474 THE EVOLUTION OF LIFE. 



libriiim of inner actions, corresponding with outer actions, 

 which constitutes the life of an organism, must either be 

 overthrown by a change in the outer actions, or must undergo 

 perturbations that cannot end until there is a re-adjusted 

 balance of functions and correlative adaptation of structures. 

 "Wherever the external changes are such as to be continuously 

 or frequently operative on individuals, this direct equilibra- 

 tion must go on. 



But where the external changes are either such as are 

 fatal when experienced by the individuals, or such as act on 

 the individuals in ways that do not affect the equilibrium of 

 their functions ; then the re- adjustment results through the 

 effects produced on the species as a whole — there is indirect 

 equilibration. By natural selection or survival of the fittest 

 - — by the preservation in successive generations of those 

 whose moving equilibria happen to be least at variance with 

 the requirements, there is eventually produced a changed 

 equilibrium completely in harmony with the requirements. 



And thus it results that those universal laws of the re- dis- 

 tribution of matter and motion, which are conformed to by 

 evolution in general, are conformed to by organic evolution. 



§ 174. Even were this the whole of the evidence assign- 

 able for the belief that organisms of all orders have been 

 gradually evolved, this belief would have a warrant much 

 higher than that of very many beliefs that are regarded as 

 established. When we see that there are strong a priori pro- 

 babilities in its favour, and wholly adverse to the antagonist 

 hypothesis — when an examination of the facts which natural- 

 ists have accumulated, leads us to several groups of inductions 

 which unite in supporting it — and when the characteristics 

 which conspire to show that organic evolution has been going 

 on, prove to be deducible from those universal actions known 

 to work evolution of all other kinds ; we have a combination 

 of proofs which might suffice were there no more to be said. 



But the evidence is far from exhausted. At the outset of 



