MENTAL EVOLUTION IN THE PRIMATES 1 23 



In a metal pipe, or elongated wooden box, open at both 

 ends and securely fixed in position, a desired object is so 

 placed as to be beyond the reach of the watching subject. 

 Nearby, but not so close to the pipe as to be viewed simul- 

 taneousl}^ with it, is a stick which might serve as instrument 

 to push the object through and out of the pipe. The situation 

 presents a type of problem appropriate alike for infants, 

 children, and the various classes of infrahuman primate. 

 As in the case of the problem just described, the human 

 subject must develop for several months before he is able to 

 solve the pipe and stick problem. Never, so far as we have 

 been able to learn, has such a problem been solved by lemur- 

 hke primates or by monkeys. It has, however, been solved in 

 several instances by the chimpanzee, under conditions which 

 seemingly precluded the possibility of chance or of previous 

 experience with a similar problematic situation. At the level 

 of the apes we discover, it seems, that measure of selective 

 adaptation and of insight which renders possible prompt 

 adjustment to this type of novel problem. Man, beyond a 

 certain stage in childhood, has no particular difficulty in 

 understanding and adapting to such a situation. 



By yet another simple experiment we would exhibit the 

 contrast between lemur and monkey, on the one hand, and 

 ape and man, on the other. If food or other desired object be 

 suspended beyond the reach of the subject and a number of 

 boxes be placed within easy reach, we naturally should 

 expect a human subject to solve this problem promptly 

 by building the boxes into a pyramid, so placed that from it 

 the objective can readily be reached. This type of solution 

 is not possible to the human infant, but appears at a certain 

 stage of childhood. It is impossible, so far as we know, to 

 monkeys and to more primitive primates, but certain at least 

 of the anthropoid apes succeed. Indeed, the chimpanzee 

 and orang-outan in this type of experiment very clearly 

 manifest their adaptive superiority to the monkey, to the 

 human infant, and to the very young child. 



These several illustrative experiments, chosen from among 

 scores which are available in the scientific literature or in our 

 experience, indicate the major grounds for the statement that 

 behavioral adaptation with insight or partial understanding 



