THE HUMAN SPECIES 529 



to generation by teaching and example, it is cumulative in content and 

 endures as long as does the group. It changes, for the most part slowly but 

 sometimes rapidly; and it lives in the minds of men. 



Man became man when he gained the rudiments of culture, sometime 

 about the beginning of the Pleistocene. Before that he had been only one 

 among the beasts, dependent for adaptation upon slow evolutionary 

 changes in his body; but with the acquisition of tools, fire, and speech it 

 was as though he had emerged onto a new and freer evolutionary plane. 

 Now he could create extracorporeal organs at need — stone weapons more 

 deadly than teeth or claws, a hairy coat to warm his naked body, or a 

 pry pole to give him giant strength. He could even somewhat change his 

 environment; with fire he could cook and eat previously unusable foods, 

 ward off fierce predators, and survive the glacial winters. Speech allowed 

 him to exchange ideas, act in concert with his fellows, and even more 

 important, pass on his accumulated lore to his children. Tools, fire and 

 speech marked the beginning of culture, and the Emergence of Man. 



Since that beginning no group of people has existed without some form 

 of culture, however primitive. So long as men lived in small, relatively 

 isolated groups or tribes, each such group had its own culture with its 

 own local peculiarities. Changes came chiefly from within, and were 

 naturally very slow. But cultural elements — ideas and techniques — are 

 readily transmitted from one group of people to another through both 

 peaceful and warlike contact. By late Pleistocene times people had become 

 more numerous and the contacts between them multiplied, so that dif- 

 fusion of cultural elements became more rapid. Since human populations 

 began their rapid growth some 7 millenniums ago, there has been a con- 

 tinued acceleration in the tempo of cultural change. The spread of a new 

 idea or invention in modern societies has become almost instantaneous 

 in contrast to the slow diffusion of earlier times. All the advanced cul- 

 tures have borrowed widely from each other, so that they have become 

 more and more alike at the same time that they were coming to include 

 more and more people. The many originally separate cultural streams are 

 flowing into a few great rivers. 



Culture has obviously been effective in adapting man to environment 

 and environment to man. It has also been potent in shaping man's 

 heredity. Cultural differences between groups often act as isolating 

 factors that hinder extensive interbreeding. They may affect birth and 

 death rates and hence the rate of growth of populations and the distribu- 

 tion of age classes within them. Cidture partially shelters the individual 

 from the direct influence of the environment; selection therefore comes to 

 operate more at the group level, so that peoples with more effective 

 cultures increase at the expense of peoples with less effective ones. Above 

 all else, it was cultural advances that ultimately led to the tremendous 



