Bonobos are the only primates that do not kill others of their kind

We've always thought of ourselves as unique, haven't we? But when you peel back the layers, you find that humans, like all species, are connected by the threads of evolution.

One such thread is the instinct to stand together in the face of external threats. The “common enemy effect” is a phenomenon in which we unite with others over a common enemy or problem.

Humans do it, chimpanzees do it, and now we've learned that even our peaceful relatives, the bonobos, exhibit this behavior in their own subtle ways. At some point in their evolution, bonobos decided to make social bonds their priority.

Threats from outgroups and cohesion within the group

The discovery suggests that the link between out-group threat and in-group cohesion may have emerged several million years ago, before our evolutionary paths diverged.

The study was conducted by an international team of researchers led by Kyoto University. They suggested that outgroup threats and ingroup cohesion might be an adaptation to group-based competition, an idea that has been around since Darwin's time.

But one question was burning under their nails: What about the species that are not known for their bitter rivalries within their groups? And what about the bonobos?

Bonobo Basics

Bonobos are one of our closest primate relatives and share about 98.7% of their DNA with humans. These intelligent apes are known for their peaceful and cooperative social structures, which clearly distinguish them from their more aggressive chimpanzee relatives.

They live in matriarchal societies in which women take the lead, and they often use sexual behavior to resolve conflicts and build social bonds.

With their slender bodies, dark faces and pink lips, bonobos are fairly easy to distinguish from chimpanzees, and their expressive, human-like eyes show a lot of emotion and understanding.

Bonobos live by foraging for fruits, leaves, and small animals. They are naturally arboreal and spend a lot of time in trees, but are also quite adept on the ground.

Finally, they communicate using a mixture of vocalizations, gestures and facial expressions, demonstrating their complex and highly developed social intelligence.

Exploring the evolution of bonobo goodness

Imagine this: Eight groups of bonobos, spread across five sites in four countries, are part of an experiment designed to replicate previous studies with chimpanzees. The procedure was simple: expose the bonobos to the vocalizations of other groups and observe their reactions.

James Brooks, the study's lead author, was as curious as the rest of us. “We had no idea how this would turn out. If the link between group cohesion and outgroup competition was not adaptive due to the lack of lethal competition between groups, the whole thing would make no sense. But if this effect had evolved before the split between humans, chimpanzees and bonobos, we might find some remnants in modern bonobos,” he said.

The results were surprising and at the same time revealing. The bonobos obviously responded attentively to the calls of unfamiliar groups, but their bond with their own group was only slightly increased compared to the chimpanzees.

Bonobos were observed to sit upright more often and rest less, indicating a slight increase in social grooming, a crucial behavior for strengthening social bonds.

Social dynamics in the evolution of bonobos

The bonobos' reactions during the study trigger a fascinating discourse about the social dynamics within their groups.

In contrast to chimpanzees, who often react to threats from other groups with increased aggression, bonobos are known for their relatively peaceful coexistence.

This raises an interesting question: How do these opposing responses contribute to our understanding of primate social behavior?

The study suggests that while bonobos are aware of external vocalizations, they maintain group cohesion in subtle ways by prioritizing social bonds over defensive aggression.

This behavior may reflect an evolutionary strategy that emphasizes forming alliances in the face of potential threats, thereby promoting cooperation within groups rather than competition between them.

Impact on nature conservation

The insights gained from this research extend far beyond academia; they have significant implications for conservation efforts and our understanding of human behavior.

The realization that evolutionary traits of our primate relatives can shed light on why and how we interact socially underscores the importance of protecting species like the bonobo.

Her unique perspective on social interaction provides a valuable lens through which we can examine human responses to conflict and cooperation today.

As we face global challenges that require intercultural collaboration, understanding the nuances of social behavior across species can reveal ways to strengthen our own community bonds and promote understanding in an increasingly interconnected world.

Evolution of bonobos and group conflicts

The authors suggest that our common ancestor, who roamed the Earth 5-6 million years ago, may have experienced group-based conflict. But as the intensity decreased over the course of bonobos' evolution, the strength of this effect also decreased.

“Although our research reveals deep roots of group conflict within our species, the real lesson is that it can be overcome. Not just in individual cases, but at the species level,” Brooks said.

Compare this to other species of apes – gorillas, orangutans, chimpanzees, gibbons and humans – all of which have been observed killing each other.

Bonobos seem to have found a way to break this vicious pattern. And that's not just because they no longer commit lethal attacks today, but, more importantly, because they stopped doing so millions of years ago.

Significance of the study

“Humans are capable of both: we can commit cruel acts against people we consider outside our group, but we are also capable of cooperating across boundaries,” said the study's lead author, Shinya Yamamoto.

“Bonobos teach us that the way our ancestors treated other groups does not seal our fate. Our own species has elements of both chimpanzee and bonobo group relationships, so it is crucial that we understand how both could evolve and how they came to be.”

So the next time you find yourself caught up in a heated debate, think of our peaceful cousins, the bonobos. After all, they have proven that it is possible to adapt, evolve and, most importantly, choose peace over conflict.

The study was published in the journal PLUS ONE.

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