CHAPTER 2.XXVIII._The Variation of Animals and Plants under Domestication

CONCLUDING REMARKS.

DOMESTICATION.

NATURE AND CAUSES OF VARIABILITY.

SELECTION.

DIVERGENCE AND DISTINCTNESS OF CHARACTER.

EXTINCTION OF RACES.

CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN.

ANTIQUITY OF CERTAIN RACES.

THE QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED.

As summaries have been added to nearly all the chapters, and as, in the

chapter on pangenesis, various subjects, such as the forms of reproduction,

inheritance, reversion, the causes and laws of variability, etc., have been

recently discussed, I will here only make a few general remarks on the more

important conclusions which may be deduced from the multifarious details given

throughout this work.

Savages in all parts of the world easily succeed in taming wild animals; and

those inhabiting any country or island, when first visited by man, would

probably have been still more easily tamed. Complete subjugation generally

depends on an animal being social in its habits, and on receiving man as the

chief of the herd or family. In order that an animal should be domesticated it

must be fertile under changed conditions of life, and this is far from being

always the case. An animal would not have been worth the labour of

domestication, at least during early times, unless of service to man. From

these circumstances the number of domesticated animals has never been large.

With respect to plants, I have shown in the ninth chapter how their varied

uses were probably first discovered, and the early steps in their cultivation.

Man could not have known, when he first domesticated an animal or plant,

whether it would flourish and multiply when transported to other countries,

therefore he could not have been thus influenced in his choice. We see that

the close adaptation of the reindeer and camel to extremely cold and hot

countries has not prevented their domestication. Still less could man have

foreseen whether his animals and plants would vary in succeeding generations

and thus give birth to new races; and the small capacity of variability in the

goose has not prevented its domestication from a remote epoch.

With extremely few exceptions, all animals and plants which have been long

domesticated have varied greatly. It matters not under what climate, or for

what purpose they are kept, whether as food for man or beast, for draught or

hunting, for clothing or mere pleasure,--under all these circumstances races

have been produced which differ more from one another than do the forms which

in a state of nature are ranked as different species. Why certain animals and

plants have varied more under domestication than others we do not know, any

more than why some are rendered more sterile than others under changed

conditions of life. But we have to judge of the amount of variation which our

domestic productions have undergone, chiefly by the number and amount of

difference between the races which have been formed, and we can often clearly

see why many and distinct races have not been formed, namely, because slight

successive variations have not been steadily accumulated; and such variations

will never be accumulated if an animal or plant be not closely observed, much

valued, and kept in large numbers.

The fluctuating, and, as far as we can judge, never-ending variability of our

domesticated productions,--the plasticity of almost their whole organisation,-

-is one of the most important lessons which we learn from the numerous details

given in the earlier chapters of this work. Yet domesticated animals and

plants can hardly have been exposed to greater changes in their conditions of

life than have many natural species during the incessant geological,

geographical, and climatal changes to which the world has been subject; but

domesticated productions will often have been exposed to more sudden changes

and to less continuously uniform conditions. As man has domesticated so many

animals and plants belonging to widely different classes, and as he certainly

did not choose with prophetic instinct those species which would vary most, we

may infer that all natural species, if exposed to analogous conditions, would,

on an average, vary to the same degree. Few men at the present day will

maintain that animals and plants were created with a tendency to vary, which

long remained dormant, in order that fanciers in after ages might rear, for

instance, curious breeds of the fowl, pigeon, or canary-bird.

From several causes it is difficult to judge of the amount of modification

which our domestic productions have undergone. In some cases the primitive

parent-stock has become extinct; or it cannot be recognised with certainty,

owing to its supposed descendants having been so much modified. In other cases

two or more closely-allied forms, after being domesticated, have crossed; and

then it is difficult to estimate how much of the character of the present

descendants ought to be attributed to variation, and how much to the influence

of the several parent-stocks. But the degree to which our domesticated breeds

have been modified by the crossing of distinct species has probably been much

exaggerated by some authors. A few individuals of one form would seldom

permanently affect another form existing in greater numbers; for, without

careful selection, the stain of the foreign blood would soon be obliterated,

and during early and barbarous times, when our animals were first

domesticated, such care would seldom have been taken.

There is good reason to believe in the case of the dog, ox, pig, and of some

other animals, that several of our races are descended from distinct wild

prototypes; nevertheless the belief in the multiple origin of our domesticated

animals has been extended by some few naturalists and by many breeders to an

unauthorised extent. Breeders refuse to look at the whole subject under a

single point of view; I have heard it said by a man, who maintained that our

fowls were descended from at least half-a-dozen aboriginal species, that the

evidence of the common origin of pigeons, ducks and rabbits, was of no avail

with respect to fowls. Breeders overlook the improbability of many species

having been domesticated at an early and barbarous period. They do not

consider the improbability of species having existed in a state of nature

which, if they resembled our present domestic breeds, would have been highly

abnormal in comparison with all their congeners. They maintain that certain

species, which formerly existed, have become extinct, or are now unknown,

although formerly known. The assumption of so much recent extinction is no

difficulty in their eyes; for they do not judge of its probability by the

facility or difficulty of the extinction of other closely-allied wild forms.

Lastly, they often ignore the whole subject of geographical distribution as

completely as if it were the result of chance.

Although from the reasons just assigned it is often difficult to judge

accurately of the amount of change which our domesticated productions have

undergone, yet this can be ascertained in the cases in which all the breeds

are known to be descended from a single species,--as with the pigeon, duck,

rabbit, and almost certainly with the fowl; and by the aid of analogy this can

be judged of to a certain extent with domesticated animals descended from

several wild stocks. It is impossible to read the details given in the earlier

chapters and in many published works, or to visit our various exhibitions,

without being deeply impressed with the extreme variability of our

domesticated animals and cultivated plants. No part of the organisation

escapes the tendency to vary. The variations generally affect parts of small

vital or physiological importance, but so it is with the differences which

exist between closely-allied species. In these unimportant characters there is

often a greater difference between the breeds of the same species than between

the natural species of the same genus, as Isidore Geoffroy has shown to be the

case with size, and as is often the case with the colour, texture, form, etc.,

of the hair, feathers, horns, and other dermal appendages.

It has often been asserted that important parts never vary under

domestication, but this is a complete error. Look at the skull of the pig in

any one of the highly improved breeds, with the occipital condyles and other

parts greatly modified; or look at that of the niata ox. Or, again, in the

several breeds of the rabbit, observe the elongated skull, with the

differently shaped occipital foramen, atlas, and other cervical vertebrae. The

whole shape of the brain, together with the skull, has been modified in Polish

fowls; in other breeds of the fowl the number of the vertebrae and the forms

of the cervical vertebrae have been changed. In certain pigeons the shape of

the lower jaw, the relative length of the tongue, the size of the nostrils and

eyelids, the number and shape of the ribs, the form and size of the

oesophagus, have all varied. In certain quadrupeds the length of the

intestines has been much increased or diminished. With plants we see wonderful

differences in the stones of various fruits. In the Cucurbitaceae several

highly important characters have varied, such as the sessile position of the

stigmas on the ovarium, the position of the carpels, and the projection of the

ovarium out of the receptacle. But it would be useless to run through the many

facts given in the earlier chapters.

It is notorious how greatly the mental disposition, tastes, habits, consensual

movements, loquacity or silence, and tone of voice have varied and been

inherited in our domesticated animals. The dog offers the most striking

instance of changed mental attributes, and these differences cannot be

accounted for by descent from distinct wild types.

New characters may appear and old ones disappear at any stage of development,

being inherited at a corresponding stage. We see this in the difference

between the eggs, the down on the chickens and the first plumage of the

various breeds of the fowl; and still more plainly in the differences between

the caterpillars and cocoons of the various breeds of the silk-moth. These

facts, simple as they appear, throw light on the differences between the

larval and adult states of allied natural species, and on the whole great

subject of embryology. New characters first appearing late in life are apt to

become attached exclusively to that sex in which they first arose, or they may

be developed in a much higher degree in this than in the other sex; or again,

after having become attached to one sex, they may be transferred to the

opposite sex. These facts, and more especially the circumstance that new

characters seem to be particularly liable, from some unknown cause, to become

attached to the male sex, have an important bearing on the acquirement of

secondary sexual characters by animals in a state of nature.

It has sometimes been said that our domestic races do not differ in

constitutional peculiarities, but this cannot be maintained. In our improved

cattle, pigs, etc., the period of maturity, including that of the second

dentition, has been much hastened. The period of gestation varies much, and

has been modified in a fixed manner in one or two cases. In some breeds of

poultry and pigeons the period at which the down and the first plumage are

acquired, differs. The number of moults through which the larvae of silk-moths

pass, varies. The tendency to fatten, to yield much milk, to produce many

young or eggs at a birth or during life, differs in different breeds. We find

different degrees of adaptation to climate, and different tendencies to

certain diseases, to the attacks of parasites, and to the action of certain

vegetable poisons. With plants, adaptation to certain soils, the power of

resisting frost, the period of flowering and fruiting, the duration of life,

the period of shedding the leaves or of retaining them throughout the winter,

the proportion and nature of certain chemical compounds in the tissues or

seeds, all vary.

There is, however, one important constitutional difference between domestic

races and species; I refer to the sterility which almost invariably follows,

in a greater or less degree, when species are crossed, and to the perfect

fertility of the most distinct domestic races, with the exception of a very

few plants, when similarly crossed. It is certainly a most remarkable fact

that many closely-allied species, which in appearance differ extremely little,

should yield when crossed only a few more or less sterile offspring, or none

at all; whilst domestic races which differ conspicuously from each other are,

when united, remarkably fertile, and yield perfectly fertile offspring. But

this fact is not in reality so inexplicable as it at first appears. In the

first place, it was clearly shown in the nineteenth chapter that the sterility

of crossed species does not depend chiefly on differences in their external

structure or general constitution, but on differences in the reproductive

system, analogous to those which cause the lessened fertility of the

illegitimate unions of dimorphic and trimorphic plants. In the second place,

the Pallasian doctrine, that species after having been long domesticated lose

their natural tendency to sterility when crossed, has been shown to be highly

probable or almost certain. We cannot avoid this conclusion when we reflect on

the parentage and present fertility of the several breeds of the dog, of the

Indian or humped and European cattle, and of the two chief kinds of pigs.

Hence it would be unreasonable to expect that races formed under domestication

should acquire sterility when crossed, whilst at the same time we admit that

domestication eliminates the normal sterility of crossed species. Why with

closely-allied species their reproductive systems should almost invariably

have been modified in so peculiar a manner as to be mutually incapable of

acting on each other--though in unequal degrees in the two sexes, as shown by

the difference in fertility between reciprocal crosses of the same species--we

do not know, but may with much probability infer the cause to be as follows.

Most natural species have been habituated to nearly uniform conditions of life

for an incomparably longer time than have domestic races; and we positively

know that changed conditions exert an especial and powerful influence on the

reproductive system. Hence this difference may well account for the difference

in the power of reproduction between domestic races when crossed and species

when crossed. It is probably in chief part owing to the same cause that

domestic races can be suddenly transported from one climate to another, or

placed under widely different conditions, and yet retain in most cases their

fertility unimpaired; whilst a multitude of species subjected to lesser

changes are rendered incapable of breeding.

The offspring of crossed domestic races and of crossed species resemble each

other in most respects, with the one important exception of fertility; they

often partake in the same unequal degree of the characters of their parents,

one of which is often prepotent over the other; and they are liable to

reversion of the same kind. By successive crosses one species may be made to

absorb completely another, and so it notoriously is with races. The latter

resemble species in many other ways. They sometimes inherit their newly-

acquired characters almost or even quite as firmly as species. The conditions

leading to variability and the laws governing its nature appear to be the same

in both. Varieties can be classed in groups under groups, like species under

genera, and these under families and orders; and the classification may be

either artificial,--that is, founded on any arbitrary character,--or natural.

With varieties a natural classification is certainly founded, and with species

is apparently founded, on community of descent, together with the amount of

modification which the forms have undergone. The characters by which domestic

varieties differ from one another are more variable than those distinguishing

species, though hardly more so than with certain polymorphic species; but this

greater degree of variability is not surprising, as varieties have generally

been exposed within recent times to fluctuating conditions of life, and are

much more liable to have been crossed; they are also in many cases still

undergoing, or have recently undergone, modification by man's methodical or

unconscious selection.

Domestic varieties as a general rule certainly differ from one another in less

important parts than do species; and when important differences occur, they

are seldom firmly fixed; but this fact is intelligible, if we consider man's

method of selection. In the living animal or plant he cannot observe internal

modifications in the more important organs; nor does he regard them as long as

they are compatible with health and life. What does the breeder care about any

slight change in the molar teeth of his pigs, or for an additional molar tooth

in the dog; or for any change in the intestinal canal or other internal organ?

The breeder cares for the flesh of his cattle being well marbled with fat, and

for an accumulation of fat within the abdomen of his sheep, and this he has

effected. What would the floriculturist care for any change in the structure

of the ovarium or of the ovules? As important internal organs are certainly

liable to numerous slight variations, and as these would probably be

transmitted, for many strange monstrosities are inherited, man could

undoubtedly effect a certain amount of change in these organs. When he has

produced any modification in an important part, he has generally done so

unintentionally, in correlation with some other conspicuous part. For

instance, he has given ridges and protuberances to the skulls of fowls, by

attending to the form of the comb, or to the plume of feathers on the head. By

attending to the external form of the pouter-pigeon, he has enormously

increased the size of the oesophagus, and has added to the number of the ribs,

and given them greater breadth. With the carrier-pigeon, by increasing through

steady selection the wattles on the upper mandible, he has greatly modified

the form of the lower mandible; and so in many other cases. Natural species,

on the other hand, have been modified exclusively for their own good, to fit

them for infinitely diversified conditions of life, to avoid enemies of all

kinds, and to struggle against a host of competitors. Hence, under such

complex conditions, it would often happen that modifications of the most

varied kinds, in important as well as in unimportant parts, would be

advantageous or even necessary; and they would slowly but surely be acquired

through the survival of the fittest. Still more important is the fact that

various indirect modifications would likewise arise through the law of

correlated variation.

Domestic breeds often have an abnormal or semi-monstrous character, as amongst

dogs, the Italian greyhound, bulldog, Blenheim spaniel, and bloodhound,--some

breeds of cattle and pigs,--several breeds of the fowl,--and the chief breeds

of the pigeon. In such abnormal breeds, parts which differ but slightly or not

at all in the allied natural species, have been greatly modified. This may be

accounted for by man's often selecting, especially at first, conspicuous and

semi-monstrous deviations of structure. We should, however, be cautious in

deciding what deviations ought to be called monstrous: there can hardly be a

doubt that, if the brush of horse-like hair on the breast of the turkey-cock

had first appeared in the domesticated bird, it would have been considered as

a monstrosity; the great plume of feathers on the head of the Polish cock has

been thus designated, though plumes are common on the heads of many kinds of

birds; we might call the wattle or corrugated skin round the base of the beak

of the English carrier-pigeon a monstrosity, but we do not thus speak of the

globular fleshy excrescence at the base of the beak of the Carpophaga

oceanica.

Some authors have drawn a wide distinction between artificial and natural

breeds; although in extreme cases the distinction is plain, in many other

cases it is arbitrary; the difference depending chiefly on the kind of

selection which has been applied. Artificial breeds are those which have been

intentionally improved by man; they frequently have an unnatural appearance,

and are especially liable to lose their characters through reversion and

continued variability. The so-called natural breeds, on the other hand, are

those which are found in semi-civilised countries, and which formerly

inhabited separate districts in nearly all the European kingdoms. They have

been rarely acted on by man's intentional selection; more frequently by

unconscious selection, and partly by natural selection, for animals kept in

semi-civilised countries have to provide largely for their own wants. Such

natural breeds will also have been directly acted on by the differences,

though slight, in the surrounding conditions.

There is a much more important distinction between our several breeds, namely,

in some having originated from a strongly-marked or semi-monstrous deviation

of structure, which, however, may subsequently have been augmented by

selection; whilst others have been formed in so slow and insensible a manner,

that if we could see their early progenitors we should hardly be able to say

when or how the breed first arose. From the history of the racehorse,

greyhound, gamecock, etc., and from their general appearance, we may feel

nearly confident that they were formed by a slow process of improvement; and

we know that this has been the case with the carrier-pigeon, as well as with

some other pigeons. On the other hand, it is certain that the ancon and

mauchamp breeds of sheep, and almost certain that the niata cattle, turnspit,

and pug-dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-

billed ducks, etc., suddenly appeared in nearly the same state as we now see

them. So it has been with many cultivated plants. The frequency of these cases

is likely to lead to the false belief that natural species have often

originated in the same abrupt manner. But we have no evidence of the

appearance, or at least of the continued procreation, under nature, of abrupt

modifications of structure; and various general reasons could be assigned

against such a belief.

On the other hand, we have abundant evidence of the constant occurrence under

nature of slight individual differences of the most diversified kinds; and we

are thus led to conclude that species have generally originated by the natural

selection of extremely slight differences. This process may be strictly

compared with the slow and gradual improvement of the racehorse, greyhound,

and gamecock. As every detail of structure in each species has to be closely

adapted to its habits of life, it will rarely happen that one part alone will

be modified; but, as was formerly shown, the co-adapted modifications need not

be absolutely simultaneous. Many variations, however, are from the first

connected by the law of correlation. Hence it follows that even closely-allied

species rarely or never differ from one another by one character alone; and

the same remark is to a certain extent applicable to domestic races; for

these, if they differ much, generally differ in many respects.

Some naturalists boldly insist (28/1. Godron 'De l'Espece' 1859 tome 2 page 44

etc.) that species are absolutely distinct productions, never passing by

intermediate links into one another; whilst they maintain that domestic

varieties can always be connected either with one another or with their

parent-forms. But if we could always find the links between the several breeds

of the dog, horse, cattle, sheep, pigs, etc., there would not have been such

incessant doubts whether they were descended from one or several species. The

greyhound genus, if such a term may be used, cannot be closely connected with

any other breed, unless, perhaps, we go back to the ancient Egyptian

monuments. Our English bulldog also forms a very distinct breed. In all these

cases crossed breeds must of course be excluded, for distinct natural species

can thus be likewise connected. By what links can the Cochin fowl be closely

united with others? By searching for breeds still preserved in distant lands,

and by going back to historical records, tumbler-pigeons, carriers, and barbs

can be closely connected with the parent rock-pigeon; but we cannot thus

connect the turbit or the pouter. The degree of distinctness between the

various domestic breeds depends on the amount of modification which they have

undergone, and more especially on the neglect and final extinction of

intermediate and less-valued forms.

It has often been argued that no light is thrown on the changes which natural

species are believed to undergo from the admitted changes of domestic races,

as the latter are said to be mere temporary productions, always reverting, as

soon as they become feral, to their pristine form. This argument has been well

combated by Mr. Wallace (28/2. 'Journal Proc. Linn. Soc.' 1858 volume 3 page

60.) and full details were given in the thirteenth chapter, showing that the

tendency to reversion in feral animals and plants has been greatly

exaggerated, though no doubt it exists to a certain extent. It would be

opposed to all the principles inculcated in this work, if domestic animals,

when exposed to new conditions and compelled to struggle for their own wants

against a host of foreign competitors, were not modified in the course of

time. It should also be remembered that many characters lie latent in all

organic beings, ready to be evolved under fitting conditions; and in breeds

modified within recent times, the tendency to reversion is particularly

strong. But the antiquity of some of our breeds clearly proves that they

remain nearly constant as long as their conditions of life remain the same.

It has been boldly maintained by some authors that the amount of variation to

which our domestic productions are liable is strictly limited; but this is an

assertion resting on little evidence. Whether or not the amount of change in

any particular direction is limited, the tendency to general variability is,

as far as we can judge, unlimited. Cattle, sheep, and pigs have varied under

domestication from the remotest period, as shown by the researches of

Rutimeyer and others; yet these animals have been improved to an unparalleled

degree, within quite recent times, and this implies continued variability of

structure. Wheat, as we know from the remains found in the Swiss lake-

dwellings, is one of the most anciently cultivated plants, yet at the present

day new and better varieties frequently arise. It may be that an ox will never

be produced of larger size and finer proportions, or a racehorse fleeter, than

our present animals, or a gooseberry larger than the London variety; but he

would be a bold man who would assert that the extreme limit in these respects

has been finally attained. With flowers and fruit it has repeatedly been

asserted that perfection has been reached, but the standard has soon been

excelled. A breed of pigeons may never be produced with a beak shorter than

that of the present short-faced tumbler, or with one longer than that of the

English carrier, for these birds have weak constitutions and are bad breeders;

but shortness and length of beak are the points which have been steadily

improved during the last 150 years, and some of the best judges deny that the

goal has yet been reached. From reasons which could be assigned, it is

probable that parts which have now reached their maximum development, might,

after remaining constant during a long period, vary again in the direction of

increase under new conditions of life. But there must be, as Mr. Wallace has

remarked with much truth (28/3. 'The Quarterly Journal of Science' October

1867 page 486.), a limit to change in certain directions both with natural and

domestic productions; 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 to be carried, and the power of contraction in the

muscular fibres. The English racehorse may have reached this limit; but it

already surpasses in fleetness its own wild progenitor and all other equine

species. The short-faced tumbler-pigeon has a beak shorter, and the carrier a

beak longer, relatively to the size of their bodies, than that of any natural

species of the family. Our apples, pears and gooseberries bear larger fruit

than those of any natural species of the same genera; and so in many other

cases.

It is not surprising, seeing the great difference between many domestic

breeds, that some few naturalists have concluded that each is descended from a

distinct aboriginal stock, more especially as the principle of selection has

been ignored, and the high antiquity of man, as a breeder of animals, has only

recently become known. Most naturalists, however, freely admit that our

various breeds, however dissimilar, are descended from a single stock,

although they do not know much about the art of breeding, cannot show the

connecting links, nor say where and when the breeds arose. Yet these same

naturalists declare, with an air of philosophical caution, that they will

never admit that one natural species has given birth to another until they

behold all the transitional steps. Fanciers use exactly the same language with

respect to domestic breeds; thus, an author of an excellent treatise on

pigeons says he will never allow that the carrier and fantail are the

descendants of the wild rock-pigeon, until the transitions have "actually been

observed, and can be repeated whenever man chooses to set about the task." No

doubt it is difficult to realise that slight changes added up during long

centuries can produce such great results; but he who wishes to understand the

origin of domestic breeds or of natural species must overcome this difficulty.

The causes which excite and the laws which govern variability have been

discussed so lately, that I need here only enumerate the leading points. As

domesticated organisms are much more liable to slight deviations of structure

and to monstrosities than species living under their natural conditions, and

as widely-ranging species generally vary more than those which inhabit

restricted areas, we may infer that variability mainly depends on changed

conditions of life. We must not overlook the effects of the unequal

combination of the characters derived from both parents, or reversion to

former progenitors. Changed conditions have an especial tendency to render the

reproductive organs more or less impotent, as shown in the chapter devoted to

this subject; and these organs consequently often fail to transmit faithfully

the parental characters. Changed conditions also act directly and definitely

on the organisation, so that all or nearly all the individuals of the same

species thus exposed become modified in the same manner; but why this or that

part is especially affected we can seldom or ever say. In most cases, however,

a change in the conditions seems to act indefinitely, causing diversified

variations in nearly the same manner as exposure to cold or the absorption of

the same poison affects different individuals in different ways. We have

reason to suspect that an habitual excess of highly-nutritious food, or an

excess relatively to the wear and tear of the organisation from exercise, is a

powerful exciting cause of variability. When we see the symmetrical and

complex outgrowths, caused by a minute drop of the poison of a gall-insect, we

may believe that slight changes in the chemical nature of the sap or blood

would lead to extraordinary modifications of structure.

The increased use of a muscle with its various attached parts, and the

increased activity of a gland or other organ, lead to their increased

development. Disuse has a contrary effect. With domesticated productions,

although their organs sometimes become rudimentary through abortion, we have

no reason to suppose that this has ever followed solely from disuse. With

natural species, on the contrary, many organs appear to have been rendered

rudimentary through disuse, aided by the principle of the economy of growth

together with intercrossing. Complete abortion can be accounted for only by

the hypothesis given in the last chapter, namely, the final destruction of the

germs or gemmules of useless parts. This difference between species and

domestic varieties may be partly accounted for by disuse having acted on the

latter for an insufficient length of time, and partly from their exemption

from any severe struggle for existence entailing rigid economy in the

development of each part, to which all species under nature are subjected.

Nevertheless the law of compensation or balancement, which likewise depends on

the economy of growth, apparently has affected to a certain extent our

domesticated productions.

As almost every part of the organisation becomes highly variable under

domestication, and as variations are easily selected both consciously and

unconsciously, it is very difficult to distinguish between the effects of the

selection of indefinite variations and the direct action of the conditions of

life. For instance, it is possible that the feet of our water-dogs and of the

American dogs which have to travel much over the snow, may have become

partially webbed from the stimulus of widely extending their toes; but it is

more probable that the webbing, like the membrane between the toes of certain

pigeons, spontaneously appeared and was afterwards increased by the best

swimmers and the best snow-travellers being preserved during many generations.

A fancier who wished to decrease the size of his bantams or tumbler-pigeons

would never think of starving them, but would select the smallest individuals

which spontaneously appeared. Quadrupeds are sometimes born destitute of hair

and hairless breeds have been formed, but there is no reason to believe that

this is caused by a hot climate. Within the tropics heat often causes sheep to

lose their fleeces; on the other hand, wet and cold act as a direct stimulus

to the growth of hair; but who will pretend to decide how far the thick fur of

arctic animals, or their white colour, is due to the direct action of a severe

climate, and how far to the preservation of the best-protected individuals

during a long succession of generations?

Of all the laws governing variability, that of correlation is one of the most

important. In many cases of slight deviations of structure as well as of grave

monstrosities, we cannot even conjecture what is the nature of the bond of

connexion. But between homologous parts--between the fore and hind limbs--

between the hair, hoofs, horns, and teeth--which are closely similar during

their early development and which are exposed to similar conditions, we can

see that they would be eminently liable to be modified in the same manner.

Homologous parts, from having the same nature, are apt to blend together, and,

when many exist, to vary in number.

Although every variation is either directly or indirectly caused by some

change in the surrounding conditions, we must never forget that the nature of

the organisation which is acted on, is by far the more important factor in the

result. We see this in different organisms, which when placed under similar

conditions vary in a different manner, whilst closely-allied organisms under

dissimilar conditions often vary in nearly the same manner. We see this, in

the same modification frequently reappearing in the same variety at long

intervals of time, and likewise in the several striking cases given of

analogous or parallel variations. Although some of these latter cases are due

to reversion, others cannot thus be accounted for.

From the indirect action of changed conditions on the organisation, owing to

the reproductive organs being thus affected--from the direct action of such

conditions, and these will cause the individuals of the same species either to

vary in the same manner, or differently in accordance with slight differences

in their constitution--from the effects of the increased or decreased use of

parts--and from correlation,--the variability of our domesticated productions

is complicated to an extreme degree. The whole organisation becomes slightly

plastic. Although each modification must have its own exciting cause, and

though each is subjected to law, yet we can so rarely trace the precise

relation between cause and effect, that we are tempted to speak of variations

as if they arose spontaneously. We may even call them accidental, but this

must be only in the sense in which we say that a fragment of rock dropped from

a height owes its shape to accident.

It may be worth while briefly to consider the result of the exposure to

unnatural conditions of a large number of animals of the same species and

allowed to cross freely with no selection of any kind, and afterwards to

consider the result when selection is brought into play. Let us suppose that

500 wild rock-pigeons were confined in their native land in an aviary and fed

in the same manner as pigeons usually are; and that they were not allowed to

increase in number. As pigeons propagate so rapidly, I suppose that a thousand

or fifteen hundred birds would have to be annually killed. After several

generations had been thus reared, we may feel sure that some of the young

birds would vary, and the variations would tend to be inherited; for at the

present day slight deviations of structure often occur and are inherited. It

would be tedious even to enumerate the multitude of points which still go on

varying or have recently varied. Many variations would occur in correlation

with one another, as the length of the wing and tail feathers--the number of

the primary wing-feathers, as well as the number and breadth of the ribs, in

correlation with the size and form of the body--the number of the scutellae

with the size of the feet--the length of the tongue with the length of the

beak--the size of the nostrils and eyelids and the form of lower jaw in

correlation with the development of wattle--the nakedness of the young with

the future colour of the plumage--the size of the feet with that of the beak,

and other such points. Lastly, as our birds are supposed to be confined in an

aviary, they would use their wings and legs but little, and certain parts of

the skeleton, such as the sternum, scapulae and feet, would in consequence

become slightly reduced in size.

As in our assumed case many birds have to be indiscriminately killed every

year, the chances are against any new variety surviving long enough to breed.

And as the variations which arise are of an extremely diversified nature, the

chances are very great against two birds pairing which have varied in the same

manner; nevertheless, a varying bird even when not thus paired would

occasionally transmit its character to its young; and these would not only be

exposed to the same conditions which first caused the variation in question to

appear, but would in addition inherit from their modified parent a tendency

again to vary in the same manner. So that, if the conditions decidedly tended

to induce some particular variation, all the birds might in the course of time

become similarly modified. But a far commoner result would be, that one bird

would vary in one way and another bird in another way; one would be born with

a beak a little longer, and another with a shorter beak; one would gain some

black feathers, another some white or red feathers. And as these birds would

be continually intercrossing, the final result would be a body of individuals

differing from each other in many ways, but only slightly; yet more than did

the original rock-pigeons. But there would not be the least tendency towards

the formation of several distinct breeds.

If two separate lots of pigeons were treated in the manner just described, one

in England and the other in a tropical country, the two lots being supplied

with different kinds of food, would they after many generations differ? When

we reflect on the cases given in the twenty-third chapter, and on such facts

as the difference in former times between the breeds of cattle, sheep, etc.,

in almost every district of Europe, we are strongly inclined to admit that the

two lots would be differently modified through the influence of climate and

food. But the evidence on the definite action of changed conditions is in most

cases insufficient; and, with respect to pigeons, I have had the opportunity

of examining a large collection of domesticated kinds, sent to me by Sir W.

Elliot from India, and they varied in a remarkably similar manner with our

European birds.

If two distinct breeds were mingled together in equal numbers, there is reason

to suspect that they would to a certain extent prefer pairing with their own

kind; but they would often intercross. From the greater vigour and fertility

of the crossed offspring, the whole body would by this means become

interblended sooner than would otherwise have occurred. From certain breeds

being prepotent over others, it does not follow that the interblended progeny

would be strictly intermediate in character. I have, also, proved that the act

of crossing in itself gives a strong tendency to reversion, so that the

crossed offspring would tend to revert to the state of the aboriginal rock-

pigeon; and in the course of time they would probably be not much more

heterogeneous in character than in our first case, when birds of the same

breed were confined together.

I have just said that the crossed offspring would gain in vigour and

fertility. From the facts given in the seventeenth chapter there can be no

doubt of this fact; and there can be little doubt, though the evidence on this

head is not so easily acquired, that long-continued close interbreeding leads

to evil results. With hermaphrodites of all kinds, if the sexual elements of

the same individual habitually acted on each other, the closest possible

interbreeding would be perpetual. But we should bear in mind that the

structure of all hermaphrodite animals, as far as I can learn, permits and

frequently necessitates a cross with a distinct individual. With hermaphrodite

plants we incessantly meet with elaborate and perfect contrivances for this

same end. It is no exaggeration to assert that, if the use of the talons and

tusks of a carnivorous animal, or of the plumes and hooks on a seed, may be

safely inferred from their structure, we may with equal safety infer that many

flowers are constructed for the express purpose of ensuring a cross with a

distinct plant. From these various considerations, not to mention the result

of a long series of experiments which I have tried, the conclusion arrived at

in the chapter just referred to--namely, that great good of some kind is

derived from the sexual concourse of distinct individuals--must be admitted.

To return to our illustration: we have hitherto assumed that the birds were

kept down to the same number by indiscriminate slaughter; but if the least

choice be permitted in their preservation, the whole result will be changed.

Should the owner observe any slight variation in one of his birds, and wish to

obtain a breed thus characterised, he would succeed in a surprisingly short

time by careful selection. As any part which has once varied generally goes on

varying in the same direction, it is easy, by continually preserving the most

strongly marked individuals, to increase the amount of difference up to a

high, predetermined standard of excellence. This is methodical selection.

If the owner of the aviary, without any thought of making a new breed, simply

admired, for instance, short-beaked more than long-beaked birds, he would,

when he had to reduce the number, generally kill the latter; and there can be

no doubt that he would thus in the course of time sensibly modify his stock.

It is improbable, if two men were to keep pigeons and act in this manner, that

they would prefer exactly the same characters; they would, as we know, often

prefer directly opposite characters, and the two lots would ultimately come to

differ. This has actually occurred with strains or families of cattle, sheep,

and pigeons, which have been long kept and carefully attended to by different

breeders, without any wish on their part to form new and distinct sub-breeds.

This unconscious kind of selection will more especially come into action with

animals which are highly serviceable to man; for every one tries to get the

best dogs, horses, cows, or sheep, without thinking about their future

progeny, yet these animals would transmit more or less surely their good

qualities to their offspring. Nor is any one so careless as to breed from his

worst animals. Even savages, when compelled from extreme want to kill some of

their animals, would destroy the worst and preserve the best. With animals

kept for use and not for mere amusement, different fashions prevail in

different districts, leading to the preservation, and consequently to the

transmission, of all sorts of trifling peculiarities of character. The same

process will have been pursued with our fruit-trees and vegetables, for the

best will always have been the most largely cultivated, and will occasionally

have yielded seedlings better than their parents.

The different strains, just alluded to, which have been actually produced by

breeders without any wish on their part to obtain such a result, afford

excellent evidence of the power of unconscious selection. This form of

selection has probably led to far more important results than methodical

selection, and is likewise more important under a theoretical point of view

from closely resembling natural selection. For during this process the best or

most valued individuals are not separated and prevented from crossing with

others of the same breed, but are simply preferred and preserved; yet this

inevitably leads to their gradual modification and improvement; so that

finally they prevail, to the exclusion of the old parent-form.

With our domesticated animals natural selection checks the production of races

with any injurious deviation of structure. In the case of animals which, from

being kept by savages or semi-civilised people, have to provide largely for

their own wants under different circumstances, natural selection will have

played a more important part. Hence it probably is that they often closely

resemble natural species.

As there is no limit to man's desire to possess animals and plants more and

more useful in any respect, and as the fancier always wishes, owing to

fashions running into extremes, to produce each character more and more

strongly pronounced, there is, through the prolonged action of methodical and

unconscious selection, a constant tendency in every breed to become more and

more different from its parent-stock; and when several breeds have been

produced and are valued for different qualities, to differ more and more from

each other. This leads to Divergence of Character. As improved sub-varieties

and races are slowly formed, the older and less improved breeds are neglected

and decrease in number. When few individuals of any breed exist within the

same locality, close interbreeding, by lessening their vigour and fertility,

aids in their final extinction. Thus the intermediate links are lost, and the

remaining breeds gain in Distinctness of Character.

In the chapters on the Pigeon, it was proved by historical evidence and by the

existence of connecting sub-varieties in distant lands that several breeds

have steadily diverged in character, and that many old and intermediate sub-

breeds have been lost. Other cases could be adduced of the extinction of

domestic breeds, as of the Irish wolf-dog, the old English hound, and of two

breeds in France, one of which was formerly highly valued. (28/4. M. Rufz de

Lavison in 'Bull. Soc. Imp. d'Acclimat.' December 1862 page 1009.) Mr.

Pickering remarks (28/5. 'Races of Man' 1850 page 315.) that "the sheep

figured on the most ancient Egyptian monuments is unknown at the present day;

and at least one variety of the bullock, formerly known in Egypt, has in like

manner become extinct." So it has been with some animals and with several

plants cultivated by the ancient inhabitants of Europe during the neolithic

period. In Peru, Von Tschudi (28/6. 'Travels in Peru' English translation page

177.) found in certain tombs, apparently prior to the dynasty of the Incas,

two kinds of maize not now known in the country. With our flowers and culinary

vegetables, the production of new varieties and their extinction has

incessantly recurred. At the present time improved breeds sometimes displace

older breeds at an extraordinarily rapid rate; as has recently occurred

throughout England with pigs. The Longhorn cattle in their native home were

"suddenly swept away as if by some murderous pestilence," by the introduction

of Shorthorns. (28/7. Youatt on 'Cattle' 1834 page 200. On Pigs see

'Gardener's Chronicle' 1854 page 410.)

What grand results have followed from the long-continued action of methodical

and unconscious selection, regulated to a certain extent by natural selection,

we see on every side of us. Compare the many animals and plants which are

displayed at our exhibitions with their parent-forms when these are known, or

consult old historical records with respect to their former state. Most of our

domesticated animals have given rise to numerous and distinct races, but those

which cannot be easily subjected to selection must be excepted--such as cats,

the cochineal insect, and the hive-bee. In accordance with what we know of the

process of selection, the formation of our many races has been slow and

gradual. The man who first observed and preserved a pigeon with its oesophagus

a little enlarged, its beak a little longer, or its tail a little more

expanded than usual, never dreamed that he had made the first step in the

creation of a pouter, carrier, and fantail-pigeon. Man can create not only

anomalous breeds, but others having their whole structure admirably co-

ordinated for certain purposes, such as the racehorse and dray-horse, or the

greyhound and bulldog. It is by no means necessary that each small change of

structure throughout the body, leading towards excellence, should

simultaneously arise and be selected. Although man seldom attends to

differences in organs which are important under a physiological point of view,

yet he has so profoundly modified some breeds, that assuredly, if found wild,

they would be ranked as distinct genera.

The best proof of what selection has effected is perhaps afforded by the fact

that whatever part or quality in any animal, and more especially in any plant,

is most valued by man, that part or quality differs most in the several races.

This result is well seen by comparing the amount of difference between the

fruits produced by the several varieties of fruit-trees, between the flowers

of our flower-garden plants, between the seeds, roots, or leaves of our

culinary and agricultural plants, in comparison with the other and not valued

parts of the same varieties. Striking evidence of a different kind is afforded

by the fact ascertained by Oswald Heer (28/8. 'Die Pflanzen der Pfahlbauten'

1865.) namely, that the seeds of a large number of plants,--wheat, barley,

oats, peas, beans, lentils, poppies,--cultivated for their seed by the ancient

Lake-inhabitants of Switzerland, were all smaller than the seeds of our

existing varieties. Rutimeyer has shown that the sheep and cattle which were

kept by the earlier Lake-inhabitants were likewise smaller than our present

breeds. In the middens of Denmark, the earliest dog of which the remains have

been found was the weakest; this was succeeded during the Bronze age by a

stronger kind, and this again during the Iron age by one still stronger. The

sheep of Denmark during the Bronze period had extraordinarily slender limbs,

and the horse was smaller than our present animal. (28/9. Morlot 'Soc. Vaud.

des Scien. Nat.' Mars 1860 page 298.) No doubt in most of these cases the new

and larger breeds were introduced from foreign lands by the immigration of new

hordes of men. But it is not probable that each larger breed, which in the

course of time has supplanted a previous and smaller breed, was the descendant

of a distinct and larger species; it is far more probable that the domestic

races of our various animals were gradually improved in different parts of the

great Europaeo-Asiatic continent, and thence spread to other countries. This

fact of the gradual increase in size of our domestic animals is all the more

striking as certain wild or half-wild animals, such as red-deer, aurochs,

park-cattle, and boars (28/10. Rutimeyer 'Die Fauna der Pfahlbauten' 1861 s.

30.) have within nearly the same period decreased in size.

The conditions favourable to selection by man are,--the closest attention to

every character,--long-continued perseverance,--facility in matching or

separating animals,--and especially a large number being kept, so that the

inferior individuals may be freely rejected or destroyed, and the better ones

preserved. When many are kept there will also be a greater chance of the

occurrence of well-marked deviations of structure. Length of time is all-

important; for as each character, in order to become strongly pronounced, has

to be augmented by the selection of successive variations of the same kind,

this can be effected only during a long series of generations. Length of time

will, also, allow any new feature to become fixed by the continued rejection

of those individuals which revert or vary, and by the preservation of those

which still inherit the new character. Hence, although some few animals have

varied rapidly in certain respects under new conditions of life, as dogs in

India and sheep in the West Indies, yet all the animals and plants which have

produced strongly marked races were domesticated at an extremely remote epoch,

often before the dawn of history. As a consequence of this, no record has been

preserved of the origin of our chief domestic breeds. Even at the present day

new strains or sub-breeds are formed so slowly that their first appearance

passes unnoticed. A man attends to some particular character, or merely

matches his animals with unusual care, and after a time a slight difference is

perceived by his neighbours;--the difference goes on being augmented by

unconscious and methodical selection, until at last a new sub-breed is formed,

receives a local name, and spreads; but by this time its history is almost

forgotten. When the new breed has spread widely, it gives rise to new strains

and sub-breeds, and the best of these succeed and spread, supplanting other

and older breeds; and so always onwards in the march of improvement.

When a well-marked breed has once been established, if not supplanted by still

further improved sub-breeds, and if not exposed to greatly changed conditions

of life inducing further variability or reversion to long-lost characters, it

may apparently last for an enormous period. We may infer that this is the case

from the high antiquity of certain races; but some caution is necessary on

this head, for the same variation may appear independently after long

intervals of time, or in distant places. We may safely assume that this has

occurred with the turnspit-dog, of which one is figured on the ancient

Egyptian monuments--with the solid-hoofed swine (28/11. Godron 'De l'Espece'

tome 1 1859 page 368.) mentioned by Aristotle--with five-toed fowls described

by Columella--and certainly with the nectarine. The dogs represented on the

Egyptian monuments, about 2000 B.C., show us that some of the chief breeds

then existed, but it is extremely doubtful whether any are identically the

same with our present breeds. A great mastiff sculptured on an Assyrian tomb,

640 B.C., is said to be the same with the dog still imported from Thibet into

the same region. The true greyhound existed during the Roman classical period.

Coming down to a later period, we have seen that, though most of the chief

breeds of the pigeon existed between two and three centuries ago, they have

not all retained exactly the same character to the present day; but this has

occurred in certain cases in which no improvement was desired, for instance,

in the case of the Spot and Indian ground-tumbler.

De Candolle (28/12. 'Geographie Botan.' 1855 page 989.) has fully discussed

the antiquity of various races of plants; he states that the black seeded

poppy was known in the time of Homer, the white-seeded sesamum by the ancient

Egyptians, and almonds with sweet and bitter kernels by the Hebrews; but it

does not seem improbable that some of these varieties may have been lost and

reappeared. One variety of barley and apparently one of wheat, both of which

were cultivated at an immensely remote period by the Lake-inhabitants of

Switzerland, still exist. It is said (28/13. Pickering 'Races of Man' 1850

page 318.) that "specimens of a small variety of gourd which is still common

in the market of Lima were exhumed from an ancient cemetery in Peru." De

Candolle remarks that, in the books and drawings of the sixteenth century, the

principal races of the cabbage, turnip, and gourd can be recognised: this

might have been expected at so late a period, but whether any of these plants

are absolutely identical with our present sub-varieties is not certain. It is,

however, said that the Brussels sprout, a variety which in some places is

liable to degeneration, has remained genuine for more than four centuries in

the district where it is believed to have originated. (28/14. 'Journal of a

Horticultural Tour' by a Deputation of the Caledonian Hist. Soc. 1823 page

293.)

In accordance with the views maintained by me in this work and elsewhere, not

only the various domestic races, but the most distinct genera and orders

within the same great class--for instance, mammals, birds, reptiles, and

fishes--are all the descendants of one common progenitor, and we must admit

that the whole vast amount of difference between these forms has primarily

arisen from simple variability. To consider the subject under this point of

view is enough to strike one dumb with amazement. But our amazement ought to

be lessened when we reflect that beings almost infinite in number, during an

almost infinite lapse of time, have often had their whole organisation

rendered in some degree plastic, and that each slight modification of

structure which was in any way beneficial under excessively complex conditions

of life has been preserved, whilst each which was in any way injurious has

been rigorously destroyed. And the long-continued accumulation of beneficial

variations will infallibly have led to structures as diversified, as

beautifully adapted for various purposes and as excellently co-ordinated, as

we see in the animals and plants around us. Hence I have spoken of selection

as the paramount power, whether applied by man to the formation of domestic

breeds, or by nature to the production of species. I may recur to the metaphor

given in a former chapter: if an architect were to rear a noble and commodious

edifice, without the use of cut stone, by selecting from the fragments at the

base of a precipice wedge-formed stones for his arches, elongated stones for

his lintels, and flat stones for his roof, we should admire his skill and

regard him as the paramount power. Now, the fragments of stone, though

indispensable to the architect, bear to the edifice built by him the same

relation which the fluctuating variations of organic beings bear to the varied

and admirable structures ultimately acquired by their modified descendants.

Some authors have declared that natural selection explains nothing, unless the

precise cause of each slight individual difference be made clear. If it were

explained to a savage utterly ignorant of the art of building, how the edifice

had been raised stone upon stone, and why wedge-formed fragments were used for

the arches, flat stones for the roof, etc.; and if the use of each part and of

the whole building were pointed out, it would be unreasonable if he declared

that nothing had been made clear to him, because the precise cause of the

shape of each fragment could not be told. But this is a nearly parallel case

with the objection that selection explains nothing, because we know not the

cause of each individual difference in the structure of each being.

The shape of the fragments of stone at the base of our precipice may be called

accidental, but this is not strictly correct; for the shape of each depends on

a long sequence of events, all obeying natural laws; on the nature of the

rock, on the lines of deposition or cleavage, on the form of the mountain,

which depends on its upheaval and subsequent denudation, and lastly on the

storm or earthquake which throws down the fragments. But in regard to the use

to which the fragments may be put, their shape may be strictly said to be

accidental. And here we are led to face a great difficulty, in alluding to

which I am aware that I am travelling beyond my proper province. An omniscient

Creator must have foreseen every consequence which results from the laws

imposed by Him. But can it be reasonably maintained that the Creator

intentionally ordered, if we use the words in any ordinary sense, that certain

fragments of rock should assume certain shapes so that the builder might erect

his edifice? If the various laws which have determined the shape of each

fragment were not predetermined for the builder's sake, can it be maintained

with any greater probability that He specially ordained for the sake of the

breeder each of the innumerable variations in our domestic animals and

plants;--many of these variations being of no service to man, and not

beneficial, far more often injurious, to the creatures themselves? Did He

ordain that the crop and tail-feathers of the pigeon should vary in order that

the fancier might make his grotesque pouter and fantail breeds? Did He cause

the frame and mental qualities of the dog to vary in order that a breed might

be formed of indomitable ferocity, with jaws fitted to pin down the bull for

man's brutal sport? But if we give up the principle in one case,--if we do not

admit that the variations of the primeval dog were intentionally guided in

order that the greyhound, for instance, that perfect image of symmetry and

vigour, might be formed,--no shadow of reason can be assigned for the belief

that variations, alike in nature and the result of the same general laws,

which have been the groundwork through natural selection of the formation of

the most perfectly adapted animals in the world, man included, were

intentionally and specially guided. However much we may wish it, we can hardly

follow Professor Asa Gray in his belief "that variation has been led along

certain beneficial lines," like a stream "along definite and useful lines of

irrigation." If we assume that each particular variation was from the

beginning of all time preordained, then that plasticity of organisation, which

leads to many injurious deviations of structure, as well as the redundant

power of reproduction which inevitably leads to a struggle for existence, and,

as a consequence, to the natural selection or survival of the fittest, must

appear to us superfluous laws of nature. On the other hand, an omnipotent and

omniscient Creator ordains everything and foresees everything. Thus we are

brought face to face with a difficulty as insoluble as is that of free will

and predestination.

INDEX.

ABBAS PACHA, a fancier of fantailed pigeons.

ABBEY, Mr., on grafting.

-on mignonette.

ABBOTT, Mr. Keith, on the Persian tumbler pigeon.

ABBREVIATION of the facial bones.

ABORTION of organs.

ABSORPTION of minority in crossed races.

ABUTILON, graft hybridisation of.

ACCLIMATISATION, of maize.

ACERBI, on the fertility of domestic animals in Lapland.

Achatinella.

Achillea millefolium, bud variation in.

Aconitum napellus, roots of, innocuous in cold climates.

Acorus calamus, sterility of.

ACOSTA, on fowls in South America at its discovery.

Acropera, number of seeds in.

ADAM, M., origin of Cytisus adami.

ADAM, W., on consanguineous marriages.

ADAMS, on hereditary diseases.

ADVANCEMENT in scale of organisation.

Aegilops triticoides, observations of Fabre and Godron on.

-increasing fertility of hybrids of, with wheat.

Aesculus pavia, tendency of, to become double.

Aethusa cynapium.

AFFINITY, sexual elective.

AFRICA, white bull from.

-feral cattle in.

-food-plants of savages of.

-South, diversity of breeds of cattle in.

-West, change in fleece of sheep in.

Agave vivipara, seeding of, in poor soil.

AGE, changes in trees, dependent on.

-as bearing on pangenesis.

AGOUTI, fertility of, in captivity.

AGRICULTURE, antiquity of.

Agrostis, seeds of, used as food.

AGUARA.

AINSWORTH, Mr., on the change in the hair of animals at Angora.

AKBAR KHAN, his fondness for pigeons,

Alauda arvensis.

ALBIN, on "Golden Hamburgh" fowls.

-figure of the hook-billed duck.

ALBINISM.

ALBINO, negro, attacked by insects.

ALBINOES, heredity of.

ALBINUS, thickness of the epidermis on the palms of the hands in man.

ALCO.

ALDROVANDI, on rabbits.

-description of the nun pigeon.

-on the fondness of the Dutch for pigeons in the seventeenth century.

-notice of several varieties of pigeons.

-on the breeds of fowls.

-on the origin of the domestic duck.

ALEFIELD, Dr., on the varieties of peas and their specific unity.

-on the varieties of beans.

ALEXANDER the Great, his selection of Indian cattle.

ALGAE, retrogressive metamorphosis in.

-division of zoospores of,

ALLEN, J., birds in United States.

ALLEN, W., on feral fowls.

ALLMAN, Professor, on a monstrous Saxifraga geum.

-on the Hydroida.

ALMOND, antiquity of.

-bitter, not eaten by mice.

Alnus glutinosa, and incana, hybrids of.

ALPACA, selection of.

Althaea rosea.

Amaryllis.

Amaryllis vittata, effect of foreign pollen on.

AMAUROSIS, hereditary.

Amblystoma lurida.

AMERICA, limits within which no useful plants have been furnished by.

-colours of feral horses in.

-North, native cultivated plants of.

-skin of feral pig from.

-South, variations in cattle of.

AMMON, on the persistency of colour in horses.

Amygdalus persica.

Anagallis arvensis.

ANALOGOUS variation.

-in horses,

-in the horse and ass.

-in fowls.

Anas boschas.

-skull of, figured.

"ANCON" sheep of Massachusetts.

ANDALUSIAN fowls.

ANDALUSIAN rabbits.

ANDERSON, J., on the origin of British sheep.

-on the selection of qualities in cattle.

-on a one-eared breed of rabbits.

-on the inheritance of characters from a one-eared rabbit, and three-legged

bitch.

-on the persistency of varieties of peas.

-on the production of early peas by selection.

-on the varieties of the potato.

-on crossing varieties of the melon.

-on reversion in the barberry.

ANDERSON, Mr., on the reproduction of the weeping ash by seed.

-on the cultivation of the tree paeony in China.

ANDERSSON, Mr., on the Damara, Bechuana, and Namaqua cattle.

-on the cows of the Damaras.

-selection practised by the Damaras and Namaquas.

-on the use of grass-seeds and the roots of reeds as food in South Africa.

Anemone coronaria, doubled by selection.

ANGINA pectoris, hereditary, occurring at a certain age.

ANGLESEA, cattle of.

ANGOLA sheep.

ANGORA, change in hair of animals at.

-cats of.

-rabbits of,

ANIMALS, domestication of, facilitated by fearlessness of man.

-refusal of wild, to breed in captivity.

-compound, individual peculiarities of, reproduced by budding.

-variation by selection in useful qualities of.

ANNUAL plants, rarity of bud-variation in.

ANOMALIES in the osteology of the horse.

ANOMALOUS breeds of pigs.

-of cattle.

Anser albifrons, characters of, reproduced in domestic geese.

Anser aegyptiacus.

Anser canadensis.

Anser ferus, the original of the domestic goose.

-fertility of cross of, with domestic goose.

ANSON, on feral fowls in the Ladrones.

ANTAGONISM between growth and reproduction.

Anthemis nobilis, bud-variation in flowers of.

-becomes single in poor soil.

ANTHERS, contabescence of.

ANTIGUA, cats of.

-changed fleece of sheep in.

Antirrhinum majus, peloric.

-double-flowered.

-bud-variation in.

ANTS, individual recognition of.

APHIDES, attacking pear-trees.

-development of.

APOPLEXY, hereditary, occurring at a certain age.

APPLE.

-fruit of, in Swiss lake-dwellings.

-rendered fastigiate by heat in India.

-bud-variation in the.

-with dimidiate fruit.

-with two kinds of fruit on the same branch.

-artificial fecundation of.

-St. Valery.

-reversion in seedlings of.

-crossing of varieties of.

-growth of the, in Ceylon.

-winter majetin, not attacked by coccus.

-flower-buds of, attacked by bullfinches.

-American, change of, when grown in England.

APRICOT.

-glands on the leaves of.

-analogous variation in the.

Aquila fusca, copulating in captivity.

Aquilegia vulgaris.

ARAB boarhound, described by Harcourt.

Arabis blepharophylla and A. soyeri, effects of crossing.

Aralia trifoliata, bud-variation in leaves of.

ARAUCARIAS, young, variable resistance of, to frost.

ARCHANGEL pigeon.

ARCTIC regions, variability of plants and shells of.

Aria vestita, grafted on thorns.

ARISTOPHANES, fowls mentioned by.

ARISTOTLE, on solid-hoofed pigs.

-domestic duck unknown to.

-on the assumption of male characters by old hens.

ARNI, domestication of the.

ARNOLD, Mr., experiments of pollen on the maize.

ARRESTS of development.

ARTERIES, increase of anastomosing branches of, when tied.

ARU Islands, wild pig of.

ARUM, Polynesian varieties of.

Ascaris, number of eggs of.

ASH, varieties of the.

-weeping.

-simple-leaved.

-bud-variation in.

-effects of graft upon the stock in the.

-production of the blotched Breadalbane.

-weeping, capricious reproduction of, by seed.

Asinus burchellii.

Asinus hemionus.

Asinus indicus.

Asinus quagga.

Asinus taeniopus, the original of the domestic ass.

ASPARAGUS, increased fertility of cultivated.

ASS, early domestication of the.

-breeds of.

-small size of, in India.

-stripes of.

-dislike of, to cross water.

-reversion in.

-hybrid of the, with mare and zebra.

-prepotency of the, over the horse.

-crossed with wild ass.

-variation and selection of the.

ASSYRIAN sculpture of a mastiff.

ASTERS.

ASTHMA, hereditary.

ATAVISM. See Reversion.

ATHELSTAN, his care of horses.

ATKINSON, Mr., on the sterility of the Tarroo silk-moth in confinement.

AUBERGINE.

AUDUBON, on feral hybrid ducks.

-on the domestication of wild ducks on the Mississippi.

-on the wild cock turkey visiting domestic hens.

-fertility of Fringilla ciris in captivity.

-fertility of Columba migratoria and leucocephala in captivity.

-breeding of Anser canadensis in captivity.

AUDUBON and Bachman, on the change of coat in Ovis montana.

-sterility of Sciurus cinerea in confinement.

AURICULA, effect of seasonal conditions on the.

-blooming of.

AUSTRALIA, no generally useful plants derived from.

-useful plants of, enumerated by Hooker.

AUSTRIA, heredity of character in emperors of.

AUTENRIETH, on persistency of colour in horses.

AVA, horses of.

Avena fatua, cultivability of.

'AYEEN Akbery' pigeons mentioned in the.

AYRES, W.P., on bud-variation in pelargoniums.

Azalea indica, bud-variation in.

AZARA, on the feral dogs of La Plata.

-on the crossing of domestic with wild cats in Paraguay.

-on hornlike processes in horses.

-on curled hair in horses.

-on the colours of feral horses.

-on the cattle of Paraguay and La Plata.

-on a hornless bull.

-on the increase of cattle in South America.

-on the growth of horns in the hornless cattle of Corrientes.

-on the "Niata" cattle.

-on naked quadrupeds.

-on a race of black-skinned fowls in South America.

-on a variety of maize.

BABINGTON, C.C., on the origin of the plum.

-British species of the genus Rosa.

-distinctness of Viola lutea and tricolor.

BACHMANN, Mr., on the turkey.