For decades, a tidy story has circulated in books, documentaries, and even scientific discussions about our closest relatives: Chimpanzees and bonobos. Chimpanzees are often portrayed as the violent apes: Territorial, competitive, and prone to aggression. Bonobos, in contrast, have earned a reputation as the peaceful ones: Cooperative, female-led, and gentle.

The contrast has been so influential that scientists have used it to think about the origins of human nature itself. If chimpanzees represent the aggressive side of our evolutionary heritage, perhaps bonobos show an alternative path, one where cooperation and tolerance took the lead. But new research suggests the reality may be more complicated.

Looking beyond the stereotype

Researchers associated with the University of Antwerp and Zoo Antwerp recently examined aggression in 22 groups of apes living in European zoos: Nine groups of chimpanzees and thirteen groups of bonobos, totalling 189 individuals. By studying these apes in similar environments, the researchers could reduce many of the ecological differences that affect behaviour in the wild, such as the need to forage for food or the presence of predators. Using detailed behavioural observations, the researchers mapped who was aggressive toward whom inside each group. They also looked at different kinds of aggression, ranging from aggression types without physical contact like displays and threats to those that involve more severe physical contact like kicking and biting.

The result? Bonobos were not less aggressive overall than chimpanzees. When researchers accounted for factors like group size and the ratio of males to females, both species showed similar overall levels of aggression. Even when focusing only on physical aggression, the more serious kind, the difference between species still did not appear. That finding runs counter to the long-standing assumption that bonobos are simply the “nicer” ape.

The real difference lies in gender dynamics

Although the overall level of aggression was similar, the direction of aggression differed dramatically between the species. In chimpanzee groups, aggression tended to flow from males toward females. This reflects the male-dominated hierarchies typical of chimpanzee societies, where males often use aggression to maintain status or control.

Bonobos showed the reverse pattern. In their groups, females were more likely to direct aggression toward males. This pattern fits what researchers already know about bonobo societies. Female bonobos often form strong alliances, which can give them significant social power. In many groups, females collectively keep males in check. So rather than one species being more aggressive than the other, the study suggests that aggression is organized differently depending on social structure.

Not all ape societies are the same

Another striking discovery was just how much variation existed between individual groups. Some bonobo groups were among the most aggressive in the study. Others were among the least. The same was true for chimpanzee groups.

This growing evidence suggests that ape societies, just like human ones, can vary widely in their social behaviour – including levels of aggression - depending on group history, relationships, and social dynamics. In other words, behaviour isn’t just determined by species. Culture and local social structure play a big role too.

Rethinking the “self-domestication” idea

The findings also raise questions about a popular evolutionary theory known as the self-domestication hypothesis. According to this idea, bonobos evolved reduced aggression because females preferred calmer, less aggressive males over many generations. This selection pressure supposedly led to the more tolerant and cooperative bonobo societies we see today.

But the new results don’t fully support that picture. Male bonobos in the study showed similar levels of aggression to male chimpanzees, suggesting aggression itself may not have been dramatically reduced. Instead, the difference may lie in how aggression is distributed within their society. In chimpanzees, it is largely male-driven and directed at both males and females. In bonobos, it is more balanced between sexes but most often directed toward males.

What this means for understanding human evolution

Chimpanzees and bonobos are our closest living relatives, so scientists often look to them for clues about the evolutionary roots of human behaviour. If the traditional “violent chimpanzee vs. peaceful bonobo” contrast turns out to be oversimplified, that has implications for how we think about ourselves.

Rather than viewing aggression as something fixed in our evolutionary heritage, the findings suggest it may be flexible and shaped by social systems, including alliances, power dynamics, and group culture. In other words, aggression may not be a simple biological destiny. Even among our closest relatives, it depends heavily on who holds power, how groups are organized, and how individuals interact.

And that realization makes the story of human nature, and ape behaviour, far more interesting than the old stereotype ever did.

Read the full study in Science Advances.