DIRECT EQUILIBRATION. 435 



have been in each case modifications involved by the 

 establishment of a new balance with the new combination of 

 conditions. In every species throughout all geologic time, 

 there has been perpetually going on a rectification of the 

 equiKbrium, that has been perpetually disturbed by the 

 alteration of surrounding circumstances ; and every further 

 heterogeneity has been the addition of a structural change 

 entailed by a new equilibration, to the structural changes 

 entailed by previous equilibrations. There can be no other 

 ultimate interpretation of the matter, since change can have 

 no other goal. Any fresh force brought to bear on an 

 aggregate in a state of moving equilibrium, must do one of 

 two things : it must either overthrow the moving equi- 

 librium altogether, or it must alter without overthrowing it ; 

 and the alteration must end in the establishment of a new 

 moving equilibrium. Hence in organisms, death or restora- 

 tion of the physiological balance, are the only alternatives. 



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 individuala 



