Chimpanzees Have a Violent Reputation — But They Aren’t More Aggressive Than Bonobos

For years, chimpanzees and bonobos have been used as a kind of evolutionary mirror of human nature. Chimpanzees are often described as violent and territorial, while bonobos are known for their peaceful and cooperative societies. But this contrast is perhaps too simplistic.

Researchers analyzing the aggressive behavior of 22 groups of chimpanzees and bonobos housed in zoos found no significant differences in overall aggression between the two species, according to a study published in Scientific advances. Rather, the difference lies in how aggression is distributed within their social groups.

“Some see in them a reflection of our nature,” said co-author Emile Bryon in a press release. “Aggressive and belligerent like chimpanzees, or peaceful like bonobos. The truth is that, evolutionarily speaking, we are equally related to both species. And the dichotomy between aggressive chimpanzees and peaceful bonobos might be less clear than previously thought.”

Learn more: Wild chimpanzees could consume two alcoholic drinks a day

Chimpanzee and bonobo fighting models

Although the overall level of aggression was similar, the researchers found a significant difference in the tendency to initiate it.

“In chimpanzees, aggression comes primarily from males and is directed at everyone. In bonobos, aggression comes from everyone but is primarily directed at males,” Bryon explained.

This model reflects the different social dynamics of the two species. Chimpanzee societies are dominated by males, who often compete intensely with each other and assert control over other members of the group. Bonobo societies, in contrast, are structured around female alliances that can collectively dominate males.

As a result, male bonobos rarely direct their aggression toward females and instead tend to target other males.

The violent reputation of chimpanzees

In the wild, chimpanzees have been observed engaging in violent confrontations with neighboring groups, sometimes described as warlike raids. Researchers have also documented cases of infanticide, in which infants from rival groups are killed – behaviors that have helped cement the idea that chimpanzees are the more aggressive of the two species.

But new observations have begun to complicate this picture. Some recent studies have found higher aggression in male chimpanzees, while others have reported the opposite pattern, with male bonobos showing more aggression.

Rethinking the idea of ​​“self-domestication”

One explanation scientists have proposed for bonobos’ reputation as peaceful apes is known as the self-domestication hypothesis. Chimpanzees and bonobos live in different ecological environments separated by the Congo River. Chimpanzee habitats tend to be more competitive for food and experience greater pressure from predators, while bonobo habitats appear more stable.

According to the self-domestication hypothesis, these calmer conditions could have allowed female bonobos to form coalitions giving them greater social power. Over time, females may have favored less aggressive males as partners, gradually selecting for more tolerant behavior. But the new study raises questions about this explanation.

“Neither our results nor more recent findings in nature support the predictions of the self-domestication hypothesis in bonobos. Bonobo males are not significantly less aggressive than chimpanzee males,” Bryon said.

Instead, the researchers found that levels of aggression varied greatly between individual groups, regardless of species. Some groups were relatively peaceful, while others were much more aggressive. Studying great apes in zoos has allowed researchers to compare their behavior under similar environmental conditions, helping to isolate differences between species.

“The overlap in aggressive behaviors we observed in zoos provides valuable information,” Bryon said. “Future studies on wild populations will help confirm whether they exhibit the same patterns and differences in aggression.”

Understanding these patterns could ultimately help researchers better interpret the evolutionary roots of aggression in humans — and why the simple story of violent chimpanzees and peaceful bonobos may never have been entirely accurate.

Learn more: Chimpanzees, like humans, break down complex tasks into smaller pieces

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