140 READINGS IN BIOLOGICAL SCIENCE 



use to which the chips can be put. Moreover, from their behavior in the 

 fact of situations new to them we must allow them at least the rudiments 

 of reasoning power. One of the best-known experiments used to determine 

 this consists in putting a banana in the middle of a pipe, where the ape 

 cannot reach it from either end. After trying direct methods and con- 

 vincing himself that they are useless, the ape will take a stick and push 

 the banana along the pipe, then go around to the other end and get it. 

 Between the first direct attempts and the use of the stick there will usually 

 be a period of physical quiescence during which the animal is mentally 

 sizing up the situation. During this period mental images of the banana 

 in various non-existent positions must be formed and various methods of 

 getting it into one of these positions pictured, tested against past experi- 

 ence, and discarded, for when the ape begins operations once more he 

 usually seems to have a clear idea of what he is going to do. Moreover, 

 once the problem has been solved, the solution is remembered and the 

 same thing will be done immediately when he is again confronted by the 

 same situation. Apes can even go a step further and fit two sticks together 

 to get a poking tool of the necessary length. In one instance a female 

 chimpanzee confronted by the pipe-and-banana problem and given a 

 pair of sticks which could be fitted together tried them singly and then 

 gave up and began to play with them. When they fitted together by 

 accident, she showed signs of considerable excitement, took them apart 

 and fitted them once more, then used them to get the banana. Even after 

 getting it, her interest in the sticks continued, and she kept joining and 

 separating them until she had mastered the principle. It is difficult to see 

 how the mental processes underlying such behavior differ from those of 

 a man who makes a discovery and realizes its possible application. Apes 

 will also cooperate in projects for getting food, showing by their actions 

 that they are able to comprehend both the basic situation and what the 

 other apes who are working with them are trying to do. 



In all fields where exact tests can be applied, chimpanzees seem to have 

 the same mental powers as human children three to four years of age. 

 There is a strong presumption, therefore, that the differences in animal 

 and human mentality are purely quantitative. The ape stops at a certain 

 point in the development of the mind, while the human goes on. However, 

 as the ape cannot tell us what is going on inside his head, the best that 

 we can do at present is to render the Scottish verdict of "not proven." Even 

 if there are qualitative differences in human and ape thinking, so many 

 of the thought processes appear to be the same that no scientist would 

 doubt that human thinking is a direct outgrowth of animal thinking. Human 

 intelligence, like the brain which produces it, is the result of certain 

 recognizable tendencies in mammalian evolution. 



No one can deny that there are profound quantitative differences in 

 human and ape thinking. The facts are too obvious to require exposition. 



