306 MIND IN EVOLUTION CHAP, xn 



of development effects a correlation between related 

 elements of experience and action. As applied to the apes, 

 this conclusion appears very probable indeed ; and as 

 applied to some other mammals, it is, I think, a better 

 provisional hypothesis than any other that I know. As a 

 provisional hypothesis, its truth will be assumed in the 

 rest of this work. 1 



1 The considerable body of investigation undertaken in America since 

 the above was written by such observers as Yerkes, Watson, Haggerty, 

 Berry, Cole, and many others, has yielded very diverse results in different 

 cases, but as a whole has tended to confirm the hypothesis here put for- 

 ward, with the limitation that intelligence on the higher level is the excep- 

 tion, so that only the most alert individuals will give clear signs of it, and 

 that only under favourable circumstances. With the questions raised by 

 accounts of the Elberfeld horses I deal in the Appendix. 



