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Neural Dot Net Pt 3 The Adaline Network

, 23 Oct 2003
A neural network library in C#.
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                                     1859
                             THE ORIGIN OF SPECIES
                               by Charles Darwin
                                      1859
INTRODUCTION
  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.
cannot here give references and authorities for my several statements;
and I must trust to the reader reposing some confidence in my
accuracy. No doubt errors will have crept in, though I hope I have
always been cautious in trusting to good authorities alone. I can here
give only the general conclusions at which I have arrived, with a
few facts in illustration, but which, I hope, in most cases will
suffice. No one can feel more sensible than I do of the necessity of
hereafter publishing in detail all the facts, with references, on
which my conclusions have been grounded; and I hope in a future work
to do this. For I am well aware that scarcely a single point is
discussed in this volume on which facts cannot be adduced, often
apparently leading to conclusions directly opposite to those at
which I have arrived. A fair result can be obtained only by fully
stating and balancing the facts and arguments on both sides of each
question; and this 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,
&c., 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 amongst 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

  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 indirectly 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 incidentally 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 indefinite. 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, &c. 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, show us what singular modifications might
result in the case of plants from a chemical change in the nature of
the sap.
  Indefinite 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
indefinite 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 amongst many individuals living together, may be
considered as the indefinite effects of the conditions of life on each
individual organism, in nearly the same manner as the chill affects
different men in an indefinite 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 indirect 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 Kreuter 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 exceptions, 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, &c., and sometimes by seed. They occur rarely under
nature, but are far from rare under culture. As a single bud out of
the 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 amongst animals and plants. From facts
collected by Heusinger, it appears that white sheep and pigs are
injured by certain plants, whilst 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, &c.;
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's treatise, in two large
volumes, is the fullest and the best on this subject. No breeder
doubts how strong is the tendency to inheritance; 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 amongst individuals, apparently exposed to the same
conditions, any very rare deviation, due to some extraordinary
combination of circumstances, appears in the parent- say, once amongst
several million individuals- and it reappears in the child, the mere
doctrine of chances almost compels us to attribute its reappearance to
inheritance. Every one must have heard of cases of albinism, prickly
skin, hairy bodies, &c., appearing in several members of the same
family. If strange and rare deviations of structure are really
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 characters 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 silkworm are known to appear at the
corresponding caterpillar or cocoon stage. But hereditary diseases and
some other facts make me believe that the rule has a wider
extension, and that, when there is no apparent reason why a
peculiarity should appear at any particular age, yet that it does tend
to appear in the offspring at the same period at which it first
appeared in the parent. I believe this rule to be of the highest
importance in explaining the laws of embryology. These remarks are
of course confined to the first appearance of the peculiarity, and not
to 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 have been 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, whilst kept
under the same conditions, and whilst 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 character 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 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 backwards 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
Reer 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 man 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 for ever
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 wild duck and
rabbit.
  The doctrine of the origin of our several domestic races from
several aboriginal stocks, has been carried to an absurd extreme by
some authors. They believe that every race which breeds true, let
the distinctive characters be ever so slight, has had its wild
prototype. At this rate there must have existed at least a score of
species of wild cattle, as many sheep, and several goats, in Europe
alone, and several even within Great Britain. One author believes that
there formerly existed 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, &c., but that each of these kingdoms
possesses several peculiar breeds of cattle, sheep, &c., 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,
&c.- 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, bulldog, &c., 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 everything 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 tailfeathers, 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 fliers, are unlikely to be
exterminated; and the common rock-pigeon, which has the same habits
with the domestic breeds, has not been exterminated even on several of
the smaller British islets, or on the shores of the Mediterranean.
Hence the supposed extermination of so many species having similar
habits with the rock-pigeon seems 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 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-civilised 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-civilised 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
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, would be 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 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 tailfeathers 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 90,000
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 cannot be rivalled by any mechanical
contrivance, is only a variety of the wild Dipsacus; and this amount
of change may have suddenly arisen in a seedling. So it has probably
been with the turnspit dog; and this is known to have been the case
with the ancon sheep. But when we compare the dray-horse and
race-horse, the dromedary and camel, the various breeds of sheep
fitted either for cultivated land or mountain pasture, with the wool
of one breed good for one purpose, and that of another breed for
another purpose; when we compare the many breeds of dogs, each good
for man in different ways; when we compare the game-cock, so
pertinacious in battle, with other breeds so little quarrelsome,
with "everlasting layers" which never desire to sit, and with the
bantam so small and elegant; when we compare the host of agricultural,
culinary, orchard, and flower-garden races of plants, most useful to
man at different seasons and for different purposes, or so beautiful
in his eyes, we must, I think, look further than to mere
variability. We cannot suppose that all the breeds were suddenly
produced as perfect and as useful as we now see them; indeed, in
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 as
they please. If I had space I could quote numerous passages to this
effect from highly competent authorities. Youatt, who was probably
better acquainted with the works of agriculturists than almost any
other 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 generally due to crossing different breeds; all the best
breeders are strongly opposed to this practice, except sometimes
amongst closely allied sub-breeds. And when a cross has been made, the
closest selection is far more indispensable even than in ordinary
cases. If selection consisted merely in separating some very
distinct variety, and breeding from it, the principle would be so
obvious as hardly to be worth notice; but its importance consists in
the great effect produced by the accumulation in one direction, during
successive generations, of differences absolutely inappreciable by
an uneducated eye- differences which I for one have vainly attempted
to appreciate. Not one man in a thousand has accuracy of eye and
judgment sufficient to become an eminent breeder. If, gifted with
these qualities, 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 has not been 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, &c., 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 can 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's
spaniel has been unconsciously modified to a large extent since the
time of that monarch. Some highly competent authorities are
convinced that the setter is directly derived from the spaniel, and
has probably been slowly altered from it. It is known that the English
pointer has been greatly changed within the last century, and in
this case the change has, it is believed, been chiefly effected by
crosses with the 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 two distinct strains.
The two flocks of Leicester sheep kept by Mr. Buckley and Mr. Burgess,
as Mr. Youatt remarks, "have been purely bred from the original
stock of Mr. Bakewell for upwards of fifty years. There is not a
suspicion existing in the mind of any one at all acquainted with the
subject, that the owner of either of them has deviated in any one
instance from the pure blood of Mr. Bakewell's flock, and yet the
difference between the sheep possessed by these two gentlemen is so
great that they have the appearance of being quite different
varieties."
  If there exist savages so barbarous as never to think of the
inherited character of the offspring of their domestic animals, yet
any one animal particularly useful to them, for any special purpose,
would be carefully preserved during famines and other accidents, to
which savages are so liable, and such choice animals would thus
generally leave more offspring than the inferior ones; so that in this
case there would be a kind of unconscious selection going on. We see
the value set on animals even by the barbarians of Tierra del Fuego,
by their killing and devouring their old women, in times of dearth, as
of less value than their dogs.
  In plants the same gradual process of improvement, through the
occasional preservation of the best individuals, whether or not
sufficiently distinct to be ranked at their first appearance, as
distinct varieties, and whether or not two or more species or races
have become blended together by crossing, may plainly be recognised in
the increased size and beauty which we now see in the varieties of the
heartsease, rose, pelargonium, dahlia, and other plants, when compared
with the older varieties or with their parent-stocks. No one would
ever expect to get a first-rate heartsease or dahlia from the seed
of a wild plant. No one would expect to raise a first-rate melting
pear from the seed of the wild pear, though he might succeed from a
poor seedling growing wild, if it had come from a garden-stock. The
pear, though cultivated in classical times, appears, from Pliny's
description, to have been a fruit of very inferior quality. I have
seen great surprise expressed in horticultural works at the
wonderful skill of gardeners, in having produced such splendid results
from such poor materials; but the art 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 characters 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.
I 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. 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 would
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 parts 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
slightest 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 cannot 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, &c., may be attributed in main part to selection not
having been brought into play: in cats, from the difficulty in pairing
them; in donkeys, from only a few being kept by poor people, and
little attention paid to their breeding; 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 afterwards 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 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 incomparably 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, &c., 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.

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