214 THE SOCIAL LIFE OF ANIMALS 



tribal policy. War in this sense enters fairly late 

 into the development of human societies." 



It is not impossible to break down and re-make in- 

 stinctive behavior, as the change in marriage cus- 

 toms since the days of the cave man shows us. Never- 

 theless, it is much easier to change learned behavior 

 patterns, one of which these experts believe war to 

 be. 



We must still take account of individual aggres- 

 siveness, and the fact that man appears to be rela- 

 tively easy to lead into mass combat. Even if war- 

 making is not instinctive, if it is a learned pattern 

 of social behavior, there is evidence that it has 

 existed for some fifty centuries, and it would prob- 

 ably require at least a few centuries of intelligent 

 and fairly concerted effort by those who do not be- 

 lieve in its utility to unlearn the habit. 



There is a second important set of biological proc- 

 esses which at first sight appear to work inevitably 

 toward the production of war. These center about 

 the question of overpopulation, that is to say, about 

 the relation human numbers bear to habitable land 

 areas. This is the next primary problem which we 

 must consider. 



Over the world there is a limited range of habit- 

 able land; and thus far we have no intimation of 

 any practical method of emigration to neighboring 



