468 THE EVOLUTION OF LIFE. 



processes of change entailed by them, we see that these, too, 

 have varied in their proportions that which was originally 

 the most important and almost the sole process, becoming 

 gradually less important, if not at last the least important. 

 Always there must have been, and always there must con-' 

 tinue to be, a survival of the fittest : natural selection must 

 have been in operation at the outset, and can never cease to 

 operate. While yet organisms had comparatively feeble 

 powers of co-ordinating their actions, and adjusting them to 

 environing actions, natural selection worked almost alone in 

 moulding and re-moulding organisms into fitness for their 

 changing environments ; and natural selection has re- 

 mained almost the sole agency by which plants and in- 

 ferior orders of animals have been modified and developed. 

 The equilibration of organisms that are comparatively passive, 

 is necessarily effected indirectly, by the action of incident 

 forces on the species as a whole. But along with the gradual 

 evolution of organisms having some activity, there grows up 

 a kind of equilibration that is relatively direct. In propor- 

 tion as the activity increases, direct equilibration plays a 

 more important part. Until, when the nervo-muscular 

 apparatus becomes greatly developed, and the power of vary- 

 ing the actions to fit the varying requirements becomes con- 

 siderable, the share taken by direct equilibration rises into 

 co-ordinate importance. We have seen reason to think that 

 as fast as essential faculties multiply, and as fast as the num- 

 ber of organs that co-operate in any given function increases, 

 indirect equilibration through natural selection, becomes less 

 and less capable of producing specific adaptations ; and re- 

 mains fully capable only of maintaining the general fitness 

 of constitution to conditions. Simultaneously, the production 

 of adaptations by direct equilibration, takes the first place 

 indirect equilibration serving to facilitate it. Until at length, 

 among the civilized human races, the equilibration becomes 

 mainly direct : the action of natural selection being restricted 

 to the destruction of those who are constitutionally too feeble 



