GENERAL CONCLUSIONS 473 



tion in North America. Savage argues wisely that phyletic age, 

 relict occurrence, and vagility must be taken into account, but he 

 doesn't indicate just how. Other frequently expounded criteria are 

 just mentioned, along with Mathew's hypothesis that primitive 

 forms are peripheral. 



Savage sharply criticizes the location of the major center of 

 origin in the Old World tropics, on the basis of the evidence that the 

 present Holarctica is temperate to boreal. As both he and Mac- 

 Ginitie (2) point out, the northern lands were subtropical through 

 much of Cenozoic time. Obviously, much of evolutionary history is 

 still hidden in a fog of ignorance. The task of the historians of life 

 has barely begun. And until we know the past, we cannot fully 

 understand the present nor guess the future. 



Several of the authors hold to the view long championed by 

 Chaney and by Axelrod, and here expounded by MacGinitie (2), 

 that world climate became progressively more arid and cooler 

 through Tertiary time, while increased relief and other factors 

 caused greater local diversity. It seems that there was a general 

 northward shift in the climatic zones. All this caused a great trans- 

 location of the geo-floras, and, presumably, of the accompanying 

 animal communities. Some zoologists, for example Peabody and 

 J. M. Savage (8), have been bold enough to reconstruct origins and 

 dispersals of certain animals on the basis of the history of the geo- 

 floras with which they infer these animals were associated. Are they 

 treading on firm ground or on quicksand? 



It seems to be the general consensus that the vast uniformity of 

 life that characterized the early Cenozoic, in both space and time, 

 gradually changed to diversity throughout Tertiary time, in a grand 

 crescendo that reached ecstatic proportions in the Pleistocene. 

 Martin (15) and Blair (17) have compiled impressive evidence favor- 

 ing the view, which seems to me to be well justified, that the Ice 

 Ages were periods of intense cold, during which climatic belts were 

 displaced far southward (and far downward on the mountains), and 

 during which even the tropics were very considerably cooled. Dur- 

 ing the Wisconsin period the temperate biota of eastern North 

 America seems to have been forced into refugia in Florida and 

 Mexico (Blair, 17), while in the West (Miller, 9) there was extensive 

 extermination of the freshwater fauna in the north and a vast 

 development of lakes in the Great Basin and southward. 



