246 INTRODUCTION TO EVOLUTION 



Cro-Magnon man probably reached Europe as an invader, coming, 

 according to the prevalent idea, from Asia. Carbon- 14 dating of objects 

 from the Aurignacian culture indicates that these people lived in Europe 

 some 27,000 years ago, well before the end of the last glaciation. 



Eventually the Aurignacians were replaced by people having a different 

 Old Stone Age culture, the Magdalenian. The Magdalenians lived in Eu- 

 rope some 15,000 years ago, and in turn were replaced by a succession of 

 people of other cultures: the Mesolithic peoples who developed agricul- 

 ture and domesticated animals, and the Neolithic (New Stone Age) peo- 

 ples who advanced still further in perfecting tools and in communal living. 

 It is generally believed that these later peoples constituted additional 

 waves of invaders, probably from Asia, but we have little real knowledge 

 of their origin, or of the evolutionary history of the modern races which 

 in time replaced these older cultural groups. 



All of these people were Homo sapiens of the modern type, judging from 

 their skeletons. Variations in structure occurred, but these variations did 

 not surpass the range of variation exhibited by modern man. 



By 10,000 years ago, and probably before that date (perhaps as long ago 

 as 37,000 years in the case of America: Krieger, 1957), Homo sapiens had 

 reached such out-of-the-way regions of the world as Australia and North 

 America. 



Human Evolution 



How shall we picture the evolution of man? It is frequently diagramed 

 as a tree with limbs, branches, and twigs. But such a picture makes no pro- 

 vision for the diversity of men living at any one time, with the complexi- 

 ties introduced by migrations and gene exchange between populations that 

 intermarry. A twig arises from one branch, not several branches, whereas 

 a descendant may have drawn his genes from several ancestral groups. The 

 tree as a means of picturing human evolution has outlived its usefulness. 

 Fig. 11.16 is an attempt to avoid these shortcomings by picturing human 

 evolution in terms of a pattern of interlacing, interweaving lines. The in- 

 tent is to convey the impression of many ancestral lines crossing and re- 

 crossing as new forms arose, differentiated, combined characteristics by 

 mating with other populations, and passed on their genes to descendants in 

 varying proportion. The thought is that no one hominid living at a certain 

 time was the ancestor of all hominids living at a later time, but that, rather, 

 each later hominid received his collection of genes from varying predeces- 

 sors, some of whom contributed more than others. As we have stressed 



