372 KEY. J. T. GULICK ON 



minate division of the species into sections that are prevented 

 from freely crossing through their being under the care of sepa- 

 rate tribes of men, and which is changed into decided Segregation 

 through the diversity of selection, or of some other transforming 

 principle, to which the different sections are sure to be 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 influ- 

 ences dividing the individuals of one species into sections that 

 are prevented from crossing ; and if they are, how far this Inde- 

 pendent Generation involves Segregate Generation. 



In my paper entitled " Divergent Evolution through Cumu- 

 lative 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 com- 

 pletely parallel in its character to the segregation tliat is designedly 

 produced by the pigeon-fancier between his various breeds of 

 pigeons. 



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

 indiscriminate division of the species, which often results from 

 migration or geological changes, and sometimes from other causes, 

 inevitably involves some Segregation ; and whenever the trans- 

 forming influences of the other factors of evolution begin to 

 operate in the different sections, this initial Segregation is in- 

 evitably 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 difterent sections, even when 

 exposed to the same environments. Having shown that the 

 forms of Segregation produced in nature are analogous to those 

 produced in artificial breeding, — 



(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 



