THE HUMAN SIDE OF APES
exhibit ideational behavior; they act with insight. It remains for further patient, critical research to analyze this behavior more adequately and to compare it with our own action under identical conditions.”
One of the striking characteristics of apes and monkeys is the time and effort they spend in mere play. A cow, when her hunger is satisfied, is content to rest indefinitely. But not so the ape. He must be actively exploring, romping with his fellows, climbing, swinging, or pulling things to pieces. In this way he learns much about the properties of things in his environment. His ability to use his hands in manipulating objects gives him a great advantage over the lower mammals in adding to his store of knowledge. Along with his better structural equipment he is endowed with a strong natural curiosity, which is not confined merely to things that immediately affect his welfare but manifests itself in a sort of pure intellectual interest in objects per se. As the ape grows older his playfulness and his spontaneous curiosity gradually diminish, and he becomes more stolid, inactive, and incurious, like so many uneducated human beings.
Chimpanzees express joy and satisfaction by smiles and laughter, especially in play and when they are tickled or given a favorite food. They often show sympathy and affection in very human ways. Madam Abreu, in describing her efforts to catch one of her chimpanzees that had escaped and taken refuge in a mango tree, writes: “I went to the tree, and speaking to him pretended that I was injured in the arm and suffering. Immediately, on seeing that I was in trouble, he jumped from the tree and coming to me held my arm and kissed it strongly. And so we were able to catch him.”
“Impressive indeed,” says Dr. Yerkes, “‘is the thoughtful-
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