Chap. XXI. SELECTION. 233 



circumstances inconceivably complex and liable to change, 

 modifications of tlie most varied nature in the internal organs 

 as well as in external characters, in the functions and mutual 

 relations of parts, will be rigorously tested, preserved, or 

 rejected. Natural selection often checks man's comparatively 

 feeble and capricious attempts at improvement ; and if it were 

 not so, the result of his work, and of nature's work, would be 

 even still more different. Nevertheless, we must not overrate 

 the amount of difference between natural species and domestic 

 races ; the most experienced naturalists have often disputed 

 whether the latter are descended from one or from several 

 aboriginal stocks, and this clearly shows that there is no 

 palpable difference between species and races. 



Domestic races propagate their kind far more truly, and 

 endure for much longer periods, than most naturalists are 

 willing to admit. Breeders feel no doubt on this head : ask 

 a man who has long reared Shorthorn or Hereford cattle, 

 Leicester or Southdown sheep, Spanish or Game poultry, 

 tumbler or carrier-pigeons, whether these races may not have 

 been derived from common progenitors, and he will probably 

 laugh you to scorn. The breeder admits that he may hope 

 to produce sheep with finer or longer wool and with better 

 carcases, or handsomer fowls, or carrier-pigeons with beaks 

 just perceptibly longer to the practised eye, and thus be 

 successful at an exhibition. Thus far he will go, but 

 no farther. He does not reflect on what follows from 

 adding up during a long course of time many slight, 

 successive modifications ; nor does he reflect on the former 

 existence of numerous varieties, connecting the links in each 

 divergent line of descent. He concludes, as was shown in 

 the earlier chapters, that all the chief breeds to which he 

 has long attended are aboriginal productions. The systematic 

 naturalist, on the other hand, who generally knows nothing 

 of the art of breeding, who does not pretend to know how 

 and when the several domestic races were formed, who cannot 

 have seen the intermediate gradations, for they do not now 

 exist, nevertheless feels no doubt that these races are sprung 

 from a single source. But ask him whether the closely 

 allied natural species which he has studied may not have 



