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 is evident that 

 endeavor according to endowment may produce under one environ- 

 ment what natural selection produces when aided by local separation 



