HUMAN AND ANIMAL EVOLUTION CONTRASTED 35 



but is acquired anew by each individual after years 

 of training. 



From all these considerations together it becomes 

 evident that among the lowest orders of nature the 

 factor of social inheritance plays no part, and that 

 even among the higher animals just below man its 

 part is a subordinate one. Only in long-lived species 

 can it be a factor of much moment, and long-lived 

 animals are very rare. While we would not deny 

 that this factor may have had an influence in the 

 lives of some species, its influence is slight. The 

 evolution of the animal kingdom below man has been 

 the result of the action of organic heredity transmit- 

 ting congenital characteristics from generation to 

 generation. 



Organic Heredity in Man. — It is not easy to state ac- 

 curately just what man owes to organic heredity, or, 

 at all events, it is difficult to draw any clear line sep- 

 arating his organic from his social inheritance. It 

 is, of course, manifest that he owes his physical 

 nature to this law, and this includes all the features 

 of his bodily structure except such modifications of 

 his body as are due to his peculiar mode of life. If 

 he becomes a blacksmith, a watchmaker, a pianist, 

 or a baseball player, the peculiar development 

 of his arms and hands he owes to an acquire- 

 ment by social inheritance and not to organic 

 inheritance. But except for some few such charac- 

 ters man owes his physical structure to organic 

 inheritance. This physical structure, of course, 

 includes that of his brain as well as his muscles, and 

 with his brain come his mental powers. It is clear 

 that the mental powers with which he is endowed 

 come to him by organic inheritance ; but it is equally 



