430 G. R. Wieland— Polar Climate in Ti 



ime. 



dence pointin^^ to the fact, that the northern circnmpolar area 

 has probably been, ever shice the older Paleozoic at least, the 

 main evolutionary center from which animal and plant life have 

 radiated. But the theoretical view is as we see supported by 

 overwhelming proof that such has been the fact, and that it is 

 from the Arctic area that the greatest waves of change have 

 swept out to lessen and disintegrate, though I do not at all 

 mean to infer cease, in the more static conditions of the tro]Dics. 



The true nature of the southward organic stress was next 

 illustrated, and some of the peculiar climatic conditions making 

 the origin of new stocks more likely at the north were also 

 pointed out. In particular I have also shown the possible 

 connection between periods of high orbital eccentricity and the 

 origination of the organic "waves or impulses" that students 

 of the fossil record often speak of, or for which there is more 

 or less conclusive evidence, especially among Tertiary verte- 

 brates. 



These cognate facts, as thus brought together, it seems to me 

 sustain incontrovertibly our main thesis that polar cHmate has 

 been the major factor in the evolution of plants and animals. 



Peabody Museum, Yale University, 

 New Haven, Conn. 



