Capuchin Monkeys Alternate Play and Reward in a Dual Computerized Task

Many animals cooperate with one another to achieve outcomes that they could not obtain on their own. One form of cooperation that has received much attention but little empirical support from experimental studies is reciprocity, leaving open the question of whether animals will work to provide benefits to others. Although there is some evidence of reciprocal behavior in animals, early work in macaque monkeys showed that while they would initially work to pay another individual (who could then return the favor), they ceased doing so over time. Here, we extended this investigation of reciprocity to capuchin monkeys (Cebus apella), a species known for cooperating and providing each other with rewards in other contexts. We investigated whether capuchin monkeys would engage in a dual computer task that required alternating work by two animals, such that food rewards earned by one individual were delivered to the partner. Unlike previous research, capuchin monkeys sustained work on the task when their actions benefited only another monkey, even with progressively longer delays between the subject’s actions that rewarded the partner and the partner’s subsequent actions that rewarded the subject. A separate question was the degree to which subjects understood their actions as social. We assessed whether subjects’ behaviors were influenced by the presence or absence of a partner. Subjects behaved differently in the two conditions, indicating that future research investigating what subjects understand about their partners is warranted.