Bonobos Display Similar Cooperative Behavior to Humans, Collaborating with Unrelated Individuals from Different Groups

Unrelated humans consistently work together and distribute resources amongst varying social groups without any apparent immediate benefits. This social characteristic was previously thought to be unique to human beings. However, according to a new study, it seems that bonobos may also exhibit this trait.

The cooperation and bonding between human beings, even without immediate rewards, is believed to be a cornerstone of human civilization. As such, examining bonobos' ability to form connections across different groups, even when no instant benefit is evident, can provide valuable insight into the evolution that led to our complex societies. These findings were reported by researchers in the Science journal on November 16.

Both bonobos (P. paniscus) and chimpanzees (Pan troglodytes) live in social groups with members who are not necessarily closely related. However, bonobos are generally more tolerant and relaxed towards other groups, unlike the more territorial chimpanzees. It has been observed that bonobos occasionally engage in grooming activities and food sharing with non-family individuals from other social groups. These behaviors, however, needed to be quantified further.

In order to do so, behavioral ecologists Liran Samuni from the German Primate Center in Göttingen and Martin Surbeck from Harvard University observed two groups of bonobos in the Kokolopori Bonobo Reserve located in Congo. They recorded instances of grooming and food sharing among the bonobos over a two-year period.

The researchers did not fail to note that conflict and competition among bonobos were not non-existent. They documented instances when bonobos allied with members of the other group for the purpose of attacking a third party.

The two bonobo groups came into contact with each other frequently during the research period. In fact, they spent about a fifth of the total investigation period interacting with each other. These interactions ranged from a single hour to several weeks, allowing more long-term relationships to form.

Multiple instances of cooperative behavior were documented while the bonobos were in each other's company. For example, 10% of the over 3,700 grooming interactions happened between bonobos from different groups. Additionally, 15% of alliances formed for attacking were also between members of different bonobo groups.

This type of behavior was not a rarity, as suggested by Samuni. A considerable 6% of all the food shares happened across different groups. Furthermore, the individuals prone to cooperative behavior within their own groups were more likely to interact with members of the other group who exhibited the same predispositions. The researchers also point out that the cooperative behaviors were not always reciprocated.

The overall findings of the study supplement previous evidence from captive bonobos displaying a similar behavior. This suggests that cooperation across different groups may be innate to the bonobo species. The evolution of such behavior does not occur easily when it involves non-relatives since the evolutionary benefits are more indirect.

Interestingly, bonobos are not the only animals with such behavior. Male dolphins, for instance, form alliances with unrelated males to guard females. However, unlike the observed bonobo behavior, the dolphins' actions confer a direct benefit to them.

Food sharing between unrelated individuals, as observed in the study, is extremely rare according to Samuni. Just a handful of species, including vampire bats, bonobos, and humans perform this behavior. The behavior supports our societies by eliminating potential food shortage situations, Suhrbeck adds.

Shinya Yamamoto, a comparative cognitive psychologist at Kyoto University in Japan, states that it's humans' behavior that brings fascination to these results. While humans sometimes compete or fight with other groups, at other times, they may cooperate even with members of outgroups. The cooperative side of human evolution, especially in relation to our close relatives, the chimpanzees, is still largely undetermined.

Humans are equally related to chimpanzees and bonobos, and the new research doesn’t tell us whether early human ancestors were more like chimps with their universally rigid territories and lethal patrol groups, or like the more relaxed bonobos (SN: 9/17/14). But the finding could lead to insights into the types of conditions in which either side of the coin evolves, Surbeck says.

“Under which circumstances do you see this cooperation? Under which circumstances do you see more of a chimpanzee pattern, in permanently hostile relationships between groups?” he asks. “What shifts the needle from one to the other?”

The finding also suggests that extensive, long-term cooperation between groups can occur without the heavy influence of cultural factors and social norms. In humans, these have been considered necessary to build and sustain between-group cooperation, Samuni says.

“We are showing quite a simple system,” she says. “And we still see it emerging and in a way that is quite similar [to humans].”

There could still be a cultural component at play with these two bonobo groups, Yamamoto says. It’s possible that over generations, some bonobos have learned to be particularly social, similarly to how elements of human culture form.

This study looked at just two wild bonobo groups, and other bonobo groups are known to have variable rates of interaction with other groups, Yamamoto says. So studying more of the apes might reveal something akin to social norms.