MENTAL EVOLUTION OF MAN 201 



ferentiated digestive tracts of even the highest animals 

 have evolved from a simple sac like that of a polyp or 

 jellyfish, as we know from the independent testimony 

 of comparative anatomy and embryology ; in this case 

 also the evolution of alimentary functions is no less 

 inseparable from the transformations in structural 

 respects. And again, we cannot understand the his- 

 torical development of vision without taking into 

 account the eyes of various types belonging to lower 

 and higher animals. 



So it is with the nervous systems of man and other 

 animals, and with their functions. The nervous system 

 of the human organism comprises identical organs with 

 the same arrangements that are found in other pri- 

 mates and in lower vertebrates as well ; the differences 

 in structure are differences in the degree of the com- 

 plexity of certain parts, notably of the cerebrum. 

 Therefore the evolution of human mentality, which 

 depends upon a human type of brain as a physical basis, 

 is already demonstrated with the proof that the human 

 brain and nervous system have evolved. It is true 

 that an invariable and necessary connection between 

 mind and matter is implied in the foregoing statement, 

 and this is something which demands further consider- 

 ation at a later point. But just how the human mind 

 is produced by or depends upon the brain, is of far less 

 importance for us at this time than the obvious fact 

 that mental performance requires active nervous tis- 

 sues. So far investigation has been unable to discover 

 a valid reason for a belief in the existence of mental 

 phenomena, as such, apart from some kind of material 

 basis. And while we may prefer to restrict the use of 



