OUTLINE OF THE ARGUMENT. 235 



exposed ; for it is found that these principles when brought to bear 

 on separated sections never produce completely parallel effects. 



(2) The paramount effects of independent generation having been 

 shown in the broad fields of biological experiment presented by the 

 domestication of plants and animals, the question is next raised 

 whether species in a state of nature are subjected to influences divid- 

 ing the individuals of one species into sections that are prevented 

 from crossing; and, if they are, how far this independent generation 

 involves segregate generation. 



In my paper entitled "Divergent Evolution through Cumulative 

 Segregation," it was shown that there are many classes of activities 

 by which the individuals of a species are thus divided, and that, in 

 the majority of cases, the very process that separates them assorts 

 them into classes with reference to one or more points of character; 

 thus producing segregation that is similar in its character to the seg- 

 regation that is designedly produced by the pigeon-fancier between 

 his various breeds of pigeons. 



In the earlier half of the present paper I have shown that the 

 planting of a small colony, resulting from migration or other causes, 

 inevitably involves some segregation; and whenever the transform- 

 ing influences of the other factors of evolution begin to operate in the 

 different sections, this initial segregation is inevitably intensified and 

 the divergence increased ; for it is in the last degree improbable that 

 change produced by these principles of transformation in sections 

 that are prevented from crossing should be completely parallel in the 

 different sections, even when exposed to the same environment. 



(3) The last step is to show, as has been attempted in the latter 

 half of the present paper, that the relations to each other of varieties, 

 species, genera, and the higher groups are such as would necessarily 

 be presented if all such differences were the result of evolution that is 

 always dependent on some form of segregation, but not always on 

 diversity of natural selection, which is produced by exposure to 

 different environments. 



We have found that persistent differences, whether varietal, specific, 

 or generic, are not all adaptational, for some of them have no relation 

 to utility, and that adaptational differences are not all advantageous, 

 for some of them relate to adaptations that would meet with equal 

 success if the organisms should exchange habitats, but that in every 

 case divergence, whether utilitarian or non-utilitarian, whether advan- 

 tageous or disadvantageous, is not maintained without independent 

 generation. 



