4 THEORY OF EVOLUTION 



A third kind of evolution is one for which 

 man himself is responsible, in the sense that he 

 has brought it about, often with a definite end 

 in view. 



His mind has worked slowly from stage to 

 stage. We can often trace the history of the 

 stages through which his psychic processes 

 have passed. The evolution of the steam-boat, 

 the steam engine, paintings, clothing, instru- 

 ments of agriculture, of manufacture, or of 

 warfare (fig. 2) illustrates the history of hu- 

 man progress. There is an obvious and 

 striking similarity between the evolution of 

 man's inventions and the evolution of the shells 

 of molluscs and of the bones of mammals, yet 

 in neither case does a knowledge of the order 

 in which these things arose explain them. If 

 we appeal to the psychologist he will probably 

 tell us that human inventions are either the re- 

 sult of happy accidents, that have led to an 

 unforeseen, but discovered use; or else the use 

 of the invention was foreseen. It is to the 

 latter process more especially that the idea of 

 purpose is applied. When we come to review 

 the four great lines of evolutionary thought we 



