I04 A Factor in Evolution 



of the same species and in the same habitat. In all these 

 cases it is evident that other living creatures constitute 

 part of the environment of each, and many neuro-genctic 

 and psycho-genetic accommodations have reference to or 

 involve these other creatures. It is here that the principle 

 of imitation gets very great significance ; intelligence and 

 volition come in also later on ; and in human affairs we 

 find social cooperation. Now it is evident that when 

 young creatures have these imitative, intelligent, or quasi- 

 social tendencies to any extent, they are able to pick up, 

 for themselves, by imitation, instruction, experience gen- 

 erally, the functions which their parents and other crea- 

 tures perform in their presence. This, then, is a form of 

 ontogenetic accommodation ; it aids to keep these crea- 

 tures alive, and so to produce definite change in the way 

 explained above. It is, therefore, a special, and from 

 its wide range an extremely important, instance of the 

 operation of the general principle of organic selection. 



But it has further value : it keeps alive a series of 

 ftinctiojis which either are not yet, or 7iever do become, con- 

 genital at all. It is a means of extra-organic transmission 

 from generation to generation. It is analogous to physical 

 heredity because (i) it is a handing down of acquired 

 physical functions, while yet not by physical reproduction. 

 And (2) it directly influences physical heredity ifi the way 

 mentioned, i.e., it keeps certain variations alive, thus sets 

 the direction of ontogenetic accommodation, thereby in- 

 fluences the direction of the available congenital variations 

 of the next generation, and so determines phylogenetic 

 evolution. It is accordingly called Social Heredity above, 

 (Chap. IV. ; see also the volumes cited, particularly Social 

 and EtJiical Interpretations, Chap. II.). 



