OCR Text |
Show 16 VARIATION CHAP. I. the same species, also, often have a somewhat monstrous character; by which I mean, that, although differing from each other, and from the other species of the same genus, in several trifling respects, they often differ in an extreme degree in some one part, both when compared one with another, and more especially when compared with all the species in nature to which they are nearest allied. With these exceptions (and with that of the perfect fertility of varieties when crossed,---a subject hereafter to be discussed), domestic races of the same species differ from each other in the same manner as, only in most cases in a lesser degree than, do closelyallied species of the same genus in a state of nature. I think this must be admitted, when we find that there are hardly any domestic races, either amongst animals or plants, which have not been ranked by some competent judges as mere varieties, and by other competent judges as the descendants of aboriginally distinct species. If any marked distinction existed between domestic races and species, this source of doubt could not so perpetually recur. It has often been stated that domestic races do not differ from each other in characters of generic value. I think it could be shown that this statement is hardly correct; but naturalists differ most widely in determining what characters are of generic value; all such valuations being at present empirical. Moreover, on the view of the origin of genera which I shall presently give, we have no right to expect often to meet with generic differences in our domesticated productions. When we attempt to estimate the amount of structural difference between the domestic races of the same speci~s, we are soon involved in doubt, from not knowing whether they have descended from one or several parent-species. This point, if it could be cleared up, would be interesting; if, for instance, it could be shown that the grey- CHAP. I. UNDER DOMESTICATION. 17 hound, bloodhound, terrier, spaniel, and bull-dog, which we. all know propagate their kind so truly, were the offspnng of any single species, then such facts would have great weight in making us doubt about the immutability ?f the many very closely allied and natural species-for Instance, of the many foxes-inhabiting different quarters of the world. I do not believe, as we shall presently se.e, that. all our d_ogs have descended from any one Wild species; but, In the case of some other domestic races, th~re . is presumptive, or even strong, evidence in favour of this view. It has often been assumed that man has chosen for do~estica~ion animals and plants having an extrao~ dinary Inherent tendency to vary, and likewise to Withs~a?d diverse climates. I do not dispute that these capaCities have added largely to the value of most of our ~omesticated productions ; but how could a savage possibly know, when he . first tamed an aniinal, whether It would vary in succeeding generations, and whether it' would endure other climates? Has the little variability of the ass or guinea-fowl, or the small power of endurance of warmth by the rein-deer, or of cold by the common came~, prevented their domestication? I cannot doubt that If oth~r animals and plants, equal in number to o~r domestwated productions, and belonging to equally d~verse classes and countries, were taken from a state of nature, and could be made to breed for an equal number of generations under domestication they would ovuarr y o~ ~n average. as largely as the paren' t species of I existing domestiCated productions have varied. . n the case of most of our anciently domesticated animals and. plants, I do not think it is possible to come ;.o any definite conclusion, whether they have descended r~~ one or several species. The argument mainly re led on by those who believe in the multiple origin |