146 SOCIAL EVOLUTION 



desert. The complex bows of the Eskimo appear to be 

 due to the lack of any long elastic material for bow- 

 staves and various devices have been invented for secur- 

 ing elasticity of the bow where elastic wood is difficult 

 to obtain. Tribes without permanent habitation resort 

 to skin receptacles and baskets as substitutes for pot- 

 tery. 32 



During the thousands of years before history was 

 written primitive men were subjected to the varying 

 climatic influences which we have described. These cli- 

 matic influences were conditions to which primitive men 

 had to adjust and adapt themselves as best they might. 

 A great climatic change which caused the desiccation of 

 a large and highly populated area killed off its human 

 inhabitants by thousands. Those whose constitutions 

 were plastic enough to withstand the change and make 

 the necessary adaptations survived; others perished or 

 migrated to more favorable territory. In the course of 

 migrations, these early peoples not possessing our knowl- 

 edge of means of transportation and communication, 

 were subordinated to the natural barriers or means of 

 travel such as mountain masses and valleys. The sur- 

 face of the earth has determined the movements of popu- 

 lations and the migrations of races from those areas 

 which climatic changes have made uninhabitable. 



Valleys offer channels for the easy movement of hu- 

 manity. They are grooves which have time and again 

 determined the destination of aimless, unplanned mi- 

 grations. The passing of peoples follows these nature- 

 made highways. The maritime plain of Palestine has 

 been an established route of commerce and war from the 

 time of Sennacherib to Napoleon. Up the Danube valley 



32 Boas, op. cit., p. 1GO. 



