INTERACTION OP THE FOUR PRINCIPLES OF SEGREGATION. 55 



here proposed it is made to cover superior influence over the acquired 

 characters of associates, whether the community consists of rational 

 beings or not. A similar objection has often been urged against the 

 use of "selection" in the Darwinian sense; but, on the whole, no 

 better word has been found to designate the gaining of a full share in 

 the propagation of the next generation, and so a full share of influence 

 on the inherited characters of the community, whether it be by win- 

 ning the interest of the rational part of the environment or by secur- 

 ing adaptation to other conditions in the environment. Each new 

 term is an innovation, and like all innovations must prove its useful- 

 ness before it can prevail or be elected. 



III. Interaction of the Four Principles of Segregation. 



1. Increased Effects Produced by the Repeated Action of One Principle or the 

 Combined Action of More than One. 



Mr. Headley says that, in my terms "intensive segregation" and 

 "cumulative segregation" the words "intensive" and "cumulative" 

 are "misapplied." (See Problems of Evolution, p. 178.) I think his 

 criticism is chiefly due to his having failed to note the definitions I 

 have given to the terms and the way in which I have applied them. 

 Intensive segregation I have described as due to natural selection and 

 the other principles, producing transformation when cooperating with 

 isolation.* Cumulative segregation is due to a succession of isolations 

 coming at long intervals, in which each isolation opens the way for 

 the formation of some new habit shaping the method of dealing with 

 the environment, and, therefore, leads to the formation of a divergent 

 species. For example, if a variable species of snails, having but little 

 opportunity for transportation beyond the limits of the valley it in- 

 habits, and no power for migration beyond the same, finds its habitat in 

 the groves at one end of the chief mountain range of the island of Oahu, 

 it may become well adapted to the conditions before a branch colony 

 is planted in the next valley. Though the vegetation is the same in 

 the two valleys, the new colony may be started by a single individual, 

 whose habits lead it to prefer, for food and shade, some species of 

 plant that is but little used by the mother colony, and thus divergent 

 forms of endonomic selection shape the two colonies into two species. 

 After many years the transportation of an individual from the second 

 colony may result in the planting of a third colony with still further 

 divergent habits ; and so on till the valleys at the opposite end of the 

 mountain range have become the habitat of .species very closely re- 



* See Appendix I, Section VII, 3; also Appendix II, Section I, 8. 



