PREFACE TO THE SECOND EDITION
During the seven years which have elapsed since the publication in 1868 of the first edition of this Work, I have continued to attend to the same subjects, as far as lay in my power; and I have thus accumulated a large body of additional facts, chiefly through the kindness of many correspondents. Of these facts I have been able here to use only those which seemed to me the more important. I have omitted some statements, and corrected some errors, the discovery of which I owe to my reviewers. Many additional references have been given. The eleventh chapter, and that on Pangenesis, are those which have been most altered, parts having been remodelled; but I will give a list of the more important alterations for the sake of those who may possess the first edition of this book.
TABLE OF PRINCIPAL ADDITIONS AND CORRECTIONS IN SECOND EDITION
|
First Edition Vol. I |
Second Edition Vol. I | |
| Page | Chapter | |
| 34 | I | Dr. Burt Wilder’s observations on the brains of different breeds of the Dog. |
| 38 | I | Degeneracy of Dogs imported into Guinea. |
| 51 | II | Difference in the number of lumbar vertebræ in the races or species of the Horse. |
| 102 | III | Hairy appendages to the throats of Goats. |
| 162 | V | Sexual differences in colour in the domestic Pigeon. |
| 217 | VI | Movements like those of the Tumbler-pigeon, caused by injury to the brain. |
| 290 | VIII | Additional facts with respect to the Black-shouldered Peacock. |
| 296 | VIII | Ancient selection of Gold-fish in China. |
| 314 | IX | Major Hallett’s ‘Pedigree Wheat.’ |
| 326 | IX | The common radish descended from Raphanus raphanistrum. |
| 374 | XI | Several additional cases of bud-variation given. |
| 396 | XI | An abstract of all the cases recently published of graft-hybrids in the potato, together with a general summary on graft-hybridisation. |
| 399 | XI | An erroneous statement with respect to the pollen of the date-palm affecting the fruit of the Chamærops omitted. |
| 400 | XI | New cases of the direct action of pollen on the mother-plant. |
| 404 | XI | Additional and remarkable instances of the actions of the male parent on the future progeny of the female. |
| Vol.II | ||
| 14 | XII | An erroneous statement corrected, with respect to the regrowth of supernumerary digits after amputation. |
| 23 | XII | Additional facts with respect to the inherited effects of circumcision. |
| 23 | XII | Dr. Brown-Séquard on the inherited effects of operations on the Guinea-pig. |
| 24 | XII | Other cases of inherited mutilations. |
| Vol. II | ||
| 43 | XIII | An additional case of reversion due to a cross. |
| 72 | XIV | Inheritance as limited by sex. |
| 105 | XVI | Two varieties of maize which cannot be crossed. |
| 120 | XVII | Some additional facts on the advantages of cross-breeding in animals. |
| 123 | XVII | Discussion on the effects of the close interbreeding in the case of man. |
| 135 to 141 | XVII | Additional cases of plants sterile with pollen from the same plant. |
| 149 | XVIII | Mr. Sclater on the infertility of animals under confinement. |
| 152 | XVIII | The Aperea a distinct species from the Guinea-pig. |
| 230 | XXI | Prof. Jäger on hawks killing light-coloured pigeons. |
| 273 | XXIII | Prof. Wisemann on the effects of isolation in the development of species. |
| 281 | XXIII | The direct action of the conditions of life in causing variation. |
| 317 | XXIV | Mr. Romanes on rudimentary parts. |
| 324 to 328 | XXV | Some additional cases of correlated variability. |
| 339 | XXVI | On Geoffrey St. Hilaire’s law of “soi pour soi.” |
| 357 to 404 | XXVII | The chapter on Pangenesis has been largely altered and re-modelled; but the essential principles remain the same. |
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 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. 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.[[1]] 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.[[2]] 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 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.