286 Animal Intelligence 



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 second- 

 ary results of the tremendous increase in the number, deli- 

 cacy and complexity of associations which the human ani- 

 mal 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 idea- 

 tional life and reasoning were not new and unexplainable 

 species of intellectual life but only the natural consequences 

 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 evolu- 

 tion of living forms. 



In 1890 William James wrote, "The more sincerely one 

 seeks to trace the actual course of psychogenesis, 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 produced the human sort. If 

 we do, let us proceed to seek a possible account of how 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 intellect, that this progress 

 continues as we pass from the monkeys to man. Such a 



