DARWm, AND THE ORIGIN OF SPECIES 191 



degree operative at all, the great function of these principles must 

 be that of supplying to natural selection the incipient stages of 

 adaptive modification in all cases, where, but for this agency, there 

 would be nothing of the kind to select. 



I hope to show that formidable as this criticism appears, and 

 grave as the difficulty has seemed to many able thinkers, it is, 

 after all, verbal in origin ; and that they who believe that natu- 

 ral selection fails to account for the origin of species until some 

 other source for the incipient stages of adaptive modification has 

 been discovered are misled by words ; for no Darwinian supposes 

 that selection produces either the incipient or final stages of any 

 modification, adaptive or otherwise, although all are aware that 

 there is, unfortunately, no incompatibility between the system of 

 things and injurious modification. 



Darwin very wisely made much of the history of domesticated 

 animals and cultivated plants, for many reasons ; and, as I believe, 

 for this among others: that since the use or purpose of fancy 

 breeds is the gratification of the whim of the breeder, or conformity 

 to the arbitrary rules of fanciers' clubs, good common sense must 

 decline serious consideration of the belief that the causes of varia- 

 tion stand in any relation, incipient or otherwise, to this purpose, 

 except so far as all nature may be intended. 



Darwin writes to Asa Gray: " You lead me to infer that you 

 believe that variation has been carried along certain beneficial lines. 

 I cannot believe this: and I think you would have to believe that 

 the tail of the Fantail was led to vary in the number and direction 

 of its feathers in order to gratify the caprice of a few men." Few, 

 even among those who believe that all nature bears witness to 

 intention, will hold it good common sense to expect to discover any 

 natural laws, or causes of variation^ competent to adapt pigeons to 

 the arbitrary rules of pigeon clubs; for while we may be unable 

 to believe that fanciers can bring about any change which a suf- 

 ficient knowledge of the nature of pigeons might not have led us 

 to expect, I cannot imagine how this nature, or the history of its 

 origin, can be thought to stand, prior to selection, in any specific 

 adjustment to the caprice of pigeon-fanciers; for we are much more 

 likely to find the physical causes of this adjustment in the mechan- 

 ism of the breeders' structure than to find it in the nature of pigeons. 



