

It is well known that several animals, belonging to 
the most different classes, which inhabit the caves of 



LAWS OF VARIATION 126 

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 in- 
creased 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 affinities might have been ex- 
pected ; 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 inhabitants 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, f animals not far remote from 
ordinary forms, prepare the transition from light to 
darkness. Next follow those that are constructed for 
twilight ; and, last of all, those destined for total dark- 



126 ON THE ORIGIN OF SPECIES 

ness.' By the time that an animal had reached, after 
numberless generations, the deepest recesses, disuse 
will on this view have more or less perfectly obliter- 
ated its eyes, and natural selection will often have 
effected other changes, such as an increase in the 
length of the antenna or palpi, as a compensation 
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 New Worlds should be closely related, we might 
expect from the well-known relationship of most of 
their other productions. Far from feeling any sur- 
prise 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 fife 
have not been preserved, owing to the less severe com- 
petition 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 acclima- 
tisation. 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, acclimatisation must be readily effected during 



LAWS OF VARIATION 127 

long- continued 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 inability to pre- 
dict whether or not an imported 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 limited in their ranges by the com- 
petition of other organic beings quite as much as, or 
more than, by adaptation to particular climates. But 
whether or not the adaptation be generally very close, 
we have evidence, in the case of some few plants, of 
their becoming, to a certain extent, naturally habitu- 
ated to different temperatures, or becoming acclima- 
tised : 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 analogous obser- 
vations 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 posi- 
tively 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 origin- 
ally chosen by uncivilised man because they were 
useful and bred readily under confinement, and not 
because they were subsequently found capable of far- 



128 ON THE ORIGIN OF SPECIES 

extended transportation, I think the common 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 pro- 
portion of other animals, now in a state of nature, 
could easily be brought to bear widely different 
climates. We must not, however, push the fore- 
going 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 inclined to 
look at adaptation to any special climate as a quality 
readily grafted on an innate wide flexibility of consti- 
tution, which is common to most animals. On this 
view, the capacity of enduring the most different 
climates by man himself and by his domestic 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 innate 
constitutions, and how much to both means combined, 
is a very obscure question. That habit or custom has 
some influence I must believe, both from analogy, and 
from the incessant advice given in agricultural works, 
even in the ancient Encyclopaedias of China, to be very 
cautious in transposing animals from one district to 



LAWS OF VARIATION 129 

another ; for it is not likely that man should have suc- 
ceeded in selecting so many breeds and sub-breeds with 
constitutions specially fitted for their own districts : 
the result must, I think, be due to habit. On the other 
hand, I can see no reason to doubt that natural selection 
will continually tend to preserve those individuals which 
are born with constitutions best adapted to their native 
countries. In treatises on many kinds of cultivated 
plants, certain varieties are said to withstand 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 recom- 
mended 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 acclimatisation 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 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 consider- 
able 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. 



130 ON THE ORIGIN OF SPECIES 

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 important 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 concluded, affect the structure of the adult ; 
in the same manner as any malconformation affecting 
the early embryo, seriously affects the whole organisa- 
tion 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 pres- 
sure 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 fre- 
quently quite obscure. M. Is. Geoffroy St. Hilaire has 






LAWS OF VARIATION 131 

forcibly remarked, that certain malconformations very 
frequently, 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 deaf- 
ness 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 probably 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) and Edentata (arma- 
dilloes, scaly ant-eaters, etc.), that these are likewise 
the most abnormal in their teeth. 

I know of no case better adapted to show the im- 
portance of the laws of correlation in modifying im- 
portant structures, independently of utility and, there- 
fore, of natural selection, than that of the difference 
between the outer and inner flowers in some Compo- 
sitous and Umbelliferous plants. Every one knows the 
difference in the ray and central florets of, for instance, 
the daisy, and this difference is often accompanied with 
the abortion of parts of the flower. But, in some Com- 
positous 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 attributed 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 Umbelliferae, 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 a difference in the seeds 
of the outer and inner florets without any difference in 



132 ON THE ORIGIN OF SPECIES 

the corolla. Possibly, these several differences may be 
connected with some difference in the flow of nutri- 
ment towards the central and external flowers : we 
know, at least, than 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 ob- 
served 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 
may have come into play. But in regard to the differ- 
ences both in the internal and external structure of the 
seeds, which are not always correlated with any differ- 
ences in the flowers, it seems impossible that they can 
be in any way advantageous to the plant : yet in the 
Umbelliferae these differences are of such apparent im- 
portance — the seeds being in some cases, according to 
Tausch, orthospermous in the exterior flowers and 
coelospermous in the central flowers, — that the elder De 
Candolle founded his main divisions of the order on 
analogous differences. Hence we see that modifications 
of structure, 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 correlation of 
growth, structures which are common to whole groups 
of species, and which in truth are simply due to in- 
heritance ; for an ancient progenitor may have acquired 
through natural selection some one modification in 



LAWS OF VARIATION 133 

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 correla- 
tions, 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 should 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 propounded, at about 
the same period, their law of compensation or balance- 
ment 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 nourishment 
flows 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 accompanied 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 



134 ON THE ORIGIN OF SPECIES 

natural 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 continually trying to 
economise in every part of the organisation. If under 
changed conditions of life a structure before useful 
becomes less useful, any diminution, however slight, in 
its development, will be seized on by natural selection, 
for it will profit the individual not to have its nutriment 
wasted in building up an 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 extra- 
ordinary manner with the Proteolepas: for the carapace 
in all other cirripedes consists of the three highly- 
important 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 nutri- 
ment being wasted in developing 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 super- 



LAWS OF VARIATION 135 

fluous, without by any means causing some other part 
to be largely developed in a corresponding degree. 
And, conversely, that natural selection may perfectly 
well succeed in largely developing any organ, without 
requiring as a necessary compensation 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 constant. 
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 foregoing remark seems 
connected with the 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 
particular 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 of 
almost any shape ; whilst 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 



136 ON THE ORIGIN OF SPECIES 

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 comparison 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 generality. 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 comparison with the same part in closely 
allied species. Thus, the bat's wing is a most 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 displayed 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 remark- 
able 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 



LAWS OF VARIATION 137 

not displayed in any unusual manner — of which fact 
I think there can be little doubt. But that our rule ia 
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, whilst investigating this Order, 
and I am fully convinced that the rule almost invari- 
ably 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 illustrates 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 ex- 
tremely 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 some- 
times wholly unlike in shape ; and the amount of varia- 
tion in the individuals 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 same country vary in a remark- 
ably 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 particularly 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 
presumption is that it is of high importance to that 
species ; nevertheless the part in this case is eminently 
liable to variation. MTiy 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 



138 ON THE ORIGIN OF SPECIES 

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 selec- 
tion 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 condition. 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 emi- 
nently 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 selection is rapidly going on, there may 
always be expected to be much variability in the struc- 
ture undergoing modification. It further deserves 
notice that these variable characters, produced by 
man's selection, sometimes become attached, from 
causes quite unknown to us, more to one sex than to 



LAWS OF VARIATION 139 

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 extra- 
ordinary amount of modification implies an 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 exces- 
sively 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 approxi- 
mately the same condition to many modified descend- 
ants, 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 
comparatively 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 



140 ON THE ORIGIN OF SPECIES 

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 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 explanation 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 super- 
fluous 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 important 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 importance 
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 



LAWS OF VARIATION 141 

independently created, why should that part of the 
structure, which differs from the same part in other 
independently-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 explana- 
tion 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 state the case in another 
manner : — the points in which all the species of a 
genus resemble each other, and in which they differ 
from the species of some other genus, are called generic 
characters ; and these characters in common I attri- 
bute to inheritance from a common progenitor, for it 
can rarely have happened that natural selection will 
have modified several species, fitted to more or less 
widely-different habits, in exactly the same manner : 
and as these so-called generic characters have been 
inherited from a remote period, since that period when 
the species first branched off from their common pro- 
genitor, and subsequently have not varied or come to 
differ in any degree, or only in a slight degree, it is 
not probable that they should vary at the present day. 
On the other hand, the points in which species differ 
from other species of the same genus, are called specific 
characters ; and as these specific characters have varied 
and come to differ within the period of the branching 
off of the species from a common progenitor, it is 
probable that they should still often be in some degree 
variable, — at least more variable than those parts of 
the organisation which have for a very long period 
remained constant. 

In connection with the present subject, I will make 
only two other remarks. I think it will be admitted, 
without my entering on details, that secondary sexual 
characters are very variable ; I think it also will be 
admitted that species of the same group differ from 
each other more widely in their secondary sexual 



142 ON THE ORIGIN OF SPECIES 

characters, than in other parts of their organisation ; 
compare, for instance, the amount of difference between 
the males of gallinaceous birds, in which secondary 
sexual characters are strongly displayed, with the 
amount of difference between their females ; and the 
truth of this proposition will be granted. The cause 
of the original variability of secondary sexual characters 
is not manifest ; but we can see why these characters 
should not have been rendered as constant and uniform 
as other parts of the organisation ; for secondary sexual 
characters have been accumulated by sexual selection, 
which is less rigid in its action than ordinary selection, 
as it does not entail death, but only gives fewer off- 
spring to the less favoured males. Whatever the cause 
may be of the variability of secondary sexual characters, 
as they are highly variable, sexual selection will have 
had a wide scope for action, and may thus readily 
have succeeded in giving to the species of the same 
group a greater amount of difference in their sexual 
characters, than in other parts of their structure. 

It is a remarkable fact, that the secondary sexual 
differences between the two sexes of the same species 
are generally displayed in the very same parts of the 
organisation in which the different species of the same 
genus differ from each other. Of this fact I will give 
in illustration two instances, the first which happen to 
stand on my list ; and as the differences in these cases 
are of a very unusual nature, the relation can hardly 
be accidental. The same number of joints in the tarsi 
is a character generally common to very large groups of 
beetles, but in the Engidse, as Westwood has remarked, 
the number varies greatly ; and the number likewise 
differs in the two sexes of the same species : again in 
fossorial hymenoptera, the manner of neuration of the 
wings is a character of the highest importance, because 
common to large groups ; but in certain genera the 
neuration differs in the different species, and likewise 
in the two sexes of the same species. This relation has 
a clear meaning on my view of the subject : I look at 
all the species of the same genus as having as certainly 



LAWS OF VARIATION 143 

descended from the same progenitor, as have the two 
sexes of any one of the species. Consequently, what- 
ever part of the structure of the common progenitor, 
or of its early descendants, became variable ; variations 
of this part would, it is highly probable, be taken 
advantage of by natural and sexual selection, in order 
to fit the several species to their several places in the 
economy of nature, and likewise to fit the two sexes of the 
same species to each other, or to fit the males and females 
to different habits of life, or the males to struggle with 
other males for the possession of the females. 

Finally, then, I conclude that the greater variability 
of specific characters, or those which distinguish species 
from species, than of generic characters, or those which 
the species possess in common ; — that the frequent ex- 
treme variability of any part which is developed in a 
species in an extraordinary manner in comparison with 
the same part in its congeners ; and the slight degree 
of variability in a part, however extraordinarily it may 
be developed, if it be common to a whole group of 
species ; — that the great variability of secondary sexual 
characters, and the great amount of difference in these 
same characters between closely-allied species ; — that 
secondary sexual and ordinary specific differences are 
generally displayed in the same parts of the organisa- 
tion, — 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 selec- 
tion being less rigid than ordinary selection, — and to 
variations in the same parts having been accumulated 
by natural and sexual selection, and having been thus 
adapted for secondary sexual, and for ordinary specific 
purposes. 



144 ON THE ORIGIN OF SPECIES 

Distinct species present analogous variations; 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 propositions 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 constitution and tendency to variation, when 
acted on by similar unknown influences. In the vege- 
table 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 vera causa of 
community of descent, and a consequent tendency 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 



LAWS OF VARIATION 146 

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, per- 
haps for hundreds of generations. But when a breed 
has been crossed only once by some other breed, 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 
1 in 2048 ; and yet, as we see, it is generally believed 
that a tendency to reversion 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 generations, the most probable hypothesis 
is, not that the offspring suddenly takes after an ancestor 
some hundred generations distant, but that in each 
successive generation there has been a tendency to re- 
produce the character in question, which at last, under 
unknown favourable conditions, gains an ascendancy. 
For instance, it is probable that in each generation of 
the barb-pigeon, which produces most rarely a blue 
and black-barred bird, there has been a tendency in 
each generation in the plumage to assume this colour. 
This view is hypothetical, but could be supported by 
some facts ; and I can see no more abstract improba- 



146 ON THE ORIGIN OF SPECIES 

bility in a tendency to produce any character being 
inherited for an endless number of generations, than 
in quite useless or rudimentary organs being, as we all 
know them to be, thus inherited. Indeed, we may 
sometimes observe a mere tendency to produce a rudi- 
ment inherited : for instance, in the common snap- 
dragon (Antirrhinum) a rudiment of a fifth stamen so 
often appears, that this plant must have an inherited 
tendency to produce it. 

As all the species of the same genus are supposed, on 
my theory, to have descended from a common parent, 
it might be expected that they would occasionally vary 
in an analogous manner ; so that a variety of one species 
would resemble in some of its characters another 
species ; this other species being on my view only a 
well-marked and permanent variety. But characters 
thus gained would probably be of an unimportant 
nature, for the presence of all important characters 
will be governed by natural selection, in accordance 
with the diverse habits of the species, and will not be 
left to the mutual action of the conditions of life and of 
a similar inherited constitution. It might further be 
expected that the species of the same genus would 
occasionally exhibit reversions to lost ancestral char- 
acters. As, however, we never know the exact char- 
acter of the common ancestor of a group, we could not 
distinguish these two cases : if, for instance, we did 
not know that the rock-pigeon was not feather-footed 
or turn-crowned, we could not have told, whether these 
characters in our domestic breeds were reversions or 
only analogous variations ; but we might have inferred 
that the blueness was a case of reversion, from the 
number of the markings, which are correlated with 
the blue tint, and which it does not appear probable 
would all appear together from simple variation. More 
especially we might have inferred this, from the blue 
colourand marks so often appearing when distinct breeds 
of diverse colours are crossed. Hence, though under 
nature it must generally be left doubtful, what cases 
are reversions to an anciently existing character, and 



LAWS OF VARIATION 147 

what are new but analogous variations, yet we ought, 
on my theory, sometimes to find the varying offspring 
of a species assuming characters (either from reversion 
or from analogous variation) which already occur in 
some other members of the same group. And this un- 
doubtedly is the case in nature. 

A considerable part of the difficulty in recognising a 
variable species in our systematic works, is due to its 
varieties mocking, as it were, some of the other species 
of the same genus. A considerable catalogue, also, 
could be given of forms intermediate between two other 
forms, which themselves must be doubtfully ranked as 
either varieties or species ; and this shows, unless all 
these forms be considered as independently created 
species, that the one in varying has assumed some of 
the characters of the other, so as to produce the inter- 
mediate form. But the best evidence is afforded by 
parts or organs of an important and uniform nature 
occasionally varying so as to acquire, in some degree, 
the character of the same part or organ in an allied 
species. I have collected a long list of such cases ; but 
here, as before, I lie under a great disadvantage in not 
being able to give them. I can only repeat that such 
cases certainly do occur, and seem to me very remark- 
able. 

I will, however, give one curious and complex case, 
not indeed as affecting any important character, but 
from occurring in several species of the same genus, 
partly under domestication and partly under nature. 
It is a case apparently of reversion. The ass not rarely 
has very distinct transverse bars on its legs, like those 
on the legs of the zebra : it has been asserted that 
these are plainest in the foal, and from inquiries which 
I have made, I believe this to be true. It has also 
been asserted that the stripe on each shoulder is some- 
times double. The shoulder-stripe is certainly very 
variable in length and outline. A white ass, but not an 
albino, has been described without either spinal or 
shoulder stripe ; and these stripes are sometimes very 
obscure, or actually quite lost, in dark-coloured asses. 



148 ON THE ORIGIN OF SPECIES 

The koulan of Pallas is said to have been seen with a 
double shoulder-stripe. The hemionus has no shoulder- 
stripe ; but traces of it, as stated by Mr. Blyth and 
others, occasionally appear : and I have been informed 
by Colonel Poole that the foals of this species are 
generally striped on the legs, and 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 collected cases in 
England of the spinal stripe in horses of the most dis- 
tinct 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 examination 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 informa- 
tion 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 



LAWS OF VARIATION 149 

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 in- 
cluded, from one between brown and black to a close 
approach 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 aboriginal 
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 satis- 
fied with this theory, and should be loth to apply it to 
breeds so distinct as the heavy Belgian cart-horse, 
Welch 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 I 
so much striped that any one 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 subsequently pro- 
duced 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, 



150 ON THE ORIGIN OF SPECIES 

nevertheless had all four legs barred, and had three 
short shoulder-stripes, like those on the dun Welch 
pony, and even had some zebra-like stripes on the sides 
of its face. With respect to this last fact, I was so con- 
vinced that not even a stripe of colour appears from 
what would commonly 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 
eminently 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 approaches to that of the general 
colouring of the other species of the genus. The 
appearance of the stripes is not accompanied by any 
change of form or by any other new character. We 
see this tendency to become striped most strongly dis- 
played 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 
(including two or three sub-species or geographical 
races) of a bluish colour, with certain bars and other 
marks ; and when any breed assumes by simple varia- 
tion a bluish tint, these bars and other marks in- 
variably reappear ; but without any other change of 
form or character. WTien the oldest and truest breeds 
of various colours are crossed, we see a strong tendency 
for the blue tint and bars and marks to reappear in the 
mongrels. I have stated that the most probable hypo- 
thesis 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 



LAWS OF VARIATION 151 

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 constructed, 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 inde- 
pendently created, will, I presume, assert that each 
species has been created with a tendency to vary, both 
under nature and under domestication, in this par- 
ticular 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 distant 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 deception ; 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. 
But whenever we have the means of instituting a com- 
parison, the same laws appear to have acted in pro- 
ducing the lesser differences 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 
modifications. Habit in producing constitutional dif- 
ferences, and use in strengthening and disuse in weak- 



152 ON THE ORIGIN OF SPECIES 

ening 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 some- 
times affect softer and internal parts. When one part 
is largely developed, perhaps it tends to draw nourish- 
ment from the adjoining parts ; and every part of the 
structure which can be saved without detriment to the 
individual, will be saved. Changes of structure at an 
early age will generally affect parts subsequently de- 
veloped ; 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 organ- 
isation more specialised, and are higher in the scale. 
Rudimentary organs, from being useless, will be disre- 
garded 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 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 differentiation, 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 vari- 
able, and such characters differ much in the species 
of the same group. Variability in the same parts of 



LAWS OF VARIATION 153 

the organisation has generally 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 extraordinary size or in an extra- 
ordinary 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 pro- 
cess, 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 
when a species with any extraordinarily-developed 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 ex- 
posed to similar influences will naturally tend to present 
analogous variations, and these same species may occa- 
sionally revert to some of the characters of their ancient 
progenitors. Although new and important modifica- 
tions may not arise from reversion and analogous 
variation, 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 ON THEORY 

Difficulties on the theory of descent with modification— 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 rum 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 maybe classed under 
the following heads : — Firstly, why, if species have 
descended from other species by insensibly fine grada- 
tions, do we not everywhere see innumerable 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 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 

154 



DIFFICULTIES ON THEORY 155 

such wonderful structure, as the eye, of which we hardly 
as yet fully understand 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 discussed — Instinct 
and Hybridism in separate chapters. 

On the absence or rarity of transitional varieties. — 
As natural selection acts solely by the preservation of 
profitable modifications, each new form will tend in a 
fully-stocked 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 generally 
have been exterminated by the very process of forma- 
tion 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 this question in the 
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 
profound 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 withstand 
an enormous amount of future degradation ; and such 
fossiliferous masses can be accumulated only where much 



156 ON THE ORIGIN OF SPECIES 

sediment is deposited on the shallow bed of the sea, 
whilst it slowly subsides. These contingencies will 
concur only rarely, and after enormously long intervals. 
Whilst the bed of the sea is stationary or is rising, or 
when 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 collections 
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 generally meet at succes- 
sive 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 inhabited by each. By my theory these 
allied species have descended from a common parent ; 
and during the process of modification, each has be- 
come adapted to the conditions of life of its own 
region, and has supplanted and exterminated its 
original parent and all the transitional varieties be- 
tween 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 intermediate conditions of life, why do 
we not now find closely-linking intermediate varieties ? 
This difficulty for a long time quite confounded me. 
But I think it can be in large part explained. 

In the first place we should be extremely cautious 
in inferring, because an area is now continuous, that 



DIFFICULTIES ON THEORY 157 

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 possi- 
bility of intermediate varieties existing in the inter- 
mediate zones. By changes in the form of the land 
and of climate, marine areas now 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 perfectly denned 
species have been formed on strictly continuous areas ; 
though I do not doubt that the formerly broken condi- 
tion 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 some- 
what abruptly rarer and rarer on the confines, and 
finally disappearing. Hence the neutral territory be- 
tween 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 dis- 
appears. 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 condi- 
tions of life as the all-important elements of distribu- 
tion, 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 inhabitants 



158 ON THE ORIGIN OF SPECIES 

of any country by no means exclusively 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 denned objects (however they may have become 
so), not blending one into another by insensible grada- 
tions, the range of any one species, depending as it 
does on the range of others, will tend to be sharply 
denned. 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 exter- 
mination ; and thus its geographical range will come 
to be still more sharply defined. 

If I am right in believing that allied or represent- 
ative species, when inhabiting a continuous area, are 
generally so distributed that each has a wide range, 
with a comparatively 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 well-marked 
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 numerically than the forms which they 
connect. Now, if we may trust these facts and infer- 
ences, and therefore conclude that varieties linking 
two other varieties together have generally existed in 
lesser numbers than the forms which they connect, 



DIFFICULTIES ON THEORY 159 

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 exter- 
minated 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 
consideration, 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 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 well - marked 
varieties than do the rarer species. I may illustrate 
what I mean by supposing three varieties of sheep to 
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 inhabitants are all trying with equal steadiness and 
skill to improve their stocks by selection ; the chance? 
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 



160 ON THE ORIGIN OF SPECIES 

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, inter- 
mediate hill-variety. 

To sum up, I believe that species come to be toler- 
ably well-defined objects, and do not at any one period 
present an inextricable chaos of varying and inter- 
mediate 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 inhabit- 
ants. And such new places will depend on slow 
changes of climate, or on the occasional immigration 
of new inhabitants, 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 reacting on 
each other. So that, in any one region and at any 
one time, we ought only to see a few species presenting 
slight modifications of structure in some degree per- 
manent ; 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 amongst 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, inter- 
mediate 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 



DIFFICULTIES ON THEORY 1G1 

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 
intermediate 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 
modification 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 selection and gain further advantages. 

Lastly, looking not to any one time, but to all time, 
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 evi- 
dence of their former existence could be found only 
amongst fossil remains, which are preserved, 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 carnivorous 
animals exist having every intermediate grade between 
truly aquatic and 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 

M 



162 ON THE ORIGIN OF SPECIES 

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 insecti- 
vorous 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 dis- 
advantage, 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 closely allied 
species of the same genus ; and of diversified habits, 
either constant or occasional, in the same species. And 
it seems to me that nothing less than a long list of such 
cases is sufficient to lessen the difficulty in any par- 
ticular 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 remarked, with the posterior part of their bodies 
rather wide 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 oi 



DIFFICULTIES ON THEORY 163 

the squirrels would decrease In numbers or become 
exterminated, unless they also became modified and 
improved in structure in a corresponding manner. 
Therefore, I can see no difficulty, more especially 
under changing conditions of life, in the continued 
preservation of individuals with fuller and fuller flank- 
membranes, each modification being useful, each being 
propagated, until by the accumulated effects of this 
process of natural selection, a perfect so-called flying 
squirrel was produced. 

Now look at the Galeopithecus or flying lemur, 
which formerly was falsely ranked amongst 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-mem- 
brane is, also, furnished with an extensor muscle. 
Although no graduated links of structure, fitted for 
gliding through the air, now connect the Galeopithecus 
with the other Lemuridae, yet I see no difficulty in 
supposing that such links formerly 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 insuperable 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 
apparatus 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 



164 ON THE ORIGIN OF SPECIES 

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 con- 
ditions. 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 show what diversified means of transition are 
possible. 

Seeing that a few members of such water-breathing 
classes as the Crustacea and Mollusca are adapted to 
live on the land ; and seeing that we have flying birds 
and mammals, flying insects of the most diversified 
types, and formerly had flying reptiles, it is con- 
ceivable that flying-fish, which now glide far through 
the air, slightly rising and turning by the aid of their 
fluttering fins, might have been modified into perfectly 
winged animals. If this had been effected, who would 
have ever imagined that in an early transitional state 
they had been inhabitants of the open ocean, and 
had used their incipient organs of flight exclusively, as 
far as we know, to escape being devoured by other 
fish? 

When we see any structure highly perfected for any 
particular habit, as the wings of a bird for flight, we 
should bear in mind that animals displaying early 
transitional grades of the structure will seldom continue 
to exist to the present day, for they will have been 
supplanted by the very process of perfection through 
natural selection. Furthermore, we may conclude that 
transitional grades between structures fitted for very 
different habits of life will rarely have been developed 
at an early period in great numbers and under many 
subordinate forms. Thus, to return to our imaginary 
illustration of the flying-fish, it does not seem probable 
that fishes capable of true flight would have been 
developed under many subordinate forms, for taking 
prey of many kinds in many ways, on the land and iD 



DIFFICULTIES ON THEORY 165 

the water, until their organs of flight had come to a 
high stage of perfection, so as to have given them a 
decided advantage over other animals in the battle of 
life. Hence the chance of discovering species with 
transitional grades of structure in a fossil condition 
will always be less, from their having existed in lesser 
numbers, than in the case of species with fully developed 
structures. 

I will now give two or three instances of diversified 
and of changed habits in the individuals of the same 
species. When either case occurs, it would be easy for 
natural selection to fit the animal, by some modification 
of its structure, for its changed habits, or exclusively 
for one of its several different habits. But it is difficult 
to tell, and immaterial for us, whether habits generally 
change first and structure afterwards ; or whether 
slight modifications of structure lead to changed habits ; 
both probably often change almost simultaneously. 
Of cases of changed habits it will suffice merely to 
allude to that of the many British insects which now 
feed on exotic plants, or exclusively on artificial 
substances. Of diversified habits innumerable instances 
could be given : I have often watched a tyrant fly- 
catcher (Saurophagus sulphuratus) in South America, 
hovering over one spot and then proceeding to another, 
like a kestrel, and at other times standing stationary 
on the margin of water, and then dashing like a king- 
fisher at a fish. In our own country the larger 
titmouse (Parus major) may be seen climbing branches, 
almost like a creeper ; it often, like a shrike, kills small 
birds by blows on the head ; and I have many times 
seen and heard it hammering the seeds of the yew on 
a branch, and thus breaking them like a nuthatch. 
In North America the black bear was seen by Hearne 
swimming for hours with widely open mouth, thus 
catching, almost like a whale, insects in the water. 

As we sometimes see individuals of a species following 
habits widely different from those of their own species 
and of the other species of the same genus, we might 
expect, on my theory, that such individuals would 



166 ON THE ORIGIN OF SPECIES 

occasionally have given rise to new species, having 
anomalous habits, and with their structure either 
slightly or considerably modified from that of their 
proper type. And such instances do occur in nature. 
Can a more striking instance of adaptation be given 
than that of a woodpecker for climbing trees and for 
seizing insects in the chinks of the bark ? Yet in North 
America there are woodpeckers which feed largely on 
fruit, and others with elongated wings which chase 
insects on the wing ; and on the plains of La Plata, 
where not a tree grows, there is a woodpecker, which 
in every essential part of its organisation, even in its 
colouring, in the harsh tone of its voice, and undulatory 
flight, told me plainly of its close blood-relationship 
to our common species ; yet it is a woodpecker which 
never climbs a tree ! 

Petrels are the most aerial and oceanic of birds, yet 
in the quiet Sounds of Tierra del Fuego, the Puffinuria 
berardi, in its general habits, in its astonishing power 
of diving, its manner of swimming, and of flying when 
unwillingly it takes flight, would be mistaken by any 
one for an auk or grebe ; nevertheless, it is essentially 
a petrel, but with many parts of its organisation pro- 
foundly modified. On the other hand, the acutest 
observer by examining the dead body of the water-ouzel 
would never have suspected its sub-aquatic habits ; yet 
this anomalous member of the strictly terrestrial thrush 
family wholly subsists by diving, — grasping the stones 
with its feet and using its wings under water. 

He who believes that each being has been created as 
we now see it, must occasionally have felt surprise 
when he has met with an animal having habits and 
structure not at all in agreement. What can be 
plainer than that the webbed feet of ducks and geese 
are formed for swimming ? yet there are upland geese 
with webbed feet which rarely or never go near the 
water ; and no one except Audubon has seen the 
frigate-bird, which has all its four toes webbed, alight 
on the surface of the sea. On the other hand grebes 
and coots are eminently aquatic, although their toes 



DIFFICULTIES ON THEORY 167 

are only bordered by membrane. What seems plainer 
than that the long toes of grallatores are formed for 
walking over swamps and floating plants, yet the 
water-hen is nearly as aquatic as the coot ; and the 
landrail nearly as terrestrial as the quail or partridge. 
In such cases, and many others could be given, habits 
have changed without a corresponding change of 
structure. The webbed feet of the upland goose may 
be said to have become rudimentary in function, 
though not in structure. In the frigate-bird, the 
deeply-scooped membrane between the toes shows that 
structure has begun to change. 

He who believes in separate and innumerable acts of 
creation will say, that in these cases it has pleased the 
Creator to cause a being of one type to take the place 
of one of another type ; but this seems to me only 
re-stating the fact in dignified language. He who 
believes in the struggle for existence and in the 
principle of natural selection, will acknowledge that 
every organic being is constantly endeavouring to 
increase in numbers ; and that if any one being vary 
ever so little, either in habits or structure, and thus 
gain an advantage over some other inhabitant of the 
country, it will seize on the place of that inhabitant, 
however different it may be from its own place. Hence 
it will cause him no surprise that there should be 
geese and frigate-birds with webbed feet, living on the 
dry land or most rarely alighting on the water ; that 
there should be long-toed corncrakes living in meadows 
instead of in swamps ; that there should be wood- 
peckers where not a tree grows ; that there should be 
diving thrushes, and petrels with the habits of auks. 

Organs of extreme perfection and complication. — To 
suppose that the eye, with all its inimitable contriv- 
ances for adjusting the focus to different distances, for 
admitting different amounts of light, and for the 
correction of spherical and chromatic aberration, could 
have been formed by natural selection, seems, I freely 
confess, absurd in the highest possible degree. Yet 



168 ON THE ORIGIN OF SPECIES 

reason tells me, that if numerous gradations from a 
perfect and complex eye to one very imperfect and 
simple, each grade being useful to its possessor, can 
be shown to exist ; if further, the eye does vary 
ever so slightly, and the variations be inherited, 
which is certainly the case ; and if any variation or 
modification in the organ be ever useful to an animal 
under changing conditions of life, then the difficulty 
of believing that a perfect and complex eye could be 
formed by natural selection, though insuperable by 
our imagination, can hardly be considered real. How 
a nerve comes to be sensitive to light, hardly concerns 
us more than how life itself first originated ; but I may 
remark that several facts make me suspect that any 
sensitive nerve may be rendered sensitive to light, and 
likewise to those coarser vibrations of the air which 
produce sound. 

In looking for the gradations by which an organ in 
any species has been perfected, we ought to look 
exclusively to its lineal ancestors ; but this is scarcely 
ever possible, and we are forced in each case to look to 
species of the same group, that is to the collateral 
descendants from the same original parent-form, in 
order to see what gradations are possible, and for the 
chance of some gradations having been transmitted 
from the earlier stages of descent, in an unaltered or 
little altered condition. Amongst existing Vertebrata, 
we find but a small amount of gradation in the 
structure of the eye, and from fossil species we can 
learn nothing on this head. In this great class we 
should probably have to descend far beneath the 
lowest known fossiliferous stratum to discover the 
earlier stages, by which the eye has been perfected. 

In the Articulata we can commence a series with an 
optic nerve merely coated with pigment, and without 
any other mechanism ; and from this low stage, 
numerous gradations of structure, branching off in two 
fundamentally different lines, can be shown to exist, 
until we reach a moderately high stage of perfection. 
In certain crustaceans, for instance, there i3 a double 



DIFFICULTIES ON THEORY 169 

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 convex at their upper ends 
and must act by convergence ; and at their lower ends 
there seems to be an imperfect vitreous substance. 
With these facts, here far too briefly and imperfectly 
given, which show that there is much graduated diver- 
sity in the eyes of living crustaceans, and bearing in 
mind how small the number of living animals is in 
proportion to those which 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 inexplic- 
able, 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 imagination ; though I 
have felt the difficulty far too keenly to be surprised 
at any degree of hesitation in extending the principle 
of 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 long-continued efforts of the highest 
human intellects ; and we naturally infer that the eye 
has been formed by a somewhat analogous process. 
But may not this inference be presumptuous ? Have 
we any right to assume that the Creator works by 
intellectual powers like those of man? If we must 
compare the eye to an optical instrument, we ought in 
imagination to take a thick layer of transparent tissue, 



170 ON THE ORIGIN OF SPECIES 

with a nerve sensitive to light beneath, and then sup- 
pose every part of this layer to be continually changing 
slowly in density, so as to separate into layers of differ- 
ent densities and thicknesses, placed at different dis- 
tances from each other, and with the surfaces of each 
layer slowly changing in form. Further we must sup- 
pose that there is a power always intently watching 
each slight accidental alteration in the transparent 
layers ; and carefully selecting each alteration which, 
under varied circumstances, 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 could 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, accord- 
ing to my theory, there has been much extinction. Or 
again, if we look to an organ common to all the mem- 
bers 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 



DIFFICULTIES ON THEORY 171 

an organ could not have been formed by transitional 
gradations of some kind. Numerous cases could be 
given amongst the lower animals of the same organ 
performing at the same time wholly distinct functions ; 
thus the alimentary 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 surface 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 had performed two functions, for 
one function alone, and thus wholly change its nature 
by insensible steps. Two distinct organs sometimes 
perform simultaneously the same function in the same 
individual ; to give one instance, there are fish with 
gills or branchiae that breathe the air dissolved in the 
water, at the same time that they breathe free air in 
their swimbladders, this latter organ having a ductus 
pneumaticus for its supply, and being divided by highly 
vascular partitions. In these cases one of the two 
organs might with ease be modified and perfected so as 
to perform all the work by itself, being aided during 
the process of modification by the other organ ; and 
then this other organ might be modified for some other 
and quite distinct purpose, or be quite obliterated. 

The illustration of the swim bladder in fishes is a 
good one, because it shows us clearly the highly 
important fact that an organ originally constructed for 
one purpose, namely flotation, may be converted into 
one for a wholly different purpose, namely respiration. 
The swimbladder has, also, been worked in as an 
accessory to the auditory organs of certain fish, or, for 
I do not know which view is now generally held, a 
part of the auditory apparatus has been worked in as a 
complement to the swimbladder. All physiologists 
admit that the swimbladder is homologous, or ' ideally 
similar' in position and structure with the lungs 
of the higher vertebrate animals : hence there 
seems to me to be no great difficulty in believ- 
ing that natural selection has actually converted a 



172 ON THE ORIGIN OF SPECIES 

gwimbladder into a lung, or organ used exclusively foi 
respiration. 

1 can, indeed, hardly doubt that all vertebrate 
animals having true lungs have descended by ordinary 
generation from an ancient prototype, of which we 
know nothing, furnished with a floating apparatus or 
swimbladder. We can thus, as I infer from Professor 
Owen's interesting description of these parts, under- 
stand the strange fact that every particle of food and 
drink which we swallow has to pass over the orifice 
of the trachea, with some risk of falling into the lungs, 
notwithstanding the beautiful contrivance by which 
the glottis is closed. In the higher Vertebrata the 
branchiae have wholly disappeared — the slits on the 
sides of the neck and the loop-like course of the 
arteries still marking in the embryo their former posi- 
tion. But it is conceivable that the now utterly lost 
branchiae might have been gradually worked in by 
natural selection for some quite distinct purpose : in 
the same manner as, on the view entertained by some 
naturalists that the branchiae and dorsal scales of Anne- 
lids are homologous with the wings and wing-covers of 
insects, it is probable that organs which at a very 
ancient period served for respiration have been actually 
converted into organs of flight. 

In considering transitions of organs, it is so important 
to bear in mind the probability of conversion from one 
function to another, that I will give one more instance. 
Pedunculated cirripedes have two minute folds of skin, 
called by me the ovigerous frena, which serve, through 
the means of a sticky secretion, to retain the eggs until 
they are hatched within the sack. These cirripedes 
have no branchiae, the whole surface of the body and 
sack, including the small frena, serving for respiration. 
The Balanidae or sessile cirripedes, on the other hand, 
have no ovigerous frena, the eggs lying loose at the 
bottom of the sack, in the well-enclosed shell ; but 
they have large folded branchiae. Now I think no one 
will dispute that the ovigerous frena in the one family 
are strictly homologous with the branchiae of the other 



DIFFICULTIES ON THEORY 173 

family ; indeed, they graduate into each other. There- 
fore I do not doubt that little folds of skin, which 
originally served as ovigerous frena, but which, like- 
wise, very slightly aided the act of respiration, have 
been gradually converted by natural selection into 
branchiae, simply through an increase in their size and 
the obliteration of their adhesive glands. If all ped- 
unculated cirripedes had become extinct, and they 
have already suffered far more extinction than have 
sessile cirripedes, who would ever have imagined that 
the branchiae in this latter family had originally existed 
as organs for preventing the ova from being washed 
out of the sack ? 

Although we must be extremely cautious in con- 
cluding that any organ could not possibly have been 
produced by successive transitional gradations, yet, un- 
doubtedly, grave cases of difficulty occur, some of which 
will be discussed in my future work. 

One of the gravest is that of neuter insects, which 
are often very differently constructed from either the 
males or fertile females ; but this case will be treated 
of in the next chapter. The electric organs of fishes 
offer another case of special difficulty ; it is impossible 
to conceive by what steps these wondrous organs have 
been produced ; but, as Owen and others have re- 
marked, 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 different habits of life, we may 
attribute its presence to inheritance from a common 
ancestor ; and its absence in some of the members to 



174 ON THE ORIGIN OF SPECIES 

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 descendants have lost. The 
presence of luminous organs in a few insects, belong- 
ing to different families and orders, offers a parallel 
case of difficulty. Other cases could be given ; for 
instance in plants, 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 amongst 
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 
appearance and function of the organ may be the same, 
yet some fundamental difference can generally be de- 
tected. I am inclined to believe that in nearly the 
same way as two men have sometimes independently 
hit on the very same invention, so natural selection, 
working for the good of each being and taking advan- 
tage of analogous variatious, has sometimes modified 
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 difficult to con- 
jecture by what transitions organs could have arrived 
at their present state ; yet, considering that the pro- 
portion of living and known forms to the extinct and 
unknown is very small, I have been astonished how 
rarely an organ can be named, towards which no tran- 
sitional grade is known to lead. The truth of this 
remark is indeed shown by that old but somewhat 
exaggerated canon in natural history of e 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 



DIFFICULTIES ON THEORY 175 

prodigal in variety, but niggard in innovation. Why, 
on the theory of Creation, should this be so? ^v hy 
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 under- 
stand why she should not ; for natural selection can 
act only by taking advantage of slight successive varia- 
tions ; 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 
importance does not seem sufficient to cause the pre- 
servation of successively varying individuals. I have 
sometimes felt as much difficulty, though of a very 
diiferent 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 con- 
stitutional differences, might assuredly be acted on by 
natural selection. The tail of the giraffe looks like an 
artificially constructed fly-flapper ; and it seems at first 
incredible that this could have been adapted for its 
present purpose by successive slight modifications, each 
better and better, for so trifling an object as driving 
away flies ; yet we should pause before being too posi- 
tive even in this case, for we know that the distribu- 
tion and existence of cattle and other animals in South 



176 ON THE ORIGIN OF SPECIES 

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 pro- 
genitor, 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 structure 
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 purposes, 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 influence on the organisation ; 
that characters reappear from the law of reversion ; 
that correlation of growth will have had a most im- 
portant influence in modifying various structures ; and 
finally, that sexual selection will often have largely 
modified the external characters of animals having a 
will, to give one male an advantage in fighting with 



DIFFICULTIES ON THEORY 177 

another or in charming- tbe 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 taken advantage of by the de- 
scendants 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 woodpeckers alone had existed, 
and we did not know that there were many black and 
pied kinds, I dare say that we should have thought 
that the green colour was a beautiful adaptation to 
hide this tree-frequenting bird from its enemies ; 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 advantage 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 adaptation 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 the 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 

N 



178 ON THE ORIGIN OF SPECIES 

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 immedi- 
ately made conscious of this by reflecting on the differ- 
ences in the breeds of our domesticated animals in 
different countries, — more especially in the less civil- 
ised 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 differ from lowland breeds ; and a 
mountainous 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 homo- 
logous 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 speculate 
on the relative importance of the several known and 
unknown laws of variation ; 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 



DIFFICULTIES ON THEORY 179 

precise cause of the slight analogous differences be- 
tween species. I might have adduced for this same 
purpose the differences 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 possessor. 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 
probably have had some little effect on structure, 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 characters 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 inherit- 
ance ; 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 
same 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 



180 ON THE ORIGIN OF SPECIES 

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 nipper, but a foot with five toes fitted for walking 
or grasping ; and we may further 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 progenitors, 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 selec- 
tion, subjected formerly, as now, to the several laws 
of inheritance, 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 having 
been 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 produce any modi- 
fication in any one species exclusively for the good of 
another species ; though throughout nature one species 
incessantly takes advantage of, and profits by, the 
structure of another. But natural selection can and 
does often produce structures 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 annihilate 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 rattlesnake has a poison-fang for its 



DIFFICULTIES ON THEORY 181 

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 modified ; 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 selec- 
tion 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 aberra- 
tion of light is 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 multi- 
tude of inimitable contrivances 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 



182 ON THE ORIGIN OF SPECIES 

animals, cannot be withdrawn, owing to the backward 
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 origin- 
ally existed in a remote progenitor as a boring and 
serrated instrument, 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 intensi- 
fied, 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 produc- 
tion 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 industrious and sterile sisters ? It may be diffi- 
cult, 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 undoubt- 
edly 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 inexor- 
able principle of natural selection. If we admire the 
several ingenious contrivances, by which the flowers of 
the orchis 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 dis- 
cussed some of the difficulties and objections which may 
be urged against my theory. Many of them are very 
serious ; but I think that in the discussion light has beeo 



DIFFICULTIES ON THEORY 183 

thrown on several facts, which on the theory of inde- 
pendent 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 selection 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 continual 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 in- 
termediate variety will often be formed, fitted for an 
intermediate zone ; but from reasons assigned, the inter- 
mediate variety will usually exist in lesser numbers than 
the two forms which it connects ; consequently the two 
latter, during the course of further modification, from 
existing in greater numbers, will have a great advantage 
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 selec- 
tion from an animal which at first could only glide 
through the air. 

We have seen that a species may under new condi- 
tions of life change its habits, or have diversified habits, 
with some habits very unlike those of its nearest con- 
geners. 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 any one ; yet in the case 



184 ON THE ORIGIN OF SPECIES 

of any organ, if we know of a long series of gradations 
in complexity, each good for its possessor, then, under 
changing conditions of life there is no logical impossi- 
bility in the acquirement of any conceivable degree of 
perfection through natural selection. In the cases in 
which we know of no intermediate 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 meta- 
morphoses in function are at least possible. For instance, 
a swim-bladder has apparently been converted into an 
air-breathing lung. The same organ having performed 
simultaneously very different functions, and then having 
been specialised for one function ; and two very distinct 
organs having performed at the same time the same 
function, the one having been perfected whilst 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 unim- 
portant for the welfare of a species, that modifications 
in its structure could not have been slowly accumulated 
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 advantageous to a 
species, have been subsequently taken advantage of by 
the still further modified descendants of this species. We 
may, also, believe that a part formerly of high import- 
ance 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 selec- 
tion, — a power which 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 well-stocked 



DIFFICULTIES ON THEORY 185 

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 inha- 
bitants of another and generally larger country. For in 
the larger country there will have existed more indi- 
viduals, and more diversified forms, and the competition 
will have been severer, and thus the standard of perfec- 
tion will have been rendered higher. Natural selection 
will not necessarily produce absolute perfection ; 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 Conditions 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 independent 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 prin- 
ciple of natural selection. For natural selection acts by 
either now adapting the varying parts of each 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 dis- 
use, being slightly affected by the direct action of the 
external conditions of life, and being in all cases sub- 
jected 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 

Tnatincts comparable with habits, but different in their origin — 
Instincts graduated— Aphides and ants— Instincts variable- 
Domestic instincts, their origin— Natural instincts of the cuckoo, 
ostrich, and parasitic bees — Slave-making-ants— Hive-bee, its 
cell-making instinct^Dimculties on the theory of the Natural 
Selection of instincts— Neuter or sterile insects— Summary. 

The subject of instinct might have been worked into the 
previous chapters ; but I have thought that it would be 
more convenient to treat the subject separately, espe- 
cially as so wonderful an instinct as that of the hive- 
bee making its cells will probably have occurred to 
many readers, as a difficulty sufficient 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 con- 
cerned 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 
commonly embraced by this term ; but every one under- 
stands what is meant, when it is said that instinct impels 
the cuckoo to migrate and to lay her eggs in other birds' 
nests. An action, which we ourselves should require 
experience to enable us to perform, when performed by 
an animal, more especially by a very young one, without 
any experience, and when performed by many indivi- 
duals in the same way, without their knowing for what 

186 



INSTINCT 187 

purpose 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 metaphy- 
sicians have compared instinct with habit. This com- 
parison 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 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 com- 
pleted up only to the third stage, the caterpillar simply 
re-performed the fourth, fifth, and sixth stages of con- 
struction. 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 in- 
herited — and I think it can be shown that this does 
sometimes happen — then the resemblance between what 
originally was a habit and an instinct becomes so close 



188 ON THE ORIGIN OF SPECIES 

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 transmitted by inheritance 
to succeeding generations. It can be clearly shown that 
the most wonderful instincts with which we are ac- 
quainted, 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 
structures, 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 



INSTINCT 189 

such gradations ; or we ought at least to 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 
amongst extinct species, how very generally gradations, 
leading to the most complex instincts, can be discovered. 
Changes ot 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 structure, and con- 
formably 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 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 antenna? on the abdomen first of one aphis and then 
of another ; and each aphis, as soon as it felt the 
antennas, immediately lifted up its abdomen and 
excreted a limpid drop of sweet juice, which was eagerly 



190 ON THE ORIGIN OF SPECIES 

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 
convenience 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 
instincts of others, as each takes advantage of the 
weaker bodily structure of others. So again, in some 
few cases, certain instincts cannot be considered 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 instances 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 strengthened by experience, 
and by the sight of fear of the same enemy in other 
animals. But fear of man is slowly acquired, as I 
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 



INSTINCT 191 

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 individuals 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 selection, 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, or inherited 
variations of instinct in a state of nature will be 
strengthened by briefly considering 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 
likewise 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 myself 
seen a striking instance) will sometimes point and even 
back other dogs the very first time that they are taken 
out ; retrieving is certainly in some degree inherited 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 indi- 
vidual, 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 



192 ON THE ORIGIN OF SPECIES 

actions differ essentially from true instincts. If we 
were 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 grey- 
hound 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 per- 
formed 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 
successive generations made tumblers what they now 
are ; and near Glasgow there are house -tumblers, as I 



INSTINCT 193 

hear from Mr. Brent, which cannot fly eighteen inches 
high without going head over heels. It may be doubted 
whether any one 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 com- 
pulsory 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 tameness, simply to habit 
and long-continued close confinement. 

Natural instincts are lost under domestication : 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 domestication. 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 ! No doubt they occasionally 



194 ON THE ORIGIN OF SPECIES 

do make an attack, and are then beaten ; and if not 
cured, they are destroyed ; so that habit, with soma 
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 originally 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 surrounding grass or 
thickets ; and this is 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 
accumulating 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, probably, 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-making 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 im- 



INSTINCT 195 

mediate 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 inconveniently 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 oc- 
casionally 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 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 advantage 
having been taken of the mistaken maternal instinct of 
another bird, than by their own mother's care, en- 
cumbered 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 ad- 
vantage. 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 rearing 
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, according 
to Dr. Gray and to some other observers, the European 
cuckoo has not utterly lost all maternal love and care 
for her own offspring. 



196 ON THE ORIGIN OF SPECIES 

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 Gallinaceae ; 
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 perfected ; 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 re- 
markable 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 
necessary if they had to store food for their own young. 
Some species, likewise, of Sphegidae (wasp-like insects) 
are parasitic on other species ; and M. Fab re has lately 
shown 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 occa- 
sional 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. 

Slave-making instinct. — This remarkable instinct was 
first discovered in the Formica (Polyerges) rufescens by 
Pierre Huber, a better observer even than his celebrated 



INSTINCT 197 

father. This ant is absolutely dependent on its slaves ; 
without their aid, the species would certainly be- 
come extinct in a single year. The males and fertile 
females do no work. The workers or sterile females, 
though most energetic and courageous in capturing 
slaves, do no other work. They are incapable of making 
their own nests, or of feeding their own larvae. When 
the old nest is found inconvenient, and they have to 
migrate, it is the slaves which determine the migration, 
and actually carry their masters in their jaws. So 
utterly helpless are the masters, that when Huber shut 
up thirty of them without a slave, but with plenty of 
the food which they like best and with their larvsB and 
pupae to stimulate them to work, they did nothing ; they 
could not even feed themselves, and many perished of 
hunger. Huber then introduced a single slave (F. 
fusca), and she instantly set to work, fed and saved the 
survivors ; made some cells and tended the larvae, and 
put all to rights. What can be more extraordinary 
than these well-ascertained facts ? If we had not 
known of any other slave-making ant, it would have 
been hopeless to have speculated how so wonderful an 
instinct could have been perfected. 

Another species, Formica sanguinea, was likewise 
first discovered by P. Huber to be a slave-making ant. 
This species is found in the southern parts of England, 
and its habits have been attended to by Mr. F. Smith, 
of the British Museum, to whom I am much indebted 
for information on this and other subjects. Although 
fully trusting to the statements of Huber and Mr. 
Smith, I tried to approach the subject in a sceptical 
frame of mind, as any one 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 communities, and have never been 
observed in the nests of F. sanguinea. The slaves are 



198 ON THE ORIGIN OF SPECIES 

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 occa- 
sionally come out, and like their masters are much 
agitated and defend the nest : when the nest is much 
disturbed and the larvaB and pupae are exposed, the 
slaves work energetically with their masters in carrying 
them away to a place of safety. Hence, it is clear, that 
the slaves feel quite at home. During the months of 
June and July, on three successive years, I have watched 
for many hours several nests in Surrey and Sussex, and 
never saw a slave either leave or enter a nest. As, 
during these months, the slaves are very few in number, 
I thought that they might behave differently when 
more numerous ; but Mr. Smith informs me that he has 
watched the nests at various hours during May, J\ ae 
and August, both in Surrey and Hampshire, aDd has 
never seen the slaves, though present in large numbers 
in August, either leave or enter the nest. Hence he 
considers them as strictly household slaves. The 
masters, on the other hand, may be constantly seen 
bringing in materials for the nest, and food of all 
kinds. During the present year, however, in the 
month of July, I came across a community with an 
unusually large stock of slaves, and I observed a few 
slaves mingled with their masters leaving the nest, and 
marching along the same road to a tall Scotch fir-tree, 
twenty -five yards distant, which they ascended to- 
gether, probably in search of aphides or cocci. Ac- 
cording to Huber, who had ample opportunities for 
observation, in Switzerland the slaves habitually work 
with their masters in making the nest, and they alone 
open and close the doors in the morning and evening ; 
and, as Huber expressly states, their principal office is 
to search for aphides. This difference in the usual 
habits of the masters and slaves in the two countries, 
probably depends merely on the slaves being captured 
in greater numbers in Switzerland than in England. 

One day I fortunately witnessed a migration of F. 
sanguines from one nest to another, and it was a most 



INSTINCT 199 

interesting spectacle to behold the masters carefully 
carrying 1 (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 haunting 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. san- 
guinea. The latter ruthlessly killed their small op- 
ponents, and carried their dead bodies as food to their 
nest, twenty-nine yards distant ; but they were pre- 
vented from getting any pupae to rear as slaves. I then 
dug up a small parcel of the pupae of F. -fusca from an- 
other 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 victorious 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 frag- 
ments 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 cour- 
ageous, 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 acci- 
dentally 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 
•een 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 



200 ON THE ORIGIN OF SPECIES 

ants had crawled away, they took heart and carried 
off the pupae. 

One evening- I visited another community of F. san- 
guinea, 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 individuals 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 con- 
firmation by me, in regard to the wonderful instinct of 
making slaves. Let it be observed what a contrast the 
instinctive 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 deter- 
mine when and where a new nest shall be formed, and 
when they migrate, the masters carry the slaves. Both 
in Switzerland and England the slaves seem to have 
the exclusive care of the larvae, and the masters alone 
go on slave-making expeditions. 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 may be 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. 



INSTINCT 201 

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 
pupaB 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 more advantageous to this species to 
capture workers than to procreate them — the habit of 
collecting pupae 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 
supposing 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 beautifully adapted to 
its end, without enthusiastic admiration. We hear 
from mathematicians that bees have practically solved 
a recondite problem, 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 incon- 
ceivable how they can make all the necessary angles 



202 ON THE ORIGIN OF SPECIES 

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, 
X think, to follow from a few very simple instincts. 

I was led to investigate this subject by Mr. Water- 
house, 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, sometimes 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 composition 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 struc- 
ture 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 com- 
pleted ; but this is never permitted, the bees building 
perfectly flat walls of wax between the spheres which 



INSTINCT 203 

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 imitation 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 
surfaces 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 layer, the 
resulting structure would probably have been as perfect 
as the comb of the hive-bee. Accordingly I wrote to 
Professor Miller, of Cambridge, and this geometer has 
kindly read over the following statement, drawn up 
from his information, 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 J 2, or 
radius x ] «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 



204 ON THE ORIGIN OF SPECIES 

every angle identically the same with the best measure- 
ments 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 intersect 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 adjoining 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 modifica- 
tions of instincts in themselves not very wonderful, — 
hardly 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 experiment. 
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 



INSTINCT 205 

were converted 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 1 to me 
to observe that wherever several bees had begun to 
excavate 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 (i.e. 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 bottons of the basins, if they had been 
excavated to the same depth as in the former experi- 
ment, 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 
vermilion wax having been left ungnawed, were 
situated, as far as the eye could judge, exactly along 
the planes of imaginary 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 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 



206 ON THE ORIGIN OF SPECIES 

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 inter- 
mediate planes or planes of intersection. 

Considering how flexible thin wax is, I do not see 
that there is any difficulty in the bees, whilst 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 just-commenced cell, which were slightly 
concave on one side, where I suppose that the bees had 
excavated too quickly, and convex on the opposed side, 
where the bees had worked less quickly. In one well- 
marked instance, I put the comb back into the hive, 
and allowed the bees to go on working for a short 
time, and again examined the cell, and I found that 
the rhombic plate had been completed, and had become 
perfectly flat : it was absolutely impossible, from 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 vermilion 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 three-sided pyramidal base of any 



INSTINCT 207 

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 com- 
plete the upper edges of the rhombic plates, until the 
hexagonal walls are commenced. Some of these state- 
ments 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 conform- 
able 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 con- 
struction 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 specimens 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 commenced and those com- 
pleted, being thus crowned by a strong coping of wax, 



208 ON THE ORIGIN OF SPECIES 

the bees can cluster and crawl over the comb without 
injuring the delicate hexagonal walls, which are only 
about one four-hundredth 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 under- 
standing how the cells are made, that a multitude of 
bees all work together ; 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 construction seems to be 
a sort of balance struck between many bees, all in- 
stinctively 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 inter- 
section 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 



INSTINCT 209 

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 adjoin- 
ing 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 subversive of 
the foregoing theory ; namely, that the cells on the 
extreme margin of wasp-combs are sometimes strictly 
hexagonal ; but I have not space here to enter on this 
subject. Nor does there seem to me any great diffi- 
culty in a single insect (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 conceivable 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 architectural instincts, all 
tending towards the present perfect plan of construc- 
tion, could have profited the progenitors of the hive- 
bee ? I think the answer is not difficult : it is knowD 

P 



210 ON THE ORIGIN OF SPECIES 

that bees are often hard pressed to get sufficient 
nectar ; and I am informed by Mr. Tegetmeier that it 
has been experimentally found that no less than from 
twelve to fifteen pounds of dry sugar are consumed by 
a hive of bees for the secretion of each pound of wax ; 
to that a prodigious quantity of fluid nectar must be 
collected and consumed by the bees in a hive for the 
secretion of the wax necessary for the construction of 
their combs. Moreover, 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 m ust 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 circumstance determined, 
as it probably often does determine, the numbers of a 
humble-bee which could exist in a country ; and let 
us further suppose that the community lived through- 
out the winter, and consequently required a store of 
honey : there can in this case be no doubt that it would 
be an advantage to our humble-bee, if a slight modifica- 
tion of her instinct led her to make her waxen cells 
near together, so as to intersect a little ; for a wall in 
common even to two adjoining cells, would save some 
little wax. Hence it would continually be more and 
more advantageous to our humble-bee, if she were to 
make her cells more and more regular, nearer together, 
and aggregated into a mass, like the cells of the 
Melipona ; for in this case a large part of the bounding 
surface of each cell would serve to bound other cells, 
and much wax would be saved. Again, from the same 
cause, it would be advantageous to the Melipona, if 
she were to make her cells closer together, and more 
regular in every way than at present ; for then, as we 



INSTINCT 211 

have seen, the spherical surfaces would wholly dis- 
appear, and would all be replaced by plane surfaces ; 
and the Melipona would make a comb as perfect as that 
of the hive-bee. Beyond this stage of perfection in 
architecture, natural selection could not lead ; for the 
comb of the hive-bee, as far as we can see, is absolutely 
perfect in economising wax. 

Thus, as I believe, the most wonderful of all known 
instincts, that of the hive -bee, can be explained by 
natural selection having taken advantage of numerous, 
successive, slight modifications of simpler instincts ; 
natural selection having by slow degrees, more and 
more perfectly, led the bees to sweep equal spheres 
at a given distance from each other in a double 
layer, and to build up and excavate the wax along 
the planes of intersection. The bees, of course, no 
more knowing that they swept their spheres at one 
particular distance from each other, than they know 
what are the several angles of the hexagonal prisms 
and of the basal rhombic plates. The motive power of 
the process of natural selection having been economy 
of wax ; that individual swarm which wasted least 
honey in the secretion of wax, having succeeded best, 
and having transmitted by inheritance its newly ac- 
quired economical instinct to new swarms, which in 
their turn will have had the best chance of succeeding 
in the struggle for existence. 

No doubt many instincts of very difficult explanation 
could be opposed to the theory of natural selection, — 
cases, in which we cannot see how an instinct could 
possibly have originated ; cases, in which no interme- 
diate gradations are known to exist ; cases of instinct 
of apparently such trifling importance, that they could 
hardly have been acted on by natural selection ; cases 
of instincts almost identically the same in animals so 
remote in the scale of nature, that we cannot account 
for their similarity by inheritance from a common 
parent, and must therefore believe that they have 
been acquired by independent acts of natural selection. 



212 ON THE ORIGIN OF SPECIES 

I will not here enter on these several cases, but will 
confine myself to one special difficulty, which at first 
appeared to me insuperable, and actually fatal to my 
whole theory. I allude to the neuters or sterile females 
in insect-communities : for these neuters often differ 
widely in instinct and in structure from both the males 
and fertile females, and yet, from being sterile, they 
cannot propagate their kind. 

The subject well deserves to be discussed at great 
length, but I will here take only a single case, that 
of working or sterile ants. How the workers have 
been rendered sterile is a difficulty ; but not much 
greater than that of any other striking modification of 
structure ; for it can be shown that some insects and 
other articulate animals in a state of nature occasion- 
ally become sterile ; and if such insects had been 
social, and it had been profitable to the community 
that a number should have been annually born capable 
of work, but incapable of procreation, I can see no 
very great difficulty in this being effected by natural 
selection. But I must pass over this preliminary diffi- 
culty. The great difficulty lies in the working ants 
differing widely from both the males and the fertile 
females in structure, as in the shape of the thorax and 
in being destitute of wings and sometimes of eyes, and 
in instinct. As far as instinct alone is concerned, 
the prodigious difference in this respect between the 
workers and the perfect females, would have been far 
better exemplified by the hive-bee. If a working ant 
or other neuter insect had been an animal in the 
ordinary state, I should have unhesitatingly assumed 
that all its characters had been slowly acquired through 
natural selection ; namely, by an individual having 
been born with some slight profitable modification of 
structure, this being inherited by its offspring, which 
again varied and were again selected, and so onwards. 
But with the working ant we have an insect differing 
greatly from its parents, yet absolutely sterile ; so that 
it could never have transmitted successively acquired 
modifications of structure or instinct to its progeny. 



INSTINCT 213 

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 corre- 
lated 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 differ- 
ences in the horns of different breeds of cattle in 
relation to an artificially imperfect 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 mem- 
bers of insect - communities : the difficulty lies in 
understanding how such correlated modifications of 
structure could have been slowly accumulated by 
natural selection. 

This difficulty, though appearing insuperable, is 
lessened, or, as I believe, disappears, when it is re- 
membered 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 confidence 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 carefully 'watching which indi- 
vidual 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 



214 ON THE ORIGIN OF SPECIES 

with social insects : a slight modification of structure, 
or instinct, correlated with the sterile condition of 
certain members of the community, has been advan- 
tageous to the community : consequently the fertile 
males and females of the same community flourished, 
and transmitted to their fertile offspring a tendency to 
produce sterile members having the same modification. 
And I believe that this process has been repeated, 
until that prodigious 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 instincts 
extraordinarily 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, and 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 
facts at once annihilate my theory. In 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 



INSTINCT 215 

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 occasionally to find 
neuter-insects of the same species, in the same nest, 
presenting gradations of structure ; and this we do find, 
even often, considering how few neuter-insects out of 
Europe have been carefully examined. Mr. F. Smith 
has shown how surprisingly the neuters of severa] 
British ants differ from each other in size and some- 
times 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 
perfect 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 rudimentary. Having carefully dissected several 
specimens of these workers, I can affirm that the eyes 
are far more rudimentary in the smaller workers than 
can be accounted for merely by their proportionally 
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 con- 
dition. 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 



216 ON THE ORIGIN OF SPECIES 

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 
well-developed ocelli. 

I may give one other case : so confidently did I 
expect to find gradations in important points of struc- 
ture between the different 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 measure- 
ments, but a strictly accurate illustration : the differ- 
ence 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 workmen had heads four in- 
stead of three times as big as those of the smaller men, 
and jaws nearly five times as big. The jaws, more- 
over, 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 ; 



INSTINCT 217 

— 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 community, 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 dis- 
tinctly 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 knowledge and manufac- 
tured 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 
mtercrossed, and their instincts and structure would 
have become blended. And nature has, as I believe, 
effected this admirable division of labour in the com- 
munities 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 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 accumulation of 
numerous, slight, and as we must call them accidental, 
variations, which are in any manner profitable, with- 
out exercise or habit having come into play. For no 
amount of exercise, or habit, or volition, in the utterly 
sterile members of a community could possibly affect 



218 ON THE ORIGIN OF SPECIES 

the structure or instincts of the fertile members, which 
alone leave descendants. I am surprised that no one 
has advanced this demonstrative case of neuter insects, 
against the well-known 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 import- 
ance to each animal. Therefore I 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, to the best of my judgment, 
annihilate it. On the other hand, the fact that in- 
stincts 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 to corroborate 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 conditions of life, yet often re- 
taining nearly the same instincts. For instance, we can 
understand on the principle of inheritance, 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 



INSTINCT 219 

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 satisfac- 
tory to look at such instincts as the young cuckoo eject- 
ing its foster-brothers, — ants making slaves, — the larvae 
of ichneumonidae feeding within the live bodies of cater- 
pillars, — 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. 



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 con- 
ditions 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 naturalists is that 
species, when intercrossed, have been specially endowed 
with the quality of sterility, in order to prevent the con- 
fusion 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, inas- 
much 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 succes- 
sive profitable degrees of sterility. I hope, however, to 
be able to show that sterility is not a specially acquired 
or endowed quality, but is incidental on other acquired 
differences. 

In treating this subject, two classes of facts, to a large 
extent fundamentally different, have generally been con- 
founded together ; namely, the sterility of two species 

220 



HYBRIDISM 221 

when first crossed, and the sterility of the hybrids pro- 
duced from them. 

Pure species have of course their organs of reproduc- 
tion in a perfect condition, yet when intercrossed they 
produce either few or no offspring*. Hybrids, on the 
other hand, have their reproductive organs functionally 
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 
probably 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 import- 
ance with the sterility of species ; for it seems to make 
a broad and clear distinction 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, Kolreuter and 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 universal ; 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 unhesitatingly 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 
aeeds, in order to show that there is any degree of 



222 ON THE ORIGIN OF SPECIES 

sterility. He always compares the maximum number 
of seeds produced by two species when crossed and by 
their hybrid offspring, with the average number pro- 
duced by both pure parent-species in a state of nature. 
But a serious cause of error seems to me to be here 
introduced : a plant to be hybridised must be castrated, 
and, what is often more important, must be secluded 
in order to prevent pollen being brought to it by insects 
from other plants. Nearly all the plants experiment- 
ised on by Gartner were potted, and apparently were 
kept in a chamber in his house. That these processes 
are 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 artifi- 
cially fertilised with their own pollen, and (excluding 
all cases such as the Leguminosae, in which there is an 
acknowledged difficulty in the manipulation) half of 
these twenty plants had their fertility in some degree 
impaired. Moreover, as Gartner during several years 
repeatedly crossed the primrose and cowslip, 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 to- 
gether ; 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 fer- 
tility 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, 
Kolreuter and Gartner, should have arrived at dia- 



HYBRIDISM 223 

metrically opposite conclusions 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 evi- 
dence 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 evidence from this source graduates away, and 
is doubtful in the same degree as is the evidence derived 
from other constitutional and structural differences. 

In regard to the sterility of hybrids in successive 
generations ; though Gartner was enabled to rear some 
hybrids, carefully guarding them from a cross with 
either pure parent, for six or seven, and in one case for 
ten generations, yet he asserts positively that their fer- 
tility never increased, but generally greatly decreased. 
I do not doubt that this is usually the case, and that 
the fertility often suddenly decreases in the first few 
generations. Nevertheless I believe that in all these 
experiments 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 in- 
dividual or variety increases fertility, that I cannot doubt 
the correctness of this almost universal belief amongst 
breeders. Hybrids are seldom raised by experimen- 
talists 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 indi- 
vidual 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 statement repeatedly made by 
Gartner, namely, that if even the less fertile hybrids 



224 ON THE ORIGIN OF SPECIES 

be artificially fertilised with hybrid pollen of the same 
kind, their fertility, notwithstanding the frequent ill 
effects of manipulation, sometimes decidedly increases, 
and goes on increasing. Now, in artificial fertilisation 
pollen is as often taken by chance (as I know from my 
own experience) 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 experiments are in 
progress, so careful an observer 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 accounted 
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 as the 
pure parent -species — as are Kolreuter and Gartner 
that some degree of sterility between distinct species is 
a universal law of nature. He experimentised on some 
of the very same species as did Gartner. The differ- 
ence in their results may, I think, be in part accounted 
for by Herbert's great horticultural skill, and by his 
having hothouses at his command. Of his many im- 
portant statements I will here give only a single one as 
an example, namely, that "every ovule in a pod of 
Crinum capense fertilised by C. revolutum produced a 
plant, which (he says) I never saw to occur in a case of 
its natural fecundation." So that we here have perfect, 
or even more than commonly perfect, fertility in a first 
cross between two distinct species. 

This case of the Crinum leads me to refer to a most 
singular fact, namely, that there are individual plants 
of certain species of Lobelia and of some other genera, 
which can be far more easily fertilised by the pollen of 



HYBRIDISM 225 

another and distinct species, than by their own pollen ; 
and all the individuals of nearly all the species of Hip- 
peastrum seem to be in this predicament. For these 
plants have been found to yield seed to the pollen of a 
distinct species, though quite sterile with their own 
pollen, notwithstanding that their own pollen was 
found to be perfectly good, for it fertilised distinct 
species. So that certain individual plants and all the 
individuals of certain species can actually be hybridised 
much more readily than they can be self-fertilised ! 
For instance, a bulb of Hippeastrum aulicum produced 
four flowers ; three were fertilised by Herbert with 
their own pollen, and the fourth was subsequently 
fertilised by the pollen of a compound hybrid descended 
from three other and distinct species : the result was 
that ' the ovaries of the three first flowers soon ceased 
to grow, and after a few days perished entirely, whereas 
the pod impregnated by the pollen of the hybrid made 
vigorous growth and rapid progress to maturity, and 
bore good seed, which vegetated freely.' In a letter 
to me, in 1839, Mr. Herbert told me that he had then 
tried the experiment during five years, and he con- 
tinued to try it during several subsequent years, and 
always with the same result. This result has, also, 
been confirmed by other observers in the case of Hip- 
peastrum with its sub-genera, and in the case of some 
other genera, as Lobelia, Passiflora, and Verbascum. 
Although the plants in these experiments appeared 
perfectly healthy, and although both the ovules and 
pollen of the same flower were perfectly good with 
respect to other species, yet as they were functionally 
imperfect in their mutual self-action, we must infer 
that the plants were in an unnatural state. Neverthe- 
less these facts show on ^hat slight and mysterious 
causes the lesser or greater fertility of species when 
crossed, in comparison with the -*ame species when self- 
fertilised, sometimes depends. 

The practical experiments of horticulturists, though 
not made with scientific precision, aeserve some notice. 
It is notorious in how complicated a manner the species 

Q 



226 ON THE ORIGIN OF SPECIES 

of Pelargonium, Fuchsia, Calceolaria, Petunia, Rhodo- 
dendron, etc., have been crossed, yet many of these 
hybrids seed freely. For instance, Herbert asserts that 
a hybrid from Calceolaria integrifolia and plantaginea, 
species most widely dissimilar in general habit, ' re- 
produced itself as perfectly as if it had been a natural 
species from the mountains of Chile.' 1 have taken 
some pains to ascertain the degree of fertility of some 
of the complex crosses of Rhododendrons, and I am 
assured that many of them are perfectly fertile. Mr. 
C. Noble, for instance, informs me that he raises stocks 
for grafting from a hybrid between Rhod. Ponticum 
and Catawbiense, and that this hybrid ' seeds as freely 
as it is possible to imagine.' Had hybrids, when fairly 
treated, gone on decreasing in fertility in each suc- 
cessive generation, as Gartner believes to be the case, 
the fact would have been notorious to nurserymen. 
Horticulturists raise large beds of the same hybrids, 
and such alone are fairly treated, for by insect agency 
the several individuals of the same hybrid variety are 
allowed to freely cross with each other, and the in- 
jurious influence of close interbreeding is thus pre- 
vented. Any one may readily convince himself of the 
efficiency of insect-agency by examining the flowers 
of the more sterile kinds of hybrid rhododendrons, 
which produce no pollen, for he will find on their 
stigmas plenty of pollen brought from other flowers. 

In regard to animals, much fewer experiments have 
been carefully tried than with plants. If our systematic 
arrangements can be trusted, that is if the genera of 
animals are as distinct from each other, as are the genera 
of plants, then we may infer that animals more widely 
separated in the scale of nature can be more easily 
crossed than in the case of plants ; but the hybrids 
themselves are, I think, more sterile. I doubt whether 
any case of a perfectly fertile hybrid animal can be con- 
sidered as thoroughly well authenticated. It should, 
however, be borne in mind that, owing to few animals 
breeding freely under confinement, few experiments 
have been fairly tried : for instance, the canary-bird 



HYBRIDISM 227 

has been crossed with nine other finches, but as not 
one of these nine species breeds freely in confinement, 
we have no right to expect that the first crosses between 
them and the canary, or that their hybrids, should be 
perfectly fertile. Again, with respect to the fertility 
in successive generations of the more fertile hybrid 
animals, I hardly know of an instance in which two 
families of the same hybrid have been raised at the 
same time from different parents, so as to avoid the 
ill effects of close interbreeding. On the contrary, 
brothers and sisters have usually been crossed in each 
successive generation, in opposition to the constantly 
repeated admonition of every breeder. And in this 
case, it is not at all surprising that the inherent 
sterility in the hybrids should have gone on increasing. 
If we were to act thus, and pair brothers and sisters in 
the case of any pure animal, which from any cause 
had the least tendency to sterility, the breed would 
assuredly be lost in a very few generations. 

Although I do not know of any thoroughly well- 
authenticated cases of perfectly fertile hybrid animals, 
I have some reason to believe that the hybrids from 
Cervulus vaginalis and Reevesii, and from Phasianus 
colchicus with P. torquatus and with P. versicolor are 
perfectly fertile. There is no doubt that these three 
pheasants, namely, the common, the true ring-necked, 
and the Japan, intercross, and are becoming blended to- 
gether in the woods of several parts of England. The 
hybrids from the common and Chinese geese (A. 
cygnoides), species which are so different that they are 
generally ranked in distinct genera, have often bred in 
this country with either pure parent, and in one single 
instance they have bred inter se. This was effected by 
Mr. Eyton, who raised two hybrids from the same 
parents but from different hatches ; and from these 
two birds he raised no less than eight hybrids (grand- 
children of the pure geese) from one nest. In India, 
however, these cross-bred geese must be far more 
fertile ; for I am assured by two eminently capable 
judges, namely Mr. Blyth and Captain Hutton, that 



228 ON THE ORIGIN OF SPECIES 

whole flocks of these crossed geese are kept in various 
parts of the country ; and as they are kept for profit, 
where neither pure parent -species exists, they must 
certainly be highly fertile. 

A doctrine which originated with Pallas, has been 
largely accepted by modern naturalists ; namely, that 
most of our domestic animals have descended from two 
or more wild species, since commingled by inter- 
crossing. On this view, the aboriginal species must 
either at first have produced quite fertile hybrids, or 
the hybrids must have become in subsequent genera- 
tions quite fertile under domestication. This latter 
alternative seems to me the most probable, and I am 
inclined to believe in its truth, although it rests on no 
direct evidence. I believe, for instance, that our dogs 
have descended from several wild stocks ; yet, with 
perhaps the exception of certain indigenous domestic 
dogs of South America, all are quite fertile together ; 
and analogy makes me greatly doubt, whether the 
several aboriginal species would at first have freely 
bred together and have produced quite fertile hybrids. 
So again there is reason to believe that our European 
and the humped Indian cattle are quite fertile together ; 
but from facts communicated to me by Mr. Blyth, I 
think they must be considered as distinct species. On 
this view of the origin of many of our domestic animals, 
we must either give up the belief of the almost uni- 
versal sterility of distinct species of animals when 
crossed ; or we must look at sterility, not as an in- 
delible characteristic, but as one capable of being 
removed by domestication. 

Finally, looking to all the ascertained facts on the 
intercrossing of plants and animals, it may be concluded 
that some degree of sterility, both in first crosses and in 
hybrids, is an extremely general result ; but that it 
cannot, under our present state of knowledge, be con- 
sidered as absolutely universal. 

Laws governing the Sterility of first Crosses and of 
Hybrids. — We will now consider a little more in detail 



HYBRIDISM 229 

the circumstances and rules governing the sterility of 
first crosses and of hybrids. Our chief object will be to 
see whether or not the rules indicate that species have 
specially been endowed with this quality, in order to 
prevent their crossing and blending together in utter 
confusion. The following rules and conclusions are 
chiefly drawn up from Gartner's admirable work on the 
hybridisation of plants. I have taken much pains to 
ascertain how far the rules apply to animals, and con- 
sidering 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 differ- 
ent 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 produce. 
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 pro- 
ducing a greater and greater number of seeds up to 
perfect fertility. 

Hybrids from two species which are very difficult to 



230 ON THE ORIGIN OF SPECIES 

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 
hybrids thus produced — two classes of facts which are 
generally confounded 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, ror 
instance in Dianthus, these two opposite cases occur. 

The fertility, both of first crosses and of hybrids, is 
more easily affected by unfavourable conditions, than 
is the fertility of pure species. But the degree of 
fertility is likewise innately variable ; for it is not 
always the same when the same two species are crossed 
under the same circumstances, but depends in part 
upon the constitution 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 resem- 
blance between species in structure 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 systematic 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 



HYBRIDISM 231 

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 Diantbus, 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 distinct 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 char- 
acter is sufficient to prevent 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 in the cotyledons, can be 
crossed. Annual and perennial plants, deciduous and 
evergreen 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 recip- 
rocally 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 com- 
pletely 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 imperceptible by us, and confined to the 
reproductive system. This difference in the result of 



232 ON THE ORIGIN OF SPECIES 

reciprocal crosses between the same two species waa 
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 re- 
ciprocal 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 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 amongst hybrids which are usually 
intermediate in structure between their parents, ex- 
ceptional 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 other hybrids 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. 



HYBRIDISM 233 

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 
and distinct 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 
unfavourable 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 two species is not always governed 
by their systematic affinity or degree of resemblance to 
each other. This latter statement 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 differ- 
ence, and occasionally the widest possible difference, in 
the facility of effecting a union. The hybrids, more- 
over, produced from reciprocal crosses often differ in 
fertility. 

Now do these complex and singular rules indicate 
that species have been endowed with sterility simply to 
prevent their becoming 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 im- 
portant to keep from blending together ? Why should 
the degree of sterility be innately variable in the in- 
dividuals 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 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 per- 
mitted ? to grant to species the special power of produc- 
ing hybrids, and then to stop their further propagation 



234 ON THE ORIGIN OF SPECIES 

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 the other hand, 
appear to me clearly to indicate that the sterility both 
of first crosses and of hybrids is simply incidental or 
dependent on unknown differences, chiefly in the repro- 
ductive 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 element of the other, but not in a re- 
versed 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 en- 
dowed 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 



HYBRIDISM 235 

each other. 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 varie- 
ties of the apricot and peach on certain varieties of the 
plum. 

As Gartner found that there was sometimes an innate 
difference in different individuals 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 gooseberry. 

We have seen that the sterility of hybrids, which 
have their reproductive organs in an imperfect con- 
dition, 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 are reminded 
by this latter fact of the extraordinary case of Hippe- 
astrum, 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 



236 ON THE ORIGIN OF SPECIES 

the curious and complex laws governing the facility 
with which trees can be grafted on each other as in- 
cidental on 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 reproductive 
systems. These differences, in both cases, follow to a 
certain extent, as might have been expected, systematic 
affinity, by which every kind of resemblance and dis- 
similarity 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. 

Causes of the Sterility of first Crosses and of Hybrids. — 
We may now look a little closer at the probable causes 
of the sterility of first crosses and of hybrids. These 
two cases are fundamentally different, for, as just 
remarked, in the union of two pure species the male 
and female sexual elements are perfect, whereas in 
hybrids they are imperfect. Even in first crosses, the 
greater or lesser difficulty in effecting a union ap- 
parently depends on several distinct causes. There 
must sometimes be a physical impossibility in the male 
element reaching the ovule, as would be the case with a 
plant having a pistil too long for the pollen-tubes to 
reach the ovarium. It has also been observed that 
when pollen of one species is placed on the stigma of a 
distinctly allied species, though the pollen tubes pro- 
trude, they do not penetrate the stigmatic surface. 
Again, the male element may reach the female element, 
but be incapable of causing an embryo to be developed, 
as seems to have been the case with some of Thuret's 
experiments on Fuci. No explanation can be given 
of these facts, any more than why certain trees cannot 
be grafted on others. Lastly, an embryo may be 



HYBRIDISM 237 

developed, and then perish at an early period. This 
latter alternative has not been sufficiently attended 
to ; but I believe, from observations communicated to 
me by Mr. Hewitt, who has had great experience in 
hybridising gallinaceous birds, that the early death of 
the embryo is a very frequent cause of sterility in first 
crosses. I was at first very unwilling to believe in 
this view ; as hybrids, when once born, are generally 
healthy and long-lived, as we see in the case of the 
common mule. Hybrids, however, are differently cir- 
cumstanced before and after birth : when born and 
living in a country where their two parents can live, 
they are generally placed under suitable conditions of 
life. But a hybrid partakes of only half of the nature 
and constitution of its mother, and therefore before 
birth, as 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 conditions in some degree 
unsuitable, and consequently be liable to perish at an 
early period ; more especially as all very young beings 
seem eminently sensitive to injurious or unnatural con- 
ditions 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, showing that 
when animals and plants are removed from their 
natural conditions, they are extremely liable to have 
their reproductive systems seriously affected. This, in 
fact, is the great bar to the domestication of animals. 
Between the sterility thus superinduced and that of 
hybrids, there are many points of similarity. In both 
cases the sterility is independent of general health, and 
is often accompanied by excess of size or great luxuri- 
ance. In both cases, the sterility occurs in various 
degrees ; in both, the male element is the most liable 
to be affected ; but sometimes the female more than the 
male. In both, the tendency goes to a certain extent 
with systematic affinity, for whole groups of animals 
and plants are rendered impotent by the same un- 



238 ON THE ORIGIN OF SPECIES 

natural conditions ; and whole groups of species tend 
to produce sterile hybrids. On the other hand, one 
species in a group will sometimes resist great changes 
of conditions with unimpaired fertility ; and certain 
species in a group will produce unusually fertile 
hybrids. No one can tell, till he tries, whether any 
particular animal will breed under confinement or any 
exotic plant seed freely under culture ; nor can he tell, 
till he tries, whether any two species of a genus will 
produce more or less sterile hybrids. Lastly, when 
organic beings are placed during several generations 
under conditions not natural to them, they are 
extremely liable to vary, which is due, as I believe, 
to their reproductive systems having been specially 
affected, though in a lesser degree than when sterility 
ensues. So it is with hybrids, for hybrids in successive 
generations are eminently liable to vary, as every experi- 
mentalist has observed. 

Thus we see that when organic beings are placed 
under new and unnatural conditions, and when hybrids 
are produced by the unnatural crossing of two species, 
the reproductive system, independently of the general 
state of health, is affected by sterility in a very similar 
manner. In the one case, 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 possible that two 
organisations should be compounded into one, without 
some disturbance occurring in the development, or 
periodical action, or mutual relation of the different 

f>arts and organs one to another, or to the conditions of 
ife. When hybrids are able to breed inter se, they 
transmit to their offspring from generation to gene- 
ration 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 under- 



HYBRIDISM 239 

stand, excepting on vague hypotheses, several facts with 
respect to the sterility of hybrids ; for instance, the un- 
equal fertility of hybrids produced from reciprocal 
crosses ; or the increased sterility in those hybrids 
which occasionally and exceptionally resemble closely 
either pure parent. Nor do I pretend that the fore- 
going remarks go to the root of the matter : no ex- 
planation 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 dis- 
turbed, in the other case from the organisation having 
been disturbed by two organisations having been com- 
pounded 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 bene- 
ficial to all living things. We see this acted on by 
farmers and gardeners in their frequent exchanges of 
seed, 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 our 
fourth chapter, that a certain amount of crossing is in- 
dispensable even with hermaphrodites ; and that close 
interbreeding continued during several generations 
between 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 



240 ON THE ORIGIN OF SPECIES 

is crosses between the males and females of the same 
species which have varied and become slightly dif- 
ferent, give vigour and fertility to the 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 
generally 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 urged, as a most forcible argu- 
ment, that there must be some essential distinction 
between species and varieties, and that there must be 
gome error in all the foregoing remarks, inasmuch as 
varieties, however 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 produced under nature, we are immediately 
involved in hopeless difficulties ; for if two hitherto re- 
puted 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 considered by many of our best 
botanists as varieties, are said by Gartner not to be 
quite fertile when crossed, and he consequently 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 in- 
volved in doubt. For when it is stated, for instance, 
that the German Spitz dog unites more easily than 
other dogs with foxes, or that certain South American 
indigenous domestic dogs do not readily cross with 



HYBRIDISM 241 

European dogs, the explanation which will occur to 
every one, and probably the true one, is that these 
dogs have descended from several aboriginally distinct 
species. Nevertheless 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 remarkable 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 remark- 
able than at first appears. It can, in the first place, be 
clearly shown that mere external dissimilarity 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 suc- 
cessive 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 dis- 
appearing 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 pro- 
duced 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 
constitutional differences correlated with the repro- 
ductive 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 repro- 
ductive system in the several descendants from 
any one species. Seeing this difference in the pro- 
cess of selection, as carried on by man and nature, 

R 



242 ON THE ORIGIN OF SPECIES 

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 
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 remarkable, 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 



HYBRIDISM 243 

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 distinct 
species, more seed is produced by the crosses between 
the similarly coloured flowers, than between those 
which are differently 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 on certain 
varieties of hollyhock, I am inclined to suspect that 
they present analogous facts. 

Kolreuter, whose accuracy has been confirmed 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 other varieties. 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 offspring 
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 difficulty of ascer- 
taining the infertility of 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 recondite and functional differ- 
ences in the reproductive system ; from these several 
considerations and facts, I do not think that the very 
general fertility of varieties can be proved to be of uni- 
versal occurrence, or to form a fundamental distinction 



244 ON THE ORIGIN OF SPECIES 

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 slowly acquired modifications, more 
especially in the reproductive systems of the forms 
which are crossed. 

Hybrids and Mongrels compared, independently 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 unimportant 
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 distinction 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 be- 
tween very closely allied species are more variable 
than those from very distinct 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 character could be given. The 
variability, however, in the successive generations of 
mongrels is, perhaps, greater than in hybrids. 

This greater variability of mongrels than of hybrids 
does not seem to me at all surprising. For the parents 
of mongrels are varieties, and mostly domestic varieties 



HYBRIDISM 245 

(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 generations, 
is a curious fact and deserves attention. 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 impotent or at least incapable 
of its proper function of producing offspring identical 
with the parent-form. Now hybrids in the first genera- 
tion are descended from species (excluding those long 
cultivated) which have not had their reproductive 
systems in any way affected, and they are not variable ; 
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 parent-form ; but this, 
if it 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 different 
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 experi- 
ment ; and seems directly opposed to the results of 
several experiments made by Kolreuter. 

These alone are the unimportant differences, 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 



246 ON THE ORIGIN OF SPECIES 

species, follows according to Gartner the same laws. 
When two species are crossed, one has sometimes 
a prepotent 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 re- 
semble 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 compli- 
cated, partly owing to the existence of secondary sexual 
characters ; but more especially owing to prepotency 
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 maintain 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 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 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, de- 
ficiency 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 



HYBRIDISM 247 

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. — First 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 experimentalists 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. 

In the same manner as in grafting trees, the capacity 



248 ON THE ORIGIN OF SPECIES 

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 degrees 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 systems 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 uniting two species, and the degree of 
sterility of their hybrid - offspring should generally 
correspond, though due to distinct 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 produced from it, and the 
capacity of being grafted together — though this latter 
capacity evidently depends on widely different circum- 
stances — should all run, to a certain extent, parallel 
with the systematic affinity of the forms which are 
subjected to experiment ; for systematic affinity 



HYBRIDISM 249 

attempts to express all kinds of resemblance between 
all species. 

First crosses between forms known to be varieties, or 
sufficiently alike to be considered 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 differ- 
ences, 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, then, the facts briefly given in this chapter do 
not seem to me opposed to, but even rather to support 
the view, that there is no 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 tha 
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 appearance of groups of species — On their sudden 
appearance in the lowest known fossiliferous strata. 

In the sixth chapter I enumerated the chief objections 
which might be justly urged against the views main- 
tained in this volume. Most of them have now been 
discussed. One, namely the distinctness of specific 
forms, and their not being blended together by in- 
numerable transitional links, is a very obvious difficulty. 
I assigned reasons why such links do not commonly 
occur at the present day, under the circumstances 
apparently 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 

250 



IMPERFECTION OF GEOLOGICAL RECORD 251 

course of further modification and improvement. The 
main cause, however, 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 extermination 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 geo- 
logical formation and every stratum full of such inter- 
mediate links ? Geology assuredly does not reveal any 
such finely graduated organic chain ; and this, perhaps, 
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 geological 
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 picturing 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 
descendants. To give a simple illustration : the fantail 
and pouter pigeons have both descended from the rock- 
pigeon ; if we possessed 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 en- 
larged, 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 determined from a mere comparison of 
their structure with that of the rock-pigeon, whether 



262 ON THE ORIGIN OF SPECIES 

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 perhaps 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 re- 
mained for a very long period unaltered, whilst its 
descendants had undergone a vast amount of change ; 
and the principle of competition between organism and 
organism, between child and parent, willrenderthisavery 
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 differences not greater than we see between 
the varieties of the same species at the present day ; 
and these parent-species, now generally extinct, have 
in their turn been similarly connected with more 
ancient species ; and so on backwards, always con- 
verging to the common ancestor of each great class. 
So that the number of intermediate and transitional 
links, between all living and extinct species, must have 
been inconceivably great But assuredly, if this theory 
be true, such have lived upon this earth. 



IMPERFECTION OF GEOLOGICAL RECORD 253 

On the lapse of Time. — Independently of our not 
finding fossil remains of such infinitely numerous con- 
necting links, it may be objected, tbat time will not 
have sufficed for so great an amount of organic change, 
all changes having been effected very slowly through 
natural selection. It is hardly possible for me even to 
recall to the reader, who may not be a practical geo- 
logist, the facts leading the mind feebly to comprehend 
the lapse of time. He who can read Sir Charles 
Lyell's grand work on the Principles of Geology, which 
the future historian will recognise as having produced 
a revolution in natural science, yet does not admit how 
incomprehensively vast have been the past periods of 
time, may at once close this volume. Not that it 
suffices to study the Principles of Geology, or to read 
special treatises by different observers on separate 
formations, and to mark how each author attempts to 
give an inadequate idea of the duration of each forma- 
tion or even each stratum. A man must for years 
examine for himself great piles of superimposed strata, 
and watch the sea at work grinding down old rocks 
and making fresh sediment, before he can hope to 
comprehend anything of the lapse of time, the monu- 
ments of which we see around us. 

It is good to wander along lines of sea-coast, when 
formed of moderately hard rocks, and mark the process 
of degradation. The tides in most cases reach the 
cliffs only for a short time twice a day, and the waves 
eat into them only when they are charged with sand or 
pebbles ; for there is good evidence that pure water 
can effect little or nothing in wearing away rock. At 
last the base of the cliff is undermined, huge fragments 
fall down, and these remaining fixed, have to be worn 
away, atom by atom, until reduced in size they can be 
rolled about by the waves, and then are more quickly 
ground into pebbles, sand, or mud. But how often do 
we see along the bases of retreating cliffs rounded 
boulders, all thickly clothed by marine productions, 
showing how little they are abraded and how seldom 
they are rolled about ! Moreover, if we follow for a 



254 ON THE ORIGIN OF SPECIES 

few miles any line of rocky cliff, which is undergoing 
degradation, we find that it is only here and there, along 
a short length or round a promontory, that the cliffs 
are at the present time suffering. The appearance of 
the surface and the vegetation show that elsewhere 
years have elapsed since the waters washed their base. 
He who most closely studies the action of the sea on 
our shores, will, I believe, be most deeply impressed 
with the slowness with which rocky coasts are worn 
away. The observations on this head by Hugh Miller, 
and by that excellent observer Mr. Smith of Jordan 
Hill, are most impressive. With the mind thus im- 
pressed, let any one examine beds of conglomerate 
many thousand feet in thickness, which, though prob- 
ably formed at a quicker rate than many other 
deposits, yet, from being formed of worn and rounded 
pebbles, each of which bears the stamp of time, are 
good to show how slowly the mass has been accumu- 
lated. In the Cordillera I estimated one pile of con- 
glomerate at ten thousand feet in thickness. Let the 
observer remember Lyell's profound remark that the 
thickness and extent of sedimentary formations are the 
result and measure of the degradation which the earth's 
crust has elsewhere suffered. And what an amount 
of degradation is implied by the sedimentary deposits 
of many countries ! Professor Ramsay has given me 
the maximum thickness, in most cases from actual 
measurement, in a few cases from estimate, of each 
formation in different parts of Great Britain ; and this 
is the result : — 

Feet. 

Palaeozoic strata (not including igneous beds) . . 57,154 

Secondary strata 13,190 

Tertiary strata 2,240 

— making altogether 72,584 feet ; that is, very nearly 
thirteen and three-quarters British miles. Some of 
the formations, which are represented in England by 
thin beds, are thousands of feet in thickness on the 
Continent. Moreover, between each successive forma- 
tion, we have, in the opinion of most geologists, 



IMPERFECTION OF GEOLOGICAL RECORD 255 

enormously long blank periods. So that the lofty pile 
of sedimentary rocks in Britain, gives but an inadequate 
idea of the time which has elapsed during their 
accumulation ; yet what time this must have consumed ! 
Good observers have estimated that sediment is de- 
posited by the great Mississippi river at the rate of 
only 600 feet in a hundred thousand years. This 
estimate has no pretension to strict exactness ; yet, 
considering over what wide spaces very fine sediment 
is transported by the currents of the sea, the process 
of accumulation in any one area must be extremely 
slow. 

But the amount of denudation which the strata have 
in many places suffered, independently of the rate of 
accumulation of the degraded matter, probably offers 
the best evidence of the lapse of time. I remember 
having been much struck with the evidence of denuda- 
tion, when viewing volcanic islands, which have been 
worn by the waves and pared all round into per- 
pendicular cliffs of one or two thousand feet in height ; 
for the gentle slope of the lava-streams, due to their 
formerly liquid state, showed at a glance how far the 
hard, rocky beds had once extended into the open ocean. 
The same story is still more plainly told by faults, — 
those great cracks along which the strata have been 
upheaved on one side, or thrown down on the other, to 
the height or depth of thousands of feet ; for since the 
crust cracked, the surface of the land has been so 
completely planed down by the action of the sea, that 
no trace of these vast dislocations is externally visible. 

The Craven fault, for instance, extends for upwards 
of 30 miles, and along this line the vertical displace- 
ment of the strata has varied from 600 to 3000 feet. 
Prof. Ramsay has published an account of a downthrow 
in Anglesea of 2300 feet ; and he informs me that he 
fully believes there is one in Merionethshire of 12,000 
feet ; yet in these cases there is nothing on the surface 
to show such prodigious movements ; the pile of rocks 
on the one or other side having been smoothly swept 
away. The consideration of these facts impresses my 



256 ON THE ORIGIN OF SPECIES 

mind almost in the same manner as does the vain 
endeavour to grapple with the idea of eternity. 

I am tempted to give one other case, the well-known 
one of the denudation of the Weald. Though it must 
be admitted that the denudation of the Weald has been 
a mere trifle, in comparison with that which has 
removed masses of our palaeozoic strata, in parts ten 
thousand feet in thickness, as shown in Prof. Ramsay's 
masterly memoir on this subject : yet it is an admir- 
able lesson to stand on the intermediate hilly country 
and look on the one hand at the North Downs, and 
on the other hand at the South Downs ; for, remem- 
bering that at no great distance to the west the 
northern and southern escarpments meet and close, one 
can safely picture to oneself the great dome of rocks 
which must have covered up the Weald within so 
limited a period as since the latter part of the Chalk 
formation. The distance from the northern to the 
southern Downs is about 22 miles, and the thickness 
of the several formations is on an average about 1100 
feet, as I am informed by Prof. Ramsay. But if, as 
some geologists suppose, a range of older rocks under- 
lies the Weald, on the flanks of which the overlying 
sedimentary deposits might have accumulated in thinner 
masses than elsewhere, the above estimate would be 
erroneous ; but this source of doubt probably would 
not greatly affect the estimate as applied to the western 
extremity of the district. If, then, we knew the rate 
at which the sea commonly wears away a line of cliff of 
any given height, we could measure the time requisite 
to have denuded the Weald. This, of course, cannot 
be done ; but we may, in order to form some crude 
notion on the subject, assume that the sea would eat 
into cliffs 500 feet in height at the rate of one inch 
in a century. This will at first appear much too small 
an allowance ; but it is the same as if we were to 
assume a cliff one yard in height to be eaten back 
along a whole line of coast at the rate of one yard in 
nearly every twenty-two years. I doubt whether any 
rock, even as soft as chalk, would yield at this rate 



IMPERFECTION OF GEOLOGICAL RECORD 257 

excepting on the most exposed coasts ; though no doubt 
the degradation of a lofty cliff would be more rapid 
from the breakage of the fallen fragments. On the 
other hand, I do not believe that any line of coast, ten 
or twenty miles in length, ever suffers degradation at 
the same time along its whole indented length ; and we 
must remember that almost all strata contain harder 
layers or nodules, which from long resisting attrition 
form a breakwater at the base. We may at least 
confidently believe that no rocky coast 500 feet in 
height commonly yields at the rate of a foot per 
century ; for this would be the same in amount as a 
cliff one yard in height retreating twelve yards in 
twenty-two years ; and no one, I think, who has care- 
fully observed the shape of old fallen fragments at the 
base of cliffs, will admit any near approach to such 
rapid wearing away. Hence, under ordinary circum- 
stances, I should infer that for a cliff 500 feet in height, 
a denudation of one inch per century for the whole 
length would be a sufficient allowance. At this rate, 
on the above data, the 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 sur- 
face 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, 

8 



258 ON THE ORIGIN OF SPECIES 

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 ! 

On the poorness of our Palceontological collections. — 
That our palaeontological collections are very im- 
perfect, 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 
collected 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 dis- 
coveries 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 accumulat- 
ing. 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 enor- 
mously large proportion of the ocean, the bright blue 
tint of the Mater 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 preserved. For 



IMPERFECTION OF GEOLOGICAL RECORD 259 

instance, the several species of the Chthamalinaj (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 analogous case. 

With respect to the terrestrial productions 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 belonging to either 
of these vast periods, with the exception of one species 
discovered 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 preservation, far better than pages of 
detail. Nor is their rarity surprising, when we re- 
member how large a proportion of the bones of tertiary 
mammals have been discovered 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 
difficult to avoid believing that they are closely con- 
secutive. 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 
formations ; so it is in North America, and in many 



260 ON THE ORIGIN OF SPECIES 

other parts of the world. The most skilful geologist, if 
his attention had been exclusively confined to these 
large territories, 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 
accumulated. 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 com- 
position of consecutive formations, generally implying 
great changes in the geography of the surrounding 
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 geological forma- 
tions 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 suc- 
cessive and peculiar marine faunas will probably be 
preserved to a distant age. A little reflection will ex- 
plain 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 explana- 
tion, 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 



IMPERFECTION OF GEOLOGICAL RECORD 261 

must be accumulated in extremely thick, solid, or 
extensive masses, in order to withstand the incessant 
action of the waves, when first upraised and during 
subsequent oscillations of level. Such thick and ex- 
tensive accumulations of sediment 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, it 
it continue slowly to subside. In this latter case, as 
long as the rate of subsidence and supply of sediment 
nearly balance each other, the sea will remain shallow 
and favourable for life, and thus a fossiliferous forma- 
tion thick enough, when upraised, to resist any amount 
of degradation, may be formed. 

1 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 subsid- 
ence. I may add, that the only ancient tertiary forma- 
tion on the west coast of South America, which has 
been bulky enough to resist such degradation as it has 
as yet suffered, but which will hardly last to a distant 
geological age, was certainly deposited during a down- 
ward 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 



262 ON THE ORIGIN OF SPECIES 

preserve the remains before they had time to decay. 
On the other hand, as long as the bed of the sea re- 
mained stationary, thick deposits could not have been 
accumulated in the shallow parts, which are the most 
favourable 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. 

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 independently 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 circumstances 
most favourable, as previously explained, for the forma- 
tion of new varieties and species ; but during such 
periods there will generally be a blank in the geological 
record. On the other hand, during subsidence, 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 conse- 
quently during subsidence, though there will be much 
extinction, fewer new varieties or species will be formed ; 
and it is during these very periods of subsidence, 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 imperfect ; 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 commencement and at its close. Some 



IMPERFECTION OF GEOLOGICAL RECORD 263 

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 in- 
disputably 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 pre- 
tend 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 Wood- 
ward, have concluded 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 
disappearing 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 migration during climatal 
and other changes ; and when we see a species first 
appearing 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 migration from the American to the 
European seas. In examining the latest deposits of 



264 ON THE ORIGIN OF SPECIES 

various quarters of the world, it has everywhere been 
noted, that some few still existing species are common 
in the deposit, but have become extinct in the immedi- 
ately 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, probable 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 
geographical 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 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 gener- 
ally have to be a very thick one ; and the species 
undergoing modification will have had to live on the 



IMPERFECTION OF GEOLOGICAL RECORD 265 

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 counter- 
balanced 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 whilst the downward movement continues. 
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 formation, like the 
whole pile of formations in any country, has generally 
been intermittent in its accumulation. ^VTien we see, 
as is so often the case, a formation composed of beds 
of different mineralogical composition, we may reason- 
ably 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 deposi- 
tion has consumed. Many instances could be given of 
beds only a few feet in thickness, representing forma- 
tions, elsewhere thousands of feet in thickness, and 
which must 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 overlooked, intervals have occurred in its 
accumulation. In other cases we have the plainest 
evidence in great fossilised trees, still standing upright 



266 ON THE ORIGIN OF SPECIES 

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 1400 feet thick 
in Nova Scotia, with ancient root-bearing 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 geo- 
logical period. So that if such species were to undergo 
a considerable amount of modification 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. 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 transitional gradations, we should not recog- 



IMPERFECTION OF GEOLOGICAL RECORD 267 

nise their relationship, and should consequently be 
compelled to rank them all as distinct species. 

It is notorious on what excessively slight differenc&<? 
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 
of 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 dif- 
ferent, 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 discover- 
ing 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. 



268 ON THE ORIGIN OF SPECIES 

It should not be forgotten, that at the present day, 
with perfect specimens for examination, two forms can 
seldom be connected 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 
improbability 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 otherwise would have been, yet has done scarcely 
anything in breaking down the distinction between 
species, by connecting them together by numerous, 
tine, 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 fron; 
Britain to Russia ; and therefore equals all the geo- 
logical 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, 



IMPERFECTION OF GEOLOGICAL RECORD 269 

with its numerous large islands separated by wide and 
shallow seas, probably represents the former state of 
Europe, whilst most of our formations were accumu- 
lating'. The Malay Archipelago 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 terres- 
trial productions of the archipelago would be preserved 
in an excessively imperfect manner in the formations 
which we suppose to be there accumulating. I suspect 
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 sedi- 
ment 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 formations 
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; whilst 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 probablv be 
much extinction of life ; during the periods of eleva- 
tion, there would be much variation, but the geological 
record would then be 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 wih a contemporaneous accu- 
mulation of sediment, would exceed the average dura- 
tion of the same specific forms ; and these contingencies 
are indispensable for the preservation of all the transi- 
tional gradations between any two or more species. If 



270 ON THE ORIGIN OF SPECIES 

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 subsidence 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 modifications 
could be preserved in any one formation. 

Very many of the marine inhabitants of the archi- 
pelago now range thousands of miles beyond its con- 
fines ; 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. 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, accord- 
ing 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 formations, 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 branching 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 formation, would, by most palaeonto- 
logists, be ranked as distinct species. But I do not 
pretend that I should ever have suspected how poor 
a record of the mutations of life, the best preserved 
geological section presented, had not the difficulty of our 
not discovering innumerable transitional links between 
the species which appeared at the commencement and 
close of each formation, pressed so hardly on my theory. 



IMPERFECTION OF GEOLOGICAL RECORD 271 

On the sudden appearance of whole groups of Allied 
Species. — The abrupt manner in which whole groups 01 
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 over- 
rate 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 continually 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 else- 
where have long existed and have slowly multiplied 
before they invaded the 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 multipli- 
cation of species from some one or some few parent- 
forms ; and in the succeeding formation such species 
will appear as if suddenly created. 

1 may here recall a remark formerly made, namely 
that it might require a long succession of ages to adapt 
an organism 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 comparatively 
short time would be necessary to produce many divergent 



272 ON THE ORIGIN OF SPECIES 

forms, which would be able to spread rapidly and widely 
throughout the world. 

I will now give a few examples to illustrate these 
remarks, and to show how liable we are to error in 
supposing that whole groups of species have suddenly 
been produced. 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 preservation 
of footsteps in the new red sandstone 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 
impressions were really birds. Until quite recently 
these authors might have maintained, and some have 
maintained, that the whole class of birds came sud- 
denly into existence during an early tertiary period ; 
but now we know, on the authority of Professor Owen 
(as may be seen in Ly ell's Manual), that a bird 
certainly lived during the deposition of the upper 
greensand. 

I may give another instance, which from having 
passed under my own eyes has much struck me. In 
a memoir on Fossil Sessile Cirripedes, I have stated 
that, from the number of existing and extinct tertiary 



IMPERFECTION OF GEOLOGICAL RECORD 273 

species ; from the extraordinary abundance of the indi- 
viduals 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 pre- 
served 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 secondary 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 appear- 
ance of a great group of species. But my work had 
hardly been published, when a skilful palaeontologist, 
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 palaeontolo- 
gists 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 commencement of the chalk formation, 
the fact would certainly be highly remarkable ; but 



274 ON THE ORIGIN OF SPECIES 

I cannot see that it would be an insuperable difficulty 
on my theory, unless it could likewise be shown that 
the species of this group appeared suddenly and simul- 
taneously 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 Paleontology 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 for- 
merly 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 are 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 multi- 
plied ; 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 palaeontological 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 fossiliferous strata. — There is another 
and allied difficulty, which is much graver. I allude 
to the manner in which numbers of species of the same 



IMPERFECTION OF GEOLOGICAL RECORD 275 

group, suddenly appear in the lowest known fossil i- 
ferous rocks. Most of the arguments which have con- 
vinced 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 douht that all the Silurian trilobites 
have descended from some one crustacean, which must 
have lived long before the Silurian age, and which prob- 
ably 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 certainly have been long ago 
supplanted and exterminated by their numerous and 
improved 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 un- 
known, 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 



276 ON THE ORIGIN OF SPECIES 

nodules and bituminous matter in some of the lowest 
azoic rocks, probably indicates the former existence of 
life at these periods. But the difficulty of understand- 
ing the absence of vast piles of fossiliferous strata, 
which on my theory no doubt were somewhere accumu- 
lated before the Silurian epoch, is very great. If 
these most ancient beds had been wholly worn away 
by denudation, or obliterated by metamorphic action, 
we ought to find only small remnants of the forma- 
tions next succeeding them in age, and these ought to 
be very generally in a metamorphosed 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 view, that the 
older a formation is, the more it has always suffered 
he extremity of denudation and metamorphism. 

The case at present must remain inexplicable ; and 
may be truly urged as a valid argument against the 
views here entertained. To show that it may hereafter 
receive some explanation, I will give the following 
hypothesis. From the nature of the organic remains 
which do not appear to have inhabited profound depths, 
in the several formations of Europe and of the United 
States ; and from the amount of sediment, miles in 
thickness, of which the formations are composed, we 
may infer that from first to last large islands or tracts 
of land, whence the sediment was derived, occurred in 
the neighbourhood of the existing continents of Europe 
and North America. But we do not know what was 
the state of things in the intervals between the suc- 
cessive formations ; whether Europe and the United 
States during these intervals existed as dry land, or as 
a submarine surface near land, on which sediment was 
not deposited, or as the bed of an open and unfathom- 
able sea. 

Looking to the existing oceans, which are thrice as 
extensive as the land, we see them studded with many 
islands ; but not one oceanic island is as yet known to 
afford even a remnant of any palaeozoic or secondary 
formation. Hence we may perhaps infer, that during 



IMPERFECTION OF GEOLOGICAL RECORD 277 

the palaeozoic and secondary periods, neither continents 
nor continental islands existed where our oceans now 
extend ; for had they existed there, palaeozoic and 
secondary formations would in all probability have 
been accumulated from sediment derived from their 
wear and tear ; and would have been at least partially 
upheaved by the oscillations of level, which we may 
fairly conclude must have intervened during these 
enormously long periods. If then we may infer any- 
thing from these facts, we may infer that where our 
oceans now extend, oceans have extended from the 
remotest period of which we have any record ; and on 
the other hand, that where continents now exist, large 
tracts of land have existed, subjected no doubt to great 
oscillations of level, since the earliest silurian period. 
The coloured map appended to my volume on Coral 
Reefs, led me to conclude that the great oceans are 
still mainly areas of subsidence, the great archipelagoes 
still areas of oscillations of level, and the continent 
areas of elevation. But have we any right to assume 
that things have thus remained from the beginning 
of this world? Our continents seem to have been 
formed by a preponderance, during many oscillations 
of level, of the force of elevation ; but may not the 
areas of preponderant movement have changed in thf 
lapse of ages? At a period immeasurably antecedt 
to the silurian epoch, continents may have existed 
where oceans are now spread out ; and clear and open 
oceans may have existed where our continents now 
stand. Nor should we be justified in assuming that if, 
for instance, the bed of the Pacific Ocean were now 
converted into a continent, we should there find forma- 
tions older than the silurian strata, supposing such to 
have been formerly deposited ; for it might well happen 
that strata which had subsided some miles nearer to 
the centre of the earth, and which had been pressed 
on by an enormous weight of superincumbent water, 
might have undergone far more metamorphic action 
than strata which have always remained nearer to the 
surface. The immense areas in some parts of the 



278 ON THE ORIGIN OF SPECIES 

world, for instance in South America, of bare meta- 
morphic rocks, which must have been heated under 
great pressure, have always seemed to me to require 
some special explanation ; and we may perhaps believe 
that we see in these large areas, the many formations 
long anterior to the silurian epoch in a completely 
metamorphosed condition. 

The several difficulties here discussed, namely our 
not finding in the successive formations infinitely 
numerous transitional links between the many species 
which now exist or have existed ; the sudden manner 
in which whole groups of species appear in our European 
formations ; the almost entire absence, as at present 
known, of fossiliferous formations beneath the Silurian 
strata, are all undoubtedly of the gravest nature. We 
see this in the plainest manner by the fact that all the 
most eminent palaeontologists, namely Cuvier, Agassiz, 
Barrande, Falconer, E. Forbes, etc., and all our greatest 
geologists, as Lyell, Murchison, Sedgwick, etc., have 
unanimously, often vehemently, maintained the im- 
mutability of species. But I have reason to believe 
that one great authority, Sir Charles Lyell, from further 
reflection entertains grave doubts on this subject. I 
feel how rash it is to differ from these authorities, to 
whom, with others, we owe all our knowledge. Those 
who think the natural geological record in any degree 
perfect, and who do not attach much weight to the 
facts and arguments of other kinds given in this 
volume, will undoubtedly 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, relat- 
ing only to two or three countries. Of this volume, 
only here and there a short chapter has been preserved ; 
and of each page, only here and there a few lines. 
Each word of the slowly-changing language, in which 
the history is supposed to be written, being more or 
les* different in the interrupted succession of chapters, 



IMPERFECTION OF GEOLOGICAL RECORD 



£( 



may represent the apparently abruptly changed forms 
of life, entombed in our consecutive, but widely 
separated, formations. 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 appear- 
ance 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 succession of organic beings, 
better accord with the common view of the immuta- 
bility 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 observa- 
tions of Philippi in Sicily, the successive changes in 
the marine inhabitants of that island have been many 

280 



GEOLOGICAL SUCCESSION 281 

and most gradual. The secondary formations are more 
broken ; but, as Bronn has remarked, neither the 
appearance nor disappearance of their many now ex- 
tinct 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 sub-Himalayan 
deposits. The Silurian Liugula 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 Switzer- 
land. 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 ex- 
ceptions to this rule. The amount of organic change, 
as Pictet has remarked, does not strictly correspond 
with the succession of our geological formations ; so 
that between each two consecutive formations, 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 dis- 
appeared from the face of the earth, we have reason to 
believe that the same identical form never reappears. 
The strongest apparent exception to this latter rule, is 
that of the so-called c ' colonies " of M. Barrande, which 
intrude for a period in the midst of an older formation, 
and then allow the pre-existing fauna to reappear ; but 
Lyell's explanation, namely, that it is a case of tempo- 
rary 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 



282 ON THE ORIGIN OF SPECIES 

inhabitants of a country to change abruptly, or simul- 
taneously, or to an equal degree. The process of modi- 
fication must be extremely slow. The variability of 
each species is quite independent of that of all others. 
Whether such variability be taken advantage of by 
natural selection, and whether the variations be accu- 
mulated to a greater or lesser amount, thus causing a 
greater or lesser amount of modification in the varying 
species, depends on many complex contingencies, — on 
the variability being of a beneficial nature, on the 
power of intercrossing, 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 identical form much 
longer than others ; or, if changing, that it should 
change less. We see the same fact in geographical 
distribution ; 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 highly organised productions compared with 
marine and lower productions, by the more complex 
relations of the higher beings to their organic and in- 
organic conditions of life, as explained in a former 
chapter. When many of the inhabitants of a country 
have become modified and improved, we can under- 
stand, 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 improved, will be liable to be exter- 
minated. 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, 



GEOLOGICAL SUCCESSION 283 

perhaps, be nearly the same ; but as the accumulation 
of long-enduring fossiliferous formations depends on 
great masses of sediment having been deposited on 
areas whilst subsiding, our formations have been almost 
necessarily accumulated at wide and irregularly inter- 
mittent intervals ; consequently the amount of organic 
change exhibited by the fossils embedded in consecutive 
formations 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 changing drama. 

We can clearly understand why a species when once 
lost should never reappear, even if the very same con- 
ditions 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 
identically the same ; for both would almost certainly 
inherit different characters from their distinct pro- 
genitors. 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 pre- 
sent 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 fantail, 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 newly -formed 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 their appearance and dis- 
appearance as do single species, changing more or less 
quickly, and in a greater or lesser degree. A group 
doe* not reappear after it has once disappeared ; or its 



284 ON THE ORIGIN OF SPECIES 

existence, as long as it lasts, is continuous. I a,ia 
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 suc- 
cession of ages, so long must its members have con- 
tinuously existed, in order to have generated either new 
and modified or the same old and unmodified forms. 
Species of the genus Lingula, for instance, must have 
continuously 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 ap- 
pear 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 modification 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 



GEOLOGICAL SUCCESSION 285 

slowly converted into species, which in their turn pro- 
duce 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. 

On Extinction. — We have as yet spoken only inci- 
dentally of the disappearance of species and of groups 
of species. On the theory of natural selection the ex- 
tinction of old forms and the production of new and im- 
proved forms are intimately connected together. The 
old notion of all the inhabitants of the earth having 
been swept away at successive periods by catastrophes, 
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 con- 
clusion. 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 
whole groups of species last for very unequal periods ; 
some groups, as we have seen, having endured from the 
earliest known dawn of life to the present day ; some 
having disappeared before the close of the palaeozoic 
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 extermina- 
tion, 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 
Heen involved in the most gratuitous mystery. Some 



286 ON THE ORIGIN OF SPECIES 

authors have even supposed that as the individual has a 
definite length of life, so have species a definite dura- 
tion. 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 over the whole country and has increased in 
numbers at 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 sur- 
prise at its rarity ; for rarity is the attribute of a vast 
number of species of all classes, in all countries. If 
we ask ourselves why this or that species is rare, we 
answer that something is unfavourable in its conditions 
of life ; but what that something is, we can hardly ever 
tell. On the supposition of the fossil horse still exist- 
ing as a rare species, we might have felt certain from 
the analogy of all other mammals, even of the slow- 
breeding elephant, and from the history of the natural- 
isation 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 
conditions 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. 



GEOLOGICAL SUCCESSION 287 

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 individual is the forerunner of death — 
to feel no surprise at 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 com- 
petition ; and the consequent 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 neighbourhood ; 
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 appearance of new 
forms and the disappearance 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 ex- 
terminated ; 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 production of new forms has caused 
the extinction of about the same number of old forme. 



288 ON THE ORIGIN OF SPECIES 

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 extermination of the 
parent -species ; and if many new forms have been 
developed from any one species, the nearest allies of 
that species, i.e. the species of the same genus, will be 
the most liable to extermination. Thus, as I believe, a 
number of new species descended from one species, that 
is a new genus, comes to supplant an old genus, belong- 
ing 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 success- 
ful 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 other species 
which have been modified and improved, a few of the 
sufferers may often long be preserved, from being 
fitted to some peculiar line of life, or from inhabiting 
some distant and isolated station, where they have 
escaped severe competition. For instance, a single 
species of Trigonia, a great genus of shells in the 
secondary formations, survives in the Australian seas ; 
and a few members of the great and almost extinct 
group of Ganoid fishes still inhabit our fresh waters. 
Therefore the utter extinction of a group is generally, 
as we have seen, a slower process than its production. 

With respect to the apparently sudden extermination 
of whole families or orders, as of Trilobites at the close 
of the palaeozoic period and of Ammonites at the close 
of the secondary period, we must remember what has 
been already said on the probable wide intervals of time 
between our consecutive formations ; and in these inter- 
vals there may have been much slow extermination. 
Moreover, when by sudden immigration or by unusually 



GEOLOGICAL SUCCESSION 289 

rapid development, many species of a new group have 
taken possession of a new area, they will have exter- 
minated 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 partake 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 existence 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 
precisely say why this species is more abundant in in- 
dividuals 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 paheontological 
discovery is more striking than the fact, that the forms 
of life change almost simultaneously 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 re- 
mains in certain beds present an unmistakable 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 

u 



290 ON THE ORIGIN OF SPECIES 

sometimes are similarly characterised in such trifling 
points as mere superficial sculpture. Moreover 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 parallel- 
ism in the forms of life has been observed by several 
authors : so it is, according 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 
parallelism 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 in- 
ferred 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 supposed that this expression relates to 
the same thousandth or hundred-thousandth year, or 
even that it has a very strict geological sense ; for if 
all the marine animals which live at the present day in 
Europe, and all those that lived in Europe during the 
pleistocene period (an enormously remote period as 
measured by years, including the whole glacial epoch), 
were to be compared with those now living in South 



GEOLOGICAL SUCCESSION 291 

America or in Australia, the most skilful naturalist 
would hardly be able to say whether the existing or the 
pleistocene inhabitants 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 
parallelism 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 modifications 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 dif- 
ferent climates. We must, as Barrande has remarked, 
look to some special law. We shall see this more clearly 



292 ON THE ORIGIN OF SPECIES 

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 succession 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 advantage over 
older forms ; and those forms, which are already domi- 
nant, 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 pre- 
served 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 domi- 
nant, varying, and far-spreading 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 
accidents, 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 multiplication of new and domi- 
nant 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 



GEOLOGICAL SUCCESSION 293 

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 quarter of 
the world may have been most favourable for the pro- 
duction 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 circum- 
stanced in an equal degree, whenever their inhabitants 
met, the battle would be prolonged and severe ; and 
some from one birthplace and some from the other 
might be victorious. But in the course of time, the 
forms dominant in the highest degree, wherever pro- 
duced, would tend everywhere to prevail. As they pre- 
vailed, they would cause the extinction 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, succession of the same forms 
of life throughout the world, accords well with the prin- 
ciple 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 inheriting some inferiority in common ; 
and therefore as new and improved groups spread 
throughout the world, old groups will disappear from 
the world ; and the succession 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 believ- 
ing that all our greater fossiliferous formations were 
deposited during periods of subsidence ; and that 



294 ON THE ORIGIN OF SPECIES 

blank intervals of vast duration occurred during the 
periods when the bed of the sea was either station- 
ary or rising, and likewise when sediment was not 
thrown down quickly enough to embed and preserve 
organic remains. During these long and blank inter- 
vals I suppose that the inhabitants of each region 
underwent a considerable 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 move- 
ment, it is probable that strictly contemporaneous for- 
mations 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 in- 
variably been the case, and that large areas have invari- 
ably been affected by the same movements. 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 para- 
graphs, 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 modification, 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 contemporaneous, 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 ; never- 
theless he finds a surprising amount of difference in 



GEOLOGICAL SUCCESSION 295 

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 suc- 
cession 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 corre- 
sponding 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 living species. They all fall into one 
grand 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, fami- 
lies, 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 Verte- 
brata, whole pages could be filled with striking illustra- 
tions from our great palaeontologist, Owen, showing how 
extinct animals fall in between existing groups. Cuvier 
ranked the Ruminants and Pachyderms, 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 



296 ON THE ORIGIN OF SPECIES 

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 objec- 
tion is probably valid. But I apprehend that in a 
perfectly natural classification many fossil species would 
have to stand between living species, and some extinct 
genera between living genera, even between genera be- 
longing to distinct families. The most common case, 
especially 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. 

It is a common belief that the more 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 dis- 
covered having affinities directed towards very distinct 
groups. Yet if we compare the older Reptiles and 
Batrachians, the older Fish, the older Cephalopoda, 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 preliminary. 



GEOLOGICAL SUCCESSION 297 

We may suppose that the numbered 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 unimportant 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, 
a 14 , <j 14 , p 14 , will form a small family ; 6 14 and / 14 a 
closely allied family or sub-family ; and o 14 , e u , m 14 , 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 diver- 
gence 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 char- 
acter is a necessary contingency ; it depends solely on 
the descendants from a species being thus enabled to 
seize on many and different 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 throughout a 
vast period the same general characteristics. This is 
represented in the diagram by the letter f 14 . 

All the many forms, extinct and recent, descended 
from (A), make, as before remarked, 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 
gome 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 



298 ON THE ORIGIN OF SPECIES 

successive formations, 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 a 1 , a 5 , 
al0 > f S ) mZ ) m *> m9 , 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 justified, as they are interme- 
diate, 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, a 14 , etc., and & 14 , etc.) would have to be 
united into one family ; and the two other families 
(namely, a 14 to f u now including five genera, and o u 
to m li ) 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 characters, 
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 subsequently diverged. Thus 
it comes that ancient and extinct genera are often in 
some slight degree intermediate in character between 
their modified descendants, or between their collateral 
relations. 

In nature the case will be far more complicated than 
is represented in the diagram ; for the groups will 
have been more numerous, they will have endured for 
extremely unequal lengths of time, and will have been 
modified in various degrees. As we possess only the 



GEOLOGICAL SUCCESSION 299 

last volume of the geological 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 geological 
periods undergone much modification, 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 evidence of our best palaeontologi 
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 inter- 
mediate in general character between that which pre- 
ceded 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 stiil 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 extinction of 
some preceding forms, 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 geo- 
logical period undoubtedly is intermediate in char- 
acter, between the preceding 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 



300 ON THE ORIGIN OF SPECIES 

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 consecutive formations. 

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 arrange- 
ment. 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 disappear- 
ance of the species was perfect, we have no reason to 
believe that forms successively 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 terrestrial productions inhabiting separated 
districts. 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 disappearance ; 
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 intermediate 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 



GEOLOGICAL SUCCESSIOxX 301 

each other, than are the fossils from two remote forma- 
tions. 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 simul- 
taneously throughout the world, and therefore under 
the most different climates and conditions. Consider 
the prodigious vicissitudes of climate during the pleisto- 
cene period, which includes the whole glacial period, 
aud 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 forma- 
tions, though ranked as distinct species, being closely 
related, is obvious. As the accumulation of each 
formation has often been interrupted, 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 intermediate 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. \Ve 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 



302 ON THE ORIGIN OF SPECIES 

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 satisfaction what is meant by 
high and low forms. The best definition probably is, 
that the higher forms have their organs more distinctly 
specialised for different functions ; and as such division 
of physiological labour seems to be an advantage to 
each being, natural selection will constantly tend in so 
far 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 preceding forms. 
If under a nearly similar climate, the eocene inhabit- 
ants of one quarter of the world were put into com- 
petition 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 marked 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 in- 
stance, 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 see now occurring in New Zealand, and from 
hardly a single inhabitant of the southern hemisphere 



GEOLOGICAL SUCCESSION 303 

having 1 become wild in any part of Europe, we may 
doubt, if all the productions of Zew 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 embryo- 
logical 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 subordi- 
nate groups, which have branched off from each other 
within comparatively recent times. For this doctrine 
of Agassiz accords well with the theory of natural selec- 
tion. 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, whilst it leaves 
the embryo almost unaltered, continually adds, in the 
course of successive generations, more and more differ- 
ence 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 dis- 
tinct 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 discovered — a discovery of 
which the chance is very small. 



304 ON THE ORIGIN OF SPECIES 

On the Succession of the same Types within the same 
areas, during the later tertiary periods. — Mr. Clift many 
years ago snowed that the fossil mammals from the 
Australian caves were closely allied to the living mar- 
supials 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 arma- 
dillo, 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 relation- 
ship is even more clearly seen in the wonderful collec- 
tion 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." Professor Owen has subse- 
quently 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 Aralo-Caspian Sea. 

Now what does this remarkable law of the succession 
of the same types within the same areas mean? He 
would be a bold man, who after comparing the present 
climate of Australia and of parts of South America 
under the same latitude, would attempt to account, on 
the one hand, by dissimilar physical conditions for the 
dissimilarity of the inhabitants of these two continents, 
and, on the other hand, by similarity of conditions, for 
the uniformity of the same types in each during the 
later tertiary periods. Nor can it be pretended that it 
is an immutable law that marsupials should have been 



GEOLOGICAL SUCCESSION 305 

chiefly or solely produced in Australia ; or that Eden- 
tata and other American types should have been solely 
produced in South America. For we know that Europe 
in ancient times was peopled by numerous marsupials ; 
and I have shown in the publications above alluded to, 
that in America the law of distribution of terrestrial 
mammals was formerly different from what it now is. 
North America formerly partook strongly of the present 
character of the southern half of the continent ; and 
the southern half was formerly more closely allied, than 
it is at present, to the northern half. In a similar 
manner we know from Falconer and Cautley's dis- 
coveries, that northern India was formerly more closely 
related in its mammals to Africa than it is at the pre- 
sent time. Analogous facts could be given in relation 
to the distribution of marine animals. 

On the theory of descent with modification, the great 
law of the long enduring, but not immutable, succession 
of the same types within the same areas, is at once 
explained ; for the inhabitants of each quarter of the 
world will obviously tend to leave in that quarter, 
during the next succeeding period of time, closely 
allied though in some degree modified descendants. If 
the inhabitants of one continent formerly differed 
greatly from those of another continent, so will their 
modified descendants still differ in nearly the same 
manner and degree. But after very long intervals 
of time and after great geographical changes, permit- 
ting much inter -migration, the feebler will yield 
to the more dominant forms, and there will be no- 
thing immutable in the laws of past and present dis- 
tribution. 

It may be asked in ridicule, whether I suppose that 
the megatherium and other allied huge monsters have 
left behind them in South America, the sloth, armadillo, 
and anteater, as their degenerate descendants. This 
cannot for an instant be admitted. These huge animals 
have become wholly extinct, and have left no progeny. 
But in the caves of Brazil, there are many extinct 
species which are closely allied in size and in other 



306 ON THE ORIGIN OF SPECIES 

characters to the species still living in South America ; 
and some of these fossils may be the actual progenitors 
of living species. It must not be forgotten that, on my 
theory, all the species of the same genus have descended 
from some one species ; so that if six genera, each 
having eight species, be found in one geological forma- 
tion, and in the next succeeding formation there be six 
other allied or representative genera with the same 
number of species, then we may conclude that only 
one species of each of the six older genera has left 
modified descendants, constituting the six new genera. 
The other seven species of the old genera have all 
died out and have left no progeny. Or, which would 
probably be a far commoner case, two or three species 
of two or three alone of the six older genera will have 
been the parents of the six new genera ; the other old 
species and the other whole old genera having become 
utterly extinct. In failing orders, with the genera and 
species decreasing in numbers, as apparently is the case 
of the Edentata of South America, still fewer genera 
and species will have left modified blood-descendants. 

Summary of the preceding and present Chapters. — I 
have attempted to show that the geological record is 
extremely imperfect ; that only a small portion of the 
globe has been geologically explored with care ; that 
only certain classes of organic beings have been largely 
preserved in a fossil state ; that the number both of 
specimens and of species, preserved in our museums, is 
absolutely as nothing compared with the incalculable 
number of generations which must have passed away 
even during a single formation ; that, owing to sub- 
sidence being necessary for the accumulation of 
fossiliferous deposits thick enough to resist future 
degradation, enormous intervals of time have elapsed 
between the successive formations ; that there has prob- 
ably been more extinction during the periods of 
subsidence, and more variation during the periods of 
elevation, and during the latter the record will have 
been least perfectly kept ; that each single formation 



GEOLOGICAL SUCCESSION 307 

has not been continuously deposited ; that the duration 
of each formation is, perhaps, short compared with the 
average duration of specific forms ; that migration has 
played an important part in the first appearance of new 
forms in any one area and formation ; that widely 
ranging species are those which have varied most, and 
have oftenest given rise to new species ; and that varie- 
ties have at first often been local. All these causes 
taken conjointly, must have tended to make the geo- 
logical record extremely imperfect, and will to a large 
extent explain why we do not find interminable varie- 
ties, connecting together all the extinct and existing 
forms of life by the finest graduated steps. 

He who rejects these views on the nature of the 
geological record, will rightly reject my whole theory. 
For he may ask in vain where are the numberless tran- 
sitional links which must formerly have connected the 
closely allied or representative species, found in the 
several stages of the same great formation. He may dis- 
believe in the enormous intervals of time which have 
elapsed between our consecutive formations ; he may 
overlook how important a part migration must have 
played, when the formations of any one great region 
alone, as that of Europe, are considered ; he mav 
urge the apparent, but often falsely apparent, sudden 
coming in of whole groups of species. He may ask 
where are the remains of those infinitely numerous 
organisms which must have existed long before the 
first bed of the Silurian system was deposited : I can 
answer this latter question only hypothetically, by say- 
ing that as far as we can see, where our oceans now 
extend they have for an enormous period extended, and 
where our oscillating continents now stand they have 
stood ever since the Silurian epoch ; but that long 
before that period, the world may have presented a 
wholly different aspect ; and that the older continents, 
formed of formations older than any known to us, may 
now all be in a metamorphosed condition, or may he 
buried under the ocean. 

Passing from these difficulties, all the other great 



308 ON THE ORIGIN OF SPECIES 

leading facts in palaeontology seem to me simply to 
follow on the theory of descent with modification 
through natural selection. We can thus understand 
how it is that new species come in slowly and succes- 
sively ; how species of different classes do not neces- 
sarily change together, or at the same rate, or in the 
same degree ; yet in the long run that all undergo 
modification to some extent. The extinction of old 
forms is the almost inevitable consequence of the pro- 
duction of new forms. We can understand why when 
a species has once disappeared it never reappears. 
Groups of species increase in numbers slowly, and 
endure for unequal periods of time ; for the process of 
modification is necessarily slow, and depends on many 
complex contingencies. The dominant species of the 
larger dominant groups tend to leave many modified 
descendants, and thus new sub-groups and groups are 
formed. As these are formed, the species of the less 
vigorous groups, from their inferiority inherited from a 
common progenitor, tend to become extinct together, 
and to leave no modified offspring on the face of the 
earth. But the utter extinction of a whole group of 
species may often be a very slow process, from the sur- 
vival of a few descendants, lingering in protected and 
isolated situations. When a group has once wholly dis- 
appeared, it does not reappear ; for the link of genera- 
tion has been broken. 

We can understand how the spreading of the domi- 
nant forms of life, which are those that oftenest vary, 
will in the long run tend to people the world with 
allied, but modified, descendants ; and these will gener- 
ally succeed in taking the places of those groups of 
species which are their inferiors in the struggle for 
existence. Hence, after long intervals of time, the 
productions of the world will appear to have changed 
simultaneously. 

We can understand how it is that all the forms of 
life, ancient and recent, make together one grand 
system ; for all are connected by generation. We can 
understand, from the continued tendency to divergence 



GEOLOGICAL SUCCESSION 309 

of character, why the more ancient a form is, the more 
it generally differs from those now living. Why ancient 
and extinct forms often tend to fill up gaps between 
existing forms, sometimes blending two groups pre- 
viously classed as distinct into one ; but more commonly 
only bringing them a little closer together. The more 
ancient a form is, the more often, apparently, it dis- 
plays characters in some degree intermediate between 
groups now distinct ; for the more ancient a form is, 
the more nearly it will be related to, and consequently 
resemble, the common progenitor of groups, since be- 
come widely divergent. Extinct forms are seldom 
directly intermediate between existing forms ; but are 
intermediate only by a long and circuitous course 
through many extinct and very different forms. We 
can clearly see why the organic remains of closely 
consecutive 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, in so far, higher in the scale of 
nature ; and this may account for that vague yet ill- 
defined sentiment, felt by many palaeontologists, 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 disappear. On the other 



310 ON THE ORIGIN OF SPECIES 

hand, all the chief laws of palaeontology plainly pro- 
claim, as it seems to me, that species have been pro- 
duced by ordinary generation : old forms having been 
supplanted by new and improved forms of life, pro- 
duced 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 th6 
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 geographical distribu- 
tion 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 co its extreme 
southern point, we meet with the most diversified con- 
ditions ; the most humid districts, arid deserts, lofty 
mountains, grassy plains, forests, marshes, lakes, and 
great rivers, under almost every temperature. There 
is hardly a climate or condition in the Old World 
which cannot be paralleled in the New — at least as 
closely as the same species generally require ; for it is 

311 



312 ON THE ORIGIN OF SPECIES 

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 productions ! 

In the southern hemisphere, if we compare large 
tracts of land in Australia, South Africa, and western 
South America, between latitudes 25° 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 dissimilar. Or again we may com- 
pare the productions of South America south of lat. 
35° with those north of 25°, which consequently inhabit 
a considerably different climate, and they will be found 
incomparably 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 productions 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 temperate forms, as there now is for the 
strictly arctic productions. We see the same fact in 
the great difference between the inhabitants of Aus- 
tralia, Africa, and South America under the same lati- 
tude for these countries are almost as much isolated 
from each other as is possible. On each continent, 
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, 



GEOGRAPHICAL DISTRIBUTION 313 

deserts, etc., are not as impassable, or likely to have 
endured so long as the oceans separating" continents, 
the differences 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 impassable, 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 sepa- 
rated from each other by impassable barriers, either 
of land or open sea, they are wholly distinct. 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 have innu- 
merable 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 ia a 
law of the widest generality, and every continent offer* 
innumerable instances. Nevertheless the naturalist 



314 ON THE ORIGIN OF SPECIES 

in travelling, for instance, from north to south nevei 
fails to be struck by the manner in which successive 
groups of beings, specifically distinct, yet clearly re- 
lated, 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 north- 
ward 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 hares and 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, prevail- 
ing throughout space and time, over the same areas of 
land and water, and independent of their physical con- 
ditions. 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, pro- 
duces organisms quite like, or, as we see in the case of 
varieties, nearly like each other. The dissimilarity of 
the inhabitants of different regions may be attributed 
to modification through natural selection, and in a quite 
Bubordinate degree to the direct influence of different 



GEOGRAPHICAL DISTRIBUTION 315 

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 1 have already often remarked, the most im- 
portant 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 wil: 
have the best chance of seizing on new places, when 
they spread into new countries. In their new homer 
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 modification, 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 development. 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 species, which stand in direct competition with each 
other, migrate in a body into a new and afterwards 
isolated country, they will be little liable to modifica- 
tion ; for neither migration nor isolation in themselves 
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 physical con- 
ditions. As we have seen in the last chapter that some 
forms have retained nearly the same character from an 



316 ON THE ORIGIN OF SPECIES 

enormously 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 modification, there is not much difficulty in believ- 
ing 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 possible. 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 inhabiting 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 generation with subsequent 
migration, and calls in the agency of a miracle. It is 
universally admitted, that in most cases the area in- 
habited 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 



GEOGRAPHICAL DISTRIBUTION 317 

space could not be easily passed over by migration, the 
fact is given as something remarkable and exceptional. 
The capacity of migrating across the sea is more dis- 
tinctly limited in terrestrial mammals, than perhaps in 
any other organic beings ; and, accordingly, we find no 
inexplicable cases of the same mammal inhabiting dis- 
tant points of the world. No geologist will feel any 
difficulty in such cases as Great Britain having been 
formerly united to Europe, and consequently 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 Aus- 
tralia or South America ? The conditions 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 identi- 
cally the same at 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 sections 
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 oppo- 
site 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 migration 



318 ON THE ORIGIN OF SPECIES 

»nd subsistence under past and present conditions per- 
mitted, 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 interrupted or rendered discontinuous the for- 
merly 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 occurrence of the 
same terrestrial species on islands and on the mainland, 
though separated 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 ignor- 
ance 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 descended from a common 
progenitor, can have migrated (undergoing modification 
during some part of their migration) from the area 



GEOGRAPHICAL DISTRIBUTION 319 

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 understand, 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 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 con- 
cludes, 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 attributes to genera- 
tion with modification. 

The previous remarks on e 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 individuals simultaneously created. 
With those organic beings which never intercross (if 
such exist), the species, on my theory, must have de- 
scended from a succession of improved varieties, which 
will never have blended with other individuals or varie- 
ties, but will have supplanted each other ; so that, at each 
successive stage of modification and improvement, all 
the individuals of each variety will have descended from 
a single parent. But in the majority of cases, namely, 



320 ON THE ORIGIN OF SPECIES 

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 inter- 
crossing ; so that many individuals will have gone on 
simultaneously changing, and the whole amount of 
modification 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 diffi- 
culty on the theory of i single centres of creation,' I 
must say a few words on the means of dispersal. 

Meam 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 influ- 
ential : 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 



GEOGRAPHICAL DISTRIBUTION 321 

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 difficulty : 
but to the best of my judgment we are not authorised 
in admitting such enormous 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 halting- 
places 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 proceeded from a single birthplace, and 
when in the course of time we know something 
definite about the means of 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 continuously, united with each 
other, and with the many existing oceanic islands. 
Several facts in distribution, — such as the great differ- 
ence in the marine faunas on the opposite sides of 
almost every continent, — the close relation of the 
tertiary inhabitants of several lands and even seas to 
their present inhabitants, — a certain 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 



322 ON THE ORIGIN OF SPECIES 

period, as are necessitated on the view advanced by 
Forbes and admitted by his many 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 composition 
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 fossil- 
iferous or other such rocks, instead of consisting of 
mere piles of volcanic matter. 

I must now say a few words on what are called acci- 
dental 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 1 
tried, with Mr. Berkeley's aid, a few experiments, it 
was not even known how far seeds could resist the in- 
jurious 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 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 whilst green 
floated for a very short time, when dried floated much 



GEOGRAPHICAL DISTRIBUTION 323 

longer ; for instance, ripe hazel-nuts sank immediately, 
but when dried they floated for 90 days, and afterwards 
when planted they germinated ; an asparagus plant 
with ripe berries floated for 23 days, when dried it 
floated for 85 days, and the seeds afterwards germin- 
ated ; the ripe seeds of Helosciadium sank in two days, 
when dried they floated for above 90 days, and after- 
wards 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 |4 
seeds germinated after an immersion of 28 days ; and 
as $-£ plants with ripe fruit (but not all the same species 
as in the foregoing experiment) 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 
tVj- 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 -rVir plants 
belonging to one country might be floated across 924 
miles of sea to another country ; and when stranded, if 
blown to a favourable 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 flota- 
tion 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 result was that frf of his 
seeds floated for 42 days, and were then capable of 
germination. But I do not doubt that plants exposed 



324 ON THE ORIGIN OF SPECIES 

to the waves would float for a less time than those pro- 
tected from violent movement as in our experiments. 
Therefore it would perhaps be safer to assume that the 
seeds of about ifcfo 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 transported by any other means ; and Alph. 
de Candolle has shown that such plants generally have 
restricted ranges. 

But seeds may be occasionally transported in another 
manner. Drift timber is thrown up on most islands, 
even on those in the midst of the widest 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 completely enclosed by 
wood in an oak about 50 years old, three dicotyle- 
donous plants germinated: I am certain of the accu- 
racy of this observation. Again, I can show that the 
carcasses of birds, when floating on the sea, sometimes 
escape being immediately 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 circum- 
stances their rate of flight would often be 35 miles an 



GEOGRAPHICAL DISTRIBUTION 325 

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 excrement of small birds, and these seemed 
perfect, and some of them, which 1 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 germination of 
seeds ; now after a bird has found and devoured a large 
supply of food, it is positively asserted that all the grains 
do not pass into the gizzard for 12 or even 18 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 oi 
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, 
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 pas- 
them in their excrement ; and several of these seed* 
retained their power of germination. Certain seeds, 
however, were always killed by this process. 



326 ON THE ORIGIN OF SPECIES 

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 dry argillaceous earth from one foot of a partridge, 
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 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 sometimes 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 transported seeds from 
one part to another of the arctic and antarctic regions, 
as suggested 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 some- 
what 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 trans- 
port, 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 



GEOGRAPHICAL DISTRIBUTION 327 

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 seeds 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, however, 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 
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, wherej 
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 the chance be of a seed falling on favour- 
able soil, and coming to maturity ! 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 



328 ON THE ORIGIN OF SPECIES 

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 transport, during the long lapse of 
geological time, whilst 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 germinate and survive. 

Dispersal during the Glacial period. — r rhe identity of 
many plants and animals, on mountain-summits, separ- 
ated 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 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 burnt by fire do not tell their 
tale more plainly, than do the mountains of Scotland 
and Wales, with their scored flanks, polished surfaces, 



GEOGRAPHICAL DISTRIBUTION 329 

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. Throughout a large part of 
the United States, erratic boulders, and rocks scored 
by drifted icebergs and coast-ice, plainly reveal a former 
cold period. 

The former influence of the glacial climate on the 
distribution of the inhabitants of Europe, as explained 
with remarkable clearness by Edward Forbes, is sub- 
stantially as follows. But we shall follow the changes 
more readily, by supposing a new glacial period to come 
slowly on, and then pass away, as formerly occurred. 
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 become 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 circum- 
polar inhabitants, which we suppose to have everywhere 
travelled southward, are remarkably 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 migration 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 



330 ON THE ORIGIN OF SPECIES 

by the productions of the more temperate regions. 
And as the snow melted from the bases of the moun- 
tains, the arctic forms would seize on the cleared and 
thawed ground, always ascending higher and higher, 
as the warmth increased, whilst their brethren were 
pursuing 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 ex- 
terminated 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 
understand 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 migration 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 occurrence 
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 evidence, 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 evei 
been in any degree warmer than at present (as some 
geologists in the United States believe to have been 
the case, chiefly from the distribution of the fossil 



GEOGRAPHICAL DISTRIBUTION 331 

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 loner southern migra- 
tion and re-migration northward, will have been ex- 
posed to nearly the same climate, and, as is especially 
to be noticed, they will have kept in a body together ; 
consequently their mutual relations will not have been 
much disturbed, and, in accordance with the principles 
inculcated in this volume, they will not have been 
liable to much modification. But with our Alpine pro- 
ductions, left isolated from the moment of the return- 
ing 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 be- 
come mingled with ancient Alpine species, which must 
have existed on the mountains before the commence- 
ment 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 disturbed ; conse- 
quently 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 identically 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 com- 
mencement the arctic productions were as uniform 
round the polar regions as they are at the present day. 



332 ON THE ORIGIN OF SPECIES 

But the foregoing- remarks on distribution 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 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, be- 
fore the Glacial epoch, and whilst the majority of the 
inhabitants of the world were specifically 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 60°, during the 
Pliocene period lived further north under the Polar 
Circle, in latitude 66°-67° ; and that the strictly arctic 
productions 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 this continuity of the circumpolar 
land, and to the consequent freedom for intermigra- 
tion 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 



GEOGRAPHICAL DISTRIBUTION 333 

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 com- 
mencement of the Glacial period. We now see, as I 
believe, their descendants, mostly in a modified con- 
dition, in the central parts of Europe and the United 
States. On this view we can understand the relation- 
ship, with very little identity, between the productions 
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 in- 
habited 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. Conse- 
quently we have here everything favourable for much 
modification, — for far more modification than with the 
Alpine productions, left isolated, within a much more 
recent period, on the several mountain-ranges and on 



334 ON THE ORIGIN OF SPECIES 

the arctic lands of the two Worlds. Hence it has 
come, that when we compare the now living produc- 
tions 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 modifica- 
tion, for many closely allied forms now living in areas 
completely sundered. Thus, I think, we can under- 
stand the presence of many existing and tertiary repre- 
sentative 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 separated by a continent and by nearly a 
hemisphere 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 inexplicable 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 com- 
pare, for instance, certain parts of South America with 
the southern continents of the Old World, we see 
countries closely corresponding in all their physical 
conditions, but with their inhabitants utterly dissimilar. 

But we must return to our more immediate subject, 
the Glacial period. I am convinced that Forbes' s view 
may be largely extended. In Europe we have the 



GEOGRAPHICAL DISTRIBUTION 335 

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 gigantic ancient 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 lat. 36°-37% and on the shores of 
the Pacific, where the climate is now so different, as 
far south as lat. 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 structure 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 existing glacier. Further south 
on both sides of the continent, from lat. 41° to the 
southernmost extremity, we have the clearest evidence 
of former glacial action, in huge boulders transported 
far from their parent source. 

We do not know that the Glacial epoch was strictly 
simultaneous at these several far distant points on op- 
posite sides of the world. But we have good evidence 
in almost every case, that the epoch was included 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 



336 ON THE ORIGIN OF SPECIES 

geological sense, it seems to me probable that it was, dur- 
ing a part at least of the period, actually simultaneous 
throughout the world. Without 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 simultaneously 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, 
forming 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 Cordil- 
lera. On the mountains of Abyssinia, several European 
forms and some few representatives of the peculiar flora 
of the Cape of Good Hope occur. At the Cape 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, 



GEOGRAPHICAL DISTRIBUTION 337 

many plants occur, either identically the same or re- 
presenting each other, and at the same time representing 
{)lants of Europe, not found in the intervening hot low- 
ands. A list of the genera collected on the loftier 
peaks of Java raises a picture of a collection 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. 
Midler has discovered several European species ; other 
species, not introduced 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 admir- 
able Introduction 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 some- 
times 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 distribu- 
tion of terrestrial animals. In marine productions, 
similar cases occur ; as an example, 1 may quote a 
remark by the highest authority, Prof. 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 reappear- 
ance 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 



338 ON THE ORIGIN OF SPECIES 

Zealand and to Europe, but have not 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 hemi- 1 
sphere, and on the mountain-ranges of the intertropical 
regions, are not arctic, but belong to the northern tern- 4 
perate zones. As Mr. H. C. Watson has recently re- ) 
marked, ' 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 1 
the southern hemisphere are of doubtful value, being 
ranked by some naturalists as specifically 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 fore- 1 
going facts, on the belief, supported as it is by a large j 
body of geological evidence, that the whole world, or 
a large part of it, was during the Glacial period simul- 
taneously 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 temperate productions, and these by 
the arctic ; but with the latter we are not now concerned. 
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 pre- 
sent day crowded together at the Cape of Good Hope, 
and in parts of temperate Australia. As we know that 
many tropical plants and animals can withstand a con- 
siderable amount of cold, many might have escaped ex- 
termination during a moderate fall of temperature, 
more especially by escaping into the lowest, most pro- 
tected, and warmest districts. But the great fact to 



GEOGRAPHICAL DISTRIBUTION 339 

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 some- 
what 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 th&t 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 Cordil- 
lera, 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 latitude 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 tropi- 
cal and temperate vegetation, like that now growing 



340 ON THE ORIGIN OF SPECIES 

with strange luxuriance at the base of the Himalaya, as 
graphically described by Hooker. 

Thus, as I believe, a considerable number of plants, a 
few terrestrial animals, and some marine productions, 
migrated during the Glacial period from the northern 
and southern temperate zones into the intertropical 
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 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 underwent 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 them- 
selves 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 modifica- 
tions 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 hemispheres, 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 Australia, 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 preponderant migration from north to south is 
due to the greater extent of land in the north, and to 
the northern forms having existed in their own homes 



GEOGRAPHICAL DISTRIBUTION 341 

in greater numbers, and having 1 consequently been 
advanced through natural selection and competition to 
a higher state of perfection or dominating power, than 
the southern forms. And thus, when they became 
commingled 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. Some- 
thing 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, generated in the larger 
areas and more efficient 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 difficulties are re- 
moved 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 



342 ON THE ORIGIN OF SPECIES 

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 
migrated ; why certain species have been modified 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 
antarctic regions. These cannot be here discussed. I 
will only say that as far as regards the occurrence of 
identical species at points so enormously remote 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 dis- 
tinct 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 
modification, a far more remarkable case of difficulty. 
For some of these species are so distinct, that we can- 
not suppose that there has been time since the com- 
mencement of the Glacial period for their migration, 
and for their subsequent modification to the necessary 
degree. The facts seem to me 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 hemi- 
sphere, to a former and warmer period, before the 
commencement of the Glacial period, when the ant- 
arctic lands, now covered with ice, supported a highly 
peculiar and isolated flora. I suspect 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, 



GEOGRAPHICAL DISTRIBUTION 343 

and by the aid, as halting-places, 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 alternations of climate on geographical distri- 
bution. I believe that the world has recently felt one 
of his great cycles of change ; and that on this view, 
combined with modification through natural selection, 
a multitude of facts in the present distribution both 
of the same and of allied forms of life can be ex- 
plained. The living v, aters 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 mountain- 
summits, in a line gently rising from the arctic low- 
lands 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 distbibution — continued 

Distribution of fresh - water productions — On the inhabitants oil 
oceanic islands — Absence of Batrachians and of terrestrial 
Mammals — On the relation of the inhabitants of islands to 
those of the nearest mainland — On colonisation 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 id 
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 manyl 
fresh-water species, belonging to quite different classes! 
an enormous range, but allied species prevail in a 
remarkable manner throughout the world. I well 
remember, when first collecting in the fresh waters of 
Brazil, feeling much surprise at the similarity 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 

344 



GEOGRAPHICAL DISTRIBUTION 34* 

from this capacity as an almost necessary consequence. 
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 fish 
in common and some different. A few facts seem to 
favour the possibility of their occasional transport by 
accidental means ; like that of the live fish not rarely 
dropped by whirlwinds in India, and the vitality of 
their ova when removed from the water. But 1 am 
inclined to attribute the dispersal of fresh-water fish 
mainly to slight changes within the recent period in 
the level of the land, having caused rivers to flow into 
each other. Instances, also, could be given of this 
having occurred during floods, without any change of 
level. We have evidence in the loess of the Rhine of 
considerable changes of level in the land within a very 
recent geological period, and when the surface was 
peopled by existing land and fresh-water shells. The 
wide difference of the fish on opposite sides of con- 
tinuous mountain-ranges, which from an early period 
must have parted river -systems and completely pre- 
vented their inosculation, seems to lead to this same 
conclusion. With respect to allied fresh -water fish 
occurring at very distant points of the world, no doubt 
there are many cases which cannot at present be 
explained : but some fresh -water fish belong to very 
ancient forms, and in such cases there will have been 
ample time for great geographical changes, and conse- 
quently time and means for much migration. In the 
second place, salt-water fish can with care be slowly 
accustomed to live in fresh water ; and, according to 
Valenciennes, there is hardly a single group of fishes 
confined exclusively to fresh water, so that we may 
imagine that a marine member of a fresh-water group 
might travel far along the shores of the sea, and subse- 
quently become modified and adapted to the fires b. 
waters of a distant land. 

Some species of fresh-water shells have a very wide 



346 ON THE ORIGIN OF SPECIES 

range, and allied species, which, on my theory, are de- 
scended from a common parent and must have pro- 
ceeded from a single source, prevail throughout the 
world. Their distribution at first perplexed me much, 
as their ova are not likely to be transported by birds, 
and they are immediately killed by sea-water, as are 
the adults. I could not even understand how some 
naturalised species have rapidly spread throughout the 
same country. But two facts, which I have observed 
— and no doubt many others remain to be observed — 
throw some light on this subject. When a duck 
suddenly emerges from a pond covered with duck- 
weed, I have twice seen these little plants adhering to 
its back ; and it has happened to me, in removing a 
little duck- weed from one aquarium to another, that I 
have quite unintentionally stocked the one with fresh- 
water shells from the other. But another agency is 
perhaps more effectual : I suspended a duck's feet, 
which might represent those of a bird sleeping in a 
natural pond, in an aquarium, where many ova of 
fresh-water shells were hatching ; and I found that 
numbers of the extremely minute and just-hatched 
shells crawled on the feet, and clung to them so firmly 
that when taken out of the water they could not be 
jarred off, though at a somewhat more advanced age 
they would voluntarily drop off. These just hatched 
molluscs, though aquatic in their nature, survived on 
the duck's feet, in damp air, from twelve to twenty 
hours ; and in this length of time a duck or heron 
might fly at least six or seven hundred miles, and 
would be sure to alight on a pool or rivulet, if blown 
across sea to an oceanic island or to any other distant 
point Sir Charles Lyell also informs me that a 
Dyticus has been caught with an Ancylus (a fresh- 
water shell like a limpet) firmly adhering to it ; and a 
water-beetle of the same family, a Colymbetes, once 
flew on board the Beagle when forty -five miles 
distant from the nearest land : how much farther it 
might have flown with a favouring gale no one can 
tell. 



GEOGRAPHICAL DISTRIBUTION 347 

With respect to plants, it has long been known what 
enormous ranges many fresh -water and even marsh- 
species have, both over continents and to the most 
remote oceanic islands. This is strikingly shown, as 
remarked by Alph. de Candolle, in large groups of 
terrestrial plants, which have only a very few aquatic 
members ; for these latter seem immediately to acquire, 
as if in consequence, a very wide range. I think 
favourable means of dispersal explain this fact. I have 
before mentioned that earth occasionally, though 
rarely, adheres in some quantity to the feet and beaks 
of birds. Wading birds, which frequent the muddy 
edges of ponds, if suddenly flushed, would be the 
most likely to have muddy feet. Birds of this order I 
can show are the greatest wanderers, and are occa- 
sionally found on the most remote and barren islands 
in the open ocean ; they would not be likely to alight 
on the surface of the sea, so that the dirt would not be 
washed off their feet ; when making land, they would 
be sure to fly to their natural fresh-water haunts. I 
do not believe that botanists are aware how charged 
the mud of ponds is with seeds : I have tried several 
little experiments, but will here give 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 6| 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 alto- 
gether 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 



348 ON THE ORIGIN OF SPECIES 

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 distribution 
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 Nelumbium undigested ; 
or the seeds might be dropped by the bird whilst 
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 
unoccupied ; 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, compared with those on the 
land, the competition will probably be less severe 
between aquatic than between terrestrial species ; con- 
sequently 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 



GEOGRAPHICAL DISTRIBUTION 349 

migration of the same aquatic species. \Y r e should not 
forget the probability of many species having formerly 
ranged as continuously as fresh-water productions ever 
san 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 particular 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 birthplace, 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 extensions, 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 pro- 
ductions. 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. 

The species of all kinds which inhabit oceanic islands 
are few in number compared with those on equal con- 
tinental areas: Alph. de Candolle admits this for plants, 
and VVollaston for insects. If we look to the large 



350 ON THE ORIGIN OF SPECIES 

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 difference 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 
Anglesea 764, but a few ferns and a few introduced 
plants are included in these numbers, and the com- 
parison in some other respects is not quite fair. We 
have evidence that the barren island of Ascension ab- 
originally 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 
separate 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 un- 
intentionally 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 proportion of endemic 
species (i.e. those found nowhere else in the world) is 
often extremely 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 descendants. But 
it by no means follows, that, because in an island nearly 
all the species of one class are peculiar, those of another 



GEOGRAPHICAL DISTRIBUTION 361 

class, or of another section of the same class, are 
peculiar ; and this difference 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 1 
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 inter- 
crossing with the unmodified immigrants from the 
mother-country. Madeira, again, is inhabited by a 
wonderful 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 



362 ON THE ORIGIN OF SPECIES 

sure can see that their eggs or larvae, perhaps attached 
to seaweed or floating timber, or to the feet of wading - 
birds, might be transported far more easily than land- 

->lls, 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 apparently occupied by 
the other inhabitants ; 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 endemic plants have beautifully hooked 
seeds ; yet few relations are more striking than the 
adaptation of hooked seeds for transportal 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 include 
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 herb- 
aceous plant, though it would have no chance of 
successfully competing in stature with a fully de- 
veloped tree, when established on an island and having 



GEOGRAPHICAL DISTRIBUTION 353 

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 moun- 
tains 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 con- 
ditions ; indeed it seems 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 immediately 
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 

2a 



354 ON THE ORIGIN OF SPECIES 

cannot be considered as oceanic, as it lies on a bank 
connected with the mainland ; moreover, icebergs for- 
merly 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 mam- 
mals ; 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 production 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 islandsJ 
aerial mammals do occur on almost every island. Newi 
Zealand possesses two bats found nowhere else in the 
world : Norfolk Island, the Viti Archipelago, 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 pro- 
duced bats and no other mammals on remote islands S 
On my view this question can easily be answered ; for 
no terrestrial 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 distance 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 conti- 
nents and on far distant islands. Hence we have only 
to suppose that such wandering species have been modi- 
fied through natural selection in their new homes in re- 
lation to their new position, and we can understand the 



GEOGRAPHICAL DISTRIBUTION 355 

presence of endemic bats on islands, with the absence 
of all terrestrial mammals. 

Besides the absence of terrestrial mammals in rela- 
tion 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 
011 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 quad- 
rupeds. No doubt some few anomalies occur in this 
great archipelago, and there is much difficulty in form- 
ing 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 on many islands separated by similar 
channels from Australia. The West Indian Islands 
stand on a deeply submerged bank, nearly 1000 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 under- 
stand the frequent relation between the depth of the 



356 ON THE ORIGIN OF SPECIES 

lea and the degree of affinity of the mammalian inhabit- 
ants 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 inhabitants 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 notwithstand- 
ing the presence of aerial bats, — the singular propor- 
tions 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 continuous 
land with the nearest continent ; for on this latter 
view the migration would probably 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 importance of the rela- 
tion of organism to organism. 

I do not deny that there are many and grave diffi- 
culties 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 of 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 some- 
times 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 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 



GEOGRAPHICAL DISTRIBUTION 357 

for their transportal. 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 un- 
injured 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 unmistakable 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 archi- 
pelago. 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 



358 ON THE ORIGIN OF SPECIES 

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 con- 
siderable 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 Archipelagos : 
but what an entire and absolute difference in their 
inhabitants ! The inhabitants 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 explanation 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 betray- 
ing 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 icebergs, 
drifted by the prevailing currents, this anomaly dis- 
appears. 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 have 
been expected ; but it is also plainly related to South 
America, which, although the next nearest continent, 



GEOGRAPHICAL DISTRIBUTION 359 

is so enormously remote, that the fact becomes an 
anomaly. But this difficulty almost disappears on the 
view that both New Zealand, 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 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 ex- 
plained. 

The law which causes the inhabitants of an archi- 
pelago, 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 
marvellous 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 dissimilarity 
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 consider- 
ing the physical conditions of a country as the most 



360 ON THE ORIGIN OF SPECIES 

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 import- 
ant, and generally a far more important element of 
success. Now if we look to those inhabitants of the 
Galapagos Archipelago 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 modi- 
fied 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 subsequently spread from one island to another, 
it would undoubtedly be exposed to different condi- 
tions 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 Gala- 
pagos 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 



GEOGRAPHICAL DISTRIBUTION 361 

gales 01 wind are extraordinarily 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 conlined 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 closely- 
allied species invading each other's territory, when put 
into free intercommunication. Undoubtedly if one 
species has any advantage 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 re- 
member 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 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 mocking -thrush of 
Chatham Island to be blown to Charles Island, which 
has its own mocking -thrush : why should it succeed 
in establishing 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 ; 



362 ON THE ORIGIN OF SPECIES 

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 trans- 
ported 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 in- 
habited by a vast number of distinct mammals, birds, 
and plants. 

The principle which determines the general char- 
acter of the fauna and flora of oceanic islands, namely, 
that the inhabitants, 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 homes, — 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 



GEOGRAPHICAL DISTRIBUTION 363 

lakes and marshes, excepting in so far as great facility 
of transport 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 
likewise be found some identical species, showing, 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 varieties ; 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. Amongst 
mammals, we see it strikingly displayed in Bats, and 
in a lesser degree in the Felidae and CanidaB. We see 
it, if we compare the distribution of butterflies and 
beetles. So it is with most fresh-water productions, 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 the 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 ; 



364 ON THE ORIGIN OF SPECIES 

but, if the variation had been a little greater, the two 
varieties would have been ranked 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 im- 
portant 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 de- 
scended 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 diverse conditions favour- 
able for the conversion 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 ex- 
tremely 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 cli- 
matal 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 consequently 
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, probably accounts for a law which has 
long been observed, and which has lately been admirably 



GEOGRAPHICAL DISTRIBUTION 365 

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 sur- 
rounding low lands and 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 colon- 
isation 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. our 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 pro- 
foundly 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 diffi- 
culties 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 



36G ON THE ORIGIN OF SPECIES 

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 meridional belts. As 
showing how diversified are the means of occasional 
transport, I have discussed at some little length the 
means of dispersal of fresh-water productions. 

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 pro- 
ceeded from some one source ; then I think all the 
grand leading facts of geographical distribution are 
explicable on the theory of migration (generally of the 
more dominant forms of life), together with subsequent 
modification and the 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 likewise 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 



GEOGRAPHICAL DISTRIBUTION 367 

inhabited by very different forms of life ; for according 
to the length of time which has elapsed since new in- 
habitants 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 immi- 
grants were capable of varying more or less rapidly, 
there would ensue in different regions, independently of 
their physical conditions, infinitely diversified condi- 
tions 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 understand, as I have 
endeavoured to show, why oceanic islands should have 
tew 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, whilst 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 de- 
rived. 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 



368 ON THE ORIGIN OF SPECIES 

doubtful species, and of distinct but representative 
apecies. 

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 govern- 
ing 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 con- 
tinuous ; 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 con- 
ditions 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 sculpture 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, whilst others be- 
longing to a different class, 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 throughout 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 
which have changed after having migrated into distant 
quarters, in both cases the forms within each class have 
been connected by the same bond of ordinary gener- 



GEOGRAPHICAL DISTRIBUTION 369 

ation ; 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 varia- 
tion have been the same, and modifications have been 
accumulated by the same power of natural selection. 



2b 



CHAPTER XIII 

MUTUAL AFFINITIES OF ORGANIC BEINGS : MORPHOLOGY : 
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 classification — 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 — RUDIMENTARY ORGANS ; 
their origin explained — Summary. 

From the first dawn of life, all organic beings are round 
to resemble each other in descending degrees, so that 
they can be classed in groups under groups. This 
classification is evidently not arbitrary like tne group- 
ing 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 flesh, 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 Variatioi 
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 

370 



CLASSIFICATION 371 

*nd dominant species. Consequently the groups which 
Are now large, and which generally include many domi- 
nant species, tend to go on increasing indefinitely in 
size. I further attempted to show that from the vary- 
ing 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 char- 
acters 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 preceding 
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 inevitable 
result is that the modified descendants proceeding from 
one progenitor become broken up into groups subordi- 
nate 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 ecunmon 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 farther 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. 



372 ON THE ORIGIN OF SPECIES 

the grand fact in natural history of the subordination 
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 to- 
gether 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 sentence 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 of each kind 
of dog. The ingenuity and utility of this system are 
indisputable. But many naturalists think that some- 
thing 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 
Linnaeus, and which we often meet with in a more 01 
less concealed form, that the characters do not make th« 
genus, but that the genus gives the characters, seem 
imply that something more is included in our classifk 
tion, than mere resemblance. I believe that somethii 
more is included ; and that propinquity of descent, — th< 
only known cause of the similarity of organic beings,- 
is the bond, hidden as it is by various degrees of modifi- 
cation, which is partially revealed to us by our classifi- 
cations. 

Let us now consider the rules followed in classi- 
fication, and the difficulties which are encountered 01 
the view that classification either gives some unknot 
plan of creation, or is simply a scheme for enunciatii 
general propositions and of placing together the fori 
most like each other. It might have been thought (an< 



CLASSIFICATION 373 

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 resem- 
blances, 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 
resemblances we shall have to recur. It may even be 
given as a general rule, that the less any part of the 
organisation is concerned with special habits, the more 
important 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 character.' 
So with plants, how remarkable it is that the organs of 
vegetation, on which their whole life depends, are of 
little signification, 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 resem- 
blances in parts of the organisation, 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 
importance. No doubt this view of the classificatory im- 
portance of organs which are important is generally, but 
by no means always, true. But their importance for 
classification, I believe, depends on their greater con- 
stancy 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 classi- 



374 ON THE ORIGIN OF SPECIES 

ficatory 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 acknow- 
ledged in the writings of almost every author. It ! 
will suffice to quote the highest authority, Robert j 
Brown, who in speaking of certain organs in the Pro- j 
teaceae, says their generic importance, l 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 existence or absence of 
albumen, in the imbricate 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 amongst insects, in 
one great division of the Hymenoptera, 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 classification ; yet no 
one probably will say that the antennae in these two 
divisions of the same order are of unequal physiological 
importance. Any number of instances could be given 
of the varying importance for classification of the same 
important organ within the same group of beings. 

Again, no one will say that rudimentary or atrophied 
organs are of high physiological 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 rumi- 
nants, and certain rudimentary bones of the leg, are 
highly serviceable in exhibiting the close affinity be- 
tween Ruminants and Pachyderms. Robert Brown ha* 
strongly insisted on the fact that the rudimentary florets 
are of the highest importance in the classification of tha 
Grasses. 



CLASSIFICATION 376 

Numerous instances could be given of characters 
derived from parts which must be considered of very 
trifling 1 physiological importance, but which are univer- 
sally admitted as highly serviceable in the definition 
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 absolutely dis- 
tinguishes fishes and reptiles — the inflection of the angle 
of the jaws in Marsupials — 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 con- 
sidered by naturalists as important an aid in deter- 
mining 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 charac- 
ters, mainly depends on their being correlated with 
several other characters 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 classification 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 Linnaeus, 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 



376 ON THE ORIGIN OF SPECIES 

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, departing 
so wonderfully in a number of the most important 
points of structure from the proper type of the order, 
yet M. Richard sagaciously saw, as Jussieu observes, 
that this genus should still be retained amongst the 
Malpighiaceae. 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 naturalists 
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 
those for 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 im- 
portant 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 



CLASSIFICATION 377 

great naturalists, Milne Edwards and Agassiz, that em- 
bryonic 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 divi- 
sions have been founded on characters derived from the 
embryo, — on the number and position of the embry- 
onic leaves or cotyledons, and on the mode of develop- 
ment of the plumule and radicle. In our discussion 
on embryology, 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 
define 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 end3 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 unequivo- 
cally 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 entomologists 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 amongst 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 differences, 



378 ON THE ORIGIN OF SPECIES 

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 un- 
consciously 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. 1 
believe that the arrangement of the groups within each 
class, in due subordination 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 allied in the same degree in 
blood to their common progenitor, may differ greatly, 
being due to the different degrees of modification 
which they have undergone ; and this is expressed 
by the forms being ranked under different genera, 
families, sections, or orders. The reader will best 
understand what is meant, if he will take the trouble 
of referring to the diagram in the preliminary. We 
will suppose the letters A to L to represent allied 
genera, which lived during the Silurian epoch, and these 
have descended from a species which existed at an un- 
known anterior period. Species of three of these genera 
(A, F, and I) have transmitted modified descendants to 
the present day, represented by the fifteen genera (a 14 to 
z u ) on the uppermost horizontal line. Now all these 
modified descendants from a single species, are repre- 
sented as related in blood or descent to the same 
degree ; they may metaphorically be called cousins to 
the same millionth degree ; yet they differ widely 



CLASSIFICATION 379 

and in different degrees from each other. The forms 
descended from A, now broken up into two or three 
families, constitute a distinct order from those de- 
scended from I, also broken up into two families. Nor 
can the existing species, descended from A, be ranked 
in the same genus with the parent A ; or those from 
I, with the parent I. But the existing genus f m may 
be supposed to have been but slightly modified ; and 
it will then rank with the parent -genus F; just as 
some few still living organic beings belong to Silurian 
genera. So that the amount or value of the differ- 
ences between organic beings all related to each other 
in the same degree in blood, has come to be widely 
different. Nevertheless their genealogical arrange- 
ment remains strictly true, not only at the present 
time, but at each successive period of descent. All 
the modified descendants from A will have inherited 
something in common from their common parent, as 
will all the descendants from I ; so will it be with each 
subordinate branch of descendants, at each successive 
period. If, however, we choose to suppose that any of 
the descendants of A or of I have been so much modified 
as to have more or less completely lost traces of 
their parentage, in this case, their places in a natural 
classification will have been more or less completely lost, 
— as sometimes seems to have occurred with existing 
organisms. All the descendants of the genus F, along 
its whole line of descent, are supposed to have been 
but little modified, and they yet form a single genus. 
But this genus, though much isolated, will still occupy 
its proper intermediate position ; for F originally was 
intermediate in character between A and I, and the 
several genera descended from these two genera will 
have inherited to a certain extent their characters. 
This natural arrangement is shown, as far as is possible 
on paper, in the diagram, but in much too simple a 
manner. If a branching diagram had not been used, 
and only the names of the groups had been written in 
a linear series, it would have been still less possible to 
have given a natural arrangement ; and it is notoriously 



380 ON THE ORIGIN OF SPECIES 

not possible to represent in a series, on a flat surface, 
the affinities which we discover in nature amongst the 
beings of the same group. Thus, on the view which I 
hold, the natural system is genealogical in its arrange- 
ment, like a pedigree ; but the degrees of modification 
which the different groups have undergone, have to be 
expressed by ranking them under different so-called 
genera, sub - families, families, sections, orders, and 
classes. 

It may be worth while to illustrate this view of 
classification, by taking the case of languages. If we 
possessed a perfect pedigree of mankind, a genealogical 
arrangement of the races of man would afford the best 
classification of the various languages now gpoken 
throughout the world ; and if all extinct languages, and 
all intermediate and slowly changing dialects, had to 
be included, such an arrangement would, I think, be 
the only possible one. Yet it might be that some very 
ancient language had altered little, and had given rise 
to few new languages, whilst others (owing to the 
spreading and subsequent isolation and states of civilisa- 
tion of the several races, descended from a common 
race) had altered much, and had given rise to many new 
languages and dialects. The various degrees of differ- 
ence in the languages from the same stock, would have 
to be expressed by groups subordinate to groups ; but 
the proper or even only possible arrangement would still 
be genealogical ; and this would be strictly natural, as 
it would connect together all languages, extinct and 
modern, by the closest affinities, and would give the 
filiation and origin of each tongue. 

In confirmation of this view, let us glance at 
the classification of varieties, which are believed or 
known to have descended from one species. These 
*re grouped under species, with sub - varieties under 
varieties ; and with our domestic productions, several 
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 



CLASSIFICATION 381 

degrees of modification. Nearly the same rules are 
followed in classifying 1 varieties, as with species. Author? 
have insisted on the necessity of classing varieties on a 
natural instead of an artificial system ; we are cau- 
tioned, 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 serviceable, 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 
inheritance 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 nearly or 
quite lost this 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 NegTo group, however much 
he might differ in colour and other important character* 
from negroes. 

With species in a state of nature, every naturalist has 
in feet brought descent into his classification ; for he 
includes in his lowest grade, or that of a species, the 
two sexes ; and how enormously these sometimes differ 
in the most important characters, is known to every 
naturalist : scarcely a single fact can be predicated in 



382 ON THE ORIGIN OF SPECIES 

common of the males and hermaphrodites of certain 
cirripedes, when adult, and yet no one dreamg 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 considered 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 Cata- 
setum), which had previously been ranked as three 
distinct genera, were known to be sometimes produced 
on the same spike, they were immediately 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 larv» are sometimes ex- 
tremely different ; and as it has been used in classing 
varieties which have undergone a certain, and some- 
times 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 modi- 
fication 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 pedi- 
grees ; 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 con- 
ditions 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 



CLASSIFICATION 383 

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 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 correlated 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 may be 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 intermediate 
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 con- 
ditions 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 



384 ON THE ORIGIN OF SPECIES 

isolated region, have in all probability descended from 
the same parents. 

We can understand, on these views, the very im- 
portant distinction between real affinities and analogical 
or adaptive resemblances. Lamarck first called atten- 
tion 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. Amongst 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 have been drawn by some authors 
between very distinct animals. On my view of char- 
acters being of real importance for classification, only 
in so far as they reveal descent, we can clearly under- 
stand 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 conditions, and thus 
assume a close external resemblance ; but such re- 
semblances 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 



CLASSIFICATION 385 

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 per- 
haps understand how it is that a numerical parallelism 
has sometimes been observed between the sub-groups 
in distinct classes. A naturalist, 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 the 
parallelism over a wide range ; and thus the septenary, 
quinary, quaternary, and ternary classifications 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 increas- 
ing in size ; and they 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 show- 
ing 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 
process of modification, how it is that the more ancient 

2c 



386 ON THE ORIGIN OF SPECIES 

forms of life often present characters in some slight 
degree intermediate between existing groups. A few 
old and intermediate parent-forms having occasionally 
transmitted 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 gener- 
ally represented 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 richness in species, as I find after some 
investigation, 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 
conquered by more successful competitors, with a few 
members preserved by some unusual coincidence of 
favourable circumstances. 

Mr. Waterhouse has remarked that, when a member 
belonging to 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. 
Therefore 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 



CLASSIFICATION 387 

(groups have since undergone much modification in 
divergent directions. On either view we may suppose 
that the bizcacha has retained, by inheritance, 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 Marsupials, 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 re- 
semblance 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 observa- 
tions 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-relationship 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 under- 
stand the extraordinary difficulty which naturalists 
have experienced in describing, without the aid of a 
diagram, the various affinities which they perceive 



388 ON THE ORIGIN OF SPECIES 

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 denning 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 connectee 
fishes with batrachians. There has been still less ii 
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 nc 
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 whicl 
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 
natural classification, or at least a natural arrange 
ment, 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 producec 
large groups of modified descendants. Every inter- 
mediate link between these eleven genera and theii 
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 of the several groups could be dis- 
tinguished from their more immediate parents ; or these 
parents from their ancient and unknown progenitor. 
Yet the natural arrangement in the diagram would still 
hold good ; and, on the principle of inheritance , all the 



CLASSIFICATION 389 

forms descended from A, or from I, would have some- 
thing 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 diiferences between them. 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 
throughout all time and space. We shall certainly 
never succeed in making so perfect a collection : never- 
theless, 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 selection, which 
results from the struggle for existence, and which 
almost inevitably induces extinction and divergence of 
character in the many descendants from one dominant 
parent- species, explains that great and universal 
feature in the affinities of all organic beings, namely, 
their subordination in group under group. We use the 
element of descent in classing the individuals 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 1 believe this element of 
descent is the hidden bond of connection which natural- 
ists 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 arrangement, with 
the grades of difference between the descendants from 
a common parent, expressed by the terms genera, 
families, orders, 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 



390 ON THE ORIGIN OF SPECIES 

physiological importance ; why, in comparing* one group 
with a distinct group, we summarily reject analogical 
or adaptive characters, and yet use these same char- 
acters 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 connected together 
by the most complex and radiating lines of affinities. 
We shall never, probably, disentangle the inextricable 
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. 

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 organ- 
isation. This resemblance is often expressed by the 
term c 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 
interesting 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, in the same relative positions ? Geoffroy 
St. Hilaire has insisted strongly on the high importance 
of relative connection in homologous 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 



MORPHOLOGY 391 

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 hopelessness 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 inde- 
pendent creation of each being, we can only say that so it 
is ; — that it has so pleased the Creator to construct 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. In 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 mem- 
brane, 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 framework of bones or the relative con- 
nection 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 



392 ON THE ORIGIN OF SPECIES 

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. Neverthless, 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 multiplication of others, — varia- 
tions which we know to be within the limits of possi- 
bility. 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 connection 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 wonderfully complex jaws and 
legs in crustaceans. It is familiar to almost every one, 
that in a flower 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 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 crustaceans 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 extra- 
ordinary shaped pieces of bone? As Owen has remarked, 



MORPHOLOGY 393 

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, consequently 
always have fewer legs ; or conversely, 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 appen- 
dages ; in the articulata, we see the body divided into a 
series of segments, bearing external appendages ; and in 
flowering plants, we see a series of successive spiral 
whorls of leaves. An indefinite repetition of the same 
part or organ is the common characteristic (as Owen 
has observed) of ail low or little-modified forms ; there- 
fore we may readily believe that the unknown progenitor 
of the vertebrata possessed many vertebrae ; the unknown 
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 ; consequently 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 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 homo- 
logise the parts of one species with those of other and 



394 ON THE ORIGIN OF SPECIES 

distinct species, we can indicate but few serial homo- 
logies ; 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 vegetable kingdoms. 

Naturalists frequently speak of the skull as formed of 
metamorphosed vertebrae ; the jaws of crabs as meta- 
morphosed legs ; the stamens and pistils of flowers as 
metamorphosed leaves ; but it would in these cases prob- 
ably 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 — verte- 
bra? 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 
metamorphosed during a long course of descent 
from true legs, or from some simple appendage, is 
explained. 

Embryology. — It has already been casually 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, 



EMBRYOLOGY 395 

he cannot now tell whether it be that of a mamma), 
bird, or reptile. The vermiform larvae of moths, flies, 
beetles, etc., resemble each other much more closely 
than do the mature insects ; but in the case of larva- . 
the embryos are active, and have been adapted for 
special lines of life. A trace of the law of embryonic 
resemblance, sometimes 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 occasion- 
ally 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 leguminos*. 

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 condi- 
tions 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 condi- 
tions 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 



,396 ON THE ORIGIN OF SPECIES 

such special adaptations, the similarity of the larvaB 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 com- 
mon embryonic resemblance. Cirripedes afford a good 
instance of this : even the illustrious Cuvier did not per- 
ceive that a barnacle was, as it certainly is, a crustacean ; 
but a glance at the larva shows this to be the case in an 
unmistakable manner. So again the two main divi- 
sions of cirripedes, the pedunculated and sessile, which 
differ widely in external appearance, have larvae in all 
their stages barely distinguishable. 

The embryo in the course of development 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 caterpillar. In some cases, 
however, the mature animal is generally considered as 
lower in the scale than the larva, as with certain para- 
sitic 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 beautifully 
constructed natatory legs, a pair of magnificent com- 
pound eyes, and extremely complex antennae ; but they 
have a closed and imperfect mouth, and 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 be- 
come 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 reconverted into a 



EMBRYOLOGY 397 

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 larva 
become developed either into hermaphrodites having 
the ordinary structure, or into what I have called com- 
plement^ 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 importance, except- 
ing for reproduction. 

We are so much accustomed to see differences in 
structure between the embryo and the adult, and like- 
wise a close similarity in the embryos of widely different 
animals within the same class, that we might be led 
to look at these facts as necessarily contingent in some 
manner on growth. But there is no obvious reason why, 
for instance, the wing of a bat, or the fin of a porpoise, 
should not have been sketched out with all the parts 
in proper proportion, as soon as any structure became 
visible in the embryo. And in some whole groups of 
animals and in certain members of other groups, the 
embryo does not at any period differ widely from the 
adult : thus Owen has remarked in regard to cuttle-fish, 
' there is no metamorphosis ; the cephalopodic character 
is manifested long before the parts of the embryo are 
completed ; ' and again in spiders, ' there is nothing 
worthy to be called a metamorphosis.' The larvae of 
insects, whether adapted to the most diverse and active 
habits, or quite inactive, being fed by their parents or 
placed in the midst of proper nutriment, yet nearly all 
pass through a similar worm-like stage of development; 
but in some few cases, as in that of Aphis, if we look to 
the admirable drawings by Professor Huxley of the 
development of this insect, we see no trace of the 
vermiform stage. 

How, then, can we explain these several facts in 
embryology, — namely the very general, but not uni- 
versal difference in structure between the embryo and 
the adult; — of parts in the same individual embryo, 



398 ON THE ORIGIN OF SPECIES 

which ultimately become very unlike and serve for 
diverse purposes, being at this early period of growth 
alike ; — of embryos of different species within the same 
class, generally, but not universally, resembling each 
other ; — of the structure of the embryo not being closely 
related to its conditions of existence, except when the 
embryo becomes at any period of life active and has to 
provide for itself; — of the embryo apparently having 
sometimes a higher organisation than the mature 
animal, into which it is developed ? I believe that all 
these facts can be explained, as follows, on the view of 
descent with modification. 

It is commonly assumed, perhaps from monstrosities 
often affecting the embryos at a very early period, 
that slight variations necessarily appear at an equally 
early period. But we have little evidence on this head 
— indeed the evidence rather points the other way; for 
it is notorious that breeders of cattle, horses, and various 
fancy animals, cannot positively tell, until some time 
after the animal has been born, what its merits or form 
will ultimately turn out. We see this plainly in our 
own children ; we cannot always tell whether the child 
will be tall or short, or what its precise features will 
be. The question is not, at what period of life any 
variation has been caused, but at what period it is fully 
displayed. The cause may have acted, and I believe 
generally has acted, even before the embryo is formed ; 
and the variation may be due to the male and female 
sexual elements having been affected by the conditions 
to which either parent, or their ancestors, have been 
exposed. Nevertheless an effect thus caused at a very 
early period, even before the formation of the embryo, 
may appear late in life ; as when an hereditary disease, 
which appears in old age alone, has been communi- 
cated to the offspring from the reproductive element of 
one parent. Or again, as when the horns of cross-bred 
cattle have been affected by the shape of the horns of 
either parent For the welfare of a very young animal, 
as long as it remains in its mother's womb, or in the 
egg, or as long as it is nourished and protected by its 



EMBRYOLOGY 399 

parent, it must be quite unimportant whether most of 
its characters are fully acquired a little earlier or later 
in life. It would not signify, for instance,' to a bird 
which obtained its food best by having a long beak, 
whether or not it assumed a beak of this particular 
length, as long as it was fed by its parents. Hence, 
I conclude, that it is quite possible that each of the 
many successive modifications, by which each species 
has acquired its present structure, may have super- 
vened at a not very early period of life ; and some 
direct evidence from our domestic animals supports 
this view. But in other cases it is quite possible that 
each successive modification, or most of them, may 
have appeared at an extremely early period. 

I have stated in the first chapter, that there is some 
evidence to render it probable, that at whatever age 
any variation first appears in the parent, it tends to 
reappear at a corresponding age in the offspring. 
Certain variations can only appear at corresponding 
ages, for instance, peculiarities in the caterpillar, 
cocoon, or imago states of the silk-moth ; or, again, 
in the horns of almost full-grown cattle. But further 
than this, variations which, for all that we can see, 
might have appeared earlier or later in life, tend to 
appear at a corresponding age in the offspring and 
parent. I am far from meaning that this is invariably 
the case ; and I could give a good many cases of varia- 
tions (taking the word in the largest sense) which have 
supervened at an earlier age in the child than in the 
parent. 

These two principles, if their truth be admitted, will, 
I believe, explain all the above specified leading 1 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 appearing so different, are really 
varieties most closely allied, and have probably de- 
scended 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 



400 ON THE ORIGIN OF SPECIES 

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 proportional 
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, fan tails, runts, barbs, 
dragons, carriers, and tumblers. Now some of these 
birds, when mature, differ so extraordinarily 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 later embryonic stages of 



EMBRYOLOGY 401 

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 possesses them. 
And the cases just given, more especially that of 
pigeons, seem to show that the characteristic differ- 
ences which give value to each breed, and which have 
been accumulated by man's selection, have not gener- 
ally first appeared at an early period of life, and have 
been inherited by the offspring at a corresponding not 
early period. But the case of the short-faced tumbler, 
which when twelve hours old had acquired its proper 
proportions, 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 differences 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 suc- 
cessive steps of variation having supervened 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 modification 
supervening at a rather late age, and being inherited 
at a corresponding late age — the fore- limbs in the 

2d 



402 ON THE ORIGIN OF SPECIES 

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 diifer greatly from the 
fore -limbs in the 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 influ- 
ence 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 gaiu 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 generations, 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 aj 
very early age in the same manner with its parents, in 
accordance with their similar habits. Some further 



EMBRYOLOGY 403 

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 dif- 
ferent 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 differ- 
ences might, also, become correlated with successive 
stages of development ; 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 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 metamorphosis 
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, 
a'ad as all have been connected by the finest gradations, 
the best, or indeed, if our collections were nearly perfect, 
the only possible arrangement, 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 there- 
fore in that degree closely related. Thus, community in 
embryonic structure reveals community of descent. It 
will reveal this community of descent, however much 
the structure of the adult may have been modified and 
obscured ; we have seen, for instance, that cirripedes 



404 ON THE ORIGIN OF SPECIES 

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 progeni- 
tors, we can clearly see why ancient and extinct forms 
of life should resemble the embryos of their descend- 
ants, — 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 em- 
bryos, has not been obliterated, either by the successive 
variations in a long course of modification having super- 
vened 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 ex- 
tending far enough back in time, mayTemain for a loi?g 
period, or for ever, incapable of demonstration. 

Thus, as it seems to me, the leading facts in embryo- 
logy, which are second in importance to none in natural 
history, are explained on the principle of slight modifi- 
cations not appearing, in the many descendants froi 
some one ancient progenitor, at a very early period ii 
the life of each, though perhaps caused at the earliest, 
and being inherited at a corresponding not earlj 
period. Embryology rises greatly in interest, when w€ 
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 mammae are very general 
the males of mammals : I presume that the " bastard- 
wing" in birds may be safely considered as a digit ii 
a rudimentary state : in very many snakes one lobe of 



RUDIMENTARY ORGANS 406 

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 ! 

The meaning of rudimentary organs is often quite 
unmistakable : 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 some- 
times retain their potentiality, and are merely not 
developed : this seems to be the case with the mammas 
of male mammals, for many instances are on record of 
these organs having become well developed in full-grown 
males, 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 separated sexes, the male flowers 
often have a rudiment of a pistil ; and Kolreuter found 
that by crossing such male plants with an hermaphro- 
dite 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 essentially 
alike in nature. 

An organ serving for two purposes, may become rudi- 
mentary or utterly aborted for one, even the more 



406 ON THE ORIGIN OF SPECIES 

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 Composite, the 
male florets, which of course cannot be fecundated, have 
a pistil, which is in a rudimentary state, for it is not 
crowned with a stigma ; but the style remains well 
developed, and is clothed with hairs as in other Com- 
posite, 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 atrophied condition ; they may be called 
nascent, and may hereafter be developed to any extent 
by natural selection. Rudimentary organs, on the other 
hand, are essentially useless, as teeth which never cut 
through the gums ; iu 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 preservation 
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 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 J believe this to be the case, it is more probably a 



RUDIMENTARY ORGANS 407 

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, 
perhaps, 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 disappear. 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 
i9 less rudimentary, 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 
condition. 

I have now given the leading facts with respect to 
rudimentary organs. In reflecting on them, every one 



408 ON THE ORIGIN OF SPECIES 

must be struck with astonishment: for the same reason- 
ing power which tells us plainly that most parts and 
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 presence 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 rudimentary 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 produc- 
tions, — as the stump of a tail in tailless breeds, — the 
vestige of an ear in earless breeds, — the reappearance 
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, 



RUDIMENTARY ORGANS 406 

further than by showing that rudiments can be pro- 
duced ; 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 genera- 
tions 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 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 con- 
tinue slowly to reduce the organ, until it was rendered 
harmless and rudimentary. 

Any change in function, which can be effected by 
insensibly small 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 inheritance 
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 principle, also, of economy, 
explained in a former chapter, by which the materials? 
forming any part or structure, if not useful to the 



410 ON THE ORIGIN OF SPECIES 

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 under- 
stand, 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 con- 
clude that the existence of organs in a rudimentary, 
imperfect, and useless condition, 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 
throughout all time ; that the nature of the relationship, 
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 rudimentary organs, of no import- 
ance ; 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 
considered by naturalists as allied, together with their 
modification through natural selection, with its con- 
tingencies of extinction and divergence of character. 
In considering this view of classification, it should be 



SUMMARY 411 

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 similarity in organic beings, — we shall 
understand what is meant by the natural system : 
it is genealogical in its attempted arrangement, with 
the grades of acquired difference marked by the 
terms varieties, species, genera, families, orders, and 
classes. 

On this same view of descent with modification, 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 homologous parts 
constructed on the same pattern in each individual 
animal and plant. 

On the principle of successive slight variations, not 
uecessarily 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 resemblance in an indi- 
vidual embryo of the 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 pur- 
poses as different as possible. Larvae are active em- 
bryos, which have become specially modified in relation 
to their habits of life, through the principle of modifica- 
tions being 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 occur- 
rence of rudimentary organs and their final abortion, 
present to us no inexplicable difficulties ; on the con- 
trary, their presence might havo been even anticipated. 



412 ON THE ORIGIN OF SPECIES 

The importance of embryological 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 innumerable 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 immutability of 
species — How far the theory of natural selection may be ex- 
tended — 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 recapitulated. 

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 to them their full force. Nothing at first can 
appear more difficult to believe than that the more 
complex organs and instincts should have been per- 
fected, not by means superior to, though analogous with, 
human reason, but by the accumulation of innumer- 
able slight variations, each good for the individual 
possessor. Nevertheless, this difficulty, though ap- 
pearing to our imagination insuperably great, cannot 
be considered real if we admit the following proposi- 
tions, namely, — that gradations in the perfection of 
any organ or instinct which we may consider, 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 preservation of each profit- 
able deviation of structure or instinct. The truth of 
these propositions cannot, I think, be disputed. 

413 



414 ON THE ORIGIN OF SPECIES 

It is, no doubt, extremely difficult even to conjecture 
by what gradations many structures have been per- 
fected, more especially amongst 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 difficulty can be 
mastered. 

With respect to the almost universal sterility of 
species when first crossed, which forms so remarkable 
a contrast with the almost universal fertility of varieties 
when crossed, I must refer the reader to the recapitula- 
tion of the facts given at the end of the eighth chapter, 
which seem to me conclusively to show that this sterility 
is no more a special endowment than is the incapacity 
of two trees to be grafted together ; but that it is inci- 
dental 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 mongTel offspring cannot be considered as uni- 
versal ; nor is their very general fertility surprising 
when we remember 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 
produced under domestication ; and as domestication 
(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 



RECAPITULATION AND CONCLUSION 415 

that of first crosses, for their reproductive organs are 
more or less functionally impotent ; whereas in first 
crosses the organs on both sides are in a perfect con- 
dition. As we continually see that organisms of all 
kinds are rendered in some degree sterile from their 
constitutions having been disturbed by slightly differ- 
ent and new conditions of life, we need not feel 
surprise at hybrids being in some degree sterile, for 
their constitutions can hardly fail to have been dis- 
turbed from being compounded of two distinct or- 
ganisations. 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, considerable 
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 conjecture 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 bv 



416 ON THE ORIGIN OF SPECIES 

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 ob- 
viously have greatly facilitated migration. As an 
example, I have attempted to show how potent has 
been the influence of the Glacial period on the dis- 
tribution both of the same and of representative 
species throughout the world. We are as yet pro- 
foundly 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 
daring 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 may be asked, Why do 
we not see these linking forms all around us ? Why 
are not all organic beings blended together in an inex- 
tricable 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 supplanted form. Even on a wide area, 
which has during a long period remained continuous, 
and of which the climate and other conditions of life 
change insensibly in going 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 undergoing 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 intermediate zones, will be liable to be 



RECAPITULATION AND CONCLUSION 417 

supplanted by the allied forms on either hand ; and the 
latter, from existing in greater numbers, will generally 
be modified and improved at a quicker rate than the 
intermediate varieties, which exist in lesser numbers ; 
so that the intermediate varieties will, in the long run. 
be supplanted and exterminated. 

On this doctrine of the extermination of an infinitude 
of connecting links, between the living and extinct in- 
habitants of the world, and at each successive period 
between the extinct and still older species, why is not 
every geological formation charged with such links? 
Why does not every collection 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 ? AVTiy 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 such 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 sufficient 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 compared with the 
countless generations of countless species which cer- 
tainly have existed. We should not be able to 
recognise a species as the parent of any one or more 
species if we were to examine them ever so closely, 
unless we likewise possessed many of the intermediate 
links between their past or parent and present states ; 
and these many links we could hardly ever expect to 

2b 



418 ON THE ORIGIN OF SPECIES 

discover, owing to the imperfection of the geological 
record. Numerous existing doubtful forms could be 
named which are probably varieties ; but who will pre- 
tend 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 doubtful forms 
are varieties ? As long as most of the links between 
any two species are unknown, if any one link or inter- 
mediate 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 
intermediate links less likely. Local varieties will not 
spread into other and distant regions until they are con- 
siderably 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 fossiliferous forma- 
tions 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 intervals of time, geology plainly declares that 



RECAPITULATION AND CONCLUSION 419 

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 fossils from formations dis- 
tant 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 
during many years to doubt their weight. But it de- 
serves especial notice that the more important objec- 
tions 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 condi- 
tions of life ; so that this system, when not rendered 
impotent, fails to reproduce oifspring 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 
modification our domestic productions have undergone; 
but we may safely infer that the amount has been 
large, and that modifications can be inherited for long 
periods. As long as the conditions of life remain the 
same, we have reason to believe that a modification, 



420 ON THE ORIGIN OF SPECIES 

which has already been inherited 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 produced by our most anciently domesti- 
cated productions. 

Man does not actually produce variability ; he only 
unintentionally exposes organic beings to new condi- 
tions 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 individuals 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 differences so slight as to be 
quite inappreciable by an uneducated eye. This process 
of selection has been the great agency in the produc- 
tion 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 existence inevitably follows from the high 
geometrical 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 



RECAPITULATION AND CONCLUSION 421 

balance will determine 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 competition, or better 
adaptation in however slight a degree to the sur- 
rounding physical conditions, will turn the balance. 

With animals having separated sexes there will in 
most cases be a struggle between the males for posses- 
sion of the females. The most vigorous individuals, or 
those which have most successfully struggled with their 
conditions of life, will generally leave most progeny. 
But success will often depend on having special weaponp 
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 ex- 
pected that organic beings would have varied under 
nature, in the same way as they generally have varied 
under the changed conditions of domestication. 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 every one 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 



422 ON THE ORIGIN OF SPECIES 

think sufficiently distinct to be worthy of record in 
systematic works. No one can draw any clear dis- 
tinction 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 variations 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 varia- 
tions 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 constitution, structure, and habits of each 
creature, — favouring the good and rejecting the bad? 
I can see no limit to this power, in slowly and beauti- 
fully 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. I 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. 

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 demarcation 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 genu9 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 



RECAPITULATION AND CONCLUSION 423 

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 independently 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 descendants 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, characteristic of varieties of the same 
species, tend to be augmented into the greater differ- 
ences 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 belong- 
ing to the larger groups tend to give birth to new and 
dominant forms ; so that each large group tends to be- 
come 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 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, ex- 
plains the arrangement of all the forms of life, in 



424 ON THE ORIGIN OF SPECIES 

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 inexplicable on the theory of 
creation. 

As natural selection acts solely by accumulating 
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 
non facit 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 woodpecker, 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 vary- 
ing descendants of each to any unoccupied or ill-occu- 
pied 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 supposed to 
have been specially created and adapted for that coun- 
try, 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 



RECAPITULATION AND CONCLUSION 425 

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 ichneumonidaB 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 varia- 
tion 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 pro- 
duced some effect ; for it is difficult to resist this con- 
clusion when we look, for instance, at the logger-headed 
duck, which has wings incapable of flight, in nearly 
the same condition as in the domestic duck ; or when 
we look at the burrowing tucutucu, which is occasionally 
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 im- 
portant part, so that when one part has been modified 
other parts are necessarily modified. In both varieties 
and species reversions to long -lost characters occur. 
How inexplicable on the theory of creation is the occa- 
sional appearance of stripes on the shoulder 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 
progenitor, in the same manner as the several domestic 



426 ON THE ORIGIN OF SPECIES 

breeds of pigeon have descended from the blue and 
barred rock-pigeon ! 

On the ordinary view of each species having been 
independently created, why should the specific charac- 
ters, 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 independently, 
have differently coloured flowers, 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 characters 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 modification, 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 
staucture, 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 
constant 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 profitable modifications. We can thuf 



RECAPITULATION AND CONCLUSION 427 

understand 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 admirable 
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 considerably different con- 
ditions 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 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 permanent varie- 
ties, 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 successive 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 independ- 
ently 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 



428 ON THE ORIGIN OF SPECIES 

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 generation 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 character 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 gener- 
ally 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 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 endurance of 
allied forms on the same continent, — of marsupials in 
Australia, of edentata in America, and other such 
cases, — is intelligible, 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 



RECAPITULATION AND CONCLUSION 429 

descent with modification, most of the great leading 
facts in Distribution. We can see why there should be 
so striking a parallelism in the distribution of organic 
beings throughout space, and in their geological suc- 
cession throughout time ; for in both cases the beings 
have been connected by the bond of ordinary genera- 
tion, 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 
conditions, under heat and cold, on mountain and 
lowland, on deserts and marshes, most of the inhabit- 
ants within each great class are plainly related ; for 
they will generally be descendants of the same pro- 
genitors 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 
mountains, 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 relations, 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 modification in the 
two areas will inevitably be different. 

On this view of migration, with subsequent modifica- 
tion, we can see why oceanic islands should be inhabited 
by few species, but of these, that many should be 
peculiar. We can clearly see 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 



430 ON THE ORIGIN OF SPECIES 

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 representative 
species in any two areas, implies, on the theory of 
descent with modification, that the same parents for- 
merly 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 immi- 
grants 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 subordinate to group, and with extinct 
groups often falling in between recent groups, is in- 
telligible on the theory of natural selection with its 
contingencies of extinction and divergence of char- 
acter. 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 classification ; — why adaptive char- 
acters, though of paramount importance to the being, 
are of hardly any importance in classification ; why 
characters derived from rudimentary parts, though of 



RECAPITULATION AND CONCLUSION 431 

no service to the being 1 , are often of high classificatory 
value ; and why embryological characters are the most 
valuable of all. The real affinities of all organic beings 
are due to inheritance or community of descent. The 
natural system is a genealogical arrangement, in which 
we have to discover the lines of descent by the most 
permanent characters, however slight their vital im- 
portance may be. 

The framework of bones being the same in the hand 
of a man, wing of a bat, fin of the porpoise, and leg of 
the horse, — the same number of vertebra? forming the 
neck of the giraffe and of the elephant, — and innumer- 
able other such facts, at once explain themselves on 
the theory of descent with slow and slight successive 
modifications. The similarity of pattern in the wing 
and leg of a bat, though used for such different 
purpose, — in the jaws and legs of a crab, — in the 
petals, stamens, and pistils of a flower, is likewise 
intelligible on the view of the gradual modification 
of parts or organs, which were alike in the early 
progenitor of each class. On the principle of succes- 
sive variations not always supervening at an early 
age, and being inherited at a corresponding not early 
period of life, we can clearly see why the embryos 
of mammals, birds, reptiles, and fishes should be so 
closely alike, and should be so unlike the adult forms. 
We may cease marvelling at the embryo of an air- 
breathing mammal or bird having branchial slits and 
arteries running in loops, like those in a fish which 
has to breathe the air dissolved in water, by the aid of 
well-developed branchiae. 

Disuse, aided sometimes by natural selection, will 
often tend to reduce an organ, when it has become 
useless by changed habits or under changed conditions 
of life ; and we can clearly understand on this view the 
meaning of rudimentary organs. But disuse and selec- 
tion will generally act on each creature, when it has 
come to maturity and has to play its full part in the 
struggle for existence, and will thus have little power 
of acting on an organ during early life ; hence the 



432 ON THE ORIGIN OF SPECIES 

organ will not be much reduced or rendered rudi- 
mentary at this early age. The calf, for instance, has 
inherited teeth, which never cut through the gums of 
the upper jaw, from an early progenitor having well- 
developed teeth ; and we may believe, that the teeth 
in the mature animal were reduced, during successive 
generations, by disuse or by the tongue and palate 
having been better fitted by natural selection to browse 
without their aid ; whereas in the calf, the teeth have 
been left untouched by selection or disuse, and on the 
principle of inheritance at corresponding ages have 
been inherited from a remote period to the present 
day. On the view of each organic being and each 
separate organ having been specially created, how 
utterly inexplicable it is that parts, like the teeth in 
the embryonic calf or like the shrivelled wings under 
the soldered wing-covers of some beetles, should thus 
so frequently bear the plain stamp of inutility ! Nature 
may be said to have taken pains to reveal, by rudi- 
mentary organs and by homologous structure, her 
scheme of modification, which it seems that we wilfully 
will not understand. 

I have now recapitulated the chief facts and con- 
siderations which have thoroughly convinced me that 
species have been modified, during a long course of 
descent, by the preservation or the natural selection of 
many successive slight favourable variations. I cannot 
believe that a false theory would explain, as it seems to 
me that the theory of natural selection does explain, 
the several large classes of facts above specified. I see 
no good reason why the views given in this volume 
should shock the religious feelings of any one. A 
celebrated author and divine has written to me that 
'he has gradually learnt to see that it is just as noble 
a conception of the Deity to believe that He created 
a few original forms capable of self-development into 
other and needful forms, as to believe that He required 
a fresh act of creation to supply the voids caused by 
the action of His laws.' 



RECAPITULATION AND CONCLUSION 433 

Why, it may be asked, have all the most eminent 
living naturalists and geologists rejected this view of 
the mutability of species? It cannot be asserted that 
organic beings in a state of nature are subject to 
no variation ; it cannot be proved that the amount 
of variation in the course of long ages is a limited 
quantity ; no clear distinction has been, or can be, 
drawn between species and well-marked varieties. It 
cannot be maintained that species when intercrossed 
are invariably sterile, and varieties invariably fertile ; 
or that sterility is a special endowment and sign oi 
creation. The belief that species were immutable pro- 
ductions was almost unavoidable as long as the history 
of the world was thought to be of short duration ; and 
now that we have acquired some idea of the lapse of 
time, we are too apt to assume, without proof, that the 
geological record is so perfect that it would have 
afforded us plain evidence of the mutation of species, 
if they had undergone mutation. 

But the chief cause of our natural unwillingness 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 interme- 
diate 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 perceive the full effects of many slight varia- 
tions, accumulated during an almost infinite number 
of generations. 

Although 1 am fully convinced of the truth of the 
views given in this volume under the form of an 
abstract, 1 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,' e unity of design,' etc., and to think 

2f 



434 ON THE ORIGIN OF SPECIES 

that we give an explanation when we only restate a fact 
Any one whose disposition leads him to attach more 
weight to unexplained difficulties than to the explana- 
tion 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. Who- 
ever is led to believe that species are mutable will do 
good service by conscientiously expressing his convic- 
tion ; 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 natu- 
ralists, 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 sud- 
denly to flash into living tissues ? Do they believe that 
at each supposed act of creation one individual or many 



RECAPITULATION AND CONCLUSION 435 

were produced? Were all the infinitely numerous 
kinds of animals and plants created as egg's or seed, 
or as full grown? 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 connected together by chains of affinities, and all 
can be classified on the same principle, in groups sub- 
ordinate 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 structures are formed 
on the same pattern, and at an embryonic age the 
species closely resemble each other. Therefore I can- 
not doubt that the theory of descent with modification 
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 plants have descended 
from some one prototype. But analogy may be a de- 
ceitful guide. Nevertheless all living things have much 
in common, in theirchemical composition, their germinal 
vesicles, their cellular structure, and their laws of growth 
and reproduction. We see this even in so trifling a 
circumstance as that the same poison often similarly 



436 ON THE ORIGIN OF SPECIES 

affects plants and animals ; or that the poison secreted 
by the gall-fly produces monstrous growths on the 
wild rose or oak-tree. Therefore 1 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 con- 
siderable 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 distinct 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 con- 
sideration than it is at present ; for differences, how- 
ever slight, between any two forms, if not blended by 
intermediate gradations, are looked at by most natural- 
ists 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 connected at the present day by in- 
termediate gradations, whereas species were formerly 
thus connected. Hence, without rejecting the con- 
sideration of the present existence of intermediate gra- 
dations between any two 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 



RECAPITULATION AND CONCLUSION 437 

may hereafter be thought worthy of specific names, 
as with the primrose and cowslip ; and in this case 
scientific and common language will come into accord- 
ance. 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 convenience. This may not be a cheering 
prospect ; 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, rudimentary 
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 summing 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 wo 
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 corre- 
lation 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 re- 
corded species. Our classifications will come to be, a9 
far as they can be so made, genealogies ; and will then 
truly give what may be called the plan of creation. 
The rules for classifying will no doubt become simpler 



438 ON THE ORIGIN OF SPECIES 

when we have a definite object in view. We possess no 
pedigrees or armorial bearings ; and we have to dis- 
cover and trace the many diverging lines of descent in 
our natural genealogies, 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 called 
living fossils, will aid us in forming a picture of the 
ancient forms of life. Embryology will reveal to us the 
structure, in some degree obscured, of the prototypes of 
each great class. 

When we can feel assured that all the individuals of 
the same species, and all the closely allied species of 
most genera, have within a not very remote period 
descended from one parent, and have migrated from some 
one birthplace ; and when we better know the many 
means of migration, then, by the light which geology 
now throws, and will continue to throw, on former 
changes of climate and of the level of the land, we shall 
surely be enabled to trace in an admirable manner the 
former migrations of the inhabitants of the whole world. 
Even at present, by comparing the differences of the 
inhabitants of the sea on the opposite sides of a 
continent, and the nature of the various inhabitants 
of that continent in relation to their apparent means 
of immigration, some light can be thrown on ancient 
geography. 

The noble science of Geology loses glory from the 
extreme imperfection of the record. The crust of the 
earth with its embedded remains must not be looked at 
as a well-filled museum, but as a poor collection made 
at hazard and at rare intervals. The accumulation of 
each great fossiliferous formation will be recognised as 
having depended on an unusual concurrence of circum- 
stances, and the blank intervals between the successive 
stages as having been of vast duration. But we shall 
be able to gauge with some security the duration of 
these intervals by a comparison of the preceding and 
succeeding organic forms. We must be cautious in 



RECAPITULATION AND CONCLUSION 439 

attempting to correlate as strictly contemporaneous 
two formations, which include few identical species, 
by the general succession of their forms of life. As 
species are produced and exterminated by slowly 
acting and still existing causes, and not by miraculous 
acts of creation and by catastrophes ; and as the most 
important of all causes of organic change is one which 
is almost independent of altered and perhaps suddenly 
altered physical conditions, namely, the mutual relation 
of organism to organism, — the improvement of one being 
entailing the improvement or the extermination of 
others ; it follows, that the amount of organic change in 
the fossils of consecutive formations probably serves as a 
fair measure of the lapse of actual time. A number of 
species, however, keeping in a body might remain for a 
long period unchanged, whilst within this same period, 
several of these species, by migrating into new countries 
and coming into competition with foreign associates, 
might become modified ; so that we must not overrate 
the accuracy of organic change as a measure of time. 
During early periods of the earth's history, when the 
forms of life were probably fewer and simpler, the rate 
of change was probably slower ; and at the first dawn 
of life, when very few forms of the simplest structure 
existed, the rate of change may have been slow in an 
extreme degree. The whole history of the world, 
as at present known, although of a length quite in- 
comprehensible by us, will hereafter be recognised 
as a mere fragment of time, compared with the ages 
which have elapsed since the first creature, the pro- 
genitor of innumerable extinct and living descendants, 
was created. 

In the distant future I see open fields for far more 
important researches. Psychology will be based on a 
new foundation, that of the necessary acquirement of 
each mental power and capacity by gradation. Light 
will be thrown on the origin of man and his history. 

Authors of the highest eminence seem to be fully 
satisfied with the view that each species has been inde- 
pendently created. To my mind it accords better with 



440 ON THE ORIGIN OF SPECIES 

what we know of the laws impressed on matter by the 
Creator, that the production and extinction of the past 
and present inhabitants of the world should have been 
due to secondary causes, like those determining the 
birth and death of the individual, When I view all 
beings not as special creations, but as the lineal descend- 
ants of some tew being-s which lived long before the first 
bed of the Silurian system was deposited, they seem to 
me to become ennobled. Judging from the past, we may 
safely infer that not one living species will transmit 
its unaltered likeness to a distant futurity. And of the 
species now living very few will transmit progeny of 
any kind to a far distant futurity ; for the manner in 
which all organic beings are grouped, shows that the 
greater number of species of each genus, and all the 
species of many genera, have left no descendants, but 
have become utterly extinct. We can so far take a 
prophetic glance into futurity as to foretell that it will 
be the common and widely-spread species, belonging to 
the larger and dominant groups, which will ultimately 
prevail and procreate new and dominant species. As 
all the living forms of life are the lineal descendants of 
those which lived long before the Silurian epoch, we 
may feel certain that the ordinary succession by genera- 
tion 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 entangled 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, aud 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 with Reproduction ; Inheritance, 



RECAPITULATION AND CONCLUSION 441 

srhich is almost implied by reproduction ; Variability, 
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 
consequence 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 con- 
ceiving, 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, 
whilst this planet has gone cycling on according to the 
fixed law of gravity, from so simple a beginning endlc 
forms most beautiful and most wonderful have been, 
and are being, evolved. 



INDEX 



Aberrant groups, 386. 

Abyssinia, plants of, 336. 

Acclimatisation, 126. 

Affinities of extinct species, 295. 

of organic beings, 370. 

Agassiz on Amblyopsis, 126. 

on groups of species suddenly 

appearing, 271, 273. 

on embryological succession, 

303. 

on the glacial period, 328. 

on embryological characters, 

377. 

on the embryos of vertebrata, 

394. 

on parallelism of embryo- 
logical development and geo- 
logical succession, 404. 

Algae of New Zealand, 337. 

Alligators, males, fighting, 80. 

Amblyopsis, blind fish, 126. 

America, North, productions allied 
to those of Europe, 334. 

boulders and glaciers of, 

335. 



South, no modern formations 

on west coast, 260. 
Ammonites, sudden extinction of, 

288. 
Anagallis, sterility of, 222. 
Analogy of variations, 144. 
Ancylus, 346. 
Animals, not domesticated from 

being variable, 16. 
domestic, descended from 

several stocks, 17. 

acclimatisation of, 128. 



— of Australia, 105. 

— with thicker fur 
climates, 121. 

— blind, in caves, 124. 



in cold 



Animals, extinct, of Australia, 304. 

Anoinma, 216. 

Antarctic islands, ancient flora of, 

359. 
Antirrhinum, 146. 
Ants attending aphides, 189. 

slave-making instinct, 196. 

neuter, structure of, 212. 

Aphides, attended by ants, 189. 
Aphis, development of, 397. 
Apteryx, 164. 
Arab horses, 33. 
Aralo-Caspian Sea, 304. 
Archiac, M. de, on the succession 

of species, 291. 
Artichoke, Jerusalem, 129. 
Ascension, plants of, 350. 
Asclepias, pollen of, 174. 
Asparagus, 323. 
Aspicarpa, 376. 
Asses, striped, 147. 
Ateuchus, 123. 
Audubon on habits of frigate-bird, 

166. 
on variation in birds'-nests, 

190. 

on heron eating seeds, 348. 



Australia, animals of, 105. 

dogs of, 193. 

extinct animals of, 304. 

European plants in, 331. 

Azara on flies destroying cattle, 67. 
Azores, flora of, 326. 

Babington, Mr., on British plants, 

45. 
Balancement of growth, 133. 
Bamboo with hooks, 177. 
Barberry, flowers of, 89. 
Barrande, M., on Silurian colonies, 

281. 



443 



444 



ON THE ORIGIN OF SPECIES 



Sarrande, M., on the succession 

of species, 291. 
— — on parallelism of palaeozoic 

formations, 294. 
on affinities of ancient species, 

295. 
Barriers, importance of, 312. 
Batrachians on islands, 353. 
Bats, how structure acquired, 162. 

distribution of, 354. 

Bear catching water-insects, 165. 
Bee, sting of, 182. 

queen, killing rivals, 182. 

Bees fertilising flowers, 68. 

hive, not sucking the red 

clover, 86. 

hive, cell-making instinct, 

201. 

humble, cells of, 202. 

parasitic, 196. 

Beetles, wingless, in Madeira, 123. 

with deiicient tarsi, 122. 

Bentham, Mr., on British plants, 
45. 

on classification, 377. 

Berkeley, Mr., on seeds in salt- 
water, 322. 

Bermuda, birds of, 351. 

Birds acquiring fear, 190. 

annually cross the Atlantic, 

327. 

colour of, on continents, 120. 

footsteps and remains of, in 

secondary rocks, 272. 
fossil, in caves of Brazil, 304. 

of Madeira, Bermuda, and 

Galapagos, 351. 

song of males, 81. 

transporting seeds, 324. 

waders, 347. 

wingless, 122, 163. 

with traces of embryonic 

teeth, 405. 
Bizcacha, 314. 

affinities of, 3S6. 

Bladder for swimming in fish, 171. 
Blindness of cave animals, 124. 
Blyth, Mr., on distinctness of 

Indian cattle, 17. 

on striped Hemionus, 148 

on crossed geese, 227. 

Boar, shoulder-pad of, 80. 
Borrow, Mr., on the Spanish 

pointer, 32. 
Borv St. Vincent on Batrachians, 

353. 



Bosquet, M., on fossil Chthamalus, 

273. 
Boulders, erratic, on the Azores, 

326. 
Branchiae, 171. 
Brent, Mr., on house-tumblers, 

193. 

on hawks killing pigeons, 325. 

Brewer, Dr., on American cuckoo, 

195. 
Britain, mammals of, 355. 
Bronn on duration of specific 

forms, 263. 
Brown, Robert, on classification, 

374. 
Buckman on variation in plants, 10. 
Buzareingues on sterility of varie- 
ties, 242. 

Cabbage, varieties of, crossed, 90. 

Calceolaria, 226. 

Canary-birds, sterility of hybrids, 

226. 
Cape de Verde Islands, 358. 
Cape of Good Hope, plants of, 100, 

336. 
Carrier-pigeons killed by hawks, 

325. 
Cassini on flowers of compositee, 

131. 
Catasetum, 382. 
Cats, with blue eyes, deaf, 11. 

variation in habits of, 82. 

curling tail when going to 

spring, 181. 
Cattle destroying fir-trees, 66. 
destroyed by flies in La Plata, 

67. 

breeds of, locally extinct, 100. 

fertility of Indian and Euro- 
pean breeds, 228. 
Cave, inhabitants of, blind, 124. 
Centres of creation, 316. 
Cephalopoda}, development of, 397. 
Cervulus, 227. 

Cetacea, teeth and hair, 131. 
Ceylon, plants of, 3 
Chalk formation, 289. 
Characters, divergence of, 101. 

sexual, variable, 152. 

adaptive or analogical, 384. 

Charlock, 70. 

Checks to increase, 62. 

mutual, 07. 

Chickens, instinctive t*meuess of, 

194. 



indp:x 



446 



Chthamalinae, 259. 

Chthamalus, cretacean species of, 

273. 
Circumstances favourable to selec- 
tion of domestic products, 37. 

to natural selection, 92. 

Cirripedes capable of crossing, 91. 

carapace aborted, 134. 

their ovigerous frena, 172. 

fossil, 272. 

larvae of, 396. 

Classification, 370. 

Clift, Mr., on the succession of 

types, 304. 
Climate, effects of, in checking 

increase of beings, 63. 
adaptation of, to organisms, 

126. 
Cobites, intestine of, 171. 
Cockroach, 70. 
Collections, palaeontological, poor, 

258. 
Colour, influenced by climate, 

120. 
in relation to attacks by flies, 

178. 
Columba livia, parent of domestic 

pigeons, 21. 
Colymbetes, 346. 
Compensation of growth, 133. 
Composite, outer and inner florets 

of, 131. 

male flowers of, 406. 

Conclusion, general, 432. 
Conditions, slight changes in, 

favourable to fertility, 239. 
Coot, 167. 
Coral-islands, seeds drifted to, 

324. 
reefs, indicating movements 

of earth, 277. 
Corn-crake, 167. 
Correlation of growth in domestic 

productions, 11. 

of growth, 129, 178. 

Cowslip, 46. 

Creation, single centres of, 316. 
Crinum, 224. 
Crosses, reciprocal, 231. 
Crossing of domestic animals, im- 
portance in altering breeds, 18. 

advantages of, 88. 

unfavourable to selection, 92. 

Crustacea of New Zealand, 337. 
Crustacean, blind, 125. 
Cryptocerus, 214. 



Ctenomya, blind, 124. 
Cuckoo, instinct of, 195. 
Currants, grafts of, 235. 
Currents of sea, rate of, 323. 
Cuvier on conditions of existence. 
185. 

on fossil monkeys, 272. 

Fred., on instinct, 187. 

Dana, Prof., on blind cave-animals, 
126. 

on relations of crustaceans of 

Japan, 334. 
on crustaceans of New Zea- 
land, 337. 
De Candolle on struggle for exist- 
ence, 58. 

on umbelliferae, 132. 

on general affinities, 387. 

Alph., on low plants, widely 

dispersed, 865. 

on widely ranging plants 

being variable, 49. 

on naturalisation, 104. 
on winged seeds, 133. 
- on Alpine species sud- 
denly becoming rare, 157. 

on distribution of plants 

with large seeds, 324. 
on vegetation of Aus- 
tralia, 340. 
on fresh-water plants, 



347 



on insular plants, 349. 



Degradation of coast-rocks, 253. 
Denudation, rate of, 256. 

of oldest rocks, 276. 

Development of ancient forms,301. 
Devonian system, 299. 
Dianthus, fertility of crosses, 230. 
Dirt on feet of birds, 326. 
Dispersal, means of, 320. 

during glacial periods, 328. 

Distribution, geographical, 305. 

means of, 320. 

Disuse, effects of, under nature, 

122. 
Divergence of character, 101. 
Division, physiological, of labour, 

105. 
Dogs, hairless, with imperfect 

teeth, 11. 
descended from several wild 

stocks, 17. 

domestic instincts of, 192. 

inherited civilisation of, 193. 



446 



ON THE ORIGIN OF SPECIES 



Dogs, fertility of breeds together, 

228. 

of crosses, 240. 

proportions of, when young, 

399. 
Domestication, variation under, 7. 
Downing, Mr., on fruit-trees in 

America, 77. 
Downs, North and South, 256. 
Dragon-flies, intestiDes of, 171. 
Drift- timber, 324. 
Driver-ant, 216. 

Drones killed by other bees, 182. 
Duck, domestic, wings of, reduced, 

10. 

logger-headed, 163. 

Duckweed, 346. 
Dugong, affinities of, 373. 
Dung-beetles with deficient tarsi, 

122. 
Dyticus, 346. 

Earl, Mr. W., on the Malay Archi- 
pelago, 355. 

Ears, drooping, in domestic ani- 
mals, 11. 

rudimentary, 408. 

Earth, seeds in roots of trees, 324. 

Eciton, 214. 

Economy of organisation, 134. 

Edentata, teeth and hair, 131. 

fossil species of, 305. 

Edwards, Milne, on physiological 
divisions of labour, 105. 

on gradations of structure, 

174. 

on embryological characters, 

377. 

Eggs, young birds escaping from, 
79. 

Electric organs, 173. 

Elephant, rate of increase, 60. 



of glacial period, 128. 
Embryology, 394. 
Existence, struggle for, 56. 

conditions of, 185. 

Extinction, as bearing on natural 
selection, 99. 

of domestic varieties, 101. 

285. 

Eye, structure of, 168. 

correction for aberration, 181. 

Eyes reduced in moles, 124. 

Fabre, M., on parasitic sphex, 
196. 



Falconer, Dr., on naturalisation of 

plants in India, 60. 

on fossil crocodile, 281. 

on elephants and mastodons, 

300. 



and Cautley on mammals of 

sub-Himalayan beds, 305. 

Falkland Island, wolf of, 353. 

Faults, 255. 

Faunas marine, 313. 

Fear, instinctive, in birds, 190. 

Feet of birds, young molluscs ad- 
hering to, 346. 

Fertility of hybrids, 224. 

from slight changes in con- 
ditions, 239. 

of crossed varieties, 240. 

Fir-trees destroyed by cattle, 66. 

pollen of, 182. 

Fish, flying, 164. 

teleostean, sudden appearance 

of, 273. 

eating seeds, 325, 347. 

- fresh-water, distribution of, 



344. 
Fishes, ganoid, now confined to 

fresh water, 97. 

electric organs of, 173. 

ganoid, living in fresh water, 

288. 



of southern hemisphere, 337. 

Flight, powers of, how acquired, 

164. 
Flowers, structure of, in relation 

to crossing, 83. 
of compositae and umbel- 

liferse, 131. 
Forbes, E., on colours of shells, 

120. 

on abrupt range of shells in 



depth, 157. 
- on poorness 



of palaeonto- 



logical collections, 258. 

— on continuous succession of 
genera, 284. 

— on continental extensions, 



320. 



on distribution during glacial 



period, 329 
- on parallelism 



in time and 

space, 368 
Forests, changes in, in America, 

69. 
Formation. Devonian, 299. 
Formations, thickness of, in 

Britain, 254. 



INDEX 



447 



Formations, intermittent, 269. 
Formica rufescens, 190. 

sanguinea, 197. 

flava, neuter of, 215. 

Frena, ovigerous, of cirripedes, 

172. 
Fresh -water productions, dispersal 

of, 344. 
Fries on species in large genera 

being closely allied to other 

species, 52. 
Frigate-bird, 167. 
Frogs on islands, 353. 
Fruit- trees, gradual improvement 

of, 34. 

in United States, 77. 

varieties of, acclimatised 

in United States, 129. 
Fuci, crossed, 232. 
Fur, thicker in cold climates, 121. 
Furze, 395. 

Galapagos Archipelago, birds of, 

351. 

productions of, 358, 360. 

GaleopithecuB, 163. 

Game, increase of, checked by 

vermin, 63. 
Gartner on sterility of hybrids, 

221, 222. 

on reciprocal crosses, 232. 

on crossed maize and ver- 

bascum, 242. 
on comparison of hybrids and 

mongrels, 244. 
Geese, fertility when crossed, 227. 

upland, 167. 

Genealogy important in classifica- 
tion, 378. 
Geoffroy St. Hilaire on balance- 

ment, 133. 
on 

390. 



homologous organs, 



Isidore, on variability of 

repeated parts, 135. 

on correlation in mon- 
strosities, 11. 

on correlation, 130. 

on variable parts being 

often monstrous, 140. 

Geographical distribution, 305. 

Geography, ancient, 438. 

Geology, future progress of, 438. 

imperfection of the record, 

250. 

Giraffe, tail of, 175. 



Glacial period, 328. 
Gmelin on distribution, 328. 
Gnathodon, fossil, 330. 
Godwin-Austen, Mr., on the Mala) 

Archipelago, 268. 
Goethe on compensation of growth, 

133. 
Gooseberry, grafts of, 235. 
Gould, Dr. A., on land-shells, 356. 

Mr., on colours of birds, 120. 

on birds of the Galapagos, 



357. 
— on distribution 



of genera of 



birds, 303. 
Gourds, crossed, 242. 
Grafts, capacity of, 234. 
Grasses, varieties of, 103. 
Gray, Dr. Asa, on trees of United 

States, 91. 
on naturalised plants in the 

United States, 104. 
on rarity of intermediate 

varieties, 158. 

on Alpine plants, 328. 

— Dr. J. E., on striped mule, 



149. 
Grebe, 166. 

Groups, aberrant, 386. 
Grouse, colours of, 77. 

red, a doubtful species, 45. 

Growth, compensation of, 133. 
correlation of, in domestic 

products, 11. 
correlation of, 129. 



Habit, effect of, under domestica- 
tion, 10. 

effect of, under nature, 122. 

diversified, of same species, 

165. 

Hair and teeth, correlated, 131. 

Harcourt, Mr. E. V., on the birds 
of Madeira, 351. 

Hartung, M., on boulders in the 
Azores, 326. 

Hazel-nuts, 323. 

Hearne on habits of bears, 165. 

Heath, changes in vegetation, 66. 

Heer, O., on plants of Madeira, 
97. 

Helix pomatia, 357. 

Helosciadium, 323. 

Hemionus, striped, 149. 

Herbert, W., on struggle for exist- 
ence, 58. 

on sterility of hybrids, 224. 



448 



ON THE ORIGIN OF SPECIES 



Hermaphrodites crossing, 87. 
Heron eating seed, 348. 
Heron, Sir R., on peacocks, 81. 
Hensinger on white animals not 

poisoned by certain plants, 11. 
Hewitt, Mr., on sterility of first 

crosses, 237. 
Himalaya, glaciers of, 335. 

plants of, 336. 

Hippeastrum, 225. 
Holly-trees, sexes of, 84. 
Hollyhock, varieties of, crossed, 

243. 
Hooker, Dr., on trees of New 

Zealand, 91. 
on acclimatisation of Hima- 
layan trees, 127. 
— — on flowers of umbelliferse, 

131. 

on glaciers of Himalaya, 335. 

on algae of New Zealand, 337. 

on vegetation at the base of 

the Himalaya, 340. 
on plants of Tierra del Fuego, 

336. 339. 

Australian plants, 337, 



on 



359. 

— on relations of flora of South 
America, 340. 

— on flora of the Antarctic 



lands, 342, 359. 
— on the plants 
pagos, 352, 357. 



of the Gala- 



Hooks on bamboos, 177. 

to seeds on islands, 352. 

Horner, Mr., on the antiquity of 

Egyptians, 17. 
Horns, rudimentary, 408. 
Horse, fossil, in La Plata, 286. 
Horses destroyed by flies in La 

Plata, 67. 

striped, 148. 

proportions of, when young, 

400. 
Horticulturists, selection applied 

by, 30. 
Hnber on cells of bees, 207. 
P., on reason blended with 

instinct, 187. 
on habitual nature of in- 
stincts, 187. 
— — on slave-making ants, 197. 

on Melipona domestica, 202. 

Humble-bees, cells of, 202. 
Hunter, J., on secondary sexual 

characters, 136. 



Hutton, Captain, on crossed geese 

227. 
Huxley, Prof., on structure of 

hermaphrodites, 91. 
on embryological succession, 

303. 

on homologous organs, 394. 

on the development of apbis, 

397. 
Hybrids and mongrels compared, 

244. 
Hybridism, 220. 
Hydra, structure of, 171 

Ibla, 134. 

Icebergs transporting seeds, 326. 

Increase, rate of, 59. 

Individuals, numbers favourable 
to selection, 92. 

many, whether simultane- 
ously created, 319. 

Inheritance, laws of, 12. 

at corresponding ages, 13, 78. 

Insects, colour of, fitted for habi- 
tations, 77. 

sea-side, colours of, 120. 

blind, in caves, 125. 

luminous, 174. 

neuter, 212. 

Instinct, 186. 

Instincts, domestic, 193. 

Intercrossing, advantages of, 88. 

Islands, oceanic, 349. 

Isolation favourable to selection, 
95. 

Japan, productions of, 334. 

Java, plants of, 336. 

Jones, Mr. J. M., on the birds of 

Bermuda, 351. 
Jussieu on classification, 375. 

Kentucky, caves of, 124. 
Kerguelen-land, flora of, 342, 358. 
Kidney -bean, acclimatisation of, 

129. 
Kidneys of birds, 130. 
Kirby on tarsi deficient in beetles, 

122. 
Knight, Andrew, on cause of 

variation, 7. 
Kolreuter on the barberry, 89. 

on sterility of hybrids, 221. 

on reciprocal crosses, 282. 

on crossed varieties of nica- 

tiana, 243. 



INDEX 



149 



Kolreuter, on crossing male and 
hermaphrodite flowers, 405. 

Lamarck on adaptive characters, 

334. 
Land-shells, distribution of, 356. 

of Madeira, naturalised, 362. 

Languages, classification of, 3S0. 
Lapse, great, of time, 253. 
Larvae, 395. 
Laurel, nectar secreted by the 

leaves, S3. 
Laws of variation, 119. 
Leech, varieties of, 70. 
Leguminosae, nectar secreted by 

glands, 83. 
Lepidosiren, 97, 296. 
Life, struggle for, 56. 
Lingula, Silurian, 275. 
Linnaeus, aphorism of, 372. 
Lion, mane of, 80. 

young of, striped, 395. 

Lobelia fulgens, 68, 89. 
Lobelia, sterility of crosses, 224. 
Loess of the Rhine, 345. 
Lowness of structure connected 

with variability, 135. 
Lowness, related to wide distribu- 
tion, 364. 
Lubbock, Mr., on the nerves of 

coccus, 42. 
Lucas, Dr. P., on inheritance, 12. 
on resemblance of child to 

parent, 247. 
Lund and Clausen on fossils of 

Brazil, 304. 
Lyell, Sir C, on the struggle for 

existence, 58. 

on modern changes of the 

earth, 86. 

on measure of denudation, 

254. 

on a carboniferous land-shell, 

259. 

on strata beneath Silurian 

system, 275. 

on the imperfection of the 

geological record, 278. 
on the appearance of species, 

2S0. 
on Barrande's colonies, 281. 

on tertiary formations of 

Europe and North America, 
290. 

on parallelism of tertiary 

formations, 294. 



Lyell, Sir C, on transport of seeds 
by icebergs, 326. 

on great alternations of cli- 
mate, 343. 

on the distribution of fresh- 



water shells, 346. 

on land-shells of Madeira, 361. 



Lyell and Dawson on fossilised 
trees in Nova Scotia, 266. 

Macleay on analogical characters, 

3S4. 
Madeira, plants of, 97. 

beetles of, wingless, 123. 

fossil land-shells of, 304. 

birds of, 351. 

Magpie tame in Norway, 191. 

Maize, crossed, 242. 

Malay Archipelago compared with 

Europe, 26S. 

mammals of, 355. 

Malpighiaceae, 375. 
Mammae, rudimentary, 404. 
Mammals, fossil, in secondary 

formation, 272. 

insular, 353. 

Man, origin of races of, 179. 
Manatee, rudimentary nails of, 

408. 
Marsupials of Australia, 105. 

fossil species of, 304. 

Martens, M., experiment on seeds, 

323. 
Martin, Mr. W. C, on striped 

mules, 149. 
Matteucci, on the electric organs 

of rays, 173. 
Matthiola, reciprocal crosses of, 

232. 
Means of dispersal, 320. 
Melipona domestica, 202. 
Metamorphism of oldest rocks. 

276. 
Mice destroying bees, 68. 

acclimatisation of, 128. 

Migration, bears on first appear- 
ance of fossils, 267. 
Miller, Prof., on the cells of bees, 

203. 
Mirabilis, crosses of, 232. 
Missel-thrush, 70. 
Mistletoe, complex relations of, 3. 
Mississippi, rate of deposition at 

mouth, 255. 
Mocking thrush of the Galapagos, 

361. 



2g 



450 



ON THE ORIGIN OF SPECIES 



Modification of species, how far 
applicable, 435. 

Moles, blind, 124. 

Mongrels, fertility and sterility 
Of, 240. 

and hybrids compared, 244. 

Monkeys, fossil, 272. 

Monocanthus, 3S2. 

Mons, Van, on the origin of fruit- 
trees, 27. 

Moquin-Tandon on sea-side plants, 
120. 

Morphology, 390. 

Mozart, musical powers of, 188. 

Mud, seeds in, 347. 

Mules, striped, 149. 

Miiller, Dr. F., on Alpine Aus- 
tralian plants, 337. 

Murchison, Sir R., on the forma- 
tions of Russia, 259. 

on azoic formations, 275. 

on extinction, 285. 

Mustela vison, 161. 

Myanthus, 382. 

Myrmecocystus, 214. 

Myrmica, eyes of, 216. 

Nails, rudimentary, 408. 
Natural history, future progress 

of, 436. 

selection, 73. 

system, 372. 

Naturalisation of forms distinct 

from the indigenous species, 

104. 

in New Zealand, 181. 

Nautilus, Silurian, 275. 
Nectar of plants, 83. 
Nectaries, how formed, 84. 
Nelumbium luteum, 34S. 
Nests, variation in, 190. 
Neuter insects, 212. 
Newman, Mr., on humble-bees, 68. 
New Zealand, productions of, not 

perfect, 181. 

naturalised products of, 302. 

fossil birds of, 304. 

glacial action in, 335. 

crustaceans of, 337. 

algae of, 337. 

. number of plants of, 350. 

flora of, 359. 

Nicotiana, crossed varieties of, 

243. 
certain species very sterile, 

231. 



Noble, Mr., on fertility of Rhodo- 
dendron, 226. 

Nodules, phosphatic, in azoic 
rocks, 276. 

Oak, varieties of, 47. 

Onites apelles, 122. 

Orchis, pollen of, 174. 

Organs of extreme perfection, 167. 

electric, of fishes, 173. 

of little importance, 175. 

homologous, 390. 

rudiments of, and nascent, 

404. 
Ornithorhynchus, 97, 375. 
Ostrich not capable of flight, 122. 
habit of laying eggs together 

196. 
American, 

314. 
Otter, habits of, 

162. 
Ouzel, water, 166. 
Owen, Prof., on birds not flying, 

122. 

on vegetative repetition, 135. 

on variable length of arms in 

ourang-outang, 136. 
on the swim-bladder of fishes, 

172. 

— on electric organs, 173. 

on fossil horse of La Plata, 



two species of, 
how acquired, 



286. 

on relations of ruminants and 

pachyderms, 295. 

on fossil birds of New Zea- 
land, 304. 

on succession of types, 304. 

on affinities of the dugong, 

373. 

on homologous organs, 390. 

- on the metamorphosis of 



cephalopods and spiders, 397. 

Pacific Ocean, faunas of, 313. 
Paley on no organ formed to give 

pain, 181. 
Pallas on the fertility of the wild 

stocks of domestic animals, 228. 
Paraguay, cattle destroyed by 

flies, 6*7. 
Parasites, 196. 
Partridge, dirt on feet, 826. 
Parts greatly developed, variable, 

136. 
degrees of utility of, 181. 



INDEX 



451 



Parus major, 165. 
Passiflora, 225. 
Peaches in United States, 77. 
Pear, grafts of, 235. 
Pelargonium, flowers of, 132. 

sterility of, 226. 

Pelris of women, 130. 
Peloria, 132. 
Period, glacial, 328. 
Petrels, habits of, 166. 
Phasianus, fertility of hybrids, 

227. 
Pheasant, young, wild, 194. 
Philippi on tertiary species in 

Sicily, 280. 
Pictet, Prof. , on groups of species 

suddenly appearing, 271, 273. 

on rate of organic change, 

281. 

on continuous succession of 

genera, 284. 
on close alliance of fossils in 

consecutive formations, 301. 
on embryological succession, 

303. 
Pierce, Mr., on varieties of wolves, 

83. 
Pigeons with feathered feet and 

skin between toes, 11. 

breeds described, and origin 

of, 19. 

breeds of, how produced, 36, 

38. 

tumbler, not being able to 

get out of egg, 79. 

reverting to blue colour, 144. 

instinct of tumbling, 192. 

carriers, killed by hawks, 

325. 

young of, 400. 

Pistil, rudimentary, 405. 
Plants, poisonous, not affecting 
certain coloured animals, 11. 

selection applied to, 30. 

— — gradual improvement of, 34. 

not improved in barbarous 

countries, 35. 

destroyed by insects, 63. 

in midst of range, have to 

struggle with other plants, 71. 

nectar of, 83. 

fleshy, on sea-shores, 120. 

fresh-water, distribution of, 

347. 

low in scale, widely dis- 
tributed, 364. 



Plumage, laws of change in sexes 

of birds, 81. 
Plums in the United States, 77. 
Pointer dog, origin of, 32. 

habits of, 193. 

Poison not affecting certain 

coloured animals, 11. 

similar effect of, on animals 

and plants, 435. 

Pollen of fir-trees, 182. 

Poole, Col., on striped hemionus, 

149. 
Potamogeton, 348. 
Prestwich, Mr., on English and 

French eocene formations, 294. 
Primrose, 46. 

sterility of, 222. 

Primula, varieties of, 46. 

Proteolepas, 134. 

Proteus, 126. 

Psychology, future progress of, 

439. 

Quagga, striped, 148. 
Quince, grafts of, 235. 

Rabbit, disposition of young, 193. 

Races, domestic, characters of, 14. 

Race-horses, Arab, 33. 

EngliBh, 320. 

Ramond on plants of Pyrenees, 
330. 

Ramsay, Prof., on thickness of 
the British formations, 254. 

on faults, 255. 

Ratio of increase, 59. 

Rats, supplanting each other, 70. 

acclimatisation of, 128. 

blind, in cave, 125. 

Rattle-snake, 180. 

Reason and instinct, 187. 

Recapitulation, general, 413. 

Reciprocity of crosses, 231. 

Record, geological, imperfect, 250. 

Rengger on flies destroying cattle, 
67. 

Reproduction, rate of, 59. 

Resemblance to parents in mon- 
grels and hybrids, 245. 

Reversion, law of inheritance, 13. 

in pigeons to blue colour, 

144. 

Rhododendron, sterility of, 22 5. 
Richard, Prof., on Aspicarpa, 376. 
Richardson, Sir J., on structure 
of squirrels, 162. 



452 



ON THE ORIGIN OF SPECIES 



Richardson, Sir J., on fishes of 
the southern hemisphere, 337. 

Robinia, grafts of, 235. 

Rodents, blind, 124. 

Rudimentary organs, 404. 

Rudiments important for classi- 
fication, 374. 

Sagaret on grafts, 235. 

Salmons, males fighting, and 

hooked jaws of, 80. 
Salt-water, how far injurious to 

seeds, 322. 
Saurophagus sulphuratus, 165. 
Schiodte on blind insects, 125. 
Schlegel on snakes, 130. 
Sea-water, how far injurious to 

seeds, 322. 
Sebright, Sir J., on crossed 

animals, 19. 

on selection of pigeons, 29. 

Sedgwick, Prof., on groups of 

species suddenly appearing, 271. 
Seedlings destroyed by insects, 

63. 
Seeds, nutriment in, 71. 

winged, 133. 

power of resisting salt-water, 

322. 
— — in crops and intestines of 

bird3, 325. 

eaten by fish, 325, 347. 

in mud, 347. 

hooked, on islands, 352. 

Selection of domestic products, 

27. 
principle not of recent origin, 

31. 

unconscious, 32. 

natural, 73. 

sexual, 79. 

natural, circumstances 

favourable to, 92. 

Sexes, relations of, 79. 

Sexual characters variable, 142. 

selection, 79. 

Sheep, merino, their selection, 29. 

two sub-breeds unintention- 
ally produced, 33. 

mountain, varieties of, 70. 

Shells, colours of, 120. 

littoral, seldom embedded, 

258. 

fresh-water, dispersal of, 344. 

of Madeira, 350. 

land, distribution of. 357. 



Silene, fertility of crosses, 231. 
Silliman, Prof., on blind rat, 125. 
Skulls of young mammals, 177, 

392. 
Slave-making instinct, 196. 
Smith, Col. Ilamilton, on striped 

horses, 149. 

Mr. Fred., on slave-making 

ants, 197. 

■ on neuter ants, 215. 

Mr., of Jordan Hill, on the 

degradation of coast-rocks, 254. 

Snap-dragon, 146. 

Somerville, Lord, on selection of 

sheep, 29. 
Sorbus, grafts of, 235. 
Spaniel, King Charles's breed, 32. 
Species, polymorphic, 43. 

common, variable, 50. 

in large genera variable, 51. 

groups of, suddenly appear- 
ing, 271, 274. 

beneath Silurian formations, 

275. 
successively appearing, 280. 

changing simultaneously 

throughout the world, 289. 

Spencer, Lord, on increase in size 

of cattle, 33. 
Sphex, parasitic, 196. 
Spiders, development of, 397. 
Spitz-dog crossed with fox, 240. 
Sports in plants. 9. 
Sprengel, C. C, on crossing, 89. 

on ray-florets, 132. 

Squirrels, gradations in structure, 

162. 
Staffordshire heath, changes in, 

66. 
Stag-beetles, fighting, 80. 
Sterility from changed conditions 

of life, 8. 

. . of hybrids, 221. 

laws of, 228. 

causes of, 236. 

. — - from unfavourable conditions, 

238. 

■ of certain varieties, 242. 

St. Helena, productions of, 350. 
St. Hilaire, Aug., on classification, 

376. 
St. John. Mr., on habits of cats, 

83. 
Sting of bee, 182. 



Stocks, aboriginal, 
animals, 16. 



of domestio 



INDEX 



463 



Strata, thickness of, in Britain, 

254. 
Stripes on horses, 148. 
Structure, degrees of utility of, 181. 
Struggle for existence, 58. 
Succession, geological, 280. 
Succession of types in same areas, 

304. 
Swallow, one specie? supplanting 

&:i other, 70. 
Swim-bladder, 171. 
System, natural, 372. 

Tail of giraffe, 175. 

of aquatic animals, 176. 

rudimentary, 408. 

Tarsi deficient, 122. 

Tausch on umbelliferous flowers, 

132. 
Teeth and hair correlated, 131. 

embryonic, traces of, in birds, 

405. 

rudimentary, in embryonic 

calf, 405, 432. 

Tegetmeier, Mr., on cells of bees, 

204, 210. 
Temminck on distribution aiding 

classification, 377. 
Thouin on grafts, 235. 
Thrush, aquatic species of, 166. 
mocking, of the Galapagos, 



861. 



395. 



young of, spotted, 

nest of, 218. 

Thuret, M., on crossed fuci, 232. 
Thwaites, Mr. , on acclimatisation, 

127. 
Tierra del Fuego, doss of, 193. 

plants of, 339, 342. 

Timber-drift. 324. 
Time, lapse of, 253. 
Titmouse, 165. 

Toads on islands, 353. 

Tobacco, crossed varieties of, 243. 

Tomes, Mr., on the distribution of 

bats, 354. 
Transitions in varieties rare, 155. 
Trees on islands belong to peculiar 

orders, 352. 

with separated sexes, 90. 

Trifolium pratense, 68, 86. 

incarnatum, 86. 

Trigonia, 288. 
Trilobites, 275. 

sudden extinction of, 288. 

Troglodytes, 218. 



analogous 



Tucutucu, blind, 124. 
Tumbler pigeons, habits of, heredi- 
tary, 192. 

young of, 400. 

Turkey-cock, brush of hair on 

breast, 82. 
Turkey, naked skin on head, 177. 

young, wild, 194. 

Turnip and cabbage, 

variations of, 144. 
Type, unity of, 185. 
Types, succession of, in same 

areas, 304. 

Udders enlarged by use, 11. 

rudimentary, 405. 

Ulex, young leaves of, 395. 

Umbelliferse, outer and inner 
florets of, 131. 

Unity of type, 185. 

Use, effects of, under domestica- 
tion, 10. 

effects of, in a state of nature, 

122. 

Utility, how far important in the 
construction of each part, 179. 

Valenciennes on fresh-water fish, 
345. 

Variability -of mongrels and hy- 
brids, 244. 

Variation under domestication, 7. 

caused by reproductive sy- 
stem being affected by conditions 
of life, 8. 

under nature, 41. 

laws of, 119. 



Variations appearat corresponding 
ages, 13, 81. 

analogous in distinct species, 

144. 

Varieties, natural, 41. 
struggle between, 69. 

domestic, extinction of, 102. 

transitional, rarity of, 155. 

when crossed, fertile, 240. 

when crossed, sterile, 242. 

classification of, 380. 

Verbascum, sterility of. 225. 

varieties of, crossed, 242. 

Verneuil, M. de, on the succession 

of species, 291. 
Viola tricolor, 68. 
Volcanic islands, denudation of, 

255. 
Vulture, naked skin on head, 177. 



1o* 



ON THE ORIGIN OF SPECIES 



Wading-birds, 347. 
Wallace, Mr., on origin of species, 
1. 

on law of geographical dis- 
tribution, 319. 

on the Malay Archipelago, 

355. 
Wasp, sting of, 182. 
Water, fresh, productions of, 344. 
Water-hen, 167. 
Waterhouse, Mr., on Australian 

marsupials, 105. 

on greatly developed parts 

being variable, 136. 

on the cells of bees, 202. 

on general affinities, 386. 

Water-ouzel, 166. 

Watson, Mr. H. C, on range of 
varieties of British plants, 58. 

on acclimatisation, 127. 

on flora of A2ores, 826. 

on Alpine plants, 330, 838. 

on rarity of intermediate 

varieties, 158. 

Weald, denudation of, 256. 
Web of feet in water-birds, 166. 
West Indian islands, mammals of, 

354. 
Westwood on species in large 

genera being closely allied to 

others, 52. 

on the tarsi of Engidse, 142. 

— — on the antennae of hymen- 

opterous insects, 874. 
Wheat, varieties of, 103. 
White Mountains, flora of, 328. 
Wings, reduction of size, 122. 



Wings of insects homologous with 
branchiae, 172. 

rudimentary, in insects, 

405. 

Wolf crossed with dog, 192. 

of Falkland Isles, 353. 

Wollaston, Mr., on varieties of 

insects, 45. 

on fossil varieties of land- 
shells in Madeira, 48. 

on colours of insects on sea- 
shore, 120. 

on wingless beetles, 123. 

on rarity of intermediate 

varieties, 158. 

on insular insects, 849. 

on land-shells of Madeira, 

naturalised, 361. 

Wolves, varieties of, 83. 
Woodpecker, habits of, 166. 

green colour of, 177. 

Woodward, Mr., on the duration 

of specific forms, 268. 

on the continuous succession 

of genera, 284. 

on the succession of types, 

304. 

World, species changing simul- 
taneously throughout, 289. 
Wrens, nest of, 218. 

Youatt, Mr., on selection, 28. 

on sub-breeds of sheep, S3. 

on rudimentary horns in 

young cattle, 408. 

Zebra, stripes on, 147. 



THE END 



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The World's Classics 



List of Titles 

•l. Charlotte Bronte's Jane Eyre. Fourth Impression. 
*2. Lamb's Essays of Elia. Fifth Impression. 

Tennyson's Poems, 1830 -1865. With an Introduction 
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*4. Goldsmith's Vicar of Wakefield. Third Impression. 

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*8. Dickens's Oliver Twist. With 24 Illustrations by 
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*n. Darwin's Origin of Species. Fourth Impression. 
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*I3. English Songs and Ballads. Compiled by T. W. H 

Crosland. Third Impression. 
♦14. Charlotte Bronte's Shirley. Third Impression. 
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*i6. Herrick's Poems. Second Impression. 
*I7. Defoe's Robinson Crusoe. Second Impression. 
*i8. Pope's Iliad of Homer. Third Impression. 
*ig. Carlyle's Sartor Resartus. Third Impression. 

20. Swift's Gulliver's Travels. Second Impression. 
*2i. Poe's Tales of Mystery and Imagination. Third Imp. 
*22. White's Natural History of Selborne. Second Imp. 
*23. De Quincey's Opium Eater. Third Impression. 
"■24. Bacon's Essays. Third Impression. 
*25. Hazlitt's Winterslow. Second Impression. 

26. Hawthorne's Scarlet Letter. Second Impression. 
*27. Liacaulay's Lays of Ancient Rome. Second Impression 
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29. Scott's Ivanhoe. Second Impression. 
*30. Emerson's English Traits, and Representative Men. 

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♦32. Selected English Essays. Chosen and Arranged by 
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3 



The World's Classics 

List of Titles {continued) 

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*35> *44» *5 X ' *55> *^4» *^9» *74« Gibbon's Roman Empire* 

Seven Vols., with Maps. Vols. I, II, Third Impression. 

III-V, Second Impression. 
♦36. Pope's Odyssey of Homer. Second Impression. 
♦37. Dryden's Virgil. Second Impression. 
♦38. Dickens's Tale of Two Cities. Third Impression. 
♦39. Longfellow's Poems. Vol. 1. Second Impression. 
*40. Sterne's Tristram Shandy. Second Impression. 
•41, *48, *53. Buckle's History of Civilization in England. 

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♦46. Essays and Letters by Leo Tolstoy. Translated by 

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♦47. Charlotte Bronte's Villette. Second Impression. 
*4 o. A Kempis's Of the Imitation of Christ. Second Imp. 
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•53. Watts-Dunton's Aylwin. Third Impression. 
*54» *59- Adam Smith's Wealth of Nations. Two Vols. 

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♦57. Hazlitt's Spirit of the Age. Second Impression. 
*58. Robert Browning's Poems. Vol. I. Second Impression. 
*6o.' The Thoughts of Marcus Aurelius. A new transla- 
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*6l Holmes's Autocrat of the Breakfast-Table. Second 

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•62. Carlyle's On Heroes and Hero-Worship. Second 

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•63. George Eliot's Adam Bede. Second Impression. 
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♦71, *8i, *ni-*ii4. Burke's Works. Six Vols. With Prefaces 

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6 



The World's Classics 

List of Titles (continued) 

*I37. Browning's Poems. Vol. II (Dramatic Lyrics and 

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and Notes by J. Fitzmaurice-Kelly. Two Vols. 
*I53. Carlyle's Past and Present. Introduction by G. K. 

Chesterton. 
*I54. Mrs. Gaskell's North and South. Introduction by 

Clement Shorter. 

♦155. George Eliot's Scenes of Clerical Life. Intro, by 
Annie Matheson. 

*I56. Mrs. Gaskell's Sylvia's Lovers. Introduction by 

Clement Shorter. 
♦157. Mrs. Gaskell's Wives and Daughters. Introduction 

by Clement Shorter. 

*I58. Lord Dufferin's Letters from High Latitudes. Illus- 
trated. Introduction by R. W. Macan. 

7 



The World's Classics 

List of Titles (continued) 

15 9. Grant's Captain of the Guard. 

160. Marryat's Mr. Midshipman Easy. 

161. Jane Porter's The Scottish Chiefs. 

162. Ainsworth's The Tower of London. 

163. Cooper's The Last of the Mohicans. 

164. Marryat's The King's Own. With 6 Illustrations by 

Warwick Goble. 

*i65. Lytton's Harold. With 6 Illustrations by Charles 
Burton. 

166. Mayne Reid's The Rifle Rangers. With 6 Illustra- 

tions by J. E. Sutcliffe. 

167. Mayne Reid's The Scalp Hunters. With 6 Illustra- 

tions by A. H. Collins. 

*iQ8. Mrs. Gaskell's Cousin Phillis, and other Tales, &c. 

With an Introduction by Clement Shorter. 

*l69. Southey's Letters. Selected, with an Introduction, and 
Notes by Maurice H. FitzGerald. [In preparation. 

Other volumes in preparation. 

Bookcases 

In Two Sizes 

i. To hold 50 Volumes ordinary paper, or 100 Volumes 
thin paper, World's Classics size. 

In Fumed Oak, with two fixed shelves. Size 22x212*4! 
inches. Price 5*. net. 

si. To hold IOO Volumes ordinary paper, or 200 Volumes 
thin paper, World's Classics size. 

In Polished Mahogany or Mahogany French Stained and 
Ebonized, with fancy ornamental top, and three adjust- 
able shelves, best cabinet make. Size 44 x 36 x 6 inches 
Price 2 8 s. net. 

8