Humans are capable of entering into strategic cooperations with strangers and sharing their resources outside their own social group. So far, prosocial behavior towards non-kin was considered a purely human ability. This assumption was partly based on observations of chimpanzees, as our closest relatives sometimes very violently fight members of other groups. Researchers from the German Primate Center – Leibniz Institute for Primate Research (DPZ) and Harvard University have now observed the social behavior of wild bonobos (Pan paniscus), a species closely related to both chimpanzees and humans. They found that bonobo cooperation extends beyond their own social group and includes societal collaboration with other groups (Science).
Although chimpanzees and bonobos live in similarly composed social groups with multiple adults of both genders, they differ fundamentally in how interactions between groups occur. In chimpanzees, relationships between different social groups are primarily hostile. Researchers draw conclusions about human traits such as cooperation and conflict based on studies of our closest living relatives. Since past research has focused almost exclusively on the social behavior of chimpanzees, many models of human evolution assume that group enmity and violence are inherent to human nature.
However, the present study on bonobos tells a different story. When different bonobo groups encounter each other, they often travel together and eat together. Unlike in chimpanzees, the researchers did not observe any fatal conflicts in bonobos. "While observing multiple bonobo groups, we noticed the remarkable level of tolerance among members of different groups. This tolerance paves the way for prosocial cooperative behaviors such as forming alliances and sharing food across groups. This is a stark contrast to what we observe in chimpanzees," says Liran Samuni, junior research group leader at the German Primate Center and lead author of the study.
Challenging field research
Bonobos are challenging to observe in their natural habitat as they exclusively inhabit remote, largely inaccessible parts of the Democratic Republic of the Congo. Harvard Professor Martin Surbeck, who Initiated the study and established the research station in the Kokolopori Bonobo Reserve, explains, "It is through strong collaborations with and the support of the local Mongandu population in Kokolopori, in whose ancestral forest the bonobos roam, that studies of this fascinating species become possible." Surbeck adds, "Research sites, like Kokolopori, substantially contribute not only to our understanding of the species’ biology and our evolutionary history, but also play a vital role in the conservation of this endangered species."
The researchers demonstrated that bonobos do not interact randomly between groups. Instead, they cooperate with specific members of other groups who are more likely to return the favor. This results in strong bonds between prosocial individuals, even across group boundaries. Similar bonds are also a key aspect of cooperation in human societies. "It is impressive to see in bonobos that constant confrontations between neighboring societies are not the only ancient human heritage," Samuni and Surbeck agree. Bonobos show that humans are not unique in their ability to build peaceful relations between societies.
Samuni L & Surbeck M (2023): Cooperation across social borders in bonobos. Science, DOI: 10.1126/science.adg0844