MENTAL EVOLUTION OF MAN 231 



ical structures of a human body, have changed and 

 differentiated to become the widely different interpre- 

 tations of the world and supernature that are held by 

 the civilized, barbarous, and savage races of to-day. 

 As we look back over the facts that have been cited, 

 and as we contemplate the large departments of knowl- 

 edge about human psychology, mental development, 

 and racial culture which these few details illustrate, we 

 come to realize how securely founded is the doctrine 

 that even the human mind with all its varied powers 

 has grown to be what it is. Indeed, it is solely due to 

 his mental prowess that man has attained a position 

 above that of any lower animal. And yet every hu- 

 man organ and its function can be traced to something 

 in the lower world ; it is a difference only in degree 

 and not in category that science discovers. The line 

 connecting civilized man with the savage leads in- 

 evitably through the ape to the lower mammalia pos- 

 sessing intelligence, and on down to the reflex organic 

 mechanisms which end with the Amoeba. It is a long 

 distance from the mechanical activities of the proto- 

 zoon to the processes of human thought ; yet the phys- 

 ical basis of the latter is a cellular mechanism and 

 nothing more, developed during a single human life in 

 company with all other organs from a one-celled start- 

 ing-point the human egg. 



The method by which mental evolution has been 

 accomphshed is likewise demonstrable, because the 

 factors are identical with those which bring about 

 specific transformation in physical respects. This is to 



