cH. XVIII The Evolution of Evolution Theories 283 



a process ; but here in most cases ends the resemblance 

 between their thought and ours. 



Thus when Anaxim.inder spoke of a fish-Hke stage in the 

 past history of man, this was no prophecy of the modem 

 idea that a fish-like form was one of the far-off ancestors of 

 backboned animals, it was only a fancy 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 modem 

 physical science has been, or is being, slowly attained by 

 precise and patient analysis, whereas the ancient conception 

 was reached by metaphysical speculation. If we are 

 returning to the Greeks, it is on a higher turn of the spiral, 

 so far at least as the ether is concerned. 



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 inclined, 

 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 evolu- 

 tion. 



But the student cannot afford to overlook the lesson 

 which Democritus first clearly taught, that we do not 

 explain any result until we find out the natural conditions 

 which bring it about, that we only understand an effect 

 when we are able to analyse its causes. We require a so- 

 called " mechanical," or more strictly, a dynamical explana- 

 tion of results. It is easy to show that it is advantageous 

 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. Jt is 



