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

c

-^AITUE

EGGI'Mj

foO, RUE DU MAK

G K N JZ

-

<C^ - ^ £ Lui<2 t }VXDC

■*K

s*>

^

N

\

'a

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

1

7

41
56
73
119
154
186
220

250

280
311
344

370
413
443

iNawBPPp^fcH

5

v.

a
c:

»j-

w

c

a.
E

E

■ to

^

is.

4

^

O*

/6,

- -

to

■6

. S

1.

'

*

.-'■

63

\e

- J-
id.

-as-
-a-

-6,-

BO-

SS

o
o

ft

0>
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. fThe monarchs
of Iran and Turan sent him some very rare birds';
and, continues the courtly historian, fHis 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

belong1 to poor people, and are mostly in small lotst
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, a1 and m1. 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 a1 is supposed in the diagram to have
produced variety a2, which will, owing to the principle
of divergence, differ more from (A) than did variety a1.
Variety m1 is supposed to have produced two varieties,
namely raa and s2, 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 a1 to a10.
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, a10,/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 a14 and m14, 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 (w10 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 ra14
to zu, 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 (a14 to m14) ; and
(I) will have been replaced by six (nu 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 a14 and z14 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 a14, qu,
pH, will be nearly related from having recently
branched off from a10; bu and/14, from having diverged
at an earlier period from a6, will be in some degree dis-
tinct from the three first-named species ; and lastly,
o14, eu, and m14, will be nearly related one to the other,
but from having diverged at the first commencement of
the process of modification, will be widely different from
the other five species, and may constitute a sub-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 (f14) 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 f1*, and those marked o u to
m14, 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 having1 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
carrying1 (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 interesting1 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,
a14, <j14, p14, will form a small family ; 614 and /14 a
closely allied family or sub-family ; and o14, eu, m14, 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 f14.

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 a1, a5,
al0> fS) 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, a14, etc., and &14, etc.) would have to be
united into one family ; and the two other families
(namely, a14 to fu now including five genera, and ou
to mli) 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

having1 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. — rrhe 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 having1 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. \Yre 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
trifling1 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 (a14 to
zu) 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 classifying1 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 leading1 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 being1, 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

The

World's Classics

(Size 6x4 Inches)

ORDINARY EDITION

Published in NINE different styles :-

Cloth Boards, gilt back ....

1/- net

Sultan-red Leather, limp, gilt top .

1 6 net

Buckram, paper label, gilt top

1 6 net

Quarter Parchment, gilt top .

1 8 net

Lambskin, limp, gilt top

2, - net

Quarter Vellum, hand-tooled, panelled

lettering-piece, gilt top. Superior

library style .....

4/- net

Half Calf, marbled edges

4/- net

Whole Calf, marbled edges .

5/6 net

Tree Calf, marbled edges

56 net

1*

POCKET EDITION

of THE WORLD'S CLASSICS {each with c

^portrait)

is being printed on THIN PAPER, by means of which
the bulk of the stouter volumes is reduced by o?ie-half.

Limp Cloth, gilt back, gilt top . 1/- net

Sukan-red Leather, limp, gilt top . . 1/6 net
Quarter Vellum, hand-tooled, panelled

lettering-piece, gilt tor> . . . 4/- net

OF ALL BOOKSELLERS

HENRY FROWDE

OXFORD UNIVERSITY PRESS

LONDON, NEW YORK, TORONTO & MELBOURNE

The World's Classics

THE best recommendation of The World's
Classics is the books themselves, which
have earned unstinted praise from critics and all
classes of the public. Some two million copies
have been sold, and of the 162 volumes pub-
lished nearly one-half have gone into a second,
third, fourth, fifth, sixth, seventh, or eighth
impression. It is only possible to give so much
for the money when large sales are certain.
The absolute uniformity throughout the series,
the clearness of the type, the quality of the paper,
the size of the page, the printing, and the binding
— from the cheapest to the best — cannot fail to
commend themselves to all who love good litera-
ture presented in worthy form. That a high
standard is insisted upon is proved by the list of
books already published and of those on the eve
of publication. A great feature is the brief critical
introductions written by leading authorities of the
day. The volumes of The World's Classics are
obtainable in a number of different styles, the
description and prices of which are given on
page 1 ; but special attention may be called to
the sultan-red, limp leather style, which is un-
surpassable in leather bindings at the price of 1/6
net.

The Pocket Edition is printed on thin
opaque paper, by means of which the bulk is
greatly reduced, and the volumes marked with
an asterisk are now ready in this form.

August, 191 1.

$

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
by T. H. Warren. Sixth Impression.

*4. Goldsmith's Vicar of Wakefield. Third Impression.

*5. Hazlitt's Table-Talk. Fourth Impression.

*6. Emerson's Essays. 1st and 2nd Series. Fifth Impression.

♦7. Keats's Poems. Third Impression.

*8. Dickens's Oliver Twist. With 24 Illustrations by
George Cruikshank. Third Impression.

*g. Barham's Ingoldsby Legends. Fourth Impression.
*io. Emily Bronte's Wuthering Heights. Third Imp.
*n. Darwin's Origin of Species. Fourth Impression.
*I2. Bunyan's Pilgrim's Progress. Second Impression.
*I3. English Songs and Ballads. Compiled by T. W. H

Crosland. Third Impression.
♦14. Charlotte Bronte's Shirley. Third Impression.
♦15. Hazlitt's Sketches and Essays. Third Impression.
*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
*28. Thackeray's Henry Esmond. Third Impression.

29. Scott's Ivanhoe. Second Impression.
*30. Emerson's English Traits, and Representative Men.

Second Impression.
♦31. George Eliot's Mill on the Floss. Third Impression.
♦32. Selected English Essays. Chosen and Arranged by
W. Peacock. Eighth Impression.

3

The World's Classics

List of Titles {continued)

33. Home's Essays. Second Impression.
*34. Burns's Poems. Second Impression.

*35> *44» *5X' *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.

Three Vols. Vol.I.Third Imp. Vols.II and III, Second Imp.
*42, *56, *76. Chaucer's Works. From the Text of Prof.

Skeat. Three Vols. Vol. I, Second Impression.
♦43. Machiavelli's The Prince. Translated by Luigi Ricci.

Second Impression.
•45. English Prose from Mandeville to Ruskin. Chosen

and arranged by W. Peacock. Third Impression.
♦46. Essays and Letters by Leo Tolstoy. Translated by

Aylmer Maude. Third Impression.
♦47. Charlotte Bronte's Villette. Second Impression.
*4 o. A Kempis's Of the Imitation of Christ. Second Imp.
♦50. Thackeray '8 Book of Snobs, and Sketches and

Travels in London. Second Impression.
•53. Watts-Dunton's Aylwin. Third Impression.
*54» *59- Adam Smith's Wealth of Nations. Two Vols.

Second Impression.
♦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-
tion by John Jackson. Second Impression.
*6l Holmes's Autocrat of the Breakfast-Table. Second

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

Impression.
•63. George Eliot's Adam Bede. Second Impression.
♦65, *70, *77. Montaigne's Essays. Florio's trans. 3 Vols.
*66. Borrow's Lavengro. Second Impression.
♦67. Anne Bronte's Tenant of Wildfell Hall.
♦68. Thoreau's Walden. Intro, by T. Watts-Donton.

The World's Classics

List of Titles {continued)

♦71, *8i, *ni-*ii4. Burke's Works. Six Vols. With Prefaces

by Judgb Willis, F. W. Raffety, and F. H. Willis.
♦72. Twenty-three Tales by Tolstoy. Tr.byL.and A.Maudk.

Second Impression.
•73. Borrow's Romany Rye.
♦75. Borrow's Bible in Spain.
♦78. Charlotte Bronte's The Professor, and the Poems

of C.,£., and A. Bronte. Intro, by T.Watts-Dunton.
♦79. Sheridan's Plays. Introduction by Joseph Knight.
*8o. George Eliot's Silas Marner, The Lifted Veil,

Brother Jacob. Intro, by T. Watts-Dunton.
•82. Defoe's Captain Singleton. With an Introduction by

Theodore Watts-Dunton.
♦83, *84- Johnson's Lives of the Poets. With an Introduc-
tion by Arthur Waugh. Two Vols.
♦85. Matthew Arnold's Poems. With an Introduction by

Sir A. T. Quiller-Couch.
♦86. Mrs. Gaskell's Mary Barton. With an Introduction by

Clement Shorter.
•87. Hood's Poems. Edited by Walter Jerrold.
*88. Mrs. Gaskell's Ruth, Intro, by Clement Shorter.
♦89. Holmes's Professor at the Breakfast-Table. With

an Introduction by Sir W. Robertson Nicoll.
♦go. Smollett's Travels through France and Italy. With

an Introduction by T. Seccombe.

*qi,*92. Thackeray's Pen dennis. Intro, by E. Gosse. 2 Vols.

*93. Bacon's Advancement of Learning, and The New
Atlantis. With an Introduction by Professor Case.

♦94. Scott's Lives of the Novelists. With an Introduction
by Austin Dobson.

•95. Holmes's Poet at the Breakfast-Table. With an
Introduction bv Sir W. Robertson Nicoll.

*96, *97, *g8. Motley's Rise of the Dutch Republic With
an Introduction by Clement Shorter. Three Vols.

*99- Coleridge's Poems. Intro, by Sir A.T. Quiller-Couch.

*ioo-*io8. Shakespeare's Plays and Poems. With a Pre-
face by A. C. Swinburne, a Note by T. Watts-Dunton
on the special typographical features of this edition, and
Introductions to the several plays by E. Dowden. Nine
Volumes. Vols. 1-6 now ready. Vols. 7-9 ready shortly.

The World's Classics

List of Titles {continued)

♦109. George Herbert's Poems. Intro, by Arthur Wadgh.

*iio. Mrs. Gaskell's Cranford, and The Moorland Cottage.
With an Introduction by Clement Shorter.

*H5. Essays and Sketches by Leigh Hunt. With an
Introduction by R. Brimley Johnson.

*ii6. Sophocles. The Seven Plays. Translated into English
Verse by Professor Lewis Campbell.

♦117. Aeschylus. The Seven Plays. Translated into English
Verse by Professor Lewis Campbell.

*ii8. Horae Subsecivae. By Dr. John Brown. With an
Introduction by Austin Dobson.

*ng. Cobbold's Margaret Catchpole. With an Introduction
by Clement Shorter.

*I2o, *i2i. Dickens's Pickwick Papers. With 43 illustra-
tions by Seymour and ' Phiz '. Two Vols.

*i22. Mrs. Caudle's Curtain Lectures, and other Stories
and Essays, by Douglas Jerrold. With an Intro-
duction by Walter Jerrold, and 90 illustrations.

*I23. Goldsmith's Poems. Edited by Austin Dobson.

*i24. Hazlitt's Lectures on the English Comic Writers.
With an Introduction by R. Brimley Johnson.

*I25, *I26. Carlyle's French Revolution. With an Intro-
duction by C. R. L. Fletcher. Two Vols.

♦127. Home's New Spirit of the Age. With an Intro-
duction by Walter Jerrold.

*i28. Dickens's Great Expectations. 6 Illus. by W. Goble.

*I2Q. Jane Austen's Emma. Intro, by E. V. Lucas.

♦130, *I3I. Don Quixote. Jervas's translation. With an Intro.
and Notes by J. Fitzmaurice-Kelly. Two Vols.

*I32. Leigh Hunt's The Town. With an Introduction and

Notes by Austin Dobson, and a Frontispiece.
*I33. Palgrave's Golden Treasury, with additional Poems.
Fifth Impression.

•134. Aristophanes. Frere's translation of the Achar-
nians, Knights, Birds, and Frogs. With an Intro-
duction by W. W. Merry.
♦135. Marlowe's Dr. Faustus, and Goethe's Faust, Part I

(Anster's Translation). Intro, by A. W. Ward.
♦136. Butler's Analogy. Ed. W. E. Gladstone.

6

The World's Classics

List of Titles (continued)

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

Romances, Men and Women, and Dramatis Personae).
♦138. Cowper's Letters. Selected, with an Introduction, by

E. V. Lucas.
*I39. Gibbon's Autobiography. With Intro, by J. B. Bury.
♦140. Trollope's The Three Clerks. With an Introduction

by W. Teignmouth Shore.
♦141. Anne Bronte's Agnes Grey.
♦142. Fielding's Journal of a Voyage to Lisbon. With

Intro, and Notes by Austin Dobson, and 2 Illustrations.
♦143. Wells's Joseph and his Brethren. Introduction by

A. C. Swinburne, and a Note on Rossetti and Charles

Wells by Theodore Watts-Dunton.
*I44. Carlyle's Life of John Sterling. With an Intro-
duction by W. Hale White.
*I45. Ruskin's Sesame and Lilies, and The Ethics 01

the Dust. Ruskin House edition.
*I46. Ruskin's Time and Tide, and The Crown of Wild

Olive. Ruskin House edition.
♦147. Ruskin's A Joy for Ever, and The Two Paths.

With 12 Illustrations. Ruskin House edition.
*I48. Ruskin's Unto this Last, and Munera Pulveris.

Ruskin House edition.
♦149. Reynolds's Discourses. Intro. Austin Dobson.
♦150. Washington Irving's Conquest of Granada
*I5I, *I52. Lesage's Gil Bias. (Smollett's translation.) Intro.

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