EVOLUTION OF THE HUMAN INTELLECT. 6i 



account of ]low this might have happened, and finally to examine any 

 evidence that shows this possible 'how' to have been the real way in 

 which human reason has evolved. 



It has already been shown that in the animal kingdom there is, as we 

 pass from the early vertebrates down to man, a progress in the evolution 

 of the general associative process which practically equals animal in- 

 tellect, that this progress continues as M-e pass from the monkeys to 

 man. Such a progress is a real fact; it does exist as a possible vera 

 causa; it is thus at all events better than some imaginary cause of the 

 origin of human intellect, the very existence of which is in doubt. In 

 a similar manner we know that the cell structures which compose the 

 brain and the connections between which are the physiological parallel 

 of the associations animals form show as we pass down through the 

 vertebrate series an evolution along lines of increased delicacy and com- 

 plexity. That an animal associates a certain act with a certain felt 

 situation means that he forms or strengthens connections between cer- 

 tain cells. The increase in the number, delicacy and complexity of cell 

 structures is thus the basis for an increase in the number, delicacy and 

 complexity of associations. Xow the evolution noted in cell structures 

 affects man as well as the other vertebrates. He stands at the head 

 of the scale in that respect as well. May not this obvious supremacy 

 in the animal type of intellect and in the adaptation of his brain to it 

 be at the bottom of his supremacy in being the sole possessor of reason- 

 ing? 



This question becomes more pressing if we realize that we must 

 have some sort of brain correlate for ideational life and reasoning. 

 Some sort of difference in processes in the brain must be at the basis of 

 the mental differences between man and the lower animals, we should 

 all admit. And it would seem wise to look for that difference amongst 

 differences which really do or at least may exist. Now the most likely 

 brain difference between man and the lower animals for our purpose, 

 to my mind indeed the only likely one, is just this difference in the 

 fineness of organization of the cell structures. If we could show with 

 any degree of probability how it might account for the presence of 

 ideas and of reasoning we should at least have the satisfaction of deal- 

 ing with a cause actually known to exist. 



The next important fact is that the intellect of the infant six 

 months to a year old is of the animal sort, that ideational and reason- 

 ing life is not present in his case, that the only obvious intellectual 

 difference between him and a monkey is in the quantity and quality of 

 the associations formed. In the evolution of the infant's mind to its 

 adult condition we have the actual transition within an individual 

 from the animal to the human type of intellect. If we look at the 

 infant and ask what is in him to make in the future a thinker and 



