On the Origin of Species
Charles Darwin

On the Origin of Species

by Charles Darwin





'But with regard to the material world, we can at least go so far as this--
we can perceive that events are brought about not by insulated
interpositions of Divine power, exerted in each particular case, but by the
establishment of general laws.'

W. Whewell: Bridgewater Treatise.



'To conclude, therefore, let no man out of a weak conceit of sobriety, or
an ill-applied moderation, think or maintain, that a man can search too far
or be too well studied in the book of God's word, or in the book of God's
works; divinity or philosophy; but rather let men endeavour an endless
progress or proficience in both.'

Bacon: Advancement of Learning.




Down, Bromley, Kent, 

October 1st, 1859.




On the Origin of Species by Means of Natural Selection, 

or the

Preservation of Favoured Races in the Struggle for Life.

By Charles Darwin




Contents


Introduction



Chapter I

Variation under Domestication

Causes of Variability -- Effects of Habit -- Correlation of Growth --
Inheritance -- Character of Domestic Varieties -- Difficulty of
distinguishing 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.



Chapter II

Variation under Nature

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.



Chapter III

Struggle for Existence

Bears on natural selection -- The term used in a wide sense -- Geometrical
powers of increase -- Rapid increase of naturalised animals and plants --
Nature of the checks to increase -- Competition universal -- Effects of
climate -- Protection from the number of individuals -- Complex relations
of all animals and plants throughout nature -- Struggle for life most
severe between individuals and varieties of the same species; often severe
between species of the same genus -- The relation of organism to organism
the most important of all relations.



Chapter IV

Natural Selection

Natural Selection -- its power compared with man's selection -- its power
on characters of trifling importance -- its power at all ages and on both
sexes -- Sexual Selection -- On the generality of intercrosses between
individuals of the same species -- Circumstances favourable and
unfavourable to Natural Selection, namely, intercrossing, isolation, number
of individuals -- Slow action -- Extinction 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.



Chapter V

Laws of Variation

Effects of external conditions -- Use and disuse, combined with natural
selection; organs of flight and of vision -- Acclimatisation -- 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.



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 non facit saltum --
Organs of small importance -- Organs not in all cases absolutely perfect --
The law of Unity of Type and of the Conditions of Existence embraced by the
theory of Natural Selection.



Chapter VII

Instinct

Instincts 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 -
- Difficulties on the theory of the Natural Selection of instincts --
Neuter or sterile insects -- Summary.



Chapter VIII

Hybridism

Distinction between the sterility of first crosses and of hybrids --
Sterility various in degree, not universal, affected by close
interbreeding, removed by domestication -- Laws governing the sterility of
hybrids -- Sterility not a special endowment, but incidental on other
differences -- Causes of the sterility of first crosses and of hybrids --
Parallelism between the effects of changed conditions of life and crossing
-- Fertility of varieties when crossed and of their mongrel offspring not
universal -- Hybrids and mongrels compared independently of their fertility
-- Summary.



Chapter IX

On the Imperfection of the Geological Record

On the absence of intermediate varieties at the present day -- On the
nature of extinct intermediate varieties; on their number -- On the vast
lapse of time, as inferred from the rate of deposition and of denudation --
On the poorness of our palaeontological collections -- On the intermittence
of geological formations -- On the absence of intermediate varieties in any
one formation -- On the sudden appearance of groups of species -- On their
sudden appearance in the lowest known fossiliferous strata.



Chapter X

On the Geological Succession of Organic Beings

On the slow and successive appearance of new species -- On their different
rates of change -- Species once lost do not reappear -- Groups of species
follow the same general rules in their appearance and disappearance as do
single species -- On Extinction -- On simultaneous changes in the forms of
life throughout the world -- On the affinities of extinct species to each
other and to living species -- On the state of development of ancient forms
-- On the succession of the same types within the same areas -- Summary of
preceding and present chapters.



Chapter XI

Geographical Distribution

Present distribution cannot be accounted for by differences in physical
conditions -- Importance of barriers -- Affinity of the productions of the
same continent -- Centres of creation -- Means of dispersal, by changes of
climate and of the level of the land, and by occasional means -- Dispersal
during the Glacial period co-extensive with the world.



Chapter XII

Geographical Distribution -- continued

Distribution of fresh-water productions -- On the inhabitants of oceanic
islands -- Absence of Batrachians and of terrestrial Mammals -- On the
relation of the inhabitants of islands to those of the nearest mainland --
On colonisation from the nearest source with subsequent modification --
Summary of the last and present chapters.



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.



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 extended -- Effects of its adoption on
the study of Natural history -- Concluding remarks.




On the Origin 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 to me a memoir on
this subject, with a request that I would forward it to Sir Charles Lyell,
who sent it to the Linnean Society, and it is published in the third volume
of the Journal of that Society.  Sir C. Lyell and Dr. Hooker, who both knew
of my work--the latter having read my sketch of 1844--honoured me by
thinking it advisable to publish, with Mr. Wallace's excellent memoir, some
brief extracts from my manuscripts.

This Abstract, which I now publish, must necessarily be imperfect.  I
cannot here give references and authorities for my several statements; and
I must trust to the reader reposing some confidence in my accuracy.  No
doubt errors will have crept in, though I hope I have always been cautious
in trusting to good authorities alone.  I can here give only the general
conclusions at which I have arrived, with a few facts in illustration, but
which, I hope, in most cases will 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 assistance which I have received from very many
naturalists, some of them personally unknown to me.  I cannot, however, let
this opportunity pass without expressing my deep obligations to Dr. Hooker,
who for the last fifteen years has aided me in every possible way by his
large stores of knowledge and his excellent judgment.

In considering the Origin of Species, it is quite conceivable that a
naturalist, reflecting on the mutual affinities of organic beings, on their
embryological relations, their geographical distribution, geological
succession, and other such facts, might come to the conclusion that each
species had not been independently created, but had descended, like
varieties, from other species.  Nevertheless, such a conclusion, even if
well founded, would be unsatisfactory, until it could be shown how the
innumerable species inhabiting this world have been modified, so as to
acquire that perfection of structure and coadaptation which most justly
excites our admiration.  Naturalists continually refer to external
conditions, such as climate, food, &c., as the only possible cause of
variation.  In one very limited sense, as we shall hereafter see, this may
be true; but it is preposterous to 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 misseltoe, 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 misseltoe, 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 coadaptation.  At the commencement of my
observations it seemed to me probable that a careful study of domesticated
animals and of cultivated plants would offer the best chance of making out
this obscure problem.  Nor have I been disappointed; in this and in all
other perplexing cases I have invariably found that our 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 Domestication.  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 enabled 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 their
high geometrical powers of 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 profitable 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 inevitably causes much Extinction of the less improved forms of life
and induces what I have called Divergence 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 transitions, or in understanding how a simple
being or a simple organ can be changed and perfected into a highly
developed being or elaborately constructed organ; secondly the subject of
Instinct, or the mental powers of animals, thirdly, Hybridism, or the
infertility of species and the fertility of varieties when 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 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
distinguishing 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 much 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 greater
variability is simply due to our domestic productions having been raised
under conditions of life not so uniform as, and somewhat different from,
those to which the parent-species have been exposed under nature.  There
is, also, I think, some probability in the view 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
generally continues to vary for many generations.  No case is on record of
a variable being ceasing to be variable under cultivation.  Our oldest
cultivated plants, such as wheat, still often yield new varieties:  our
oldest domesticated animals are still capable of rapid improvement or
modification.

It has been disputed at what period of life the causes of variability,
whatever they may be, generally act; whether during the early or late
period of development of the embryo, or at the instant of conception. 
Geoffroy St. Hilaire's experiments show that unnatural treatment of the
embryo causes monstrosities; and monstrosities cannot be separated by any
clear line of distinction from mere variations.  But I am strongly inclined
to suspect that the most frequent cause of variability may be attributed to
the male and female reproductive elements having been affected prior to the
act of conception.  Several reasons make me believe in this; but the chief
one is the remarkable effect which confinement or cultivation has on the
functions of the reproductive system; this system appearing to be far more
susceptible than any other part of the organisation, to the action of any
change in the conditions of life.  Nothing is more easy than to tame an
animal, and few things more difficult than to get it to breed freely under
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 confinement in their native country!  This is generally
attributed to vitiated instincts; but how many cultivated plants display
the utmost vigour, and yet rarely or never seed!  In some few such cases it
has been found out that very trifling changes, such as a little more or
less water at some particular period of growth, will determine whether or
not the plant sets a seed.  I cannot here enter on the copious details
which I have collected on this curious subject; but to show how singular
the laws are which determine the reproduction of animals under confinement,
I may just mention that carnivorous animals, even from the tropics, breed
in this country pretty freely under confinement, with the exception of the
plantigrades or bear family; whereas, carnivorous birds, with the rarest
exceptions, hardly ever lay fertile eggs.  Many exotic plants have pollen
utterly worthless, in the same exact condition as in the most sterile
hybrids.  When, on the 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 unperceived causes as to fail in acting, we need not be
surprised at this system, when it does act under confinement, acting not
quite regularly, and producing offspring not perfectly like their parents
or variable.

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 most freely under the most unnatural
conditions (for instance, the rabbit and ferret kept in hutches), showing
that their reproductive system has not been thus affected; so will some
animals and plants withstand domestication or cultivation, and vary very
slightly--perhaps hardly more than in a state of nature.

A long list could easily be given of 'sporting plants;' by this term
gardeners mean a single bud or offset, which suddenly assumes a new and
sometimes very different character from that of the rest of the plant. 
Such buds can be propagated by grafting, &c., and sometimes by seed.  These
'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 attributed to the
ovules or pollen, or to both, having been affected by the treatment of the
parent prior to the act of conception.  These cases anyhow show that
variation is not necessarily connected, as some authors have supposed, with
the act of generation.

Seedlings from the same fruit, and the young of the same litter, sometimes
differ considerably from each other, though both the young and the parents,
as Muller has remarked, have apparently been exposed to exactly the same
conditions of life; and this shows how unimportant the direct effects of
the conditions of life are in comparison with the laws of reproduction, and
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, &c.,
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 seem 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 particular kinds of
food and from light, and perhaps the thickness of fur from climate.

Habit also has a deciding influence, as in the period of flowering with
plants when transported from one climate to another.  In animals it has a
more marked effect; for instance, I find in the domestic duck that the
bones of the wing weigh less and the bones of the leg more, in proportion
to the whole skeleton, than do the same bones in the wild-duck; and I
presume that this change may be safely attributed to the domestic duck
flying much less, and walking more, than its wild parent.  The great and
inherited development of the udders in cows and goats in countries where
they are habitually milked, in comparison with the state of these organs in
other countries, is another instance of the effect of use.  Not a single
domestic animal can be named which has not in some country drooping ears;
and the view suggested by some authors, that the drooping is due to the
disuse of the muscles of the ear, from the animals not being much alarmed
by danger, seems probable.

seen, and will be hereafter briefly mentioned.  I will here only allude to
what may be called correlation of growth.  Any change in the embryo or
larva will almost certainly entail changes in the mature animal.  In
monstrosities, the correlations between quite distinct parts are very
curious; and many instances are given in Isidore Geoffroy 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 appears that white sheep and pigs are differently affected
from coloured individuals by certain vegetable poisons.  Hairless dogs have
imperfect teeth; long-haired and coarse-haired 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 cultivated plants,
as on the hyacinth, potato, even the dahlia, &c.; 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 a
deviation appears not unfrequently, and we see it in the father and child,
we cannot tell whether it may not be due to the same original cause acting
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, &c.,
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 the
same peculiarity in different individuals of the same species, and 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 much more remote ancestor; why a peculiarity is often
transmitted from one sex to both sexes or to one sex alone, more commonly
but not exclusively to the like sex.  It is a fact of some little
importance to us, that peculiarities appearing in the males of our domestic
breeds are often transmitted either exclusively, or in a much greater
degree, to males alone.  A much more important rule, which I think may be
trusted, is that, at whatever period of life a peculiarity first appears,
it tends to appear in the offspring at a corresponding age, though
sometimes earlier.  In many cases this could not be otherwise:  thus the
inherited peculiarities in the horns of cattle could appear only in the
offspring when nearly mature; peculiarities in the 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 conclude that very many of the most strongly-marked domestic
varieties could not possibly live in a wild state.  In many cases we do not
know what the aboriginal stock was, and so could not tell whether or not
nearly perfect reversion had ensued.  It would be quite necessary, in order
to prevent the effects of intercrossing, that only a single variety should
be turned loose in its new home.  Nevertheless, as our varieties 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 experiment would succeed, is not of
great importance for our line of argument; for by the experiment itself the
conditions of life are changed.  If it could be shown that our domestic
varieties manifested a strong tendency to reversion,--that is, to lose
their acquired characters, whilst kept under unchanged conditions, and
whilst kept in a considerable body, so that free intercrossing might check,
by blending together, any slight deviations of structure, in such case, I
grant that we could deduce nothing from domestic varieties in regard to
species.  But there is not a shadow of evidence in favour of this view:  to
assert that we could not breed our cart and race-horses, long and
short-horned cattle, and poultry of various breeds, and esculent
vegetables, for an almost infinite number of generations, would be opposed
to all experience.  I may add, that when under nature the conditions of
life do change, variations and reversions of character 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 with species closely allied together, we
generally perceive in each domestic race, as already remarked, less
uniformity of character than in true species.  Domestic races of the same
species, also, often have a somewhat monstrous character; by which I mean,
that, although differing from each other, and from the 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 some competent
judges as mere varieties, and by other competent judges as the descendants
of aboriginally distinct species.  If any marked distinction existed
between domestic races and species, this source of doubt could not so
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 most
widely in determining what characters are of generic value; all such
valuations being at present empirical.  Moreover, on the view of the origin
of genera which I shall presently give, we have no right to expect often to
meet with generic differences in our domesticated productions.

When we attempt to estimate the amount of structural difference between the
domestic races of the same species, we are soon involved in doubt, from not
knowing whether they have descended from one or several parent-species. 
This point, if it could be cleared up, would be interesting; if, for
instance, it could be shown that the greyhound, bloodhound, terrier,
spaniel, and bull-dog, which we all know propagate their kind so 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 and natural species--for instance, of the many foxes--inhabiting
different quarters of the world.  I do not believe, as we shall presently
see, that all our dogs have descended from any one wild species; but, in
the case of some other domestic races, there is presumptive, or even
strong, evidence in favour of this view.

It has often been assumed that man has chosen for domestication animals and
plants having an extraordinary inherent tendency to vary, and likewise to
withstand diverse climates.  I do not dispute that these capacities have
added largely to the value of most of our domesticated 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 variability of the ass or guinea-fowl, or the
small power of endurance of warmth by the rein-deer, 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 productions 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 species.  The argument mainly relied on
by those who believe in the multiple origin of our domestic animals is,
that we find in the most ancient records, more especially on the monuments
of Egypt, much diversity in the breeds; and that some of the breeds closely
resemble, perhaps are identical with, those still existing.  Even if this
latter fact were found more strictly and generally true than seems to me to
be the case, what does it show, but that some of our breeds originated
there, four or five thousand years ago?  But Mr. Horner's researches have
rendered it in some degree probable that man sufficiently civilized 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
considerations, I think it highly probable that our domestic dogs have
descended from several wild species.  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 constitution, &c., of the humped Indian
cattle, that these had descended from a different aboriginal stock from our
European cattle; and several competent judges believe that these latter
have had more than one wild parent.  With respect to horses, from reasons
which I cannot give here, I am doubtfully inclined to believe, in
opposition to several authors, that all the races have descended from one
wild stock.  Mr. Blyth, whose opinion, from his large and varied stores of
knowledge, I should value more than that of almost any one, thinks that all
the breeds of poultry have proceeded from the common wild Indian fowl
(Gallus bankiva).  In regard to ducks and rabbits, the breeds of which
differ considerably from each other in structure, I do not doubt that they
all have descended from the common wild duck and rabbit.

The doctrine of the origin of our several domestic races from several
aboriginal stocks, has been carried to an absurd extreme by some authors. 
They believe that every race which breeds true, let the distinctive
characters be ever so slight, has had its wild prototype.  At this rate
there must have existed at least a score of species of wild cattle, as many
sheep, and several goats in Europe alone, and several even within Great
Britain.  One author believes that there formerly existed in Great Britain
eleven wild species of sheep peculiar to it!  When we bear in mind that
Britain has now hardly one peculiar mammal, and France but few distinct
from those of Germany and conversely, and so with Hungary, Spain, &c., but
that each of these kingdoms possesses several peculiar breeds of cattle,
sheep, &c., 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 descended from several wild species, I
cannot doubt that there has been an immense amount of inherited variation. 
Who can believe that animals closely resembling the Italian greyhound, the
bloodhound, the bull-dog, or Blenheim spaniel, &c.--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 get only 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,
&c., in the wild state.  Moreover, the possibility of making distinct races
by crossing has been greatly exaggerated.  There can be no doubt that a
race may be modified by occasional crosses, if aided by the careful
selection of those individual mongrels, which present any desired
character; but that a race could be obtained nearly intermediate between
two extremely different races or species, I can hardly believe.  Sir J.
Sebright expressly experimentised for this object, and failed.  The
offspring from the first cross between two pure breeds is tolerably and
sometimes (as I have found with pigeons) extremely uniform, and everything
seems simple enough; but when these mongrels are crossed one with another
for several generations, hardly two of them will be alike, and then the
extreme 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, I 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
considerably 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 gape of mouth.  The short-faced tumbler has a beak
in outline almost like that of a finch; and the common tumbler has the
singular and strictly inherited habit of flying at a great height in a
compact flock, and tumbling in the air head over heels.  The runt is a bird
of great size, with long, massive beak and large feet; some of the
sub-breeds of runts have very long necks, others very long wings and tails,
others 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 in inflating, may well excite astonishment
and even laughter.  The turbit has a very short and conical beak, with a
line of reversed feathers down the breast; and it has the habit of
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 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 have been specified.

In the skeletons of the several breeds, the development of the bones of the
face in length and breadth and curvature differs enormously.  The shape, as
well as the breadth and length of the ramus of the lower jaw, varies in a
highly remarkable manner.  The number of the caudal and sacral vertebrae
vary; as does the number of the ribs, together with their relative breadth
and the presence of processes.  The size and shape of the apertures in the
sternum are highly variable; so is the degree of divergence and relative
size of the two arms of the furcula.  The proportional width of the gape of
mouth, the proportional length of the eyelids, of the orifice of the
nostrils, of the tongue (not always in strict correlation with the length
of beak), the size of the crop and of the upper part of the oesophagus; the
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 descended 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 impossible to make the present
domestic breeds by the crossing of any lesser number:  how, for instance,
could a pouter be produced by crossing two breeds unless one of the
parent-stocks possessed the characteristic enormous crop?  The supposed
aboriginal stocks must all have been rock-pigeons, that is, not 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, considering their size, habits, and remarkable characters, seems
very improbable; or they must have become extinct in the wild state.  But
birds breeding on precipices, and good fliers, are unlikely to be
exterminated; and the common rock-pigeon, which has the same habits with
the domestic breeds, has not been exterminated even on several of the
smaller British islets, or on the shores of the Mediterranean.  Hence the
supposed extermination of so many species having similar habits with the
rock-pigeon seems to me a very rash assumption.  Moreover, the several
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-civilized man, as to be quite
prolific under confinement.

An argument, as it seems to me, of great weight, and applicable in several
other cases, is, that the above-specified breeds, though agreeing generally
in constitution, habits, voice, colouring, and in most parts of their
structure, with the wild rock-pigeon, yet are certainly highly abnormal in
other parts of their structure:  we may look in vain throughout the whole
great family of 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-civilized man succeeded in thoroughly domesticating several species,
but that he intentionally or by chance picked out extraordinarily abnormal
species; and further, that these very species have since all become extinct
or unknown.  So many strange contingencies seem to me improbable in the
highest degree.

Some facts in regard to the colouring of pigeons well deserve
consideration.  The rock-pigeon is of a slaty-blue, and has a white rump
(the Indian sub-species, C. intermedia of Strickland, having it bluish);
the tail has a terminal dark bar, with the bases of the outer feathers
externally edged with white; the wings have two black bars; some
semi-domestic breeds and some apparently truly wild breeds have, besides
the two black bars, the wings chequered with black.  These several marks do
not occur together in any other species of the whole family.  Now, in every
one of the domestic breeds, taking thoroughly well-bred birds, all the
above marks, even to the white edging of the outer tail-feathers, sometimes
concur 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 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 countenancing
the belief that the child ever reverts to some one ancestor, removed by a
greater number of generations.  In a breed which has been crossed only once
with some distinct breed, the tendency to reversion to any character
derived from such cross will naturally become less and less, as in each
succeeding generation there will be less of the foreign blood; but when
there has been no cross with a distinct breed, and there is a tendency in
both parents to revert to a character, which has been lost during some
former generation, this tendency, for all that we can see to the contrary,
may be transmitted 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 extend
the hypothesis so far as to suppose that species, aboriginally as distinct
as carriers, tumblers, pouters, and fantails now are, should yield
offspring perfectly fertile, inter se, seems to me rash in the extreme.

From these several reasons, namely, the improbability of man having
formerly got seven or eight supposed species of pigeons to breed freely
under domestication; these supposed species being quite unknown in a wild
state, and their becoming nowhere feral; these species having very abnormal
characters in certain respects, as compared with all other Columbidae,
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 breeds,
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 Aegyptian dynasty, about
3000 B.C., as was pointed out to me by Professor 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.  'The monarchs of Iran and Turan sent him some very rare
birds;' and, continues the courtly historian, 'His Majesty by crossing the
breeds, which method was never practised before, has improved them
astonishingly.'  About this same period the Dutch were as eager about
pigeons as were the old Romans.  The paramount importance of these
considerations in explaining the immense amount of variation which pigeons
have undergone, will be obvious when we treat of Selection.  We shall then,
also, see how it is that the breeds so often have a somewhat monstrous
character.  It is also a most favourable circumstance for the production of
distinct breeds, that male and female pigeons can be easily mated for life;
and thus different breeds can be kept together in the same aviary.

I have discussed the probable origin of domestic pigeons at some, yet quite
insufficient, length; because when I first kept pigeons and watched the
several kinds, knowing well how true they bred, I felt fully as much
difficulty in believing that they could ever 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 laugh 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 naturalists
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 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 teazle, with its hooks, which cannot be rivalled by any mechanical
contrivance, is only a variety of the wild Dipsacus; and this amount of
change may have suddenly 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 'everlasting layers' which never desire to sit,
and with the bantam so small and elegant; when we compare the host of
agricultural, culinary, orchard, and 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
competent authorities.  Youatt, who was probably better acquainted with the
works of agriculturalists than almost any other individual, and who was
himself a very good judge of an animal, speaks of the principle of
selection as 'that which enables the agriculturist, not only to modify the
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 ordinary 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
inappreciable by an uneducated eye--differences which I for one have vainly
attempted to appreciate.  Not one man in a thousand has accuracy of eye and
judgment sufficient to become an eminent breeder.  If gifted with these
qualities, and he studies his subject for years, and devotes his lifetime
to it with indomitable perseverance, he will succeed, and may make great
improvements; if he wants any of these qualities, he will assuredly fail. 
Few would readily believe in the natural capacity and years of practice
requisite to become even a skilful pigeon-fancier.

The same principles are followed by horticulturists; but the variations are
here often more abrupt.  No one supposes that our choicest productions have
been produced 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 observing the accumulated
effects of selection--namely, by comparing the diversity of flowers in the
different varieties of the same species in the flower-garden; the diversity
of leaves, pods, or tubers, or whatever part is valued, in the
kitchen-garden, in comparison with the flowers of the same varieties; and
the diversity of fruit of the same species in the orchard, in comparison
with the leaves and flowers of the same set of varieties.  See how
different the leaves of the cabbage are, and how extremely alike the
flowers; how unlike the flowers of the heartsease are, and how alike the
leaves; how much the fruit of the different kinds of gooseberries differ in
size, colour, shape, and hairiness, and yet the flowers present very slight
differences.  It is not that the varieties which differ largely in some one
point do not differ at all in other points; this is hardly ever, perhaps
never, the case.  The laws of correlation of growth, the importance of
which should never be overlooked, will ensure some differences; but, as a
general rule, I cannot doubt that the continued selection of slight
variations, either in the leaves, the flowers, or the fruit, will produce
races differing from each other chiefly in these characters.

It may be objected that the principle of selection has been reduced to
methodical practice for scarcely more than 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, I may add, 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 distinctly given in an ancient Chinese
encyclopaedia.  Explicit rules are laid down by some of the Roman classical
writers.  From passages in Genesis, it is clear that the colour of domestic
animals was at that early period attended to.  Savages now sometimes cross
their dogs with wild canine animals, to improve the breed, and they
formerly did so, as is attested by passages in Pliny.  The savages in South
Africa match their draught cattle by colour, as do some of the Esquimaux
their teams of dogs.  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 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
important.  Thus, a man who intends keeping pointers naturally tries to get
as good dogs as he can, and afterwards breeds from his own best dogs, but
he has no wish or expectation of permanently altering the breed. 
Nevertheless I cannot doubt that this process, continued during centuries,
would improve and modify any breed, in the same way as Bakewell, Collins,
&c., 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 districts, where the breed has been
less improved.  There is reason to believe that King Charles's spaniel has
been unconsciously modified to a large extent since the time of that
monarch.  Some highly competent authorities are convinced that the setter
is directly derived from the spaniel, and has probably been slowly altered
from it.  It is known that the English pointer has been greatly changed
within the last century, and in this case the change has, it is believed,
been chiefly effected by crosses with the fox-hound; but what concerns us
is, that the change has been effected unconsciously and gradually, and yet
so effectually, that, though the old Spanish pointer certainly came from
Spain, Mr. Borrow has not seen, as I am informed by him, any native dog in
Spain like our pointer.

By a similar process of selection, and by careful training, the whole body
of English 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 unconsciously followed, in so far
that the breeders could never have expected or even have wished to have
produced the result which ensued--namely, the production of two distinct
strains.  The two flocks of Leicester sheep kept by Mr. Buckley and Mr.
Burgess, as Mr. Youatt remarks, 'have been purely bred from the original
stock of Mr. Bakewell for upwards of fifty years.  There is not a suspicion
existing in the mind of any one at all acquainted with the subject that the
owner of either of them has deviated in any one instance from the pure
blood of Mr. Bakewell's flock, and yet the difference between the sheep
possessed by these two gentlemen is so great that they have the appearance
of being quite different varieties.'

If there exist savages so barbarous as never to think of the inherited
character of the offspring of their domestic animals, yet any one animal
particularly useful to them, for any special purpose, would be carefully
preserved during famines and other accidents, to which savages are so
liable, and such choice animals would thus generally leave more offspring
than the inferior ones; so that in this case there would be a kind of
unconscious selection going on.  We see the value set on animals even by
the barbarians of Tierra del Fuego, by their killing and devouring their
old women, in times of dearth, as of less value than their dogs.

In plants the same gradual process of improvement, through the occasional
preservation of the best individuals, whether or not sufficiently distinct
to be ranked at their first appearance as distinct varieties, and whether
or not two or more species or races have become blended together by
crossing, may plainly be recognised in the increased size and beauty which
we now see in the varieties of the heartsease, rose, pelargonium, dahlia,
and other plants, when compared with the older varieties or with their
parent-stocks.  No one would ever expect to get a first-rate heartsease or
dahlia from the seed of a wild plant.  No one would expect to raise a
first-rate melting pear from the seed of a wild pear, though he might
succeed from a poor seedling growing wild, if it had come from a
garden-stock.  The pear, though cultivated in classical times, appears,
from Pliny's description, to have been a fruit of very inferior quality.  I
have seen great surprise expressed in horticultural works at the wonderful
skill of gardeners, in having produced such splendid results from such poor
materials; but the art, I cannot doubt, has been simple, and, as far as the
final result is concerned, has been followed almost unconsciously.  It has
consisted in always cultivating the best known variety, sowing its seeds,
and, when a slightly better variety has chanced to appear, selecting it,
and so onwards.  But the gardeners of the classical period, who 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 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 aboriginal stocks of any useful plants, but that the native
plants have not been improved by continued selection up to a standard of
perfection comparable with that given to the plants in countries anciently
civilised.

In regard to the domestic animals kept by uncivilised man, it should not be
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
adaptation 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, excepting on
variations which are first given to him in some slight degree by nature. 
No man would ever try to make a fantail, till he saw a pigeon with a tail
developed in some slight degree in an unusual manner, or a pouter till he
saw a pigeon with a crop of somewhat unusual size; and the more abnormal or
unusual any character was when it first appeared, the more likely it would
be to catch his attention.  But to use such an expression as trying to make
a fantail, is, I have no doubt, in most cases, utterly incorrect.  The man
who first selected a pigeon with a slightly larger tail, never dreamed what
the descendants of that pigeon would become through long-continued, partly
unconscious and partly methodical selection.  Perhaps the parent bird of
all fantails had only fourteen tail-feathers somewhat expanded, like the
present Java fantail, or like 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 individuals of the same species, be
judged of by the value which would now be set on them, after several breeds
have once fairly been established.  Many slight differences might, and
indeed do now, arise 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 sometimes been noticed--namely
that we know nothing about the origin or history of any of our domestic
breeds.  But, in fact, a breed, like a dialect of a language, can hardly be
said to have had a definite origin.  A man preserves and breeds from an
individual with some slight deviation of structure, or takes more care than
usual in matching his best animals and thus improves them, and the improved
individuals slowly spread in the immediate neighbourhood.  But as yet they
will hardly 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 be a
slow process.  As soon as the points of value of the new sub-breed are once
fully acknowledged, the principle, as I have called it, of unconscious
selection will always tend,--perhaps more at one period than at another, as
the breed rises or falls in fashion,--perhaps more in one district than in
another, according to the state of civilisation of the inhabitants--slowly
to add to the characteristic features of the breed, whatever they may be. 
But the chance will be infinitely small of any record having been preserved
of such slow, varying, and insensible changes.

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 accumulation of a large amount of
modification in almost any desired direction.  But as variations manifestly
useful or pleasing to man appear only occasionally, the chance of their
appearance will be much increased by a large number of individuals being
kept; and hence this comes to be of the highest importance to success.  On
this principle Marshall has remarked, with respect to the sheep of parts of
Yorkshire, that 'as they generally belong to poor people, and are mostly in
small lots, they never can be improved.'  On the other hand, nurserymen,
from raising large stocks of the same plants, are generally far more
successful than amateurs in getting new and valuable varieties.  The
keeping of a large number of individuals of a species in any country
requires that the species should be placed under favourable 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 strawberry began to vary just
when gardeners began to attend closely to this plant.  No doubt the
strawberry had always varied since it was cultivated, but the slight
varieties had been neglected.  As soon, however, as gardeners picked out
individual plants with slightly larger, earlier, or better fruit, and
raised seedlings from them, and again picked out the best seedlings and
bred from them, then, there appeared (aided by some crossing with distinct
species) those many admirable varieties of the strawberry which have been
raised during the last thirty or forty years.

In the case of animals with separate sexes, facility in preventing crosses
is an important element of success in the formation of 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 must have largely favoured the
improvement and formation of new breeds.  Pigeons, I may add, can be
propagated in great numbers and at a very quick rate, and inferior birds
may be freely rejected, as when killed they serve for food.  On the other
hand, cats, from their nocturnal rambling habits, cannot be matched, and,
although so much valued by women and children, we hardly ever see a
distinct breed kept up; such breeds as we do sometimes see are almost
always imported from some other country, often from islands.  Although I do
not doubt that some domestic animals vary less than others, yet the rarity
or absence of distinct breeds of the cat, the donkey, peacock, goose, &c.,
may be attributed in main part to selection not having been brought into
play:  in cats, from the difficulty 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 correlation 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, aboriginally distinct, has played an important part in the
origin of our domestic productions.  When in any country several domestic
breeds have once been established, 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, &c., 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
predominant Power.



Chapter II

Variation Under Nature

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 '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 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 individuals 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 accumulate 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 variability in important
characters, and that there are not many men who will laboriously examine
internal and important organs, and compare them in many specimens 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 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 larvae 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 any
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 differences, 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 perplexing, for they seem to show
that this kind of variability 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 consequently 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, 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 intermediate 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 naturalists having sound judgment and wide
experience seems the only guide to follow.  We must, however, in many
cases, decide by a majority of naturalists, for few well-marked and
well-known varieties can be named which have not been ranked as species by
at least some competent judges.

That varieties of this doubtful nature are far from uncommon cannot be
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 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. Bentham 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 characterized as varieties
in Mr. Wollaston's admirable work, but which it cannot be doubted would be
ranked as distinct species by many entomologists.  Even Ireland has a few
animals, 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 of
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, 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 distribution, analogical variation, hybridism, &c., 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 veris and elatior.  These plants differ considerably in appearance;
they have a different flavour and emit a different odour; they flower at
slightly different periods; they grow in somewhat different stations; they
ascend mountains to different heights; they have different geographical
ranges; and lastly, according to very numerous experiments made during
several years by that most careful observer Gartner, they can be crossed
only with much difficulty.  We could hardly wish for better evidence of the
two forms being specifically distinct.  On the other hand, they are united
by many intermediate links, and it is very doubtful whether these links are
hybrids; and there is, as it seems to me, an overwhelming amount of
experimental evidence, showing that they descend from common parents, and
consequently must be ranked as varieties.

Close investigation, in most cases, will bring naturalists to an agreement
how to rank doubtful forms.  Yet it must be 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 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 impressions.  As he extends the range of his
observations, he will meet with more cases of difficulty; for he will
encounter a greater number of closely-allied forms.  But if his
observations be widely extended, he will in the end generally be enabled to
make up his own mind which to call varieties and which species; but he will
succeed in this at the expense of admitting much variation,--and the truth
of this admission will often be disputed by other naturalists.  When,
moreover, he comes to study allied forms brought from countries not now
continuous, in which case he can hardly hope to find the intermediate links
between his doubtful forms, he will have to trust almost entirely to
analogy, and his difficulties will rise to a climax.

Certainly no clear line of demarcation has as yet been drawn between
species and sub-species--that is, the forms which in the opinion of some
naturalists come very near to, but do not quite arrive at the rank of
species; or, again, between sub-species and well-marked varieties, or
between lesser varieties and individual differences.  These differences
blend into each other in an insensible series; and a series impresses the
mind with the idea of an actual passage.

Hence I look at individual differences, though of small interest to the
systematist, as of high importance for us, as being the first step towards
such slight varieties as are barely thought worth recording in works on
natural history.  And I look at varieties which are in any degree more
distinct and permanent, as steps leading to more strongly marked and more
permanent varieties; and at these latter, as leading to sub-species, and to
species.  The passage from one stage of difference to another and higher
stage may be, in some cases, due merely to the long-continued action of
different physical conditions in two different regions; but I have not much
faith in this view; and I attribute the passage of a variety, from a state
in which it differs very slightly from its parent to one in which it
differs more, to the action of natural selection in accumulating (as will
hereafter be more fully explained) differences of structure in certain
definite directions.  Hence I believe a well-marked variety may be justly
called an incipient species; but whether this belief be justifiable must be
judged of by the general weight of the several facts and views given
throughout this work.

It need not be supposed that all varieties or incipient species necessarily
attain the rank of species.  They may 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.

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 proportional 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 existence,' '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), often give rise
to varieties sufficiently well-marked to have been recorded in botanical
works.  Hence it is the most flourishing, or, as they may be called, the
dominant species,--those which range widely over the world, are the most
diffused in their own country, and are the most numerous in
individuals,--which oftenest produce well-marked varieties, or, as I
consider them, incipient species.  And this, perhaps, might have been
anticipated; for, as varieties, in order to become in any degree permanent,
necessarily have to struggle with the other inhabitants of the country, the
species which are already dominant will be the most likely to yield
offspring which, though in some slight degree modified, will 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 somewhat
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, consequently, we
might have expected to have found in the larger genera, or those including
many species, a large proportional number of dominant species.  But so many
causes tend to obscure this result, that I am surprised that my tables show
even a small majority on the side of the larger genera.  I will here allude
to only two causes of obscurity.  Fresh-water and salt-loving plants have
generally very wide ranges and are much diffused, but this seems to be
connected with the nature of the stations inhabited by them, and has little
or no relation to the size of the genera to which the species belong. 
Again, plants low in the scale of organisation are generally much more
widely diffused than plants higher in the scale; and here again there is no
close relation to the size of the genera.  The cause of lowly-organised
plants ranging widely will be discussed in our chapter on geographical
distribution.

From looking at species as only 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, circumstances 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 proportion of the species on the side of the larger
genera present varieties, than on the side of the smaller genera. 
Moreover, the species of the large genera which present any varieties,
invariably present a larger average number of varieties than do the species
of the small genera.  Both these results follow when another division is
made, and when all the smallest genera, with from only one to four species,
are absolutely excluded from the tables.  These facts are of plain
signification on the view that species are only strongly marked and
permanent varieties; for whenever 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 the manufactory still in
action, more especially as we have every reason to believe the process of
manufacturing new species to be a slow one.  And this certainly is the
case, if varieties be looked at as incipient species; for my tables clearly
show as a general rule that, wherever many species of a genus have been
formed, the species of that genus present a number of varieties, that is of
incipient species, beyond the average.  It is not that all large genera are
now varying much, and are thus increasing in the number of their species,
or that no small genera are now varying and increasing; for if this had
been so, it would have been fatal to my theory; inasmuch as geology plainly
tells us that small genera have in the lapse of time often increased
greatly in size; and that large genera have often come to their maxima,
declined, and disappeared.  All that we want to show is, that where many
species of a genus have been formed, on an average many are still forming;
and this holds good.

There are other relations between the species of large genera and their
recorded varieties which deserve notice.  We have seen that there is no
infallible criterion by which to distinguish species and well-marked
varieties; and in those cases in which intermediate links have not been
found between doubtful forms, naturalists are compelled to come to a
determination by the amount of difference between them, judging by analogy
whether or not the amount suffices to raise one or both to the rank of
species.  Hence the amount of difference is one very important criterion in
settling whether two forms should be ranked as species or varieties.  Now
Fries has remarked in regard to plants, and Westwood in regard to insects,
that in large genera the amount of difference between the species is often
exceedingly small.  I have endeavoured to test this numerically by
averages, and, as far as my imperfect results go, they always confirm the
view.  I have also consulted some sagacious and most experienced observers,
and, after deliberation, they concur in this view.  In this respect,
therefore, the species of the larger genera resemble varieties, more than
do the species of the smaller genera.  Or the case may be put in another
way, and it may be said, that in the larger genera, in which a number of
varieties or incipient species greater than the average are now
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 naturalist pretends that all the species of a genus are equally distinct
from each other; they may generally be divided into sub-genera, or
sections, or lesser groups.  As Fries has well remarked, little groups of
species are generally clustered like satellites around certain other
species.  And what are varieties but groups of forms, unequally related to
each other, and clustered round certain forms--that is, round their
parent-species?  Undoubtedly there is one most important point of
difference between varieties and species; namely, that the amount of
difference between varieties, when 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 differences between species.

There is one other point which seems to me worth notice.  Varieties
generally have much restricted ranges:  this statement is indeed scarcely
more than a truism, for if a variety were found to have a wider range than
that of its supposed parent-species, their denominations ought to be
reversed.  But there is also reason to believe, that those species which
are very closely allied to other species, and in so far resemble varieties,
often have much restricted ranges.  For instance, Mr. H. C. Watson has
marked for me in the well-sifted London Catalogue of plants (4th edition)
63 plants which are therein ranked as species, but which he considers as so
closely allied to other species as to be of doubtful value:  these 63
reputed species range on an average over 6.9 of the provinces into which
Mr. Watson has divided Great Britain.  Now, in this same catalogue, 53
acknowledged varieties are recorded, and these range over 7.7 provinces;
whereas, the species to which these varieties belong range over 14.3
provinces.  So that the acknowledged varieties have very nearly the same
restricted average range, as have those very closely allied forms, marked
for me by Mr. Watson as doubtful species, but which are almost universally
ranked by British botanists as good and true species.

Finally, then, varieties have the same general characters as species, for
they 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, notwithstanding
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 inexplicable if
each species has been independently created.

We have, also, seen that it is the most flourishing and dominant species of
the larger genera which on an average vary most; and varieties, as we shall
hereafter see, tend to become converted into new and distinct species.  The
larger genera thus tend to become larger; and throughout nature the forms
of life which are now dominant tend to become still more dominant by
leaving many modified and dominant descendants.  But by steps hereafter to
be explained, the larger genera also tend to break up into smaller genera. 
And thus, the forms of life throughout the universe become divided into
groups 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 -- Competition universal -- Effects of
climate -- Protection from the number of individuals -- Complex relations
of all animals and plants throughout nature -- Struggle for life most
severe between individuals and varieties of the same species; often severe
between species of the same genus -- The relation of organism to organism
the most important of all 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 variability;
indeed I am not aware that this has ever been disputed.  It is immaterial
for us whether a multitude of doubtful forms be called species or
sub-species or varieties; what rank, for instance, the two or three hundred
doubtful forms of British plants are entitled to hold, if the existence of
any well-marked varieties be admitted.  But the mere 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 beautiful co-adaptations most plainly in the
woodpecker and missletoe; and only a little less plainly in the humblest
parasite which clings to the hairs of a quadruped or feathers of a bird; in
the structure of the beetle which dives through the water; in the plumed
seed which is wafted by the gentlest breeze; in short, we see beautiful
adaptations 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 converted into good and distinct
species, which in most cases obviously differ from each other far more than
do the varieties of the same species?  How do those groups of species,
which constitute what are called distinct genera, and which differ from
each other more than do the species of the same genus, arise?  All these
results, as we shall more fully see in the next chapter, follow inevitably
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 relations to other organic beings and to external nature, will tend
to the preservation of that individual, and will generally be inherited by
its offspring.  The offspring, also, will thus have a better chance of
surviving, for, of the many individuals of any species which are
periodically born, but a small number can survive.  I have called this
principle, by which each slight variation, if useful, is preserved, by the
term of Natural Selection, in order to mark its relation to man's power of
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.  The elder De Candolle and Lyell have largely and
philosophically 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 individual,
but success in leaving progeny.  Two canine animals in a time of dearth,
may be truly said to struggle with each other which shall get food and
live.  But a plant on the edge of a desert is said to struggle for life
against the drought, though more properly it should be said to be 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 k