CHAPTER XIII 

 THE MENTAL LIFE OF APES AND MONKEYS 



" L'Homme ne possede aucune aptitude psychique fondamentale 

 qui, a un moindre degre", ne se manifeste chez certaines B6tes." 

 MILNE-EDWARDS, Lemons sur la Physiologic, T. 14. 



"If no organic being excepting man had possessed any mental 

 power, or if his powers had been of a wholly different nature from 

 those of the lower animals, then we should never have been able to con- 

 vince ourselves that our high faculties had been gradually developed. 

 But it can be shown that there is no fundamental difference of this 

 kind. We must also admit that there is a much wider interval in 

 mental power between one of the lowest fishes, as a lamprey or 

 lancelet, and one of the higher apes, than between an ape and man; 

 yet this interval is filled by numberless gradations." DARWIN 

 Descent of Man. 



I have reserved for a separate chapter a consideration of 

 the mental powers of the animals most closely related to 

 ourselves. Our simian cousins have long enjoyed the reputa- 

 tion of attaining, next to man, the highest psychic develop- 

 ment of any members of the animal kingdom. Much has 

 been written concerning their powers and performances, 

 but their psychology has been investigated far less exten- 

 sively and thoroughly than the importance of the subject 

 demands. It is particularly unfortunate that we know so 

 little of the most anthropoid of the ape tribe. Until recently 

 it has been exceedingly difficult to keep the larger apes long in 

 captivity, and psychologists have had few opportunities to 

 subject them to systematic experimentation. Further diffi- 

 culties are encountered owing to the large size and strength 

 of these animals, especially when these characteristics are 

 combined, as is often the case, with an unreliable or intract- 

 able disposition. 



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