INDIRECT EQUILIBRATION. 463 



not come within the class of direct equilibrations, must come 

 within the class of indirect equilibrations. 



Examination of the facts confirms this conclusion. The 

 external factors to which a species is exposed, are of two 

 kinds. They are such as act continuously or frequently on the 

 individuals ; or they are such as do not act continuously or 

 frequently on the individuals. To a factor which continuously 

 or frequently acts on the individuals, the functions of the in- 

 dividuals re-adjust themselves there is direct equilibration. 

 While a factor which does not act continuously or fre- 

 quently on the individuals, acts continuously on the species as 

 a whole either destroying such of the members as are least 

 capable of resisting it, or fostering such of the members as 

 are most capable of taking advantage of it. And by the 

 abstraction, generation after generation, of those least in 

 equilibrium with the new factor ; or by the extra multipli- 

 cation, generation after generation, of those most in equi- 

 librium with the new factor ; the species as a whole is event- 

 ually brought into complete equilibrium with the new factor 

 there is indirect equilibration. 



