62 Darwin, and after Darwin. 



Therefore we may now appreciate the importance 

 of all facts or arguments which attenuate the prob- 

 ability of natural selection having been at work. 

 This may be done by searching for cases in nature 

 where a congenital structure, although unquestionably 

 adaptive, nevertheless presents so small an amount 

 of adaptation, that we can scarcely suppose it to 

 have been arrived at by natural selection in the 

 struggle for existence, as distinguished from the 

 inheritance of functionally-produced modifications. 

 For if functionally-produced modifications are ever 

 transmitted at all, there is no limit to the minute- 

 ness of adaptive values which may thus become 

 congenital ; whereas, in order that any adaptive 

 structure or instinct should be seized upon and ac- 

 cumulated by natural selection, it must from the 

 very first have had an adaptive value sufficiently 

 great to have constituted its presence a matter of 

 life and death in the struggle for existence. Such 

 structures or instincts must not only have always 

 presented some measure of adaptive value, but 

 this must always have been sufficiently great to 

 reach what I have elsewhere called a selection- 

 value. Hence, if we meet with cases in nature where 

 adaptive structures or instincts present so low a 

 degree of adaptive value that it is difficult to con- 

 ceive how they could ever have exercised any 

 appreciable influence in the battle for life, such cases 

 may fairly be adduced in favour of the Lamarckian 

 theory. For example, the Neo- Lamarckian school of 

 the United States is chiefly composed of palaeon- 

 tologists ; and the reason of this seems to be that 

 the study of fossil forms — or of species in process of 



