作者：Darwin, Charles
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Variation of Animals and Plants under Domestication -- Volume I试读：
INTRODUCTION.
CHAPTER 1.I.
DOMESTIC DOGS AND CATS.
ANCIENT VARIETIES OF THE DOG—RESEMBLANCE OF DOMESTIC DOGS IN VARIOUS COUNTRIES TO NATIVE CANINE SPECIES—ANIMALS NOT ACQUAINTED WITH MAN AT FIRST FEARLESS—DOGS RESEMBLING WOLVES AND JACKALS—HABIT OF BARKING ACQUIRED AND LOST—FERAL DOGS—TAN-COLOURED EYE-SPOTS—PERIOD OF GESTATION- -OFFENSIVE ODOUR—FERTILITY OF THE RACES WHEN CROSSED—DIFFERENCES IN THE SEVERAL RACES IN PART DUE TO DESCENT FROM DISTINCT SPECIES—DIFFERENCES IN THE SKULL AND TEETH—DIFFERENCES IN THE BODY, IN CONSTITUTION—FEW IMPORTANT DIFFERENCES HAVE BEEN FIXED BY SELECTION—DIRECT ACTION OF CLIMATE—WATER-DOGS WITH PALMATED FEET—HISTORY OF THE CHANGES WHICH CERTAIN ENGLISH RACES OF THE DOG HAVE GRADUALLY UNDERGONE THROUGH SELECTION—EXTINCTION OF THE LESS IMPROVED SUB-BREEDS.
CATS, CROSSED WITH SEVERAL SPECIES—DIFFERENT BREEDS FOUND ONLY IN SEPARATED COUNTRIES—DIRECT EFFECTS OF THE CONDITIONS OF LIFE—FERAL CATS— INDIVIDUAL VARIABILITY.
CHAPTER 1.II.
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.
CHAPTER 1.III.
PIGS—CATTLE—SHEEP—GOATS.
PIGS BELONG TO TWO DISTINCT TYPES, SUS SCROFA AND INDICUS—TORFSCHWEIN— JAPAN PIGS—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.
CHAPTER 1.IV.
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.
CHAPTER 1.V.
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 FURCULUM—LENGTH OF WINGS—SUMMARY ON THE POINTS OF DIFFERENCE IN THE SEVERAL BREEDS.
CHAPTER 1.VI.
PIGEONS—continued.
ON THE ABORIGINAL PARENT-STOCK OF THE SEVERAL DOMESTIC RACES—HABITS OF LIFE—WILD RACES OF THE ROCK-PIGEON—DOVECOTE-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.
CHAPTER 1.VII.
FOWLS.
BRIEF DESCRIPTIONS OF THE CHIEF BREEDS—ARGUMENTS IN FAVOUR OF THEIR DESCENT FROM SEVERAL SPECIES—ARGUMENTS IN FAVOUR OF ALL THE BREEDS HAVING DESCENDED FROM GALLUS BANKIVA—REVERSION TO THE PARENT-STOCK IN COLOUR— ANALOGOUS VARIATIONS—ANCIENT HISTORY OF THE FOWL—EXTERNAL DIFFERENCES BETWEEN THE SEVERAL BREEDS—EGGS—CHICKENS—SECONDARY SEXUAL CHARACTERS— WING-AND TAIL-FEATHERS, VOICE, DISPOSITION, ETC.—OSTEOLOGICAL DIFFERENCES IN THE SKULL, VERTEBRAE, ETC.—EFFECTS OF USE AND DISUSE ON CERTAIN PARTS— CORRELATION OF GROWTH.
CHAPTER 1.VIII.
DUCK—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-BEE.
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.
CHAPTER 1.IX.
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—DIFFER LITTLE EXCEPT IN THE TUBERS— CHARACTERS INHERITED.
CHAPTER 1.X.
PLANTS continued—FRUITS—ORNAMENTAL TREES—FLOWERS.
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.
CHAPTER 1.XI.
ON BUD-VARIATION, AND ON CERTAIN ANOMALOUS MODES OF REPRODUCTION AND VARIATION.
BUD-VARIATION 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—GRAFT-HYBRIDS—ON THE SEGREGATION OF THE PARENTAL CHARACTERS IN SEMINAL HYBRIDS BY BUD-VARIATION—ON THE DIRECT OR IMMEDIATE ACTION OF FOREIGN POLLEN ON THE MOTHER-PLANT—ON THE EFFECTS OF A PREVIOUS IMPREGNATION ON THE SUBSEQUENT OFFSPRING OF FEMALE ANIMALS— CONCLUSION AND SUMMARY.
CHAPTER 1.XII.
INHERITANCE.
WONDERFUL NATURE OF INHERITANCE—PEDIGREES OF OUR DOMESTICATED ANIMALS— INHERITANCE NOT DUE TO CHANCE—TRIFLING CHARACTERS INHERITED—DISEASES INHERITED—PECULIARITIES IN THE EYE INHERITED—DISEASES IN THE HORSE— LONGEVITY AND VIGOUR—ASYMMETRICAL DEVIATIONS OF STRUCTURE—POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER AMPUTATION—CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS—WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS— COLOUR OF HORSES—NON-INHERITANCE IN CERTAIN CASES—INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION—CONCLUSION.
LIST OF ILLUSTRATIONS.
FIGURE.
1. DUN DEVONSHIRE PONY, WITH SHOULDER, SPINAL, AND LEG STRIPES.
2. HEAD OF JAPAN OR MASKED PIG.
3. HEAD OF WILD BOAR, AND OF "GOLDEN DAYS," A PIG OF THE YORKSHIRE LARGE BREED.
4. OLD IRISH PIG WITH JAW-APPENDAGES.
5. HALF-LOP RABBIT.
6. SKULL OF WILD RABBIT.
7. SKULL OF LARGE LOP-EARED RABBIT.
8. PART OF ZYGOMATIC ARCH, SHOWING THE PROJECTING END OF THE MALAR BONE OF THE AUDITORY MEATUS, OF RABBITS.
9. POSTERIOR END OF SKULL, SHOWING THE INTER-PARIETAL BONE, OF RABBITS.
10. OCCIPITAL FORAMEN OF RABBITS.
11. SKULL OF HALF-LOP RABBIT.
12. ATLAS VERTEBRAE OF RABBITS.
13. THIRD CERVICAL VERTEBRAE OF RABBITS.
14. DORSAL VERTEBRAE, FROM SIXTH TO TENTH INCLUSIVE, OF RABBITS.
15. TERMINAL BONE OF STERNUM OF RABBITS.
16. ACROMION OF SCAPULA OF RABBITS.
17. THE ROCK-PIGEON, OR COLUMBA LIVIA.
18. ENGLISH POUTER.
19. ENGLISH CARRIER.
20. ENGLISH BARB.
21. ENGLISH FANTAIL.
22. AFRICAN OWL.
23. SHORT-FACED ENGLISH TUMBLER.
24. SKULLS OF PIGEONS, VIEWED LATERALLY.
25. LOWER JAWS OF PIGEONS, SEEN FROM ABOVE.
26. SKULL OF RUNT, SEEN FROM ABOVE.
27. LATERAL VIEW OF JAWS OF PIGEONS.
28. SCAPULAE OF PIGEONS.
29. FURCULA OF PIGEONS.
30. SPANISH FOWL.
31. HAMBURGH FOWL.
32. POLISH FOWL.
33. OCCIPITAL FORAMEN OF THE SKULLS OF FOWLS.
34. SKULLS OF FOWLS, VIEWED FROM ABOVE, A LITTLE OBLIQUELY.
35. LONGITUDINAL SECTIONS OF SKULLS OF FOWLS, VIEWED LATERALLY.
36. SKULL OF HORNED FOWL, VIEWED FROM ABOVE, A LITTLE OBLIQUELY.
37. SIXTH CERVICAL VERTEBRAE OF FOWLS, VIEWED LATERALLY.
38. EXTREMITY OF THE FURCULA OF FOWLS, VIEWED LATERALLY.
39. SKULLS OF DUCKS, VIEWED LATERALLY, REDUCED TO TWO-THIRDS OF THE NATURAL SIZE.
40. CERVICAL VERTEBRAE OF DUCKS, OF NATURAL SIZE.
41. PODS OF THE COMMON PEA.
42. PEACH AND ALMOND STONES, OF NATURAL SIZE, VIEWED EDGEWAYS.
43. PLUM STONES, OF NATURAL SIZE, VIEWED LATERALLY.
TABLE 1: PRINCIPAL ADDITIONS AND CORRECTIONS IN THIS (SECOND) EDITION.
First Edition, Volume I., Page 34.Second Edition Volume I., Page 35.Dr. Burt Wilder's observations on the brains of different breeds of theDog.
First Edition, Volume I., Page 38.Second Edition Volume I., Page 40.Degeneracy of Dogs imported into Guinea.
First Edition, Volume I., Page 51.Second Edition Volume I., Page 54.Difference in the number of the lumbar vertebrae in the races or species ofthe Horse.
First Edition, Volume I., Page 102.Second Edition Volume I., Page 106.Hairy appendages to the throats of Goats.
First Edition, Volume I., Page 162.Second Edition Volume I., Page 170.Sexual differences in colour in the domestic Pigeon.
First Edition, Volume I., Page 217.Second Edition Volume I., Page 228.Movements like those of the Tumbler-pigeon, caused by injury to the brain.
First Edition, Volume I., Page 290.Second Edition Volume I., Page 306.Additional facts with respect to the Black-shouldered Peacock.
First Edition, Volume I., Page 296.Second Edition Volume I., Page 312.Ancient selection of Gold-fish in China.
First Edition, Volume I., Page 314.Second Edition Volume I., Page 332.Major Hallett's 'Pedigree Wheat.'
First Edition, Volume I., Page 326.Second Edition Volume I., Page 345.The common radish descended from Raphanus raphanistrum.
First Edition, Volume I., Page 374.Second Edition Volume I., Page 398.Several additional cases of bud-variation given.
First Edition, Volume I., Page 396.Second Edition Volume I., Page 420.An abstract of all the cases recently published of graft-hybrids in thepotato, together with a general summary on graft-hybridisation.
First Edition, Volume I., Page 399.Second Edition Volume I., Page 429.An erroneous statement with respect to the pollen of the date-palmaffecting the fruit of the Chamaerops omitted.
First Edition, Volume I., Page 400.Second Edition Volume I., Page 430.New cases of the direct action of pollen on the mother-plant.
First Edition, Volume I., Page 404.Second Edition Volume I., Page 435.Additional and remarkable instances of the action of the male parent on thefuture progeny of the female.
First Edition, Volume II., Page 14.Second Edition Volume I., Page 459.An erroneous statement corrected, with respect to the regrowth ofsupernumerary digits after amputation.
First Edition, Volume II., Page 23.Second Edition Volume I., Page 467.Additional facts with respect to the inherited effects of circumcision.
First Edition, Volume II., Page 23.Second Edition Volume I., Page 467.Dr. Brown-Sequard on the inherited effects of operations on the Guinea-pig.
First Edition, Volume II., Page 24.Second Edition Volume I., Page 469.Other cases of inherited mutilations.
First Edition, Volume II., Page 43.Second Edition Volume II., Page 17.An additional case of reversion due to a cross.
First Edition, Volume II., Page 72.Second Edition Volume II., Page 48.Inheritance as limited by sex.
First Edition, Volume II., Page 105.Second Edition Volume II., Page 83.Two varieties of maize which cannot be crossed.
First Edition, Volume II., Page 120.Second Edition Volume II., Page 99.Some additional facts on the advantages of cross-breeding in animals.
First Edition, Volume II., Page 123.Second Edition Volume II., Page 103.Discussion on the effects of close interbreeding in the case of man.
First Edition, Volume II., Page 135 to 141.Second Edition Volume II., Page 117 to 122.Additional cases of plants sterile with pollen from the same plant.
First Edition, Volume II., Page 149.Second Edition Volume II., Page 131.Mr. Sclater on the infertility of animals under confinement.
First Edition, Volume II., Page 152.Second Edition Volume II., Page 134.The Aperea a distinct species from the Guinea-pig.
First Edition, Volume II., Page 230.Second Edition Volume II., Page 215.Professor Jager on hawks killing light-coloured pigeons.
First Edition, Volume II., Page 273.Second Edition Volume II., Page 262.Professor Weismann on the effects of isolation in the development ofspecies.
First Edition, Volume II., Page 281.Second Edition Volume II., Page 271.The direct action of the conditions of life in causing variation.
First Edition, Volume II., Page 317.Second Edition Volume II., Page 309.Mr. Romanes on rudimentary parts.
First Edition, Volume II., Page 324 to 328.Second Edition Volume II., Page 316 to 327.Some additional cases of correlated variability.
First Edition, Volume II., Page 339.Second Edition Volume II., Page 333.On Geoffroy St.-Hilaire's law of "soi pour soi."
First Edition, Volume II., Page 357 to 404.Second Edition Volume II., Page 349 to 399.The chapter on Pangenesis has been largely altered and re-modelled; but theessential principles remain the same.
THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.
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 fulness.
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. (Here shown with [].) 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. (Introduction/1. To any one who has attentively read my 'Origin of Species' this Introduction will be superfluous. As I stated in that work that I should soon publish the facts on which the conclusions given in it were founded, I here beg permission to remark that the great delay in publishing this first work has been caused by continued ill- health.) 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 a man drops a piece of iron into sulphuric acid, it cannot be said strictly that he makes the sulphate of iron, he only allows their elective affinities to come into play. If organic beings had not possessed an inherent tendency to vary, man could have done nothing. (Introduction/2. M. Pouchet has recently ('Plurality of Races' English Translation 1864 page 83 etc.) insisted that variation under domestication throws no light on the natural modification of species. I cannot perceive the force of his arguments, or, to speak more accurately, of his assertions to this effect.) 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 of the laws of inheritance, of 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 highly 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 almost in any way which he chooses; and thus he can certainly produce a great result. Selection
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