Bonobos are not quite the peace-loving primates they have long been thought to be, researchers say, after finding that males show more aggression towards each other than chimpanzees.
Bonobos and chimpanzees are humans’ closest living relatives. Although chimpanzees are known to show aggression towards each other – sometimes to the point of death – bonobos have long been thought to live more harmoniously, with no known killings. The difference has led to the theory that natural selection works against aggression in male bonobos.
Now research has turned that idea on its head, revealing that bonobos show higher rates of male-on-male aggression than chimpanzees — even when researchers looked specifically at cases where the males stalled.
“This is a species with such complex behavior that to limit the species to just a hippie, for this study, it’s not going to work. It’s just too simplistic,” said Dr Maud Mouginot from Boston University, who is the first author of the research.
“I think what we know now is that bonobos and chimpanzees use aggression and they use it in different ways. And they have different strategies around it,” she said, adding that an interesting area to explore now is why and when these different strategies evolved.
Write in the journal Current BiologyMouginot and colleagues describe how they followed 12 male bonobos across three communities at the Kokolopori Bonobo Reserve in the Democratic Republic of the Congo, and 14 male chimpanzees across two communities at Gombe National Park in Tanzania.
Each male was individually followed by the researchers during his waking hours, during which his interactions with other members of his species were recorded, including aggressive physical contact, and other aggressive actions such as charging and chasing.
Overall, the team recorded 521 aggressive interactions involving tracked bonobos over 2,047 hours, and 654 aggressive interactions between the identified chimpanzees over 7,309 hours.
The team says that despite previous studies finding that chimpanzees show more severe aggression – such as murder, infanticide and sexual coercion – the results show that aggressive acts between males were 2.8 times more frequent in bonobos than in chimpanzees, with acts that involved physical contact which was specifically found 3.0 times more often.
For both species, more aggressive males had greater success in mating with females.
Yet, while not quite the model of gentlemanly chivalry, male bonobos treated females differently than chimpanzees: the team found that male-on-female aggression was less common, and female-on-male aggression more common, in the former as the latter – something the team wrote off female bonobos often outnumber males in the social group.
“We know from the literature that, for example, male and female [bonobos] form a close association … and we don’t see that in chimpanzees,” Mouginot said, noting that humans also form such associations.
The researchers add that while only 1% of aggressive acts among male bonobos involved the primates, the figure was 13% in chimpanzees – a finding that may explain the lower frequency of aggression in chimpanzees.
“It’s just more risky because obviously, if you have multiple individuals against you, you can get completely beaten,” Mouginot said.
