290 DIVERGENT EVOLUTION THROUGH SEGREGATION, 
separate generation, and therefore no separation in the sense in which 
I use the word. 
Segregate generation also consists of Separation, aggregation, and inte- 
eration; but it differs from separate generation in that in the latter the 
separation is indiscriminate, while in the former there is a more or less 
pronounced bringing together of those that are similarly endowed, with 
separation of those that are dissimilar. Segregate generation is there- 
fore the separation of dissimilars, with the aggregation and integration 
of similars. As we have already seen, segregate breeding may be pro- 
duced by separate breeding, accompanied by diversity of natural selec- 
tion in the different sections. It is almost evident that any other cause 
that develops in one or more of the separate sections of the species 
characters that are not found in the other sections will produce segre- 
gate breeding. Such cases are diversity of selection of other forms 
than natural selection, diversity in the inherited effects of use and dis- 
use (unless physiologists have been mistaken in supposing that there 
are any such effects), and diversity in the inherited characters derived 
from the direct effects of the environment (unless, again, Weismann is 
right and the general belief wrong). Segregate breeding may more- 
over be produced directly by the very way in which the separation of 
the different sections is secured. One of the best examples of this kind 
of segregation is seen in what I call industrial segregation, where the 
members of a species are distributed according to their endowments, 
those of similar endowments being brought together. In such cases, 
segregation is introduced as soon as the separation, without depend- 
ing on the subsequent action of the environment, or on diverse forms 
of use, or of selection; though there can be no doubt that, in the great 
majority of cases, diversity of use and diversity of selection of some 
kind will in time come in to intensify the result. 
There is another invariable sequence which it is necessary we should 
keep in mind if we would understand the relation in which these two 
principles stand to each other. I refer to the certainty that all pro- 
longed separate breeding will be transformed into segregate breeding. 
In other words, indiscriminate separation, in which there is no appar- 
ent difference in the different groups, is in time found to be a separa- 
tion in which there is a decided difference in the different groups. 
Whenever a sufficient number of the same species to insure propaga- 
tion are brought together in an isolated position, separate generation is 
the result; and, if this separate generation is long-continued, we have 
reason to believe it always passes into segregate generation with diver- 
gent evolution. The fundamental cause for this seems to lie in the fact 
that no two portions of a species possess exactly the same average 
character, and that the initial differences are for ever reacting on the 
environment and on each other in such a way as to insure increasing 
divergence in each successive generation as long as the individuals of 
the two groups are kept from intergenerating. In my paper on Diver- 
