DARWIN 341 



not merely the entire adaptive form of the ani- 

 mal, but even a slight adaptive variation in a 

 single character, would turn the scale in favor of 

 survival! This was during the period of his ex- 

 treme faith in the natural selection factor, which 

 reached its highest point about 1858. He grad- 

 ually^ receded from this extreme, as shown in a 

 letter to Victor Cams in 1869: *'I have been led 

 ... to infer that single variations are of even 

 less importance, in comparison with individual 

 differences, than I formerly thought." He here 

 refers to the aggregate of distinction between 

 two forms. 



This reaction was accompanied by a slow 

 change of mind toward the Lamarckian factor 

 of the inheritance of the effects of use and disuse. 

 This was brought about, apparently, not through 

 a renewed study of the Philosophie Zoologique, 

 but by Darwin's own observations upon the do- 

 mesticated animals, especially in his records of 

 structures which were developing and degenerat- 

 ing entirely apart from the main course of the 

 artificial selection of breeders, as well as from the 

 weight of utility or usefulness in the scale of sur- 

 vival in Nature. He may have been influenced 

 also by the thorough Lamarckism of Herbert 

 Spencer, although this does not appear in the 

 Life and Letters. 



Darwin's gradual recession from his exclusion 



