G. R. Wieland — Polar Climate in Time. 429 



graphic record of tlie distribiitorj movements of faimse and 

 Sorse in the Paleozoic, although there are excellent reasons 

 for supposing that even then polar climates were the most 

 important of evolutionary factors. It would seem that from the 

 origin of life down to the Mesozoic the north and south polar 

 areas may have played a well nigh equal part in creating a 

 certain southward and northward stress with, to borrow a term 

 used in different sense by Ward (Pure Sociology), a sort of 

 breaking up or KaryoMnetic origin of species in the tropics. 

 But beginning with Mesozoic time and extending to the glacial 

 period, overwhelming evidence points to the polar origin and 

 continuous outward dispersion from the north polar area of 

 most of the great plant and vertebrate groups. Whatever 

 minor role was played by the south polar area yet remains to 

 be demonstrated. The successive unheralded synchronous 

 appearance of in large part unrelated and complex northern 

 faunse, leaves us no other alternative hypothesis than that of 

 boreal origin, in spite of the fact that vertebrate fossils of 

 Mesozoic and post-Mesozoic age from the Arctic (and Antarctic) 

 area are unknown. The similarity in successive unrelated and 

 diverse faunae synchronously appearing on both sides of the 

 fairly permanent Atlantic, as the record shows, cannot be 

 accounted for throughout long periods of time on the basis of 

 lateral interchange. JSTor can similar series of changes, and 

 similar genera and even species have so often arisen inde- 

 pendently at such widely separated points, as to have pro- 

 duced the parallelism so constantly evident in the fossil verte- 

 brates of Eurasia and America. And these same principles 

 apply to the record of the post-Paleozoic florae as next reviewed 

 and shown to be in all essentials the complement of the verte- 

 brate record, and far completer. Further, it was recalled that 

 the outward movement especially of Conifers and Dicotyls from 

 the Arctic area for long periods of time, has frequently been 

 recognized by scientists. Some of the traces of this movement 

 are still evident in the present strikingly homogeneous circum- 

 boreal flora, although its main development, as in the case of 

 the vertebrates, was obscured and partially checked by the 

 appearance of glacial conditions. 



Without attempting to follow out the several lines of evi- 

 dence of northern origin and of southern migration and dis- 

 placement any further, it does appear fully conclusive that all 

 the factors of climate and therefore the main alternative poten- 

 tialities producing organic evolution^ have been in the highest 

 degree variant in the polar areas. And this being true, the 

 grouping of the continents about the north pole so that they 

 have come to cover fully 300° of the Arctic circle would make 

 it reasonable to suppose, were there not abundant direct evi- 



