120 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). 
dant form of food, which the species has heretofore only occasionally 
tasted. In the pressure for food that arises in a crowded community 
these take up their permanent abode where the new form of food is 
most accessible, and thus separate themselves from the original form of 
the species. These similarly endowed individuals will, therefore, breed 
together, and the offspring will, according to the law of divergence 
through segregation, be still better adapted to the new form of food. 
When other forms of isolation arise, they may be entirely independent 
of change in the environment, the only change being in the forms or 
functions of the organism. 
This special form of segregation is as dependent on psychological 
causes which guide the organism in finding and in adhering to the 
situation for which it is best fitted as it is on the initial divergence of 
the more strictly physiological adaptations by which it is able to 
appropriate and assimilate the peculiar form of resource. In the case 
of freely moving animals the psychological guidance is an essential 
factor in the success of the individual, while in the case of plants and 
low types of animal life the suitable situation is reached by a wide 
distribution of a vast number of seeds, spores, or germs, and the same 
situation is maintained by a loss of migrational power as soon as the 
germs begin to develop. In these lower organisms it is evident that 
the success of the individual must depend on its physiological rather 
than on its psychological adaptations; and if variation results in a 
slight difference in the kinds that succeed in germinating and in prop- 
agating in contrasted situations, we have diversity in the forms of 
natural selection affecting the seed, and the separation is what I here- 
after describe as local isolation passing into local segregation. We 
therefore see that what I here call industrial isolation depends on 
psychological powers acting in aid of divergent physiological adapta- 
tions to the environment, or in aid of adaptations that are put to 
different uses. 
Observation shows that there are a multitude of cases in which 
endeavor according to endowment brings together those similarly 
endowed, and causes them to breed together; and when the species is 
thus divided into two or more groups somewhat differently endowed, 
there will certainly be an increased divergence in the offspring of the 
parents thus segregated; and so on in each successive generation, as 
long as the individuals find their places according to their endowments, 
and thus propagate with those similarly endowed, there will be accu- 
mulated divergence in the next generation. Indeed, it isevident that 
endeavor according to endowment may produce under one environ- 
ment what natural selection produces when aided by local separation 
