452 Evolution and Modern Philosophy 



essay on Progress, he propounded the law of differentiation as a 

 general law of evolution, verified by examples from all regions of 

 experience, the evolution of species being only one of these examples. 

 On the effect which the appearance of The Origin of Species had on 

 his mind he writes in his Autobiography: "Up to that time... I held 

 that the sole cause of organic evolution is the inheritance of function- 

 ally-produced modifications. The Origin of Species made it clear to 

 me that I was wrong, and that the larger part of the facts cannot be 

 due to any such cause.... To have the theory of organic evolution 

 justified was of course to get further support for that theory of 

 evolution at large with which... all my conceptions were bound up 1 ." 

 Instead of the metaphorical expression "natural selection," Spencer 

 introduced the term " survival of the fittest," which found favour with 

 Darwin as well as with Wallace. 



In working out his ideas of evolution, Spencer found that 

 differentiation was not the only form of evolution. In its simplest 

 form evolution is mainly a concentration, previously scattered 

 elements being integrated and losing independent movement. 

 Differentiation is only forthcoming when minor wholes arise within 

 a greater whole. And the highest form of evolution is reached 

 when there is a harmony between concentration and differentiation, 

 a harmony which Spencer calls equilibration and which he defines 

 as a moving equilibrium. At the same time this definition enables 

 him to illustrate the expression "survival of the fittest." "Every 

 living organism exhibits such a moving equilibrium a balanced 

 set of functions constituting its life ; and the overthrow of this 

 balanced set of functions or moving equilibrium is what we call 

 death. Some individuals in a species are so constituted that their 

 moving equilibria are less easily overthrown than those of other 

 individuals ; and these are the fittest which survive, or, in Mr Darwin's 

 language, they are the select which nature preserves 2 ." Not only in 

 the domain of organic life, but in all domains, the summit of evolution 

 is, according to Spencer, characterised by such a harmony by a 

 moving equilibrium. 



Spencer's analysis of the concept of evolution, based on a great 

 variety of examples, has made this concept clearer and more definite 

 than before. It contains the three elements ; integration, differentia- 

 tion and equilibration. It is true that a concept which is to be valid 

 for all domains of experience must have an abstract character, and 

 between the several domains there is, strictly speaking, only a relation 

 of analogy. So there is only analogy between psychical and physical 

 evolution. But this is no serious objection, because general concepts 

 do not express more than analogies between the phenomena which 



1 Spencer, Autobiography, Vol. n. p. 50, London, 1904. a Ibid. p. 100. 



