INTERNAL FACTORS. 421 



living bodies. Here it will be needful to contemplate the 

 several resultiag proceyses as going on at on^e, in both 

 individuals and species. 



§ 154. Our postulate being that organic evolution in ge- 

 neral commenced with homogeneous organic matter, just us 

 the evolution of iadividual organisms commences, we have 

 first to remember that the state of homogeneity is an un- 

 stable state {First Princi^ples, § 109). In any aggregate 

 " the relations of oxitside and inside, and of comparative 

 nearness to neighbouring soiirces of influence, imply the re- 

 ception of influences that are unlilie in quantity or quality, 

 or both ; and it follows that unliko changes wiU be produced 

 ill the parts thus dissimilarly acted upon." Further, "if 

 any given whole, instead of beiag absolutely uniform through- 

 out, consists of parts distinguishable from each other — if 

 each of these parts, while somewhat unlike other parts, is 

 uniform within itself; then, each of them being in unstable 

 equilibrium, it follows that whUe the changes set up withia 

 it must render it multiform, they must at the same time 

 render the whole more multiform than before ; " and hence, 

 " whether that state with which we commence be or be not 

 one of perfect homogeneity, the process must equally be 

 towards a relative heterogeneity." This loss of 



homogeneity which the special iastability of organic aggre- 

 gates fits them to display more promptly and variously than 

 any other aggregates, must be shown in more numeroas 

 ways in proportion as the incident forces are more niunerous. 

 Every difierentiation of structure being a resiilt of some 

 difference ia the relations of the parts to the agencies acting 

 on them, it follows that the more multipKed and more unlike 

 the agencies, the more varied must be the differentiations 

 wrought. Hence the gravitation from a state of homogeneity 

 to a state of heterogeneity, will be conspicuously shown in 

 proportion as the environment is complex. This 



transition from a uniform to a multifonn state, must con- 



