Public Lecture - Interactions between humans: Social evaluation by capuchin monkeys

By James R. Anderson, Professor at the Department of Psychology, Kyoto University.

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Recent studies have demonstrated possible precursors of the human traits of empathy and morality in nonhuman primates. For example, capuchin monkeys are less willing to engage with a human actor who systematically refuses to help another. Furthermore, these monkeys can detect fairness or unfairness in the context of a exchange of goods between third parties.  They discriminate between an actor who exchanges in a fair manner with another and an actor who does not respect fairness in the exchange; the monkeys are significantly less likely to accept food from the unfair actor.

These findings support the hypothesis of a process of emotional bookkeeping in which witnessing repeated anti-social acts induces a negative evaluation of the anti-social actor. Recently, we have sought to better identify one of the emotions or affective states involved in such social evaluations. Two actors exchanged objects; one always acted fairly, the other sometimes acted unfairly. After the exchange, one actor started to transfer pieces of food to within reach of the observing monkey. In this situation of delay of gratification, the monkey can start to eat the food at any time, but doing so results in the actor stopping the transfers. So, to maximize the amount of food it can eat, the monkey should wait and allow more food to accumulate. 

The results showed that monkeys were less willing to delay gratification when the actor who exchanged unfairly with a third party was the one who transferred the food.  Impulsively snatching the food peaked when the monkey did not know the amount of food potentially available at the start of the transfer, in other words in a situation of uncertainty. These results recall reduced delay of gratification in young children in a similar situation. We conclude that witnessing unfairness toward a third party engenders a sense of distrust in capuchin monkeys, and that further research should address the mechanisms underlying social evaluation processes in other species.

Crédit photo: Wikivilage.co.za