The Human-Like Traits of Chimpanzee Warfare
When chimpanzees go to war.
Posted November 20, 2025 | Reviewed by Lybi Ma
We have recently read a lot about the remarkable life's work of the great chimpanzee researcher Jane Goodall, who passed away on 1 October 2025. We learned that the Kenyan archaeologist and palaeontologist Louis Leakey sent her to Gombe National Park to study chimpanzee behaviour, as he believed that studying existing great apes could tell us more about humans than the bones of early hominids could.
With an open mind, Goodall discovered that chimpanzees produce tools, form lasting social bonds, and pass on knowledge across generations (although now we know that they are not very good at this ). However, Goodall's discoveries were not all positive. She was also the first to report that chimpanzees engage in organised warfare.
Chimpanzees patrol the borders of their territory and even kill members of neighbouring groups (Watts and Mitani, 2001). Usually, chimpanzees are loud and outgoing and not very good at controlling their behaviour. However, during patrols, they often move in single file, maintaining close proximity to each other, and remain uncharacteristically silent. The patrolling individuals are extremely wary. They make frequent stops to scan the environment , paying close attention to any movement in the trees or on the ground. They also sniff the ground and vegetation, inspecting signs of other chimpanzees such as nests, food caches, and urine and faeces. They also rarely eat during patrols. Perhaps the most remarkable thing is that they remain so silent. Chimpanzees find it difficult to control their spontaneous vocalisations. However, during patrols, they refrain from calling (Boesch and colleagues, 2000). Chimpanzees understand what others can hear (Melisand colleagues, 2006) and realise that it is unwise to be noisy at the border of a territory, as members of other groups may be nearby and could attack if they detect them.
Jane Goodall began her long-term observations in Gombe. Nowadays, there are several other long-term study sites, such as Tai National Park in the Ivory Coast (where Christophe Boesch worked) and Kibale National Park in Uganda. These observations can also teach us about chimpanzee warfare.
For instance, between 1998 and 2008, members of the Ngogo chimpanzee group in Kibale killed 21 individuals from neighbouring groups. The neighbouring group suffered losses, but the Ngogo chimpanzees benefited greatly. They were able to expand their territory into an area previously inhabited by their victims. This resulted in a 22 percent increase in the size of their territory.
More land means more food. Does this also mean more offspring? In a recent study, John Mitani and his team analysed what happened before and after the 'war' (Wood and colleagues, 2025). The numbers are quite impressive. In the three years before the territorial expansion, the Ngogo female chimpanzees gave birth to 15 babies. In the three years afterwards, they gave birth to 37. In other words, their fertility rate doubled. Infant survival also improved dramatically. Before the 'war', 41 percent of the offspring died before the age of three, whereas afterwards, it was only 8 percent.
From a biological perspective, this war was hugely beneficial for the Ngogo chimpanzees. They successfully raised more offspring, thus increasing their fitness.
Humans, like chimpanzees, also benefit from expanding their territory. Of course, human warfare is much more frequent, brutal, and lethal. At this point, shouldn't we distinguish ourselves from chimpanzees and learn more from bonobos instead? Humans can only survive as a species if we consider ourselves one group facing upcoming challenges. Working together like bonobos—for example, on climate change—can make more of an impact than expanding territory.
Boesch, C., & Boesch-Achermann, H. (2000). The Chimpanzees of the Tai Forest . Oxford Univ. Press.
Melis, A. P., Call, J., & Tomasello, M. (2006). Chimpanzees (Pan troglodytes) Conceal Visual and Auditory Information From Others . Journal of Comparative Psychology, 120(2), 154-162.
Watts, D. P., & Mitani, J. C. C. (2001). Boundary Patrols and Intergroup Encounters in Wild Chimpanzees . Behaviour, 138(3), 299-327.
Wood, B. M., Watts, D. P., Langergraber, K. E., & Mitani, J. C. (2025). Female fertility and infant survivorship increase following lethal intergroup aggression and territorial expansion in wild chimpanzees . Proceedings of the National Academy of Sciences, 122(47), e2524502122.
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Juliane Bräuer, Ph.D., is the head of the DogStudies Lab at the Max Planck Institute of Geoanthropology in Jena, Germany, where she studies the cognitive aspects of dog domestication.
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