Abstract
Cooperation plays an important role in daily social interactions in humans. Wild chimpanzees have been reported to act cooperatively during hunting, but whether or not they are really engaging in cooperation is under debate. Investigation of cooperation in captive chimpanzees dates back to Kohler&rsquos observation, but experimental examination of cooperative ability in chimpanzees has been limited. The present paper describes recent advances in the study of cooperation and other related behaviors in chimpanzees, focusing on two kinds of experiments. In one of the experiments, two individuals had to move a set of heavy stones in order to obtain food under them. Two chimpanzees never succeeded in the task, but a pair of a chimpanzee and a human succeeded, and the chimpanzee began to solicit the human partner when he was not responding. In the other experiment, two individuals had to pull both ends of a string simultaneously to obtain food. The two chimpanzees did not succeed initially, but they gradually began to adjust their behavior to succeed in the task, by watching the partner and waiting for her. These studies indicate that the chimpanzees are able to comprehend some aspect of cooperation, but they never showed ostensive communicative behavior to achieve cooperation with the partner. Taken together other related studies, competitive social skill hypothesis and emotional reactivity hypothesis may have a key in understanding evolution of cooperation. However, these hypotheses seem to be insufficient in explaining the whole picture, and future research in needed especially by focusing on the nature of mother-infant relationships.
