THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION;

or, the PRESERVATION OF FAVOURED RACES IN THE STRUGGLE FOR LIFE.

By Charles Darwin, M.A., F.R.S.,

Author of "The Descent of Man," etc., etc.


Sixth London Edition, with all Additions and Corrections.


"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."--Whewell: "Bridgewater Treatise".

"The only distinct meaning of the word 'natural' is STATED, FIXED or
SETTLED; since what is natural as much requires and presupposes an
intelligent agent to render it so, i.e., to effect it continually or at
stated times, as what is supernatural or miraculous does to effect it
for once."--Butler: "Analogy of Revealed Religion".

"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".




AN HISTORICAL SKETCH OF THE PROGRESS OF OPINION ON THE ORIGIN OF
SPECIES,

PREVIOUSLY TO THE PUBLICATION OF THE FIRST EDITION OF THIS WORK.

I will here give a brief sketch of the progress of opinion on the Origin
of Species. Until recently the great majority of naturalists believed
that species were immutable productions, and had been separately
created. This view has been ably maintained by many authors. Some few
naturalists, on the other hand, have believed that species undergo
modification, and that the existing forms of life are the descendants
by true generation of pre existing forms. Passing over allusions to
the subject in the classical writers (Aristotle, in his "Physicae
Auscultationes" (lib.2, cap.8, s.2), after remarking that rain does not
fall in order to make the corn grow, any more than it falls to spoil the
farmer's corn when threshed out of doors, applies the same argument
to organisation; and adds (as translated by Mr. Clair Grece, who first
pointed out the passage to me), "So what hinders the different parts (of
the body) from having this merely accidental relation in nature? as the
teeth, for example, grow by necessity, the front ones sharp, adapted
for dividing, and the grinders flat, and serviceable for masticating
the food; since they were not made for the sake of this, but it was the
result of accident. And in like manner as to other parts in which there
appears to exist an adaptation to an end. Wheresoever, therefore, all
things together (that is all the parts of one whole) happened like as if
they were made for the sake of something, these were preserved,
having been appropriately constituted by an internal spontaneity; and
whatsoever things were not thus constituted, perished and still perish."
We here see the principle of natural selection shadowed forth, but
how little Aristotle fully comprehended the principle, is shown by his
remarks on the formation of the teeth.), the first author who in modern
times has treated it in a scientific spirit was Buffon. But as his
opinions fluctuated greatly at different periods, and as he does not
enter on the causes or means of the transformation of species, I need
not here enter on details.

Lamarck was the first man whose conclusions on the subject excited much
attention. This justly celebrated naturalist first published his views
in 1801; he much enlarged them in 1809 in his "Philosophie Zoologique",
and subsequently, 1815, in the Introduction to his "Hist. Nat. des
Animaux sans Vertebres". In these works he up holds the doctrine that
all species, including man, are descended from other species. He first
did the eminent service of arousing attention to the probability of
all change in the organic, as well as in the inorganic world, being the
result of law, and not of miraculous interposition. Lamarck seems
to have been chiefly led to his conclusion on the gradual change of
species, by the difficulty of distinguishing species and varieties,
by the almost perfect gradation of forms in certain groups, and by
the analogy of domestic productions. With respect to the means of
modification, he attributed something to the direct action of the
physical conditions of life, something to the crossing of already
existing forms, and much to use and disuse, that is, to the effects of
habit. To this latter agency he seems to attribute all the beautiful
adaptations in nature; such as the long neck of the giraffe for
browsing on the branches of trees. But he likewise believed in a law
of progressive development, and as all the forms of life thus tend to
progress, in order to account for the existence at the present day of
simple productions, he maintains that such forms are now spontaneously
generated. (I have taken the date of the first publication of Lamarck
from Isidore Geoffroy Saint-Hilaire's ("Hist. Nat. Generale", tom. ii.
page 405, 1859) excellent history of opinion on this subject. In
this work a full account is given of Buffon's conclusions on the same
subject. It is curious how largely my grandfather, Dr. Erasmus Darwin,
anticipated the views and erroneous grounds of opinion of Lamarck in
his "Zoonomia" (vol. i. pages 500-510), published in 1794. According to
Isid. Geoffroy there is no doubt that Goethe was an extreme partisan of
similar views, as shown in the introduction to a work written in 1794
and 1795, but not published till long afterward; he has pointedly
remarked ("Goethe als Naturforscher", von Dr. Karl Meding, s. 34) that
the future question for naturalists will be how, for instance, cattle
got their horns and not for what they are used. It is rather a singular
instance of the manner in which similar views arise at about the same
time, that Goethe in Germany, Dr. Darwin in England, and Geoffroy
Saint-Hilaire (as we shall immediately see) in France, came to the same
conclusion on the origin of species, in the years 1794-5.)

Geoffroy Saint-Hilaire, as is stated in his "Life", written by his
son, suspected, as early as 1795, that what we call species are various
degenerations of the same type. It was not until 1828 that he published
his conviction that the same forms have not been perpetuated since
the origin of all things. Geoffroy seems to have relied chiefly on the
conditions of life, or the "monde ambiant" as the cause of change. He
was cautious in drawing conclusions, and did not believe that existing
species are now undergoing modification; and, as his son adds, "C'est
donc un probleme a reserver entierement a l'avenir, suppose meme que
l'avenir doive avoir prise sur lui."

In 1813 Dr. W.C. Wells read before the Royal Society "An Account of a
White Female, part of whose skin resembles that of a Negro"; but his
paper was not published until his famous "Two Essays upon Dew and Single
Vision" appeared in 1818. In this paper he distinctly recognises the
principle of natural selection, and this is the first recognition which
has been indicated; but he applies it only to the races of man, and to
certain characters alone. After remarking that negroes and mulattoes
enjoy an immunity from certain tropical diseases, he observes, firstly,
that all animals tend to vary in some degree, and, secondly, that
agriculturists improve their domesticated animals by selection; and
then, he adds, but what is done in this latter case "by art, seems to
be done with equal efficacy, though more slowly, by nature, in the
formation of varieties of mankind, fitted for the country which they
inhabit. Of the accidental varieties of man, which would occur among
the first few and scattered inhabitants of the middle regions of Africa,
some one would be better fitted than others to bear the diseases of the
country. This race would consequently multiply, while the others would
decrease; not only from their in ability to sustain the attacks of
disease, but from their incapacity of contending with their more
vigorous neighbours. The colour of this vigorous race I take for
granted, from what has been already said, would be dark. But the same
disposition to form varieties still existing, a darker and a darker race
would in the course of time occur: and as the darkest would be the best
fitted for the climate, this would at length become the most prevalent,
if not the only race, in the particular country in which it had
originated." He then extends these same views to the white inhabitants
of colder climates. I am indebted to Mr. Rowley, of the United States,
for having called my attention, through Mr. Brace, to the above passage
of Dr. Wells' work.

The Hon. and Rev. W. Herbert, afterward Dean of Manchester, in the
fourth volume of the "Horticultural Transactions", 1822, and in his
work on the "Amaryllidaceae" (1837, pages 19, 339), declares that
"horticultural experiments have established, beyond the possibility of
refutation, that botanical species are only a higher and more permanent
class of varieties." He extends the same view to animals. The dean
believes that single species of each genus were created in an originally
highly plastic condition, and that these have produced, chiefly by
inter-crossing, but likewise by variation, all our existing species.

In 1826 Professor Grant, in the concluding paragraph in his well-known
paper ("Edinburgh Philosophical Journal", vol. XIV, page 283) on the
Spongilla, clearly declares his belief that species are descended
from other species, and that they become improved in the course of
modification. This same view was given in his Fifty-fifth Lecture,
published in the "Lancet" in 1834.

In 1831 Mr. Patrick Matthew published his work on "Naval Timber and
Arboriculture", in which he gives precisely the same view on the origin
of species as that (presently to be alluded to) propounded by Mr.
Wallace and myself in the "Linnean Journal", and as that enlarged in
the present volume. Unfortunately the view was given by Mr. Matthew very
briefly in scattered passages in an appendix to a work on a different
subject, so that it remained unnoticed until Mr. Matthew himself drew
attention to it in the "Gardeners' Chronicle", on April 7, 1860. The
differences of Mr. Matthew's views from mine are not of much importance:
he seems to consider that the world was nearly depopulated at successive
periods, and then restocked; and he gives as an alternative, that new
forms may be generated "without the presence of any mold or germ of
former aggregates." I am not sure that I understand some passages; but
it seems that he attributes much influence to the direct action of
the conditions of life. He clearly saw, however, the full force of the
principle of natural selection.

The celebrated geologist and naturalist, Von Buch, in his excellent
"Description Physique des Isles Canaries" (1836, page 147), clearly
expresses his belief that varieties slowly become changed into permanent
species, which are no longer capable of intercrossing.

Rafinesque, in his "New Flora of North America", published in 1836,
wrote (page 6) as follows: "All species might have been varieties once,
and many varieties are gradually becoming species by assuming constant
and peculiar characters;" but further on (page 18) he adds, "except the
original types or ancestors of the genus."

In 1843-44 Professor Haldeman ("Boston Journal of Nat. Hist. U. States",
vol. iv, page 468) has ably given the arguments for and against the
hypothesis of the development and modification of species: he seems to
lean toward the side of change.

The "Vestiges of Creation" appeared in 1844. In the tenth and much
improved edition (1853) the anonymous author says (page 155): "The
proposition determined on after much consideration is, that the several
series of animated beings, from the simplest and oldest up to the
highest and most recent, are, under the providence of God, the results,
FIRST, of an impulse which has been imparted to the forms of life,
advancing them, in definite times, by generation, through grades of
organisation terminating in the highest dicotyledons and vertebrata,
these grades being few in number, and generally marked by intervals
of organic character, which we find to be a practical difficulty in
ascertaining affinities; SECOND, of another impulse connected with the
vital forces, tending, in the course of generations, to modify organic
structures in accordance with external circumstances, as food, the
nature of the habitat, and the meteoric agencies, these being the
'adaptations' of the natural theologian." The author apparently believes
that organisation progresses by sudden leaps, but that the effects
produced by the conditions of life are gradual. He argues with much
force on general grounds that species are not immutable productions.
But I cannot see how the two supposed "impulses" account in a scientific
sense for the numerous and beautiful coadaptations which we see
throughout nature; I cannot see that we thus gain any insight how, for
instance, a woodpecker has become adapted to its peculiar habits of
life. The work, from its powerful and brilliant style, though displaying
in the early editions little accurate knowledge and a great want of
scientific caution, immediately had a very wide circulation. In my
opinion it has done excellent service in this country in calling
attention to the subject, in removing prejudice, and in thus preparing
the ground for the reception of analogous views.

In 1846 the veteran geologist M.J. d'Omalius d'Halloy published in an
excellent though short paper ("Bulletins de l'Acad. Roy. Bruxelles",
tom. xiii, page 581) his opinion that it is more probable that new
species have been produced by descent with modification than that they
have been separately created: the author first promulgated this opinion
in 1831.

Professor Owen, in 1849 ("Nature of Limbs", page 86), wrote as follows:
"The archetypal idea was manifested in the flesh under diverse such
modifications, upon this planet, long prior to the existence of those
animal species that actually exemplify it. To what natural laws or
secondary causes the orderly succession and progression of such organic
phenomena may have been committed, we, as yet, are ignorant." In his
address to the British Association, in 1858, he speaks (page li) of "the
axiom of the continuous operation of creative power, or of the ordained
becoming of living things." Further on (page xc), after referring
to geographical distribution, he adds, "These phenomena shake our
confidence in the conclusion that the Apteryx of New Zealand and the
Red Grouse of England were distinct creations in and for those islands
respectively. Always, also, it may be well to bear in mind that by the
word 'creation' the zoologist means 'a process he knows not what.'" He
amplifies this idea by adding that when such cases as that of the Red
Grouse are "enumerated by the zoologist as evidence of distinct creation
of the bird in and for such islands, he chiefly expresses that he
knows not how the Red Grouse came to be there, and there exclusively;
signifying also, by this mode of expressing such ignorance, his belief
that both the bird and the islands owed their origin to a great first
Creative Cause." If we interpret these sentences given in the same
address, one by the other, it appears that this eminent philosopher felt
in 1858 his confidence shaken that the Apteryx and the Red Grouse first
appeared in their respective homes "he knew not how," or by some process
"he knew not what."

This address was delivered after the papers by Mr. Wallace and myself on
the Origin of Species, presently to be referred to, had been read before
the Linnean Society. When the first edition of this work was published,
I was so completely deceived, as were many others, by such expressions
as "the continuous operation of creative power," that I included
Professor Owen with other palaeontologists as being firmly convinced
of the immutability of species; but it appears ("Anat. of Vertebrates",
vol. iii, page 796) that this was on my part a preposterous error. In
the last edition of this work I inferred, and the inference still seems
to me perfectly just, from a passage beginning with the words "no doubt
the type-form," etc.(Ibid., vol. i, page xxxv), that Professor Owen
admitted that natural selection may have done something in the formation
of a new species; but this it appears (Ibid., vol. iii. page 798)
is inaccurate and without evidence. I also gave some extracts from a
correspondence between Professor Owen and the editor of the "London
Review", from which it appeared manifest to the editor as well as to
myself, that Professor Owen claimed to have promulgated the theory of
natural selection before I had done so; and I expressed my surprise
and satisfaction at this announcement; but as far as it is possible to
understand certain recently published passages (Ibid., vol. iii. page
798) I have either partially or wholly again fallen into error. It
is consolatory to me that others find Professor Owen's controversial
writings as difficult to understand and to reconcile with each other,
as I do. As far as the mere enunciation of the principle of natural
selection is concerned, it is quite immaterial whether or not Professor
Owen preceded me, for both of us, as shown in this historical sketch,
were long ago preceded by Dr. Wells and Mr. Matthews.

M. Isidore Geoffroy Saint-Hilaire, in his lectures delivered in 1850 (of
which a Resume appeared in the "Revue et Mag. de Zoolog.", Jan., 1851),
briefly gives his reason for believing that specific characters "sont
fixes, pour chaque espece, tant qu'elle se perpetue au milieu des memes
circonstances: ils se modifient, si les circonstances ambiantes viennent
a changer. En resume, L'OBSERVATION des animaux sauvages demontre deja
la variabilite LIMITEE des especes. Les EXPERIENCES sur les animaux
sauvages devenus domestiques, et sur les animaux domestiques redevenus
sauvages, la demontrent plus clairment encore. Ces memes experiences
prouvent, de plus, que les differences produites peuvent etre de VALEUR
GENERIQUE." In his "Hist. Nat. Generale" (tom. ii, page 430, 1859) he
amplifies analogous conclusions.

From a circular lately issued it appears that Dr. Freke, in 1851
("Dublin Medical Press", page 322), propounded the doctrine that all
organic beings have descended from one primordial form. His grounds of
belief and treatment of the subject are wholly different from mine;
but as Dr. Freke has now (1861) published his Essay on the "Origin of
Species by means of Organic Affinity", the difficult attempt to give any
idea of his views would be superfluous on my part.

Mr. Herbert Spencer, in an Essay (originally published in the "Leader",
March, 1852, and republished in his "Essays", in 1858), has contrasted
the theories of the Creation and the Development of organic beings
with remarkable skill and force. He argues from the analogy of domestic
productions, from the changes which the embryos of many species undergo,
from the difficulty of distinguishing species and varieties, and from
the principle of general gradation, that species have been modified;
and he attributes the modification to the change of circumstances.
The author (1855) has also treated Psychology on the principle of the
necessary acquirement of each mental power and capacity by gradation.

In 1852 M. Naudin, a distinguished botanist, expressly stated, in an
admirable paper on the Origin of Species ("Revue Horticole", page 102;
since partly republished in the "Nouvelles Archives du Museum", tom. i,
page 171), his belief that species are formed in an analogous manner as
varieties are under cultivation; and the latter process he attributes to
man's power of selection. But he does not show how selection acts under
nature. He believes, like Dean Herbert, that species, when nascent,
were more plastic than at present. He lays weight on what he calls the
principle of finality, "puissance mysterieuse, indeterminee; fatalite
pour les uns; pour les autres volonte providentielle, dont l'action
incessante sur les etres vivantes determine, a toutes les epoques de
l'existence du monde, la forme, le volume, et la duree de chacun d'eux,
en raison de sa destinee dans l'ordre de choses dont il fait partie.
C'est cette puissance qui harmonise chaque membre a l'ensemble, en
l'appropriant a la fonction qu'il doit remplir dans l'organisme general
de la nature, fonction qui est pour lui sa raison d'etre." (From
references in Bronn's "Untersuchungen uber die Entwickelungs-Gesetze",
it appears that the celebrated botanist and palaeontologist Unger
published, in 1852, his belief that species undergo development and
modification. Dalton, likewise, in Pander and Dalton's work on Fossil
Sloths, expressed, in 1821, a similar belief. Similar views have, as is
well known, been maintained by Oken in his mystical "Natur-Philosophie".
From other references in Godron's work "Sur l'Espece", it seems that
Bory St. Vincent, Burdach, Poiret and Fries, have all admitted that
new species are continually being produced. I may add, that of the
thirty-four authors named in this Historical Sketch, who believe in
the modification of species, or at least disbelieve in separate acts
of creation, twenty-seven have written on special branches of natural
history or geology.)

In 1853 a celebrated geologist, Count Keyserling ("Bulletin de la Soc.
Geolog.", 2nd Ser., tom. x, page 357), suggested that as new diseases,
supposed to have been caused by some miasma have arisen and spread over
the world, so at certain periods the germs of existing species may have
been chemically affected by circumambient molecules of a particular
nature, and thus have given rise to new forms.

In this same year, 1853, Dr. Schaaffhausen published an excellent
pamphlet ("Verhand. des Naturhist. Vereins der Preuss. Rheinlands",
etc.), in which he maintains the development of organic forms on the
earth. He infers that many species have kept true for long periods,
whereas a few have become modified. The distinction of species he
explains by the destruction of intermediate graduated forms. "Thus
living plants and animals are not separated from the extinct by new
creations, but are to be regarded as their descendants through continued
reproduction."

A well-known French botanist, M. Lecoq, writes in 1854 ("Etudes sur
Geograph." Bot. tom. i, page 250), "On voit que nos recherches sur la
fixite ou la variation de l'espece, nous conduisent directement aux
idees emises par deux hommes justement celebres, Geoffroy Saint-Hilaire
et Goethe." Some other passages scattered through M. Lecoq's large
work make it a little doubtful how far he extends his views on the
modification of species.

The "Philosophy of Creation" has been treated in a masterly manner by
the Rev. Baden Powell, in his "Essays on the Unity of Worlds", 1855.
Nothing can be more striking than the manner in which he shows that the
introduction of new species is "a regular, not a casual phenomenon," or,
as Sir John Herschel expresses it, "a natural in contradistinction to a
miraculous process."

The third volume of the "Journal of the Linnean Society" contains
papers, read July 1, 1858, by Mr. Wallace and myself, in which, as
stated in the introductory remarks to this volume, the theory of
Natural Selection is promulgated by Mr. Wallace with admirable force and
clearness.

Von Baer, toward whom all zoologists feel so profound a respect,
expressed about the year 1859 (see Prof. Rudolph Wagner,
"Zoologisch-Anthropologische Untersuchungen", 1861, s. 51) his
conviction, chiefly grounded on the laws of geographical distribution,
that forms now perfectly distinct have descended from a single
parent-form.

In June, 1859, Professor Huxley gave a lecture before the Royal
Institution on the "Persistent Types of Animal Life". Referring to such
cases, he remarks, "It is difficult to comprehend the meaning of such
facts as these, if we suppose that each species of animal and plant, or
each great type of organisation, was formed and placed upon the surface
of the globe at long intervals by a distinct act of creative power; and
it is well to recollect that such an assumption is as unsupported by
tradition or revelation as it is opposed to the general analogy of
nature. If, on the other hand, we view "Persistent Types" in relation to
that hypothesis which supposes the species living at any time to be the
result of the gradual modification of pre-existing species, a hypothesis
which, though unproven, and sadly damaged by some of its supporters,
is yet the only one to which physiology lends any countenance; their
existence would seem to show that the amount of modification which
living beings have undergone during geological time is but very small in
relation to the whole series of changes which they have suffered."

In December, 1859, Dr. Hooker published his "Introduction to the
Australian Flora". In the first part of this great work he admits the
truth of the descent and modification of species, and supports this
doctrine by many original observations.

The first edition of this work was published on November 24, 1859, and
the second edition on January 7, 1860.



CONTENTS.


  INTRODUCTION


  CHAPTER I.

  VARIATION UNDER DOMESTICATION.

  Causes of Variability--Effects of Habit and the use or disuse of
  Parts--Correlated Variation--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--Principles of Selection,
  anciently followed, their 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 each country vary more frequently 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.

  Its bearing on natural selection--The term used in a wide
  sense--Geometrical ratio 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; OR THE SURVIVAL OF THE FITTEST.

  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 the results of 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--Advance in organisation--Low forms preserved--Convergence of
  character--Indefinite multiplication of species--Summary.


  CHAPTER V.

  LAWS OF VARIATION.

  Effects of changed conditions--Use and disuse, combined with natural
  selection; organs of flight and of vision--Acclimatisation--Correlated
  variation--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 OF THE THEORY.

  Difficulties of the theory of descent with modification--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--Modes 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.

  MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.

  Longevity--Modifications not necessarily simultaneous--Modifications
  apparently of no direct service--Progressive development--Characters of
  small functional importance, the most constant--Supposed incompetence
  of natural selection to account for the incipient stages of useful
  structures--Causes which interfere with the acquisition through natural
  selection of useful structures--Gradations of structure with changed
  functions--Widely different organs in members of the same class,
  developed from one and the same source--Reasons for disbelieving in
  great and abrupt modifications.


  CHAPTER VIII.

  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, molothrus, ostrich, and parasitic bees--Slave-making
  ants--Hive-bee, its cell-making instinct--Changes of instinct and
  structure not necessarily simultaneous--Difficulties on the theory of
  the Natural Selection of instincts--Neuter or sterile insects--Summary.


  CHAPTER IX.

  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, not accumulated by natural selection--Causes of
  the sterility of first crosses and of hybrids--Parallelism between the
  effects of changed conditions of life and of crossing--Dimorphism and
  Trimorphism--Fertility of varieties when crossed and of their mongrel
  offspring not universal--Hybrids and mongrels compared independently of
  their fertility--Summary.


  CHAPTER X.

  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 lapse
  of time, as inferred from the rate of denudation and of deposition--On
  the lapse of time as estimated in years--On the poorness of our
  palaeontological collections--On the intermittence of geological
  formations--On the denudation of granitic areas--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--Antiquity of the habitable earth.


  CHAPTER XI.

  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 chapter.


  CHAPTER XII.

  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--Alternate Glacial periods in the north and
  south.


  CHAPTER XIII.

  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 chapter.


  CHAPTER XIV.

  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 XV.

  RECAPITULATION AND CONCLUSION.

  Recapitulation of the objections to 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.


  GLOSSARY OF SCIENTIFIC TERMS.


  INDEX.




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 organic beings inhabiting South
America, and in the geological relations of the present to the past
inhabitants of that continent. These facts, as will be seen in the
latter chapters of this volume, seemed 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 (1859) nearly finished; but as it will take me many 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. In 1858 he sent me a
memoir on this subject, with a request that I would forward it to Sir
Charles Lyell, who sent it to the Linnean Society, and it is published
in the third volume of the Journal of that Society. Sir C. Lyell and Dr.
Hooker, who both knew of my work--the latter having read my sketch
of 1844--honoured me by thinking it 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 may 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 is here impossible.

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 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 justly excites our admiration. Naturalists
continually refer to external conditions, such as climate, food, etc.,
as the only possible cause of variation. In one 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
mistletoe, which draws its nourishment from certain trees, which has
seeds that must be transported by certain birds, and which has flowers
with separate sexes absolutely requiring the agency of certain insects
to bring pollen from one flower to the other, it is equally preposterous
to account for the structure of this parasite, with its relations to
several distinct organic beings, by the effects of external conditions,
or of habit, or of the volition of the plant itself.

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 among all organic beings throughout the world, which
inevitably follows from the high geometrical ratio of their increase,
will be considered. 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 leads to what I have called divergence of character.
In the next chapter I shall discuss the complex and little known laws
of variation. In the five succeeding chapters, the most apparent and
gravest difficulties in accepting the theory will be given: namely,
first, the difficulties of transitions, or how a simple being or a
simple organ can be changed and perfected into a highly developed
being or into an 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 twelfth and thirteenth, their geographical
distribution throughout space; in the fourteenth, 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 make due allowance
for our profound ignorance in regard to the mutual relations of the
many 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 until recently
entertained, 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 most important, but not
the exclusive, means of modification.




CHAPTER I. VARIATION UNDER DOMESTICATION.

 Causes of Variability--Effects of Habit and the use and disuse of
 Parts--Correlated Variation--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--Principles of Selection,
 anciently followed, their Effects--Methodical and Unconscious
 Selection--Unknown Origin of our Domestic Productions--Circumstances
 favourable to Man's power of Selection.


CAUSES OF VARIABILITY.

When we compare the individuals of the same variety or sub-variety of
our older cultivated plants and animals, one of the first points which
strikes us is, that they generally differ more from each other than do
the individuals of any one species or variety in a state of nature. And
if 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, we are driven to conclude that this
great variability is 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 had been exposed under nature. There
is, also, some probability in the view propounded by Andrew Knight, that
this variability may be partly connected with excess of food. It seems
clear that organic beings must be exposed during several generations to
new conditions to cause any great amount of variation; and that, when
the organisation has once begun to vary, it generally continues varying
for many generations. No case is on record of a variable organism
ceasing to vary under cultivation. Our oldest cultivated plants, such
as wheat, still yield new varieties: our oldest domesticated animals are
still capable of rapid improvement or modification.

As far as I am able to judge, after long attending to the subject, the
conditions of life appear to act in two ways--directly on the whole
organisation or on certain parts alone and in directly by affecting the
reproductive system. With respect to the direct action, we must bear in
mind that in every case, as Professor Weismann has lately insisted,
and as I have incidently shown in my work on "Variation under
Domestication," there are two factors: namely, the nature of the
organism and the nature of the conditions. The former seems to be much
the more important; for nearly similar variations sometimes arise under,
as far as we can judge, dissimilar conditions; and, on the other hand,
dissimilar variations arise under conditions which appear to be
nearly uniform. The effects on the offspring are either definite or in
definite. They may be considered as definite when all or nearly all the
offspring of individuals exposed to certain conditions during several
generations are modified in the same manner. It is extremely difficult
to come to any conclusion in regard to the extent of the changes which
have been thus definitely induced. There can, however, be little doubt
about many slight changes, such as size from the amount of food,
colour from the nature of the food, thickness of the skin and hair from
climate, etc. Each of the endless variations which we see in the plumage
of our fowls must have had some efficient cause; and if the same cause
were to act uniformly during a long series of generations on many
individuals, all probably would be modified in the same manner. Such
facts as the complex and extraordinary out growths which variably
follow from the insertion of a minute drop of poison by a gall-producing
insect, shows us what singular modifications might result in the case of
plants from a chemical change in the nature of the sap.

In definite variability is a much more common result of changed
conditions than definite variability, and has probably played a more
important part in the formation of our domestic races. We see in
definite variability in the endless slight peculiarities which
distinguish the individuals of the same species, and which cannot be
accounted for by inheritance from either parent or from some more remote
ancestor. Even strongly-marked differences occasionally appear in the
young of the same litter, and in seedlings from the same seed-capsule.
At long intervals of time, out of millions of individuals reared in the
same country and fed on nearly the same food, deviations of structure so
strongly pronounced as to deserve to be called monstrosities arise; but
monstrosities cannot be separated by any distinct line from slighter
variations. All such changes of structure, whether extremely slight or
strongly marked, which appear among many individuals living together,
may be considered as the in definite effects of the conditions of life
on each individual organism, in nearly the same manner as the chill
effects different men in an in definite manner, according to their
state of body or constitution, causing coughs or colds, rheumatism, or
inflammation of various organs.

With respect to what I have called the in direct action of changed
conditions, namely, through the reproductive system of being affected,
we may infer that variability is thus induced, partly from the fact of
this system being extremely sensitive to any change in the conditions,
and partly from the similarity, as Kolreuter and others have remarked,
between the variability which follows from the crossing of distinct
species, and that which may be observed with plants and animals when
reared under new or unnatural conditions. Many facts clearly show how
eminently susceptible the reproductive system is to very slight changes
in the surrounding conditions. Nothing is more easy than to tame an
animal, and few things more difficult than to get it to breed freely
under confinement, even when the male and female unite. How many animals
there are which will not breed, though kept in an almost free state in
their native country! This is generally, but erroneously attributed to
vitiated instincts. Many cultivated plants display the utmost vigour,
and yet rarely or never seed! In some few cases it has been discovered
that a very trifling change, such as a little more or less water at some
particular period of growth, will determine whether or not a plant will
produce seeds. I cannot here give the details which I have collected and
elsewhere published on this curious subject; but to show how singular
the laws are which determine the reproduction of animals under
confinement, I may 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, which seldom produce
young; whereas, carnivorous birds, with the rarest exception, hardly
ever lay fertile eggs. Many exotic plants have pollen utterly worthless,
in the same condition as in the most sterile hybrids. When, on the one
hand, we see domesticated animals and plants, though often weak and
sickly, breeding 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 to act, we need not be surprised at
this system, when it does act under confinement, acting irregularly,
and producing offspring somewhat unlike their parents. I may add that
as some organisms breed freely under the most unnatural conditions--for
instance, rabbits and ferrets kept in hutches--showing that their
reproductive organs are not easily affected; so will some animals
and plants withstand domestication or cultivation, and vary very
slightly--perhaps hardly more than in a state of nature.

Some naturalists have maintained that all variations are connected with
the act of sexual reproduction; but this is certainly an error; for I
have given in another work a long list of "sporting plants;" as they are
called by gardeners; that is, of plants which have suddenly produced a
single bud with a new and sometimes widely different character from that
of the other buds on the same plant. These bud variations, as they may
be named, can be propagated by grafts, offsets, etc., and sometimes
by seed. They occur rarely under nature, but are far from rare under
culture. As a single bud out of many thousands produced year after year
on the same tree under uniform conditions, has been known suddenly to
assume a new character; and as buds on distinct trees, growing
under different conditions, have sometimes yielded nearly the same
variety--for instance, buds on peach-trees producing nectarines, and
buds on common roses producing moss-roses--we clearly see that the
nature of the conditions is of subordinate importance in comparison
with the nature of the organism in determining each particular form of
variation; perhaps of not more importance than the nature of the spark,
by which a mass of combustible matter is ignited, has in determining the
nature of the flames.

EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; CORRELATED
VARIATION; INHERITANCE.

Changed habits produce an inherited effect as in the period of the
flowering of plants when transported from one climate to another. With
animals the increased use or disuse of parts has had a more marked
influence; thus 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 this change may
be safely attributed to the domestic duck flying much less, and walking
more, than its wild parents. The great and inherited development of the
udders in cows and goats in countries where they are habitually milked,
in comparison with these organs in other countries, is probably another
instance of the effects of use. Not one of our domestic animals can be
named which has not in some country drooping ears; and the view which
has been suggested that the drooping is due to disuse of the muscles of
the ear, from the animals being seldom much alarmed, seems probable.

Many laws regulate variation, some few of which can be dimly seen, and
will hereafter be briefly discussed. I will here only allude to what may
be called correlated variation. Important changes in the embryo or larva
will probably 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 which are entirely white and have blue eyes are generally
deaf; but it has been lately stated by Mr. Tait that this is confined to
the males. Colour and constitutional peculiarities go together, of which
many remarkable cases could be given among animals and plants. From
facts collected by Heusinger, it appears that white sheep and pigs
are injured by certain plants, while dark-coloured individuals escape:
Professor Wyman has recently communicated to me a good illustration of
this fact; on asking some farmers in Virginia how it was that all their
pigs were black, they informed him that the pigs ate the paint-root
(Lachnanthes), which coloured their bones pink, and which caused
the hoofs of all but the black varieties to drop off; and one of the
"crackers" (i.e. Virginia squatters) added, "we select the black members
of a litter for raising, as they alone have a good chance of living."
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 modify unintentionally other parts of the structure,
owing to the mysterious laws of correlation.

The results of the various, unknown, or but dimly understood laws of
variation are infinitely complex and diversified. It is well worth while
carefully to study the several treatises on some of our old cultivated
plants, as on the hyacinth, potato, even the dahlia, etc.; and it
is really surprising to note the endless points of structure and
constitution in which the varieties and sub-varieties differ slightly
from each other. The whole organisation seems to have become plastic,
and departs in a slight 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,
are endless. Dr. Prosper Lucas' treatise, in two large volumes, is the
fullest and the best on this subject. No breeder doubts how strong is
the tendency to inheritance; that like produces like is his fundamental
belief: doubts have been thrown on this principle only by theoretical
writers. When any deviation of structure often appears, and we see it
in the father and child, we cannot tell whether it may not be due to the
same cause having acted on both; but when among individuals, apparently
exposed to the same conditions, any very rare deviation, due to some
extraordinary combination of circumstances, appears in the parent--say,
once among several million individuals--and it reappears in the
child, the mere doctrine of chances almost compels us to attribute
its reappearance to inheritance. Every one must have heard of cases of
albinism, prickly skin, hairy bodies, etc., appearing in several members
of the same family. If strange and rare deviations of structure are
truly inherited, less strange and commoner deviations may be freely
admitted to be inheritable. Perhaps the correct way of viewing the whole
subject would be, to look at the inheritance of every character whatever
as the rule, and non-inheritance as the anomaly.

The laws governing inheritance are for the most part unknown; no one
can say why the same peculiarity in different individuals of the same
species, or in different species, is sometimes inherited and sometimes
not so; why the child often reverts in certain characteristics to its
grandfather or grandmother or 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 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 the 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 reappear in the offspring at a corresponding
age, though sometimes earlier. In many cases this could not be
otherwise; thus the inherited peculiarities in the horns of cattle could
appear only in the offspring when nearly mature; peculiarities in the
silk-worm are known to appear at the 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 the primary cause which may have acted on the ovules or on the male
element; in nearly the same manner as the increased length of the horns
in the offspring from a short-horned cow by a long-horned bull, 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 invariably 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 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 DEFINITE action of the poor
soil--that they would, to a large extent, or even wholly, revert to the
wild aboriginal stock. Whether or not the experiment would succeed is
not of great importance for our line of argument; for by the experiment
itself the conditions of life are changed. If it could be shown that our
domestic varieties manifested a strong tendency to reversion--that is,
to lose their acquired characters, while kept under the same conditions
and while kept in a considerable body, so that free intercrossing might
check, by blending together, any slight deviations in their structure,
in such case, I grant that we could deduce nothing from domestic
varieties in regard to species. But there is not a shadow of evidence
in favour of this view: to assert that we could not breed our cart
and race-horses, long and short-horned cattle, and poultry of various
breeds, and esculent vegetables, for an unlimited number of generations,
would be opposed to all experience.

CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF DISTINGUISHING BETWEEN
VARIETIES AND SPECIES; ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORE
SPECIES.

When we look to the hereditary varieties or races of our domestic
animals and plants, and compare them with closely allied species, we
generally perceive in each domestic race, as already remarked, less
uniformity of character than in true species. Domestic races often
have a somewhat monstrous character; by which I mean, that, although
differing from each other and from other species of the same genus, in
several trifling respects, they often differ in an extreme degree in
some one part, both when compared one with another, and more especially
when compared with the species under 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
do the closely allied species of the same genus in a state of nature,
but the differences in most cases are less in degree. This must be
admitted as true, for the domestic races of many animals and plants have
been ranked by some competent judges as the descendants of aboriginally
distinct species, and by other competent judges as mere varieties.
If any well marked distinction existed between a domestic race and a
species, this source of doubt would not so perpetually recur. It has
often been stated that domestic races do not differ from each other in
characters of generic value. It can be shown that this statement is not
correct; but naturalists differ much in determining what characters are
of generic value; all such valuations being at present empirical. When
it is explained how genera originate under nature, it will be seen that
we have no right to expect often to find a generic amount of difference
in our domesticated races.

In attempting to estimate the amount of structural difference between
allied domestic races, we are soon involved in doubt, from not knowing
whether they are 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 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 closely
allied natural species--for instance, of the many foxes--inhabiting the
different quarters of the world. I do not believe, as we shall presently
see, that the whole amount of difference between the several breeds of
the dog has been produced under domestication; I believe that a small
part of the difference is due to their being descended from distinct
species. In the case of strongly marked races of some other domesticated
species, there is presumptive or even strong evidence that all are
descended from a single wild stock.

It has often been assumed that man has chosen for domestication animals
and plants having an extraordinary inherent tendency to vary, and
likewise to withstand diverse climates. I do not dispute that these
capacities have added largely to the value of most of our domesticated
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
and goose, or the small power of endurance of warmth by the reindeer,
or of cold by the common camel, prevented their domestication? I
cannot doubt that if other animals and plants, equal in number to our
domesticated productions, and belonging to equally diverse classes and
countries, were taken from a state of nature, and could be made to breed
for an equal number of generations under domestication, they would on
an average vary 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,
it is not possible to come to any definite conclusion, whether they are
descended from one or several wild species. The argument mainly relied
on by those who believe in the multiple origin of our domestic animals
is, that we find in the most ancient times, on the monuments of Egypt,
and in the lake-habitations of Switzerland, much diversity in the
breeds; and that some of these ancient breeds closely resemble, or are
even identical with, those still existing. But this only throws far
backward the history of civilisation, and shows that animals were
domesticated at a much earlier period than has hitherto been supposed.
The lake-inhabitants of Switzerland cultivated several kinds of wheat
and barley, the pea, the poppy for oil and flax; and they possessed
several domesticated animals. They also carried on commerce with other
nations. All this clearly shows, as Heer has remarked, that they had at
this early age progressed considerably in civilisation; and this again
implies a long continued previous period of less advanced civilisation,
during which the domesticated animals, kept by different tribes in
different districts, might have varied and given rise to distinct races.
Since the discovery of flint tools in the superficial formations of many
parts of the world, all geologists believe that barbarian men existed at
an enormously remote period; and we know that at the present day there
is hardly a tribe so barbarous as not to have domesticated at least the
dog.

The origin of most of our domestic animals will probably forever remain
vague. But I may here state that, looking to the domestic dogs of the
whole world, I have, after a laborious collection of all known facts,
come to the conclusion that several wild species of Canidae have been
tamed, and that their blood, in some cases mingled together, flows in
the veins of our domestic breeds. In regard to sheep and goats I can
form no decided opinion. From facts communicated to me by Mr. Blyth,
on the habits, voice, constitution and structure of the humped Indian
cattle, it is almost certain that they are descended from a different
aboriginal stock from our European cattle; and some competent judges
believe that these latter have had two or three wild progenitors,
whether or not these deserve to be called species. This conclusion, as
well as that of the specific distinction between the humped and common
cattle, may, indeed, be looked upon as established by the admirable
researches of Professor Rutimeyer. With respect to horses, from reasons
which I cannot here give, I am doubtfully inclined to believe, in
opposition to several authors, that all the races belong to the same
species. Having kept nearly all the English breeds of the fowl alive,
having bred and crossed them, and examined their skeletons, it appears
to me almost certain that all are the descendants of the wild Indian
fowl, Gallus bankiva; and this is the conclusion of Mr. Blyth, and
of others who have studied this bird in India. In regard to ducks and
rabbits, some breeds of which differ much from each other, the evidence
is clear that they are all descended from the common duck and wild
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 eleven wild species of sheep peculiar to Great Britain! When we
bear in mind that Britain has now not one peculiar mammal, and France
but few distinct from those of Germany, and so with Hungary, Spain,
etc., but that each of these kingdoms possesses several peculiar breeds
of cattle, sheep, etc., we must admit that many domestic breeds must
have originated in Europe; for whence otherwise could they have been
derived? So it is in India. Even in the case of the breeds of the
domestic dog throughout the world, which I admit are descended from
several wild species, it cannot be doubted that there has been an
immense amount of inherited variation; for who will believe that animals
closely resembling the Italian greyhound, the bloodhound, the bull-dog,
pug-dog, or Blenheim spaniel, etc.--so unlike all wild Canidae--ever
existed in a state of nature? It has often been loosely said that all
our races of dogs have been produced by the crossing of a few
aboriginal species; but by crossing we can only get forms in some degree
intermediate between their parents; and if we account for our several
domestic races by this process, we must admit the former existence of
the most extreme forms, as the Italian greyhound, bloodhound, bull-dog,
etc., in the wild state. Moreover, the possibility of making distinct
races by crossing has been greatly exaggerated. Many cases are on record
showing that a race may be modified by occasional crosses if aided
by the careful selection of the individuals which present the desired
character; but to obtain a race intermediate between two quite distinct
races would be very difficult. Sir J. Sebright expressly experimented
with this object and failed. The offspring from the first cross between
two pure breeds is tolerably and sometimes (as I have found with
pigeons) quite uniform in character, and every thing seems simple
enough; but when these mongrels are crossed one with another for several
generations, hardly two of them are alike, and then the difficulty of
the task becomes manifest.

BREEDS OF THE DOMESTIC PIGEON, THEIR DIFFERENCES AND ORIGIN.

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 considerable antiquity. I
have associated with several eminent fanciers, and have been permitted
to join two of the London Pigeon Clubs. The diversity of the breeds is
something astonishing. Compare the English carrier and the short-faced
tumbler, and see the wonderful difference in their beaks, entailing
corresponding differences in their skulls. The carrier, more especially
the male bird, is also remarkable from the wonderful development of the
carunculated skin about the head, and this is accompanied by greatly
elongated eyelids, very large external orifices to the nostrils, and a
wide gape of mouth. The short-faced tumbler has a beak in outline almost
like that of a finch; and the common tumbler has the singular inherited
habit of flying at a great height in a compact flock, and tumbling in
the air head over heels. The runt is a bird of great size, with long,
massive beak and large feet; some of the sub-breeds of runts have very
long necks, others very long wings and tails, others singularly short
tails. The barb is allied to the carrier, but, instead of a long beak,
has a very short and 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 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, 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
the members of the great pigeon family: these feathers are kept expanded
and are carried so erect that in good birds the head and tail touch: the
oil-gland is quite aborted. Several other less distinct breeds might be
specified.

In the skeletons of the several breeds, the development of the bones of
the face, in length and breadth and curvature, differs enormously. The
shape, as well as the breadth and length of the ramus of the lower jaw,
varies in a highly remarkable manner. The caudal and sacral vertebrae
vary in number; 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 the wing and tail to each other and to the body;
the relative length of the leg and foot; 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, and in some breeds the voice and disposition, differ
remarkably. Lastly, in certain breeds, the males and females have come
to differ in 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 be ranked by him as well-defined species. Moreover, I do not
believe that any ornithologist would in this case 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 would call them,
could be shown him.

Great as are the differences between the breeds of the pigeon, I am
fully convinced that the common opinion of naturalists is correct,
namely, that all are 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, they did not breed or willingly perch
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
improbable; or they must have become extinct in the wild state. But
birds breeding on precipices, and good flyers, 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 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 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 difficult to get wild animals 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 of great weight, and applicable in several other cases, is,
that the above-specified breeds, though agreeing generally with the wild
rock-pigeon in constitution, habits, voice, colouring, and in most parts
of their structure, yet are certainly highly abnormal in other parts; we
may look in vain through 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 are 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, with white loins;
but the Indian sub-species, C. intermedia of Strickland, has this
part bluish. The tail has a terminal dark bar, with the outer feathers
externally edged at the base with white. The wings have two black bars.
Some semi-domestic breeds, and some 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 birds belonging to
two or more distinct breeds are crossed, none of which are blue or have
any of the above-specified marks, the mongrel offspring are very apt
suddenly to acquire these characters. To give one instance out of
several which I have observed: I crossed some white fantails, which
breed very true, with some black barbs--and it so happens that blue
varieties of barbs are so rare that I never heard of an instance in
England; and the mongrels were black, brown and mottled. I also crossed
a barb with a spot, which is a white bird with a red tail and red spot
on the forehead, and which notoriously breeds very true; the mongrels
were dusky and mottled. I then crossed one of the mongrel barb-fantails
with a mongrel barb-spot, and they produced a bird of as beautiful a
blue colour, with the white loins, 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 are descended from the
rock-pigeon. But if we deny this, we must make one of the two following
highly improbable suppositions. Either, first, 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 no instance is known of crossed descendants
reverting to an ancestor of foreign blood, removed by a greater number
of generations. In a breed which has been crossed only once the tendency
to revert to any character derived from such a 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, and there
is a tendency in the breed to revert to a character which was 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 of reversion are often
confounded together by those who have written on inheritance.

Lastly, the hybrids or mongrels from between all the breeds of the
pigeon are perfectly fertile, as I can state from my own observations,
purposely made, on the most distinct breeds. Now, hardly any cases
have been ascertained with certainty of hybrids from two quite distinct
species of animals being perfectly fertile. Some authors believe
that long-continued domestication eliminates this strong tendency to
sterility in species. From the history of the dog, and of some other
domestic animals, this conclusion is probably quite correct, if applied
to species closely related to each other. But to extend it 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 made seven or eight supposed species of pigeons to breed freely
under domestication--these supposed species being quite unknown in a
wild state, and their not having become anywhere feral--these species
presenting certain very abnormal characters, as compared with all other
Columbidae, though so like the rock-pigeon in most other respects--the
occasional reappearance of the blue colour and various black marks in
all the breeds, both when kept pure and when crossed--and lastly, the
mongrel offspring being perfectly fertile--from these several reasons,
taken together, we may safely conclude that all our domestic breeds are
descended from the rock-pigeon or Columba livia with its geographical
sub-species.

In favour of this view, I may add, firstly, that the wild C. livia 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, that although an English carrier or a
short-faced tumbler differs immensely in certain characters from the
rock-pigeon, yet that by comparing the several sub-breeds of these two
races, more especially those brought from distant countries, we can
make, between them and the rock-pigeon, an almost perfect series; so
we can in some other cases, but not with all the breeds. Thirdly,
those characters which are mainly distinctive of each breed are in each
eminently variable, 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; and the explanation of this fact will be
obvious when we 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 likewise be
obvious when we treat of selection. We shall then, also, see how it is
that the several 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, well knowing how truly they breed, I
felt fully as much difficulty in believing that since they had been
domesticated they had all proceeded from a common parent, as any
naturalist could in coming to a similar conclusion in regard to the
many species of finches, or other groups of birds, in nature. One
circumstance has struck me much; namely, that nearly all the breeders of
the various domestic animals and the cultivators of plants, with whom
I have 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, or both from a common parent-stock, 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 are 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?

PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED, AND THEIR EFFECTS.

Let us now briefly consider the steps by which domestic races have been
produced, either from one or from several allied species. Some effect
may be attributed to the direct and definite action of the external
conditions of life, and some to habit; but he would be a bold man who
would account by such agencies for the differences between 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 teasel, with its hooks, which can not 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 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 can not suppose
that all the breeds were suddenly produced as perfect and as useful as
we now see them; indeed, in many 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 have made 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 their 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 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 animals, 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." 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 been
exported to almost every quarter of the world. The improvement is by no
means generally due to crossing different breeds; all the best breeders
are strongly opposed to this practice, except sometimes among closely
allied sub-breeds. And when a cross has been made, the closest selection
is far more indispensable even than in ordinary cases. If selection
consisted merely in separating some very distinct variety and 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 several 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, likewise followed; for hardly any one is so
careless as to breed from his worst animals.

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--I speak after careful observation--perhaps never, the case. The
law of correlated variation, the importance of which should never be
overlooked, will ensure some differences; but, as a general rule, it
cannot be doubted that the continued selection of slight variations,
either in the leaves, the flowers, or the fruit, will produce races
differing from each other chiefly in these characters.

It may be objected that the principle of selection has been reduced to
methodical practice for scarcely more than three-quarters of a century;
it has certainly been more attended to of late years, and many treatises
have been published on the subject; and the result has been, in a
corresponding degree, rapid and important. But it is very far from
true that the principle is a modern discovery. I could give several
references to works of high antiquity, in which the full importance of
the principle is acknowledged. 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
states that good domestic breeds are highly valued by the negroes in 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.

UNCONSCIOUS SELECTION.

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 of the kind in the country. But, for our purpose, a form 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 we may infer that this process, continued during
centuries, would improve and modify any breed, in the same way as
Bakewell, Collins, etc., by this very same process, only carried on more
methodically, did greatly modify, even during their 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 have been made long ago, which may serve for
comparison. In some cases, however, unchanged, or but little changed,
individuals of the same breed exist in less civilised districts, where
the breed has been less improved. There is reason to believe that King
Charles' 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 foxhound; 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, English
race-horses have come to surpass in fleetness and size the parent Arabs,
so that the latter, by the regulations for the Goodwood Races, are
favoured in the weights which 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 various old treatises of the former
and present state of carrier and tumbler pigeons in Britain, India,
and Persia, we can 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 unconscious, in so far that the
breeders could never have expected, or even wished, to produce the
result which ensued--namely, the production of the 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 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 chanced
to appear, selecting it, and so onwards. But the gardeners of the
classical period, who cultivated the best pears which 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, thus slowly and unconsciously accumulated,
explains, as I believe, the well-known fact, that in a 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 acquired by 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 why the
varieties kept by savages, as has been remarked by some authors,
have more of the character of true species than the varieties kept in
civilised countries.

On the view here given of the 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
have been set on any slight differences in the individuals of the same
species, be judged of by the value which is now set on them, after
several breeds have fairly been established. It is known that with
pigeons many slight variations now occasionally appear, but these are
rejected as faults or deviations from the standard of perfection in
each breed. The common goose has not given rise to any marked varieties;
hence the Toulouse and the common breed, which differ only in colour,
that most fleeting of characters, have lately been exhibited as distinct
at our poultry-shows.

These views appear to explain what has sometimes been noticed, namely,
that we know hardly anything 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 a distinct 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 animals slowly spread in the immediate
neighbourhood. But they will as yet hardly have a distinct name,
and from being only slightly valued, their history will have been
disregarded. When further improved by the same slow and gradual process,
they will spread more widely, and will be 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 of a new sub-breed will be a slow process. As soon as the
points of value are once 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.

CIRCUMSTANCES FAVOURABLE TO MAN'S POWER OF SELECTION.

I will 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. Hence number is of the highest importance for
success. On this principle Marshall formerly remarked, with respect
to the sheep of part of Yorkshire, "As they generally belong to poor
people, and are mostly IN SMALL LOTS, they never can be improved." On
the other hand, nurserymen, from keeping large stocks of the same plant,
are generally far more successful than amateurs in raising new and
valuable varieties. A large number of individuals of an animal or
plant can be reared only where the conditions for its propagation are
favourable. When the individuals are scanty all will be allowed to
breed, whatever their quality may be, and this will effectually prevent
selection. But probably the most important element is that the animal or
plant should be so highly valued by man, that the closest attention is
paid to even the slightest deviations in its qualities or structure.
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 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 (with some aid by crossing distinct species)
those many admirable varieties of the strawberry were raised which have
appeared during the last half-century.

With animals, facility in preventing crosses is an important element
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 improved and kept true, though mingled in the same aviary; and this
circumstance must have largely favoured the 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, can not be easily matched, and, although so much valued
by women and children, we rarely see a distinct breed long kept up; such
breeds as we do sometimes see are almost always imported from some other
country. Although I do not doubt that some domestic animals vary less
than others, yet the rarity or absence of distinct breeds of the cat,
the donkey, peacock, goose, etc., may be attributed in main part
to selection not having been brought into play: in cats, from the
difficulty in pairing them; in donkeys, from only a few being kept by
poor people, and little attention paid to their breeding; for recently
in certain parts of Spain and of the United States this animal has been
surprisingly modified and improved by careful selection; 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; but the goose, under the conditions to which it is exposed when
domesticated, seems to have a singularly inflexible organisation, though
it has varied to a slight extent, as I have elsewhere described.

Some authors have maintained that the amount of variation in our
domestic productions is soon reached, and can never afterward be
exceeded. It would be somewhat rash to assert that the limit has been
attained in any one case; for almost all our animals and plants have
been greatly improved in many ways within a recent period; and this
implies variation. It would be equally rash to assert that characters
now increased to their utmost limit, could not, after remaining fixed
for many centuries, again vary under new conditions of life. No doubt,
as Mr. Wallace has remarked with much truth, a limit will be at last
reached. For instance, there must be a limit to the fleetness of any
terrestrial animal, as this will be determined by the friction to
be overcome, the weight of the body to be carried, and the power of
contraction in the muscular fibres. But what concerns us is that the
domestic varieties of the same species differ from each other in almost
every character, which man has attended to and selected, more than do
the distinct species of the same genera. Isidore Geoffroy St. Hilaire
has proved this in regard to size, and so it is with colour, and
probably with the length of hair. With respect to fleetness, which
depends on many bodily characters, Eclipse was far fleeter, and
a dray-horse is comparably stronger, than any two natural species
belonging to the same genus. So with plants, the seeds of the different
varieties of the bean or maize probably differ more in size than do the
seeds of the distinct species in any one genus in the same two families.
The same remark holds good in regard to the fruit of the several
varieties of the plum, and still more strongly with the melon, as well
as in many other analogous cases.

To sum up on the origin of our domestic races of animals and plants.
Changed conditions of life are of the highest importance in causing
variability, both by acting directly on the organisation, and
indirectly by affecting the reproductive system. It is not probable
that variability is an inherent and necessary contingent, under all
circumstances. The greater or less force of inheritance and reversion
determine whether variations shall endure. Variability is governed
by many unknown laws, of which correlated growth is probably the most
important. Something, but how much we do not know, may be attributed to
the definite action of the conditions of life. Some, perhaps a great,
effect may be attributed to the increased use or disuse of parts. The
final result is thus rendered infinitely complex. In some cases the
intercrossing of aboriginally distinct species appears to have played
an important part in the origin of our breeds. When several breeds have
once been formed in any country, their occasional intercrossing, with
the aid of selection, has, no doubt, largely aided in the formation
of new sub-breeds; but the importance of crossing has been much
exaggerated, both in regard to animals and to those plants which are
propagated by seed. With plants which are temporarily propagated by
cuttings, buds, etc., the importance of crossing is immense; for the
cultivator may here disregard the extreme variability both of hybrids
and of mongrels, and the sterility of hybrids; but plants not propagated
by seed are of little importance to us, for their endurance is only
temporary. Over all these causes of change, the accumulative action of
selection, whether applied methodically and quickly, or unconsciously
and slowly, but more efficiently, seems to have been 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 each country vary more frequently 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 properly, a
long catalogue of dry facts ought to be given; but these I shall reserve
for a future work. Nor shall I here discuss the various definitions
which have been given of the term species. No one definition has
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,
generally injurious, or not useful to the species. 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 a few
generations? And in this case I presume that the form would be called a
variety.

It may be doubted whether sudden and considerable deviations of
structure, such as we occasionally see in our domestic productions, more
especially with plants, are ever permanently propagated in a state
of nature. Almost every part of every organic being is so beautifully
related to its complex conditions of life that it seems as improbable
that any part should have been suddenly produced perfect, as that a
complex machine should have been invented by man in a perfect state.
Under domestication monstrosities sometimes occur which resemble normal
structures in widely different animals. Thus pigs have occasionally been
born with a sort of proboscis, and if any wild species of the same genus
had naturally possessed a proboscis, it might have been argued that this
had appeared as a monstrosity; but I have as yet failed to find, after
diligent search, cases of monstrosities resembling