OUTLINE OF THE ARGUMENT. i 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 isin 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. 
