Chimpanzee and bonobo societies differ fundamentally. While males dominate among chimps, females are at the top of the hierarchy for bonobos, and new research published in Royal Society Open Science suggests that this may be down to the savage warfare that chimps wage.

Despite chimpanzees having been known about in the western world perhaps for thousands of years, because of how similar the two ape species appear, the bonobo was not formally described as a separate species until 1928. Since then, it has become apparent that, despite living in very similar environments and looking morphologically alike, the two animals are strikingly different indeed.

“While chimpanzee males are highly territorial, with hostile and sometimes lethal intergroup encounters, bonobos have rather peaceful relationships between groups and lack lethal violence during encounters,” explained Martin Surbeck, who led this latest study. Chimpanzees tend to settle disputes through aggression, bonobos seem to do it through sex.

And it was this stark difference in behaviors that spurred Surbeck and his team on to figuring out what impact it has on their societies. It appears that part of the reason why the two apes' social structures may be so different is down to the fact that chimpanzees wage what we call in human cultures “war.”

After studying five separate groups of chimpanzees and two individual groups of bonobos, they found that this warfare may be the reason why bonobo societies are dominated by females, and chimpanzee communities are dominated by males. It turns out that while all chimpanzee groups were sexually segregated, with males preferring to socialize with males, in the bonobo communities both the sexes preferentially liked to socialize with females.

The researchers argue that the warfare observed in one species and not the other can help to explain these social differences. Chimps need to cooperate with other males while they undertake border patrols, hunting, and conflict, and so may prefer to spend time socializing with each other to strengthen these bonds. Male bonobos, on the other hand, are much less territorial, and instead look to their mothers to cooperate with in order to boost their rank in the hierarchy.  

One of the most striking discoveries made about chimpanzees is their tendency towards violence. It is now fairly well known that the apes will brutally attack chimpanzees from neighboring communities, but in some cases, this is taken much further. One of the best-known examples is the Gombe Chimpanzee War, which took place over a period of four years in the 1970s. When one group of chimps split, conflict erupted, with one side systematically wiping out every single male from the other, and then making a land grab for their territory.