CHAPTER XIII 
THE MENTAL LIFE OF APES AND MONKEYS 
‘“‘L’Homme ne posséde aucune aptitude psychique fondamentale 
qui, 4 un moindre degré, ne se manifeste chez certaines Bétes.””— 
Mitne-Epwarps, Legons sur la Physiologie, T. 14. 
“Tf 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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