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INTRODUCTION ... Page 1

DOMESTIC DOGS AND CATS.

CATS, CROSSED WITH SEVERAL SPECIES--DIFFERENT BREEDS FOUND ONLY IN SEPARATED COUNTRIES--DIRECT EFFECTS OF THE CONDITIONS OF LIFE--FERAL CATS--INDIVIDUAL VARIABILITY ... Page 15

HORSES AND ASSES.

HORSE.--DIFFERENCES IN THE BREEDS--INDIVIDUAL VARIABILITY OF--DIRECT EFFECTS OF THE CONDITIONS OF LIFE--CAN WITHSTAND MUCH COLD--BREEDS MUCH MODIFIED BY SELECTION--COLOURS OF THE HORSE--DAPPLING--DARK STRIPES ON THE SPINE, LEGS, SHOULDERS, AND FOREHEAD--DUN-COLOURED HORSES MOST FREQUENTLY STRIPED--STRIPES PROBABLY DUE TO REVERSION TO THE PRIMITIVE STATE OF THE HORSE.

ASSES.--BREEDS OF--COLOUR OF--LEG- AND SHOULDER-STRIPES--SHOULDER-STRIPES SOMETIMES ABSENT, SOMETIMES FORKED ... Page 49

PIGS--CATTLE--SHEEP--GOATS.

PIGS BELONG TO TWO DISTINCT TYPES, SUS SCROFA AND INDICA--TORF-SCHWEIN--JAPAN PIG--FERTILITY OF CROSSED PIGS--CHANGES IN THE SKULL OF THE HIGHLY CULTIVATED RACES--CONVERGENCE OF CHARACTER--GESTATION--SOLID-HOOFED SWINE--CURIOUS APPENDAGES TO THE JAWS--DECREASE IN SIZE OF THE TUSKS--YOUNG PIGS LONGITUDINALLY STRIPED--FERAL PIGS--CROSSED BREEDS.

CATTLE.--ZEBU A DISTINCT SPECIES--EUROPEAN CATTLE PROBABLY DESCENDED FROM THREE WILD FORMS--ALL THE RACES NOW FERTILE TOGETHER--BRITISH PARK CATTLE--ON THE COLOUR OF THE ABORIGINAL SPECIES--CONSTITUTIONAL DIFFERENCES--SOUTH AFRICAN RACES--SOUTH AMERICAN RACES--NIATA CATTLE--ORIGIN OF THE VARIOUS RACES OF CATTLE.

SHEEP.--REMARKABLE RACES OF--VARIATIONS ATTACHED TO THE MALE SEX--ADAPTATIONS TO VARIOUS CONDITIONS--GESTATION OF--CHANGES IN THE WOOL--SEMI-MONSTROUS BREEDS.

GOATS.--REMARKABLE VARIATIONS OF ... Page 65

DOMESTIC RABBITS.

DOMESTIC RABBITS DESCENDED FROM THE COMMON WILD RABBIT--ANCIENT DOMESTICATION--ANCIENT SELECTION--LARGE LOP-EARED RABBITS--VARIOUS BREEDS--FLUCTUATING CHARACTERS--ORIGIN OF THE HIMALAYAN BREED--CURIOUS CASE OF INHERITANCE--FERAL RABBITS IN JAMAICA AND THE FALKLAND ISLANDS--PORTO SANTO FERAL RABBITS--OSTEOLOGICAL CHARACTERS--SKULL--SKULL OF HALF-LOP RABBITS--VARIATIONS IN THE SKULL ANALOGOUS TO DIFFERENCES IN DIFFERENT SPECIES OF HARES--VERTEBRAE--STERNUM--SCAPULA--EFFECTS OF USE AND DISUSE ON THE PROPORTIONS OF THE LIMBS AND BODY--CAPACITY OF THE SKULL AND REDUCED SIZE OF THE BRAIN--SUMMARY ON THE MODIFICATIONS OF DOMESTICATED RABBITS ... Page 103

DOMESTIC PIGEONS.

ENUMERATION AND DESCRIPTION OF THE SEVERAL BREEDS--INDIVIDUAL VARIABILITY--VARIATIONS OF A REMARKABLE NATURE--OSTEOLOGICAL CHARACTERS: SKULL, LOWER JAW, NUMBER OF VERTEBRAE--CORRELATION OF GROWTH: TONGUE WITH BEAK; EYELIDS AND NOSTRILS WITH WATTLED SKIN--NUMBER OF WING-FEATHERS, AND LENGTH OF WING--COLOUR AND DOWN--WEBBED AND FEATHERED FEET--ON THE EFFECTS OF DISUSE--LENGTH OF FEET IN CORRELATION WITH LENGTH OF BEAK--LENGTH OF STERNUM, SCAPULA, AND FURCULA--LENGTH OF WINGS--SUMMARY ON THE POINTS OF DIFFERENCE IN THE SEVERAL BREEDS ... Page 131

ON THE ABORIGINAL PARENT-STOCK OF THE SEVERAL DOMESTIC RACES--HABITS OF LIFE--WILD RACES OF THE ROCK-PIGEON--DOVECOT-PIGEONS--PROOFS OF THE DESCENT OF THE SEVERAL RACES FROM COLUMBA LIVIA--FERTILITY OF THE RACES WHEN CROSSED--REVERSION TO THE PLUMAGE OF THE WILD ROCK-PIGEON--CIRCUMSTANCES FAVOURABLE TO THE FORMATION OF THE RACES--ANTIQUITY AND HISTORY OF THE PRINCIPAL RACES--MANNER OF THEIR FORMATION--SELECTION--UNCONSCIOUS SELECTION--CARE TAKEN BY FANCIERS IN SELECTING THEIR BIRDS--SLIGHTLY DIFFERENT STRAINS GRADUALLY CHANGE INTO WELL-MARKED BREEDS--EXTINCTION OF INTERMEDIATE FORMS--CERTAIN BREEDS REMAIN PERMANENT, WHILST OTHERS CHANGE--SUMMARY ... Page 180

FOWLS.

DUCKS--GOOSE--PEACOCK--TURKEY--GUINEA-FOWL--CANARY-BIRD--GOLD-FISH-- HIVE-BEES--SILK-MOTHS.

DUCKS, SEVERAL BREEDS OF--PROGRESS OF DOMESTICATION--ORIGIN OF, FROM THE COMMON WILD-DUCK--DIFFERENCES IN THE DIFFERENT BREEDS--OSTEOLOGICAL DIFFERENCES--EFFECTS OF USE AND DISUSE ON THE LIMB-BONES.

GOOSE, ANCIENTLY DOMESTICATED--LITTLE VARIATION OF--SEBASTOPOL BREED.

PEACOCK, ORIGIN OF BLACK-SHOULDERED BREED.

TURKEY, BREEDS OF--CROSSED WITH THE UNITED STATES SPECIES--EFFECTS OF CLIMATE ON.

GUINEA-FOWL, CANARY-BIRD, GOLD-FISH, HIVE-BEES.

SILK-MOTHS, SPECIES AND BREEDS OF--ANCIENTLY DOMESTICATED--CARE IN THEIR SELECTION--DIFFERENCES IN THE DIFFERENT RACES--IN THE EGG, CATERPILLAR, AND COCOON STATES--INHERITANCE OF CHARACTERS--IMPERFECT WINGS--LOST INSTINCTS--CORRELATED CHARACTERS ... Page 276

CULTIVATED PLANTS: CEREAL AND CULINARY PLANTS.

PRELIMINARY REMARKS ON THE NUMBER AND PARENTAGE OF CULTIVATED PLANTS--FIRST STEPS IN CULTIVATION--GEOGRAPHICAL DISTRIBUTION OF CULTIVATED PLANTS.

CEREALIA.--DOUBTS ON THE NUMBER OF SPECIES.--WHEAT: VARIETIES OF--INDIVIDUAL VARIABILITY--CHANGED HABITS--SELECTION--ANCIENT HISTORY OF THE VARIETIES.--MAIZE: GREAT VARIATION OF--DIRECT ACTION OF CLIMATE ON.

CULINARY PLANTS.--CABBAGES: VARIETIES OF, IN FOLIAGE AND STEMS, BUT NOT IN OTHER PARTS--PARENTAGE OF--OTHER SPECIES OF BRASSICA.--PEAS: AMOUNT OF DIFFERENCE IN THE SEVERAL KINDS, CHIEFLY IN THE PODS AND SEED--SOME VARIETIES CONSTANT, SOME HIGHLY VARIABLE--DO NOT INTERCROSS.--BEANS.--POTATOES: NUMEROUS VARIETIES OF--DIFFERING LITTLE, EXCEPT IN THE TUBERS--CHARACTERS INHERITED ... Page 305

FRUITS.--GRAPES--VARY IN ODD AND TRIFLING PARTICULARS.--MULBERRY.--THE ORANGE GROUP--SINGULAR RESULTS FROM CROSSING.--PEACH AND NECTARINE--BUD-VARIATION--ANALOGOUS VARIATION--RELATION TO THE ALMOND.--APRICOT.--PLUMS--VARIATION IN THEIR STONES.--CHERRIES--SINGULAR VARIETIES OF.--APPLE.--PEAR.--STRAWBERRY--INTERBLENDING OF THE ORIGINAL FORMS.--GOOSEBERRY--STEADY INCREASE IN SIZE OF THE FRUIT--VARIETIES OF.--WALNUT.--NUT.--CUCURBITACEOUS PLANTS--WONDERFUL VARIATION OF.

ORNAMENTAL TREES--THEIR VARIATION IN DEGREE AND KIND--ASH-TREE--SCOTCH-FIR--HAWTHORN.

FLOWERS--MULTIPLE ORIGIN OF MANY KINDS--VARIATION IN CONSTITUTIONAL PECULIARITIES--KIND OF VARIATION.--ROSES--SEVERAL SPECIES CULTIVATED.--PANSY.--DAHLIA.--HYACINTH, HISTORY AND VARIATION OF ... Page 332

ON BUD-VARIATION, AND ON CERTAIN ANOMALOUS MODES OF REPRODUCTION AND VARIATION.

BUD-VARIATIONS IN THE PEACH, PLUM, CHERRY, VINE, GOOSEBERRY, CURRANT, AND BANANA, AS SHOWN BY THE MODIFIED FRUIT--IN FLOWERS: CAMELLIAS, AZALEAS, CHRYSANTHEMUMS, ROSES, ETC.--ON THE RUNNING OF THE COLOUR IN CARNATIONS--BUD-VARIATIONS IN LEAVES--VARIATIONS BY SUCKERS, TUBERS, AND BULBS--ON THE BREAKING OF TULIPS--BUD-VARIATIONS GRADUATE INTO CHANGES CONSEQUENT ON CHANGED CONDITIONS OF LIFE--CYTISUS ADAMI, ITS ORIGIN AND TRANSFORMATION--ON THE UNION OF TWO DIFFERENT EMBRYOS IN ONE SEED--THE TRIFACIAL ORANGE--ON REVERSION BY BUDS IN HYBRIDS AND MONGRELS--ON THE PRODUCTION OF MODIFIED BUDS BY THE GRAFTING OF ONE VARIETY OR SPECIES ON ANOTHER--ON THE DIRECT OR IMMEDIATE ACTION OF FOREIGN POLLEN ON THE MOTHER-PLANT--ON THE EFFECTS IN FEMALE ANIMALS OF A FIRST IMPREGNATION ON THE SUBSEQUENT OFFSPRING--CONCLUSION AND SUMMARY ... Page 373

THE

VARIATION OF ANIMALS AND PLANTS

UNDER DOMESTICATION.

INTRODUCTION.

The object of this work is not to describe all the many races of animals which have been domesticated by man, and of the plants which have been cultivated by him; even if I possessed the requisite knowledge, so gigantic an undertaking would be here superfluous. It is my intention to give under the head of each species only such facts as I have been able to collect or observe, showing the amount and nature of the changes which animals and plants have undergone whilst under man's dominion, or which bear on the general principles of variation. In one case alone, namely in that of the domestic pigeon, I will describe fully all the chief races, their history, the amount and nature of their differences, and the probable steps by which they have been formed. I have selected this case, because, as we shall hereafter see, the materials are better than in any other; and one case fully described will in fact illustrate all others. But I shall also describe domesticated rabbits, fowls, and ducks, with considerable fullness.

The subjects discussed in this volume are so connected that it is not a little difficult to decide how they can be best arranged. I have determined in the first part to give, under the heads of the various animals and plants, a large body of facts, some of which may at first appear but little related to our subject, and to devote the latter part to general discussions. Whenever I have found it necessary to give numerous details, in support of any proposition or conclusion, small type has been used. The reader will, I think, find this plan a convenience, for, if he does not doubt the conclusion or care about the details, he can easily pass them over; yet I may be permitted to say that some of the discussions thus printed deserve attention, at least from the professed naturalist.

It may be useful to those who have read nothing about Natural Selection, if I here give a brief sketch of the whole subject and of its bearing on the origin of species. This is the more desirable, as it is impossible in the present work to avoid many allusions to questions which will be fully discussed in future volumes.

From a remote period, in all parts of the world, man has subjected many animals and plants to domestication or culture. Man has no power of altering the absolute conditions of life; he cannot change the climate of any country; he adds no new element to the soil; but he can remove an animal or plant from one climate or soil to another, and give it food on which it did not subsist in its natural state. It is an error to speak of man "tampering with nature" and causing variability. If organic beings had not possessed an inherent tendency to vary, man could have done nothing. He unintentionally exposes his animals and plants to various conditions of life, and variability supervenes, which he cannot even prevent or check. Consider the simple case of a plant which has been cultivated during a long time in its native country, and which consequently has not been subjected to any change of climate. It has been protected to a certain extent from the competing roots of plants of other kinds; it has generally been grown in manured soil, but probably not richer than that of many an alluvial flat; and lastly, it has been exposed to changes in its conditions, being grown sometimes in one district and sometimes in another, in different soils. Under such circumstances, scarcely a plant can be named, though cultivated in the rudest manner, which has not given birth to several varieties. It can hardly be maintained that during the many changes which this earth has undergone, and during the natural migrations of plants from one land or island to another, tenanted by different species, that such plants will not often have been subjected to changes in their conditions analogous to those which almost inevitably cause cultivated plants to vary. No doubt man selects varying individuals, sows their seeds, and again selects their varying offspring. But the initial variation on which man works, and without which he can do nothing, is caused by slight changes in the conditions of life, which must often have occurred under nature. Man, therefore, may be said to have been trying an experiment on a gigantic scale; and it is an experiment which nature during the long lapse of time has incessantly tried. Hence it follows that the principles of domestication are important for us. The main result is that organic beings thus treated have varied largely, and the variations have been inherited. This has apparently been one chief cause of the belief long held by some few naturalists that species in a state of nature undergo change.

I shall in this volume treat, as fully as my materials permit, the whole subject of variation under domestication. We may thus hope to obtain some light, little though it be, on the causes of variability,--on the laws which govern it, such as the direct action of climate and food, the effects of use and disuse, and of correlation of growth,--and on the amount of change to which domesticated organisms are liable. We shall learn something on the laws of inheritance, on the effects of crossing different breeds, and on that sterility which often supervenes when organic beings are removed from their natural conditions of life, and likewise when they are too closely interbred. During this investigation we shall see that the principle of Selection is all important. Although man does not cause variability and cannot even prevent it, he can select, preserve, and accumulate the variations given to him by the hand of nature in any way which he chooses; and thus he can certainly produce a great result. Selection may be followed either methodically and intentionally, or unconsciously and unintentionally. Man may select and preserve each successive variation, with the distinct intention of improving and altering a breed, in accordance with a preconceived idea; and by thus adding up variations, often so slight as to be imperceptible by an uneducated eye, he has effected wonderful changes and improvements. It can, also, be clearly shown that man, without any intention or thought of improving the breed, by preserving in each successive generation the individuals which he prizes most, and by destroying the worthless individuals, slowly, though surely, induces great changes. As the will of man thus comes into play, we can understand how it is that domesticated breeds show adaptation to his wants and pleasures. We can further understand how it is that domestic races of animals and cultivated races of plants often exhibit an abnormal character, as compared with natural species; for they have been modified not for their own benefit, but for that of man.

In a second work I shall discuss the variability of organic beings in a state of nature; namely, the individual differences presented by animals and plants, and those slightly greater and generally inherited differences which are ranked by naturalists as varieties or geographical races. We shall see how difficult, or rather how impossible it often is, to distinguish between races and sub-species, as the less well-marked forms have sometimes been denominated; and again between sub-species and true species. I shall further attempt to show that it is the common and widely ranging, or, as they may be called, the dominant species, which most frequently vary; and that it is the large and flourishing genera which include the greatest number of varying species. Varieties, as we shall see, may justly be called incipient species.

But it may be urged, granting that organic beings in a state of nature present some varieties,--that their organization is in some slight degree plastic; granting that many animals and plants have varied greatly under domestication, and that man by his power of selection has gone on accumulating such variations until he has made strongly marked and firmly inherited races; granting all this, how, it may be asked, have species arisen in a state of nature? The differences between natural varieties are slight; whereas the differences are considerable between the species of the same genus, and great between the species of distinct genera. How do these lesser differences become augmented into the greater difference? How do varieties, or as I have called them incipient species, become converted into true and well-defined species? How has each new species been adapted to the surrounding physical conditions, and to the other forms of life on which it in any way depends? We see on every side of us innumerable adaptations and contrivances, which have justly excited in the mind of every observer the highest admiration. There is, for instance, a fly which deposits its eggs within the stamens of a Scrophularia, and secretes a poison which produces a gall, on which the larva feeds; but there is another insect which deposits its eggs within the body of the larva within the gall, and is thus nourished by its living prey; so that here a hymenopterous insect depends on a dipterous insect, and this depends on its power of producing a monstrous growth in a particular organ of a particular plant. So it is, in a more or less plainly marked manner, in thousands and tens of thousands of cases, with the lowest as well as with the highest productions of nature.

This problem of the conversion of varieties into species,--that is, the augmentation of the slight differences characteristic of varieties into the greater differences characteristic of species and genera, including the admirable adaptations of each being to its complex organic and inorganic conditions of life,--will form the main subject of my second work. We shall therein see that all organic beings, without exception, tend to increase at so high a ratio, that no district, no station, not even the whole surface of the land or the whole ocean, would hold the progeny of a single pair after a certain number of generations. The inevitable result is an ever-recurrent Struggle for Existence. It has truly been said that all nature is at war; the strongest ultimately prevail, the weakest fail; and we well know that myriads of forms have disappeared from the face of the earth. If then organic beings in a state of nature vary even in a slight degree, owing to changes in the surrounding conditions, of which we have abundant geological evidence, or from any other cause; if, in the long course of ages, inheritable variations ever arise in any way advantageous to any being under its excessively complex and changing relations of life; and it would be a strange fact if beneficial variations did never arise, seeing how many have arisen which man has taken advantage of for his own profit or pleasure; if then these contingencies ever occur, and I do not see how the probability of their occurrence can be doubted, then the severe and often-recurrent struggle for existence will determine that those variations, however slight, which are favourable shall be preserved or selected, and those which are unfavourable shall be destroyed.

This preservation, during the battle for life, of varieties which possess any advantage in structure, constitution, or instinct, I have called Natural Selection; and Mr. Herbert Spencer has well expressed the same idea by the Survival of the Fittest. The term "natural selection" is in some respects a bad one, as it seems to imply conscious choice; but this will be disregarded after a little familiarity. No one objects to chemists speaking of "elective affinity;" and certainly an acid has no more choice in combining with a base, than the conditions of life have in determining whether or not a new form be selected or preserved. The term is so far a good one as it brings into connection the production of domestic races by man's power of selection, and the natural preservation of varieties and species in a state of nature. For brevity sake I sometimes speak of natural selection as an intelligent power;--in the same way as astronomers speak of the attraction of gravity as ruling the movements of the planets, or as agriculturists speak of man making domestic races by his power of selection. In the one case, as in the other, selection does nothing without variability, and this depends in some manner on the action of the surrounding circumstances on the organism. I have, also, often personified the word Nature; for I have found it difficult to avoid this ambiguity; but I mean by nature only the aggregate action and product of many natural laws,--and by laws only the ascertained sequence of events.

In the chapter devoted to natural selection I shall show from experiment and from a multitude of facts, that the greatest amount of life can be supported on each spot by great diversification or divergence in the structure and constitution of its inhabitants. We shall, also, see that the continued production of new forms through natural selection, which implies that each new variety has some advantage over others, almost inevitably leads to the extermination of the older and less improved forms. These latter are almost necessarily intermediate in structure as well as in descent between the last-produced forms and their original parent-species. Now, if we suppose a species to produce two or more varieties, and these in the course of time to produce other varieties, the principle of good being derived from diversification of structure will generally lead to the preservation of the most divergent varieties; thus the lesser differences characteristic of varieties come to be augmented into the greater differences characteristic of species, and, by the extermination of the older intermediate forms, new species come to be distinctly defined objects. Thus, also, we shall see how it is that organic beings can be classed by what is called a natural method in distinct groups--species under genera, and genera under families.

As all the inhabitants of each country may be said, owing to their high rate of reproduction, to be striving to increase in numbers; as each form is related to many other forms in the struggle for life,--for destroy any one and its place will be seized by others; as every part of the organization occasionally varies in some slight degree, and as natural selection acts exclusively by the preservation of variations which are advantageous under the excessively complex conditions to which each being is exposed, no limit exists to the number, singularity, and perfection of the contrivances and co-adaptations which may thus be produced. An animal or a plant may thus slowly become related in its structure and habits in the most intricate manner to many other animals and plants, and to the physical conditions of its home. Variations in the organization will in some cases be aided by habit, or by the use and disuse of parts, and they will be governed by the direct action of the surrounding physical conditions and by correlation of growth.

On the principles here briefly sketched out, there is no innate or necessary tendency in each being to its own advancement in the scale of organization. We are almost compelled to look at the specialization or differentiation of parts or organs for different functions as the best or even sole standard of advancement; for by such division of labour each function of body and mind is better performed. And, as natural selection acts exclusively through the preservation of profitable modifications of structure, and as the conditions of life in each area generally become more and more complex, from the increasing number of different forms which inhabit it and from most of these forms acquiring a more and more perfect structure, we may confidently believe, that, on the whole, organization advances. Nevertheless a very simple form fitted for very simple conditions of life might remain for indefinite ages unaltered or unimproved; for what would it profit an infusorial animalcule, for instance, or an intestinal worm, to become highly organized? Members of a high group might even become, and this apparently has occurred, fitted for simpler conditions of life; and in this case natural selection would tend to simplify or degrade the organization, for complicated mechanism for simple actions would be useless or even disadvantageous.

In a second work, after treating of the Variation of organisms in a state of nature, of the Struggle for Existence and the principle of Natural Selection, I shall discuss the difficulties which are opposed to the theory. These difficulties may be classed under the following heads:--the apparent impossibility in some cases of a very simple organ graduating by small steps into a highly perfect organ; the marvellous facts of Instinct; the whole question of Hybridity; and, lastly, the absence, at the present time and in our geological formations, of innumerable links connecting all allied species. Although some of these difficulties are of great weight, we shall see that many of them are explicable on the theory of natural selection, and are otherwise inexplicable.

In scientific investigations it is permitted to invent any hypothesis, and if it explains various large and independent classes of facts it rises to the rank of a well-grounded theory. The undulations of the ether and even its existence are hypothetical, yet every one now admits the undulatory theory of light. The principle of natural selection may be looked at as a mere hypothesis, but rendered in some degree probable by what we positively know of the variability of organic beings in a state of nature,--by what we positively know of the struggle for existence, and the consequent almost inevitable preservation of favourable variations,--and from the analogical formation of domestic races. Now this hypothesis may be tested,--and this seems to me the only fair and legitimate manner of considering the whole question,--by trying whether it explains several large and independent classes of facts; such as the geological succession of organic beings, their distribution in past and present times, and their mutual affinities and homologies. If the principle of natural selection does explain these and other large bodies of facts, it ought to be received. On the ordinary view of each species having been independently created, we gain no scientific explanation of any one of these facts. We can only say that it has so pleased the Creator to command that the past and present inhabitants of the world should appear in a certain order and in certain areas; that He has impressed on them the most extraordinary resemblances, and has classed them in groups subordinate to groups. But by such statements we gain no new knowledge; we do not connect together facts and laws; we explain nothing.

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