6o POPULAR SCIENCE MONTHLY. 



becoming more complex and more delicate. The fish can learn to go 

 to certain places, to take certain paths, to bite at certain things and 

 refuse others, but not much more. It is an arduous proceeding for him 

 to learn to get out of a small pen by swimming up through a hole in a 

 screen. The monkey can learn to do all sorts of things. It is a com- 

 paratively short and easy task for him to learn to get into a box by 

 unhooking a hook, pushing a bar around and pulling out a plug. He 

 learns quickly to climb down to a certain place when he sees a letter T 

 on a card and to stay still when he sees a K. He performs the proper 

 acts nearly as well after 50 days as he did when they were fresh in his 

 mind. 



This growth in the number, speed of formation, permanence, delicacy 

 and complexity of associations possible for an animal reaches its 

 acme in the case of man. Even if we leave out of question the power 

 of reasoning, the possession of a multitude of ideas and abstractions 

 and the power of control over impulses, purposive action, man is still 

 the intellectual leader of the animal kingdom by virtue of the superior 

 development in him of the power of forming associations between 

 situations or sense impressions and acts, by virtue of the degree to 

 which the mere learning by selection possessed by all intelligent ani- 

 mals has advanced. In man the type of intellect common to the ani- 

 mal kingdom finds its fullest development, and with it is combined 

 the hitherto non-existent power of thinking about things and rationally 

 directing action in accord with thought. 



Indeed it may be that this very reason, self -consciousness and self- 

 control which seem to sever human intellect so sharply from that of 

 all other animals are really but secondary results of the tremendous 

 increase in the number, delicacy and complexity of associations which 

 the human animal can form. It may be that the evolution of intellect 

 has no breaks, that its progress is continuous from its first appearance 

 to its present condition in adult civilized human beings. If we could 

 prove that what we call ideational life and reasoning were not new and 

 unexplainable species of intellectual life but only the natural conse- 

 quences of an increase in the number, delicacy and complexity of 

 associations of the general animal sort, we should have made out an 

 evolution of mind comparable to the evolution of living forms. 



In 1890 William James wrote, "The more sincerely one seeks to 

 trace the actual course of psycho-genesis, the steps by which as a race 

 we may have come by the peculiar mental attributes which we possess, 

 the more clearly one perceives 'the slowly gathering twilight close in 

 utter dark.' " Can we perhaps prove him a false prophet ? Let us first 

 see if there be any evidence that makes it probable that in some way 

 or another the mere extension of the animal type of intellect has pro- 

 duced the human sort. If we do let us proceed to seek a possible 



