THEOUGH CUMULATIVE SEGUE GATION. 



215 



dissimilar. Segregate Greneratioii is therefore the separation of 

 dis similars, with the aggregation and integration of similars. As 

 we have already seen, Segregate Breeding may be produced by 

 Separate Breeding accompanied by Diversity of Natural Selection 

 in the different sections. It is also 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 Segregate Breeding. Such cases are Diversity of Selec- 

 tion of other forms than Natural Selection, Diversity in the 

 inherited effects of Use and Disuse (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 wi'ong). Segregate Breeding may, moreover, 

 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 Segre- 

 gation, 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 depending 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 prolonged Separate Breeding will be trans- 

 formed into Segregate Breeding. In other words, indiscriminate 

 separation, in which there is no ajiparent difference in the dif- 

 ferent groups, is in time found to bo a separation in which there 

 is a decided difference in the different groups. Whenever a 

 sufficient number of the same species to ensure propagation are 

 brought together in an isolated position. Separate Greneration is 

 the result ; and, if this Separate Greneration is long-continued, 

 we have reason to believe, it always passes into Segregate Grenera- 

 tion with divergent evolution. The fundamental cause for this 

 seems to lie in the f^ict 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 



