CHAPTER THIRTY-SIX 



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

 Darwm tennial Addresses in Honor of Charles Darwin" was 



Centennial 



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 mos t 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, "rdumliche 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- 



C 284 3 



