NATURAL SELECTION 189 



1924, p. 117) hold ' that Darwin's views [on this subject] have 

 been brilliantly confirmed by the modern work on Mendelian 

 lines.' 



There are really two questions involved here — (i) have 

 domesticated races and forms been produced by the means 

 which Darwin considered to be influential? and (ii) is there any 

 analogy between Artificial and Natural Selection ? 



Darwin's opinions on this subject in the sixth edition of 

 ' The Origin of Species ' and in ' Variation of Animals and 

 Plants under Domestication ' are in agreement — (a) domesti- 

 cated forms vary more than the wild parent forms ; (b) such 

 variation is largely due to ' changed condition of life ' and 

 ' perhaps a great effect may be attributed to the increased 

 use or disuse of parts ' (id. 1905, vol. ii, pp. 349-50) ; (c) in 

 some cases the origin of domesticated breeds seems to have 

 been due to ' the intercrossing of aboriginally distinct species ' 

 (I.e.), though he is definitely in doubt as to how far it is really 

 efficacious in producing new forms, and elsewhere (I.e. p. 94) 

 holds that the effect of crossing has been ' greatly exaggerated.' 

 It is quite apparent that he held that there was a rich source of 

 variation for selection to draw on. There is no evidence of 

 his having attempted to discover how much of the variation 

 referred to ' changed conditions ' is inherited and therefore the 

 basis of new fixed races and strains, though he admits (I.e. 

 p. 49) that ' the greater or less force of inheritance and rever- 

 sion determines whether variations shall endure.' He did not, 

 of course, distinguish between mutations and variation due to 

 factorial recombination. It is clear, however, that in spite of 

 this somewhat ill-defined knowledge of the material available, 

 he held that human selection, applied to the ever-present store 

 of variation, had been effective. Goodrich (I.e.), in stating 

 the case in modern terms, holds that ' one mutation after 

 another is isolated and bred from, and so almost any desired 

 form is obtained.' 



This belief in the frequency of mutation is in radical con- 

 trast to the view that the efficacy of selection depends on the 

 progressive isolation of pre-existent hereditary material and 

 the continuous and carefully planned crossing of stocks of 

 known hereditary constitution, by which appropriate combina- 

 tions can be formed. The husbandman has been successful, 

 according to this view, because in stock-rearing like can be 



