Cooperation across social borders in bonobos

Abstract

Cooperation beyond familial and group boundaries is core to the functioning of human societies, yet its evolution remains unclear. To address this, we examined grooming, coalition, and food-sharing patterns in bonobos ( Pan paniscus ), one of our closest living relatives whose rare out-group tolerance facilitates interaction opportunities between groups. We show that, as in humans, positive assortment supports bonobo cooperation across borders. Bonobo cooperative attitudes toward in-group members informed their cooperative relationships with out-groups, in particular, forming connections with out-group individuals who also exhibited high cooperation tendencies. Our findings show that cooperation between unrelated individuals across groups without immediate payoff is not exclusive to humans and suggest that such cooperation can emerge in the absence of social norms or strong cultural dispositions.

Editor’s summary Humans are very good at cooperating with others outside of our family, kin, and cultural groups. Although cooperation among individuals within groups is also common in other animals, doing so outside of such groups has rarely been observed. Samuni and Surbeck looked at cooperative behaviors such as grooming and food sharing in bonobos and found that individuals that cooperated more within their own group were also more likely to cooperate with those in other groups (see the Perspective by Silk). Furthermore, such cooperation was neither rare nor opportunistic. Social openness in one of our closest relatives suggests that our cooperativeness may be older than we thought. —Sacha Vignieri

Bonobo cooperation across groups offers a window into humanity’s evolutionary past.