522 



THE EVOLUTION OF LIFE. 



terpretation of the matter, since change can have no other 

 goal. 



This equilibration between the functions of an organism 

 and the actions in its environment, may be either direct or 

 indirect. The new incident force may either immediately 

 call forth some counteracting force, and its concomitant 

 structural change; or it may be eventually balanced by some 

 otherwise-produced change of function and structure. These 

 two processes of equilibration are quite distinct, and must be 

 separately dealt with. We will devote this chapter to the 

 first of them. 



§ 160. Direct equilibration is that process currently 

 known as adaptation. We have already seen (Part II., Chap, 

 v.), that individual organisms become modified when placed in 

 new conditions of life — so modified as to re-adjust the powers 

 to the requirements; and though there is great difficulty in 

 disentangling the evidence, we found reason for thinking 

 (§82) that structural changes thus caused by functional 

 changes are inherited. In the last chapter, it was argued 

 that if, instead of the succession of individuals constituting a 

 species, there were a continuously-existing individual, any 

 functional and structural divergence produced by a new inci- 

 dent action, would increase until the new incident action was 

 counterpoised; and that the replacing of a continuously- 

 existing individual by a succession of individuals, each formed 

 out of the modified substance of its predecessor, will not pre- 

 vent the like eifect from being produced. Here we further 

 find that this limit towards which any such organic change 

 advances, in the species as in the individual, is a new moving 

 equilibrium adjusted to the new arrangement of external 

 forces. 



But now what are the conditions under which alone, direct 

 equilibration can occur? Are all the modifications that serve 

 to re-fit organisms to their environments, directly adaptive 

 modifications? And if otherwise, which are the directly 



