116 THE THEORIES OF EVOLUTION 



uals, each formed out of the modified substance of its 

 predecessors, will not prevent the like effect from be- 

 ing produced." 2 



Variation is accounted for through the principle of 

 the instability of the homogeneous, a very important 

 principle in Spencer's philosophy. Although two 

 germ cells or two individuals of the same species were 

 originally identical, they must at a certain time be- 

 come different from each other, owing to the fact that 

 they occupy different locations in space or are influ- 

 enced by dissimilar forces; different causes acting 

 upon similar objects must necessarily produce differ- 

 ent effects or else the principle of the persistence of 

 force must be rejected. 



Spencer's theory was formulated in 1864 and all 

 modern theories, not excepting Darwin's pangenesis, 

 are derived from it. Its weak point is that it ad- 

 vances principles of a general character like the per- 

 sistence of force or the instability of the homogeneous, 

 instead of offering precise physiological explanations. 

 When Spencer states, for instance, that no influence 

 exerted on the organism goes for naught but has its 

 after-effect on the offspring, one could answer that 

 the original force bearing on the parent may very well 

 expend itself in some other way and in another di- 

 rection, and that, even if it should bring about a mod- 

 ification of the offspring, there is no reason why the 



2 Ibid., p. 522. 



