88 ISOLATION AS A FACTOR 



need for analysis of scientific conceptions. Under 

 these conditions, while not departing in essentials 

 from the position of Darwin, we are forced to 

 bring forward isolation as one of the separate 

 factors in the origin of species, and the factor on 

 -which the great and growing science of animal 

 and plant geography mainly depends. 



Nearly a decade after the publication of the 

 Origin of Species, Dr. Moritz Wagner set forth 

 the factor of isolation, and showed in convincing 

 fashion its fundamental relation to the problem 

 of the origin of species. 



Wagner showed plainly that in the study of 

 the evolution of any form we need to know where 

 it lived, what it did, how it was bounded, and 

 what was its relation to other forms, geographic- 

 ally as well as morphologically. " For me," he 

 says, " it is the chorology of organisms, the study 

 of all the important phenomena embraced in the 

 geography of animals and plants, which is the 

 surest guide to the knowledge of the real phases 

 in the process of the formation of species." 



The work of Wagner, a most necessary sup- 

 plement to that of Darwin, has never received the 

 attention it deserves. This is due in part to the 

 fact that most of our investigators do not travel. 

 They know little of animal or plant geography at 

 first hand. They have had nothing to do with 

 species as hving, varying, reproducing, adapting, 

 and spreading groups of organisms. Another 

 reason lies in Wagner's own attitude of opposi- 



