A new study of our two closest living relatives finds that, at least in zoos, bonobos may not be more peaceful than chimpanzees.
Bonobos (Pan paniscus) are only found south of the Congo River in the Democratic Republic of Congo, where food is abundant and evenly distributed. Chimpanzees (Pan troglodytes) range across West, Central and East Africa, where food can be variable and patchy.
Different environmental pressures may have contributed to divergent social behavior between the closely related species. Chimpanzee societies are male-dominant, territorial, and marked by frequent aggression toward other groups. In bonobo societies, females often equal or outrank males, and they have a reputation for more peaceful intergroup relations. Bonobo females form coalitions to suppress male aggression.
However, new findings are adding nuance: One recent comparative analysis challenged bonobos’ “hippy” image; and another recent paper documents the first known death of an infant bonobo resulting from an intergroup encounter.
Building on this framework, Emile Bryon of Utrecht University in the Netherlands led a group of researchers in comparing aggression between chimpanzees and bonobos in zoos, where environmental conditions are more controlled.
Their findings, published in Science Advances, compared behaviors such as chasing, hitting, wrestling and biting in nine groups of chimpanzees and 13 groups of bonobos housed in 16 European zoos.
They found no difference in rates of overall aggression, or more severe contact aggression, between zoo-housed chimpanzees and bonobos.
However, they did find species-level differences in who used aggression. Male chimpanzees were more aggressive than females, while bonobo males and females showed similar levels of aggressive behaviors.
“Overall, our research paints a picture that matches the socio-ecology of both species; chimpanzee males are aggressive against all, whereas all bonobos are aggressive, but target mainly the males,” Bryon said in an email to Mongabay.
“We also found it interesting that female-to-female aggression is generally low in both species. Because female bonobos dominate, and dominant individuals compete amongst each other for resources, one could expect aggression among bonobo females. But our study says otherwise,” Bryon said.
Regardless of species, some zoo-housed groups were more aggressive than others, raising the question of why.
Takeshi Furuichi, who wasn’t involved with this study, is an emeritus professor at Kyoto University and author of another recent paper comparing aggression within groups of wild male chimpanzees and bonobos. He told Mongabay by email that “This study provides valuable comparative data on aggression in chimpanzees and bonobos under controlled conditions.”
However, Furuichi suggested the findings should be interpreted with caution. He noted that the “present study is limited to behavior within single zoo groups” and that “a key basis for the view that chimpanzees are more aggressive than bonobos lies in intergroup male aggression, which is frequently observed in chimpanzees and can sometimes be lethal.”
Banner image: Aggressive behavior by bonobos. Image by Nicky Staes (CC BY-SA 4.0).
This story first appeared on Mongabay
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