EVOLUTION 103 



ter apparent example of its mode of action 

 than the human species. The considerable in- 

 fluence that the kind of life that an individual 

 leads has upon his body has long been well 

 recognized, and the direct effect of this, fa- 

 vorable or unfavorable, on his offspring has 

 underlain the claims of the moralist for gen- 

 erations past. Thus the Lamarckian hypothe- 

 sis, though an impersonal explanation of trans- 

 mutation, can be easily brought into relation 

 with man's higher nature and made to point 

 a moral. 



But a very serious obstacle to the accept- 

 ance of this hypothesis has gradually arisen 

 in the otherwise easy path of the Lamarckian. 

 The slight changes which nearly every organ- 

 ism exhibits as the effects of its environment 

 and which, for Lamarck, are the actual steps 

 in evolution, are as a matter of fact just the 

 class of changes in favor of the inheritance 

 of which there is the least evidence. Any pe- 

 culiarity that an animal exhibits and that is 

 not an inheritance, but is the result of an in- 

 dividual change due either to an alteration of 

 habit or to the direct influence of the envi- 

 ronment, is called an acquired character ; and 

 the assumption that acquired characters are 



