LECTURES IN BIOLOGICAL SCIENCES 



been built up slowly and carefully by the thousands of genera- 

 tions of men who have preceded us. It is upon this heritage 

 that our present way of life depends. When men first began 

 to make tools, wear clothes, build shelters, and talk to each 

 other, they set in motion a new kind of evolution, which we call 

 socio-cultural evolution. Although built upon the foundations 

 of organic evolution, socio-cultural evolution follows new di- 

 rections and is governed by new principles. The familiar bi- 

 ological processes of mutation and genetic recombination are 

 replaced by invention, learning, and cultural spread, or diffu- 

 sion. Selection exists in socio-cultural evolution, but it makes 

 progress through differential survival of customs and inven- 

 tions rather than of men. It is thus radically different from 

 the natural selection which guides organic evolution. 



Finally, cultural evolution produces its effects in an entirely 

 new way. Through organic evolution, organisms became mod- 

 ified to suit their environment; socio-cultural evolution enables 

 man to modify the environment to suit his own needs. Animals 

 became adapted to cold climates by developing fur; man, by 

 building furnaces or by borrowing fur from animals. Birds 

 became able to fly by growing wings and profoundly modifying 

 their bodies; we fly infinitely higher and faster by elaborately 

 designed machines, which even transport a bit of low-level, 

 warm, temperate climate many miles above the earth. 



Most important, organic evolution is opportunistic in di- 

 rection. It is governed by the chance combination of environ- 

 mental factors and the types of organisms which happen to 

 exist at any one time. Socio-cultural evolution, on the other 

 hand, is determined at least in part by man's own foresight and 

 his ability to conceive of a better way of life for himself and his 

 descendants. 



We cannot overemphasize the fact that socio-cultural evolu- 

 tion is totally new in quality and has made man qualitatively 

 different from all animals. This is true in spite of the fact 

 that its beginning depended largely upon quantitative increases 

 in brain power, and that in particular mental characteristics, 

 like the ability to learn, memorize, and communicate with each 

 other, we differ only in degree from the more intelligent kinds 

 of apes. One of the most important facts about all of evolution 



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