Bonobos are the only primates, including humans, that don't kill others in their species

We’ve always considered ourselves unique, haven’t we? But peel back the layers, and you’ll find that humans, like all species, are bound by the threads of evolution.

One such thread is the instinct to come together when faced with external threats. The “common enemy effect” is a phenomenon in which we bond with others over a shared opponent or issue.

Humans do it, chimpanzees do it, and now we’ve learned that even our peaceful relatives, bonobos, exhibit this behavior in their own subtle way. At some point in their evolution, bonobos chose to make social bonding a priority.

Outgroup threats and ingroup cohesion

The discovery suggests that the link between outgroup threats and ingroup cohesion may have evolved several million years ago, before our evolutionary paths diverged.

The study was conducted by an international team of researchers led by Kyoto University. They surmised that outgroup threats and ingroup cohesion may be an adaptation for group-based competition, a notion that has floated around since Darwin’s days.

But they had a burning question – what about species that aren’t known for their fierce inter-group rivalries? What about bonobos?

Bonobo basics

Bonobos are some of our closest primate relatives, sharing about 98.7% of their DNA with us humans. These smart apes are known for their peaceful and cooperative social structures, which really sets them apart from their more aggressive chimpanzee cousins.

They live in matriarchal societies where females take the lead, and they often use sexual behaviors to sort out conflicts and build social bonds.

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

Bonobos thrive by foraging for fruits, leaves, and small animals. They’re naturally arboreal, spending plenty of time in the trees, but they’re also pretty skilled on the ground.

Lastly, they communicate using a mix of vocalizations, gestures, and facial expressions, showcasing their complex and sophisticated social intelligence.

Studying evolution of bonobo benevolence

Picture this — eight groups of bonobos spread across five sites in four countries, all part of an experiment designed to echo previous studies conducted with chimpanzees. The process was simple — expose the bonobos to vocalizations from other groups and observe their reactions.

James Brooks, the study’s lead author, was as curious as any of us. “We had no idea how this would turn out. If the bond between group cohesion and outgroup competition wasn’t adaptive due to the lack of lethal competition between groups, there would be no point. But, if the effect had evolved before the human-chimpanzee-bonobo split, we might find some vestiges in modern bonobos,” he shared.

The findings were startling yet insightful. The bonobos were clearly alert to the calls from outside groups, but their affiliation with their own group showed only a minor increase compared to chimpanzees.

Bonobos were seen sitting upright more and resting less, hinting at a slight increase in social grooming, a crucial behavior for reinforcing social bonds.

Social dynamics in bonobos evolution

The reactions of the bonobos during the study spark a fascinating discourse on social dynamics within their groups.

Unlike chimpanzees, who often exhibit heightened aggression in response to outgroup threats, bonobos are recognized for their relatively peaceful interactions.

This raises an intriguing question: how do these contrasting responses inform our understanding of social behavior in primates?

The study suggests that while awareness of external vocalizations exists, the bonobos maintain a subtle approach to group cohesion, prioritizing social bonding over defensive aggression.

This behavior may reflect an evolutionary strategy that emphasizes alliance-building in the face of potential threats, thereby fostering collaboration within rather than competition between groups.

Implications for conservation

The insights gained from this research extend well beyond the realm of academia; they carry significant implications for conservation efforts and our understanding of human behaviour.

Recognizing that evolutionary traits from our primate relatives can inform why and how we interact socially underscores the importance of preserving species like the bonobo.

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

As we navigate global challenges that require cross-cultural collaboration, appreciating the nuances of social behavior across species can illuminate pathways to strengthen our own communal ties and foster understanding in an increasingly interconnected world.

Bonobos evolution and group conflict

The authors suggest that our shared ancestor, who roamed the earth 5–6 million years ago, might have experienced some group-based conflict. But as the intensity decreased in the bonobos’ evolutionary journey, so too did the strength of the effect.

“Although our research unearths deep roots of group conflict among our species, the real takeaway is that it can be overcome. And not just in isolated incidents, but on a species level,” said Brooks.

Contrast this with other ape species — gorillas, orangutans, chimpanzees, gibbons, and humans — all of whom have been observed killing each other.

Bonobos seem to have found a way to break this vicious pattern. It’s not just because they don’t commit lethal aggression today, but more importantly, they somehow stopped doing it millions of years ago.

Significance of the study

“Humans are capable of both: we can commit horrific acts to those we see as outside our group, but we’re also capable of collaborating and working together across borders,” said study senior author Shinya Yamamoto.

“Bonobos teach us that the ways our ancestors treated other groups does not seal our fate. Our own species has elements of both chimpanzee and bonobo group relations, so it is crucial that we understand how both can, and have, evolved.”

So next time you find yourself in a heated debate, think about our peaceful cousins, the bonobos. After all, they’ve proven that it’s possible to adapt, evolve, and most importantly, choose peace over conflict.

The study is published in the journal PLOS ONE.

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