SOURCES OF CHANGE 59 



organism throws additional light on their signifi- 

 cance in evolution. Since organisms exist as reac- 

 tion products of heritage and environment, it is 

 obvious that these factors must be in harmony if 

 life is to continue. A given condition of the en- 

 vironment must be met by a particular power of 

 the organism to respond, a function which is the 

 expression of some structural component of the 

 individual. Since, at the outset of their existence, 

 individuals receive a certain equipment and are 

 produced in a suitable environment, their develop- 

 ment and the major steps of their independent life 

 are fairly uniform throughout any species. Adap- 

 tation is an inherent necessity and a universal 

 phenomenon. 



Some of the adaptations which have been ob- 

 served in the living world are wonderful, and have 

 given rise to a probably unwarranted emphasis 

 upon the adaptive value of organic structures. 

 Attention has frequently been called to the fact 

 that the mere existence of an organ does not signify 

 adaptive value. The presence of eyes is a valuable 

 adaptation for life in the open, but is of no use in 

 dark retreats. Lack of eyes must be a limitation 

 to an organism which lives in the presence of light, 

 yet many such cases occur. So too, animals with 

 eyes have been found in caves. It is necessary in 

 evaluating characters to recognize adaptation as 

 a twofold phenomenon of process and result. All 



