PREHISTORIC MAN 489 



as warm as those of today ; the ice melted back, and the displaced floras 

 and faunas reoccupied the northern lands. 



The glacial and interglacial ages are given different names in Europe 

 and in North America. For our purposes it will suffice if we keep their 

 sequence in mind. We may call the glacial ages the first, second, third, and 

 fourth glacials, 1 and the interglacials the first, the great, and the last inter- 

 glacial ages. 2 The great interglacial was several times as long as either 

 the first or the last. Each glacial age had minor climatic fluctuations, with 

 glacial maxima and milder interstadials. 



Pleistocene Changes in Life. A great many species living today have 

 come down with little change from early Pleistocene times, and few major 



Fig. 30.1. The mammoth and woolly rhinoceros spread far south into Europe during the 

 glacial ages of the Pleistocene. Both were hunted by men of the Old Stone Age. (Drawing 

 by Charles R. Knight, courtesy Chicago Natural History M useum.) 



evolutionary developments occurred during the epoch, which was after 

 all a very brief period of time from the standpoint of earth history. 

 However, in many groups there was active speciation, and a great amount 

 of extinction occurred owing to the rapid and extreme climatic fluctua- 

 tions. Floras and faunas were displaced. The ranges of species contracted 

 and expanded, changed shape and position, fragmented and reunited, 

 and fragmented once more. Under such conditions species populations 

 tend to become more variable and opportunity is given for the formation 

 of new species and subspecies at a rapid rate. Man was himself involved 

 in this evolutionary flux. Isolation and differentiation among human 

 populations through much of the Pleistocene, followed in postglacial 

 time by enormous increases in man's numbers, with migration and 



1 Called respectively Gunz, Mindel, Riss, and Wiirm in Europe, and Nebraskan, 

 Kansan, Illinoian, and Wisconsin in North America. 



2 Called Giinz-Mindel, Mindel-Riss, and Riss-Wurm in Europe, and Aftonian, 

 Yarmouth, and Sangamon in North America. 



