INTERNAL FACTORS. 509 



it will be needful to contemplate the several resulting pro- 

 cesses as going on at once, in both individuals and species. 



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

 eral commenced with homogeneous organic matter, we have 

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

 stable state {First Principles, §149). 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 one another — 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 change from a state of homogeneity to 

 a state of heterogeneity, will be marked in proportion as the 

 environing actions to which the organism is exposed are 

 complex. This transition from a uniform to a mul- 



tiform state, must continue through successive individuals. 

 Given a series of organisms, each of which is developed from 



