494 THE HISTORY OF BIOLOGY 



Latv of differentiation 

 Of Spencer's shorter articles there is one dated 1851, "The Development 

 Hypothesis," in which he clearly and definitely dissociates himself from a 

 belief in the immutability of species; a hypothesis of creation is unscientific 

 because it is incomprehensible, and the probability is that the various forms 

 of life on the earth have been modified in the course of the ages by the in- 

 fluence of different external conditions of life. In a couple of other similarly 

 pro-Darwin essays, "Progress, its Law and Cause" and "Genesis of Sci- 

 ence," he gives a more general presentation of his evolutional theory, which 

 was afterwards further developed, in view of the selection theory, into his 

 great philosophical work. According to him, the function of philosophy is 

 to combine under one common standpoint the results achieved by all other 

 sciences: physics, chemistry, and biology, as also psychology and sociology. 

 This unity common to all sciences exists in evolution. All existence is evolu- 

 tion; the heavenly bodies are undergoing change, the earth was once incan- 

 descent and has since then gone through a series of evolutional forms, and 

 all things existing on it, both animate and inanimate, are doing the same; 

 the separate plant and animal individual is being evolved, just as species 

 and genera and humanity are being evolved, individual for individual and 

 generation after generation. The question of what "evolution" is, Spencer 

 has in such circumstances to try to get answered as exhaustively as possible. 

 In the above-mentioned treatise on the law of progress he endeavours to 

 formulate the answer from a biological standpoint; starting from the evolu- 

 tion theories of C. F. Wolff, Goethe, and von Baer, he finds in agreement 

 with them that the development of the individual proceeds from the homo- 

 geneous to the heterogeneous; out of the egg, which is uniform throughout, 

 both in structure and composition, is evolved an individual possessing vari- 

 ous parts and organs, which are the more differentiated the further the de- 

 velopment proceeds. This law Spencer believes holds good for everything; 

 the earth was once uniformly incandescent, but after having cooled off, it 

 acquired an increasingly different and varying surface; all living creatures 

 were originally primitive and homogeneous, but out of these primal forms 

 there has since been developed an ever greater multiplicity of life -forms; the 

 life of the human society offers the same picture, and differences in language 

 and other manifestations of intellectual life have similarly developed. But 

 whence is this differentiation produced? Spencer answers this question with 

 the contention that every cause invariably has more than one effect; if a 

 candle is lighted, it is one simple chemical process, but it produces a number 

 of different effects — heat, light, chemical products. Thus there are created 

 on the earth an ever-increasing number of phenomena. The whole of this 

 discussion on causality is, of course, a purely metaphysical problem; against 

 the theory of evolution on which it is based it may be remarked from a 



