Selfish strategies develop in social problem situations in chimpanzee (Pan troglodytes) mother–infant pairs

摘要

Humans employ various strategies, including selfish and altruistic strategies, depending on the situation. In order to examine whether non-human animals show such flexibility or not, we analyzed chimpanzees’ selfish and cooperative behavior in two types of social problem situations. In this study, we tested chimpanzee mother–infant pairs in two adjacent booths, each equipped with a vending machine. When a token was inserted into a vending machine, the vending machine delivered food rewards to the adjacent booth. In experiment 1, a partition between the two booths was open. In experiment 2, the partition was closed and a mother and her infant were placed in separate booths, so that reciprocal cooperation was essential for them to receive rewards. The participants did not cooperate reciprocally in either experiment. In experiment 1, the chimpanzees developed selfish tactics to get rewards and changed their tactics flexibly according to the partner’s behaviors. In experiment 2, in which they could not receive rewards without cooperation, they stopped altogether inserting tokens. In both cases, the infants stopped cooperating first. These findings support the idea that chimpanzees are primarily competitive rather than cooperative. Chimpanzees’ high social intelligence might be demonstrated in the flexibility of their selfish tactics, but not in the form of reciprocal cooperation at least when food is involved. We suggest that the failure to establish reciprocal cooperation was due to the social relationship between the mother and her infant, which was characterized by infant’s privilege and mother’s tolerance.