CHAPTER THIRTY-SIX 



The ON the first day of January, 1909, a series of "Cen- 

 D ctennid tenrua l Addresses in Honor of Charles Darwin" was 

 delivered at Baltimore before the American Asso- 

 ciation for the Advancement of Science. These were 

 later published by Henry Holt & Co. in a volume 

 entitled "Fifty Years of Darwinism," such being 

 the theme of the initial paper, that by Edward B. 

 Poulton of Oxford. My contribution concerned 

 "Isolation as a Factor in Organic Evolution," a 

 topic which to a degree I had made my own. The 

 "biological friction" which impedes the distribution 

 of animals and plants and thus leads to separation of 

 forms, I insisted upon as the main cause of the minor 

 distinctions which mark the different species. The for- 

 mation of dialects and tongues among humankind is 

 a process exactly parallel in its causes and results. 



Moritz The work of Moritz Wagner on Geographical Separation, 



Wagner a mO st necessary supplement to that of Darwin, has never 

 received the attention it deserves. This is partly due to the 



fact that most of our investigators do not travel; they know 

 little of animal or plant geography at first hand; they have 

 nothing to do with species as living, varying, reproducing, 

 adapting, and spreading groups of organisms. Another reason 

 lies in Wagner's own opposition to Darwinism. He substituted 

 separation, " raumliche Sonderung" for natural selection itself, 

 and denied the potency of the latter factor. The two became 

 . . . competing, not cooperating, elements, an attitude 

 which threw on isolation the impossible task of accounting for 

 all the phenomena of adaptation. . . . 



Certain writers urge that neither selection nor isolation is 

 a factor in evolution, but rather elements in ... species- 



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