HUMAN AND ANIMAL EVOLUTION CONTRASTED 33 



mals individuals live more or less solitary lives with 

 practically uo contact with other members of their 

 own species, and under such conditions beyond ques- 

 tion social inheritance can play no part. As we go 

 lower in the scale of life the influence of social hered- 

 ity vanishes entirely, and organic inheritance is left 

 as the only method by which one generation can influ- 

 ence the next. 



In another respect also we find the action of social 

 inheritance must be limited among lower animals. 

 Since characters thus inherited must be indepen- 

 dently acquired by each generation, and, indeed, by 

 each individual, it is manifest that social inheritance 

 can be of great influence only where a generation 

 lasts long enough to make possible considerable 

 acquirements of information. It takes years of 

 training of even intelligent man to make a social indi- 

 vidual of him; and manifestly if his life extended 

 only over a single year, no matter what mental pow- 

 ers he might have, his acquirements by the time of 

 his death would be slight, and the great fabric of 

 civilization would be impossible. Now, we must re- 

 member that the great host of animals live short 

 lives. Some of thorn have a generation of only three 

 to four days; some pass from one generation to the 

 next in three to four weeks, while others may live an 

 equal number of months. Some, indeed, live for a 

 year or a few years, and some without doubt live 

 even longer than man himself. But for the most 

 part the lower animals live such short lives that an 

 acquirement of a social inheritance by the process of 

 learning would be impossible because of lack of time, 

 even were the mental powers sufficient. An insect 

 that lives its whole life in three weeks clearly could 



