ISOLATION 537 



forms — spatial, structural, habitudinal, and psychical — and 

 it has various results. 



It tends to the segregation of species into sub-species, it 

 makes it easier for new variations to establish themselves, it 

 promotes prepotency, or what the breeders call " transmitting 

 power," it fixes characters. One of the most successful breeds 

 of cattle (Polled Angus) seems to have had its source in one 

 farm-steading, its early history is one of close inbreeding, its 

 prepotency is remarkable, its success from our point of view 

 has been great. It is difficult to get secure data as to the results 

 of isolation in nature, but Gulick's recent volume on the subject 

 abounds in concrete illustrations, and we seem warranted in 

 believing that conditions of isolation have been and are of 

 frequent occurrence. 



Reibmayr has collected from human history a wealth of 

 illustrations of • various forms of isolation, and there seems 

 much to be said for his thesis that the establishment of a successful 

 race or stock requires the alternation of periods of inbreeding 

 (endogamy) in which characters are fixed, and periods of out- 

 breeding (exogamy) in which, by the introduction of fresh blood, 

 new variations are promoted. Perhaps the Jews may serve to 

 illustrate the influence of isolation in promoting stability of 

 type and prepotency ; perhaps the Americans may serve to 

 illustrate the variability which a mixture of different stocks 

 tends to bring about. In historical inquiry into the difficult 

 problem of the origin of distinct races, it seems legitimate to think 

 of periods of " mutation " — of discontinuous sporting — whichled 

 to numerous offshoots from the main stock, of the migration of 

 these variants into new environments where in relative isola- 

 tion they became prepotent and stable. 



Conclusion. — Our general position is that when we pass from 

 organisms to human societies, the whole venue changes so much 

 that we have to be very careful in our application of biological 

 formulae, (i) Thus, in regard to processes of selection, we have 



