ISOLATION 541 



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

 prepotency is remarkable, its success from man's 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 . 

 which led to numerous offshoots from the main stock, of the 

 migration of these variants into new environments where in 

 relative isolation they become prepotent and stable. 



Conclusion. Our general position is that when we pass from 

 organisms to human societies, the whole venue changes so much 

 that w T e have to be very careful in our application of biological 

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

 to recognise the intervention of rational selection as an ac- 

 celerant or as a brake on natural selection. (2) When a society 

 deliberately sets to work to select discriminately among the in- 

 dividualties which make up its own body politic, we have to do 

 with an infinitely subtler process than that observed when a 

 breeder selects in his stock, or when the physical environment 

 elimi r ates the ill-adapted members of a race. (3) There is in 



