64 THE PROBLEMS OF EVOLUTION 



sion. In both cases inherent capacity for normal 

 behavior is evident, either in the actual production 

 of the part which is later lost or in the agony re- 

 sulting from the interference with normal processes. 



The more significant individual modifications 

 have already been listed. They are due to the re- 

 sponses of the individual to external stimuli; re- 

 gardless of the particular conditions involved, they 

 always include these two factors, stimulus and 

 response, and the result is a product not only of 

 environment but also of heritage. If there is any 

 doubt of this, we have only to consider such con- 

 ditions as obtain in the albino. These individuals 

 may encounter the same stimulus that produces 

 heavy pigmentation in normal individuals but 

 they lack the hereditary ability to respond. 



There has been a tendency in the literature of 

 evolution to handle these individual adaptations 

 in separate groups. This treatment is not nec- 

 essary. Whether they fall in one of the groups 

 listed or in another they are all the result of increase 

 or decrease of some functional activity which 

 brings about a corresponding change of functional 

 capacity to meet a need arising in the life of the 

 individual. 



Most of these responses appear to be adaptive. 

 It is easy to look upon them also as positive and 

 negative in that a lessened stimulus results in a 

 lessened response and vice versa, but it seems more 



