24 Gulick — Divergent Evolution and the Darwinian Theory. 



the formation of new species lie intends to express, in opposi- 

 tion to Moritz Wagner, the opinion that a species may be trans- 

 formed into a new species without leaving its original locality, 

 but that he does not intend to say, that two or more divergent 

 species can arise in the same locality from the same stock. If 

 I interpret him rightly he considers the partial separation 

 described in the first of the paragraphs just quoted as suffi- 

 cient to allow of the formation of divergent species, when the 

 external conditions of the separate districts are sufficiently dif- 

 ferent and sufficiently permanent to secure long continued 

 divergent natural selection. That the second paragraph is to 

 be interpreted in accord with this meaning I judge from the 

 fact that natural selection is mentioned here as the cause of the 

 divergence which crossing tends to overpower, and in the 

 third paragraph, uniformity in the environment is represented 

 as ensuring uniform natural selection. The varieties that are 

 restrained from crossing with each other by diverse times and 

 habits of breeding, he must regard, sometimes "as slightly 

 divergent forms tending to disappear under the pressure of 

 uniform natural selection, and therefore never becoming sepa- 

 rate species though one of them may prevail and be established 

 as a new species ; and sometimes as forms that are becoming 

 more and more divergent, because they have found their way 

 into districts or stations where they are somewhat separated 

 from each other, and where the conditions are somewhat differ- 

 ent, and the natural selection, therefore, somewhat diversive. 



If this is not his meaning, if he intends to teach that forms 

 arising in one place and not locally separated from each other 

 can continue to diverge till they become separate species, how 

 can he say on the next page that forms isolated in a small area, 

 being exposed to uniform conditions. w T ould be modified by nat- 

 ural selection in a uniform manner. He evidently does not 

 intend to be understood as teaching that in these cases men- 

 tioned in the second paragraph there is a cause of divergent 

 evolution which produces separate varieties and species in spite 

 of the unifying influence of natural selection resulting from 

 uniform conditions. 



Dai-will's Theory of Natural Selection through the Advantage 

 of Divergence, of Character. 



There is however, one passage in the " Origin of Species " 

 which may be interpreted as assigning a cause for divergence 

 of character in representatives of the same species that are sur- 

 rounded by the same environment. These are the words ; 

 u Only those variations which are in some way profitable will 

 be preserved, or naturally selected. And here the importance 



