Appendix II. 331 



ability is accumulative, so it may be with their definite ac- 

 tion. Hence it is possible that great and definite modifications 

 of structure may result from altered conditions acting during 

 a long series of generations. In some few instances a marked 

 effect has been produced quickly on all, or nearly all, the 

 individuals which have been exposed to some considerable 

 change of climate, food, or other circumstance 1 ." 



Once more, in order to show that he retained these views 

 to the end of his life, I may quote a passage from the second 

 edition of the Descent of Man, which is the latest expression 

 of his opinion upon these points: 



"Each of the endless diversities in plumage, which we see 

 in our domesticated birds, is, of course, the result of some de- 

 finite cause ; and under natural and more uniform conditions, 

 some one tint, assuming that it -was in no way injurious, would 

 almost certainly sooner or later prevail. The free-inter- 

 crossing of the many individuals belonging to the same species 

 would ultimately tend to make any change of colour thus in- 

 duced uniform in character. .... Can we believe that the 

 very slight differences in tints and markings between, for in- 

 stance, the female black-grouse and red-grouse serve as a 

 protection ? Are partridges as they are now coloured, better 

 protected than if they had resembled quails ? Do the slight 

 differences between the females of the common pheasant, the 

 Japan and golden pheasants, serve as a protection, or might 

 not their plumage have been interchanged with impunity ? 

 From what Mr. Wallace has observed of the habits of certain 

 gallinaceous birds in the East, he thinks that such slight 

 differences are beneficial. For myself, I will only say, I am 

 not convinced 2 ." 



Yet " convinced " he certainly must have been on merely 

 a priori grounds, had he countenanced Mr. Wallace's 

 reasoning from the general theory of natural selection ; and 

 the fact that he here tails to be convinced even by "what 

 Mr. Wallace has observed of the habits of certain gallinaceous 



1 Variation, &c., vol. ii. p. 280. * Descent of Man, pp. 473-4. 



