412 THE STUDY OF ANIMAL LIFE CHAP. 



invented to get over a difficulty connected with the 

 infancy of the first human being. 



Or, when we read that several of these sages reduced 

 the world to one element, the ether, we do the progress 

 of knowledge injustice if we say that men are simply 

 returning to this after more than two thousand years. 

 For that conception of the ether which is characteristic 

 of modern physical science has been, or is being, slowly 

 attained by precise and patient analysis, whereas the 

 ancient conception was reached by metaphysical specu- 

 lation. 



When we read that Empedocles sought to explain the 

 world as the result of two principles love and hate- 

 working on the four elements, we may, if we are so in- 

 clined, call these principles " attractive and repulsive 

 forces " ; we may recognise in them the altruistic and 

 individualistic factors in organic evolution, and what not ; 

 but Empedocles was a poetic philosopher, no far-sighted 

 prophet of evolution. 



But the student cannot afford to overlook the lesson 

 which Democritus first clearly taught, that w r e do not 

 account for any result until we find out the natural con- 

 ditions which bring it about. The scientific question is 

 how any given structure came to be as it is, and this is 

 not answered by discovering its utility. It is advan- 

 tageous for a root to have a root-cap, but we wish to know 

 how the cap comes to be there. It is obvious that the 

 antlers of a stag are useful weapons, but we must inquire 

 as precisely as possible how they first appeared and still 

 grow. 



2. Aristotle. As in other departments of knowledge, 

 so in zoology the work of Aristotle is fundamental. It is 

 wonderful to think of his knowledge of the forms and 

 ways of life, or the insight with which he foresaw such 

 useful distinctions as that between analogous and homo- 

 logous organs, or his recognition of the fact of correlation, 

 of the advantages of division of labour within organisms, 

 of the gradual differentiation observed in development. 

 He planted seeds which grew after long sleep into com- 

 parative anatomy and classification. Yet with what 



