Peace-loving bonobos are more aggressive than we thought (2024)

Despite their species’ friendly reputation, bonobo males lash out at other males much more often than chimpanzee males do, a surprising study finds.

In her first week studying bonobos in the Democratic Republic of the Congo, Maud Mouginot vividly remembers seeing “two balls of fur chasing each other like crazy in the trees.”

“It was five in the morning, and the bonobos had just woken up. The field assistants said ‘This is an aggression.’ And I was like, ‘Wait, where is the peaceful bonobo in this?’” says Mouginot, now an anthropologist at Boston University.

Bonobos’ harmonious portrayal is inspired in part by their frequent use of copulation to smooth over disagreements. Unlike chimpanzees, they are also willing to share food, not only with friends, but even with bonobos they don’t know.

Mouginot had already suspected that bonobos were more complex than the stereotype suggests. But when she started comparing the recorded number of aggressive behaviors on wild bonobos and chimpanzees across five different communities, she struggled to believe her results. (Watch bonobos on the National Geographic showQueens.)

“I was so confused that I looked at each aggression one by one to make sure I had no duplicates.”

As Mouginot and colleagues report in the journalCurrent Biologythis week, it took 2,047 hours of tracking individual male bonobos in the Kokolopori Bonobo Reserve to tally 521 instances of aggression, such as chasing each other around, hitting, kicking, and biting. In Tanzania’s Gombe Stream National Park, where chimpanzees have been studied for over 60 years (supported in part by the National Geographic Society) it took researchers over 7,300 hours to count 654 aggressive acts.

“I was surprised, but the data are strong,” says Richard Wrangham, a primatologist at Harvard University who wasn’t involved in the new study.

Thou shalt not kill

Wrangham has also long been intrigued by the stark differences in behavior between chimpanzees and bonobos.

“A plausible explanation might be that aggression among bonobo males is much less dangerous than in chimpanzees, so there are fewer reasons for it to be constrained.”

Mouginot agrees. “We have no reports yet of bonobos killing each other, while there are many from chimpanzees. Chimpanzee males form coalitions, so a male who acts out against another male might face coalitionary retaliation, which can be very dangerous.” (Read how chimpanzees killed and cannibalized their former leader in Senegal.)

“So I think the costs of aggression are more unpredictable and often higher for chimpanzees, which might explain why bonobos use it more easily in everyday life.”

Bonobos also have a very different approach to territorial defense, says study co-author Martin Surbeck, a primatologist at Harvard University and a National Geographic Explorer who has studied bonobos in the wild for 20 years.

“Bonobo home ranges seem much larger than those of chimpanzees, so they might not be able to defend them as territories like chimpanzees do. While coalitions of chimpanzee males do not hesitate to kill individuals from other groups, bonobos from different groups may peacefully hang out together and even groom and share food when they encounter each other.”

Help from mom

But why do bonobo males have such a short fuse? The research suggests it somehow them better access to females. In this study, at least, the more aggressive bonobo males fathered far more young than those that were less confrontational.

This is somewhat surprising, since unlike chimpanzee males, male bonobos would get into all sorts of trouble if they were hostile to females.

“Female bonobos are aggressive to males quite frequently. They can be really mean to them,” says Michael Wilson, a primatologist at the University of Minnesota who has worked in Gombe for decades. Bonobo females band together to dominate males, and they tend to choose their own partners.

On the other hand, “female chimpanzees are very submissive toward males, and very fearful of them,” For this reason, he adds, chimpanzee males can sometimes coerce females into mating.

Mouginot suspects female bonobos aren't attracted to aggression itself, but instead the high-ranking males who use force to repel competitors when females are ready to mate.(Read how a bonobo was separated from her sister for 26 years, but she still remembered her years later.)

In fact, females may play an even more active role in the males’ success, says primatologist Takeshi Furuichi of Japan’s Kyoto University who has studied bonobos in the wild for many years.

“Male bonobos with high-ranking mothers often challenge other males with support from their mothers, who can increase their number of grandchildren in this way,” Furuichi says.

“In a recent study of our own, most aggressive interactions occurred between the sons of high-ranking mothers.”