INTERNAL FACTORS. 421 



living bodies. Here it will be needful to contemplate the 

 several resulting procei^^ses as going on at once, in both 

 individuals and species. 



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

 neral commenced with homogeneous organic matter, just as 

 the evolution of individual organisms commences, we have 

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

 stable state {First Principles^ § 109). In any aggregate 

 "the relations of outside and inside, and of comparative 

 nearness to neighbouring sources of influence, imply the re- 

 ception of influences that are unlike in quantity or quality, 

 or both ; and it follows that unlike changes will be produced 

 in the parts thus dissimilarly acted upon.'^ Further, "if 

 any given whole, instead of being 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 while the changes set up within 

 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 instability of organic aggre- 

 gates fits them to display more promptly and variously than 

 any other aggregates, must be shown in more numerous 

 ways in proportion as the incident forces are more numerous. 

 Every differentiation of structure being a result of some 

 difference in the relations of the parts to the agencies acting 

 on them, it follows that the more multiplied 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 multiform state, must con- 



