A recent study finds that bonobos are no less aggressive than chimpanzees, but levels of aggression also vary across different groups in either species.

Chimpanzees and bonobos are humans’ closest living relatives, their ancestors having diverged from ours around 6 million years ago, before our two evolutionary cousins started becoming separate species over a million years ago (Yoo et al., 2025). Chimpanzees have long been depicted as violent, with males especially “warlike” — see for instance the recent documentary Rise of the Warrior Apes (which is excellent, although it doesn’t pass the Bechdel Test). Early studies of bonobos, on the other hand, revealed different social dynamics: females dominate males, all individuals use sexual contact for establishing and maintaining social bonds, and individuals are generally less aggression compared to chimpanzees.

Because these two species are equally related to humans, they provided starkly different models for the possible ancestral conditions out of which humans evolved (Parish et al., 2000). People often look to the animal world to support their ideas of what constitues ‘human nature.’ If either chimpanzees or bonobos are selected as the proxy for our last shared ancestor millions of years ago, one could argue that humans are ‘naturally’ aggressive or peaceful.

However, reports of violent aggression among bonobos in the wild have emerged in recent years, including a likely case in which several females attacked (and probably killed) a male in their group (Pachevskaya et al., 2025). So, are chimpanzees and bonobos that different after all?

Yesterday, Emile Bryon & colleagues reported the results of a systematic comparison between chimpanzees and bonobos in terms of their aggression toward others. The researchers studied 22 groups of chimpanzees (9 groups) and bonobos (13 groups) living in zoos, examining who antagonized whom and whether this involved more of a threat or came to physical contact that could cause bodily harm. The comparison among apes living in captivity as opposed to the wild provides greater sample sizes and reduces some of the variance that could be attributed to habitat differences.

Bryon and team found that, as their article title succinctly reports, “chimpanzees are not more aggressive than bonobos but target sexes differently.” Their results support earlier observations from wild-living apes in that among chimpanzees males are extremely aggressive toward females, while among bonobos females direct more aggression toward males. Overall rates of aggression did not differ between the two species, however, and within each species different groups varied extensively; wild-living apes vary between groups in similar ways.

This variability between groups of the same species is really important. Some groups had more aggressive encounters than others, and both chimpanzees and bonobos had groups with lower rates than expected from the species-wide patterns. It is easy to overgeneralize and essentialize animals based on limited observations—in this case, that ‘bonobos make love while chimpanzees make war.’ In contrast, the study shows that there’s no one way to form a bonobo or chimpanzee society. Our closest living relatives are more flexible in their behavior than we tend to give them credit for.

The animal kingdom and especially our ape cousins are frequently invoked in order to naturalize or justify violence and inequality in the human world, and I think this study illustrates that we shouldn’t overgeneralize about other animals or ourselves. Many people including Donald Trump use naïve evolutionary reasoning to argue that ‘might makes right,’ that being a selfish asshole is a natural state molded by our evolutionary history. But as the late, great David Graeber (2015) has argued (admittedly, about bureaucracies), “The ultimate hidden truth of the world is that it is something that we make, and could just as easily make differently.” This study by Bryon and colleagues suggests that the ability to choose or avoid conflict and aggression may well be the ancestral condition out of which humanity evolved—that despite the violence and warmongering making headlines today, there’s nothing in nature that says it has to be this way.

References

Bryon, E. et al. (2026). Chimpanzees are not more aggressive than bonobos but target sexes differently. Science Advances 12, eadz2433. doi:10.1126/sciadv.adz2433

Graeber, D. (2015). The Utopia of Rules: On Technology, Stupidity, and the Secret Joys of Bureaucracy. Melville House.

Parish, A. et al., (2000), The Other “Closest Living Relative”: How Bonobos (Pan paniscus) Challenge Traditional Assumptions about Females, Dominance, Intra- and Intersexual Interactions, and Hominid Evolution. Annals of the New York Academy of Sciences, 907: 97-113. https://doi.org/10.1111/j.1749-6632.2000.tb06618.x

Pashchevskaya, S et al. (2025) Coalitionary intra-group aggression by wild female bonobos. Current Biology 35, Issue 19, R912 – R913. https://doi.org/10.1016/j.cub.2025.08.010

Yoo, D., Rhie, A., Hebbar, P. et al. (2025) Complete sequencing of ape genomes. Nature 641, 401–418. https://doi.org/10.1038/s41586-025-08816-3