34 THEORY OF ORGANIC EVOLUTION. 



hand the automatic evolution proceeds with unequal 

 rapidity, and on the other hand adaptation takes 

 place unequally. 



But in general different varieties arise socially 

 from a uniform kinship. This is because the related 

 individuals living together are unequally stimulated 

 on account of the great inequality of external influ- 

 ences which may exist at the smallest distances; and 

 also because with slight individual differences unlike 

 reactions often follow upon the same external influ- 

 ences. If identically similar individuals are equally 

 inclined to very different reactions toward the same 

 stimulus, sometimes the direction of the first varia- 

 tion decides the character of the adaptation and 

 therefore the nature of the variety, because the 

 variation, when once begun, progresses unswerv- 

 ingly even under somewhat different circumstances. * 

 Hence divergent variations are found growing 

 together in all places, which variations have begun 

 at different though neighboring points by transfor- 

 mation of the idioplasm and are soon intermingled 

 on account of the easy dissemination of seed. 



The social formation of varieties is not in general 

 interrupted by crossing, a process which governs 

 only the formation of races. It is confirmed accord- 

 ing to experience by the universally recurring fact 

 that several beginnings of the most closely related 



* It is interesting to compare this statement with Weismann's recent 

 theory of Germinal Selection. T^ans. 



