INDIRECT EQUILIBRATION. 457 



its appendages. Here, therefore, the decreased action of 

 these parts which has accompanied the growth of civilized 

 habits (the use of tools and the disuse of coarse food), must 

 have been the sole cause at work. During civilization this 

 decrease of function has affected, more or less, all individuals. 

 Through direct equilibration, diminished external stress on 

 these parts, has resulted in diminution of the internal forces 

 by which this stress is met. From generation to generation, 

 this lessening of the parts consequent "on functional decline 

 has been inherited. And since the survival of individuals 

 must always have been determined by more important struc- 

 tural traits, this trait can have neither been facilitated nor 

 retarded by natural selection. 



167. Returning from these extensive classes of facts for 

 which Mr Darwin's hypothesis does not account, to the still 

 more extensive classes of facts for which it does account, and 

 which are unaccountable on any other hypothesis ; let us 

 consider in what way this hypothesis is expressible in terms 

 of the general doctrine of evolution. Already it has been 

 pointed out that the evolving of modified types by " natural 

 selection or the preservation of favoured races in the struggle 

 for life," must be a process of equilibration, since it results 

 in the production of organisms that are in equilibrium with 

 their environments ; and at the outset of this chapter, some- 

 thing was done towards showing how this continual survival 

 of the fittest, may be understood as the progressive estab- 

 lishment of a balance between inner and outer forces. Here, 

 however, we must consider the matter more closely. It re- 

 mains to be shown that this process conforms to the same 

 general mechanical principles as do all other equilibrations. 



On previous occasions we have contemplated the assem- 

 blage of individuals composing a species, as an aggregate in 

 a state of moving equilibrium. We have seen that its 

 powers of multiplication give it an expansive force which is 

 antagonized by other forces ; and that through the rhyth- 

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