THE VOYAGE OF EVOLUTION 123 



In view of these facts and many others it is hard to avoid the 

 conclusion that the last Glacial Epoch and the succeeding period 

 of less pronounced climatic changes were peculiarly stimulating 

 to mental development. The coldest places were not favorable, 

 but on their borders where the climate was severe enough to be 

 highly bracing, but not benumbing, there occurred an extraordi- 

 nary development of brain power. As evolution counts the years 

 we are still too near to see this development in its true light. Yet 

 it can scarcely be mere chance that man rose above the animals 

 during a great glacial period such as that which directed the 

 wonderful evolutionary changes of the far earlier Permian Period. 

 Still less is it likely to be mere chance that the evolution of the 

 powers of the human brain was relatively slow until the last of 

 the four great epochs into which the Glacial Period is divided. 

 That last epoch was colder and more severe than any of the others. 

 Close to the ice-sheets it was apparently so severe that it caused 

 retrogression, but farther away it somehow provided conditions 

 such that man changed a thousand times faster than the animals 

 had changed during the vast periods of relatively uniform climate 

 in earlier geological times. Moreover, it was this last cold epoch 

 which caused most of the change in the mammals of Europe and 

 North America. So even among the higher animals we may well 

 say that the last Glacial Epoch of 50,000 years or less produced 

 most of the change which in Figure 22 has been ascribed to a 

 million years. In that case the change in animal life was at 

 least fifty times as rapid as the average during the preceding 

 geological epochs. Clearly a severe climate is wonderfully potent 

 in hastening the course of evolution. 



