INDIRECT EQUILIBRATION. 543 



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 which are in equilibrium with 

 their environments. At the outset of this chapter, something 

 was done towards showing how this continual survival of the 

 fittest may be understood as the progressive establishment 

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

 we must consider the matter more closely. 



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 energy which is 

 antagonized by other energies; and that through the rh3^th- 

 mical variations in these two sets of energies there is main- 

 tained an oscillating limit to its habitat, and an oscillating 

 limit to its numbers. On another occasion (§96) it was 

 shown that the aggregate of individuals constituting a 

 species, has a kind of general life which, " like the life of an 

 individual, is maintained by the unequal and ever-varying 

 actions of incident forces on its different parts." We saw 

 that " just as, in each organism, incident forces constantly 

 Toduce divergences from the mean state in various direc- 

 ons, which are constantly balanced by opposite divergences 

 indirectly produced by other incident forces; and just as the 

 combination of rhythmical functions thus maintained, con- 

 stitutes the life of the organism; so, in a species there is, 

 through gamogenesis, a perpetual neutralization of those con- 

 trary deviations from the mean state, which are caused in its 

 different parts by different sets of incident forces; and it is 

 similarly by the rhythmical production and compensation of 



