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 irom the general theory of natural selection ; and 

 the fact that he here fails 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. 



