Researchers studying humans’ closest living relatives bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) have debunked a long-standing myth that bonobos are the less aggressive of our primate cousins.
The new study shows that male bonobos, rather than chimpanzees, are more frequently aggressive towards other males. More aggressive males also had higher mating success in both species, despite having different mating strategies.
“Chimpanzees and bonobos use aggression in different ways for specific reasons,” says anthropologist Maud Mouginot of Boston University in the US, lead author of the paper in Current Biology.
“The idea is not to invalidate the image of bonobos being peaceful—the idea is that there is a lot more complexity in both species.”
The research team compared rates of male aggression in 3 bonobo communities at the Kokolopori Bonobo Reserve, in the Democratic Republic of Congo, and 2 chimpanzee communities at Gombe National Park in Tanzania.
They examined the behaviour of 12 male bonobos and 14 male chimpanzees by conducting “focal follows,” which involved tracking one individual’s behaviour for an entire day and taking note of how often they engaged in aggressive interactions, with whom, and whether they were physical or not.
“You go to their nests and wait for them to wake up and then you just follow them the entire day –from the moment they wake up to the moment they go to sleep at night – and record everything they do,” says Mouginot.
The researchers found that male bonobos engaged in 2.8 times more aggressive interactions, and 3 times as many physical aggressions, than male chimps.
But while male bonobos were almost exclusively aggressive toward other males, chimpanzees were more likely to act aggressively toward females. Chimpanzee aggression was also more likely to involve “coalitions” of males (13.2%) working together than bonobo aggressions (1%).
The researchers think that these coalitions might be one reason why aggression is less frequent among chimpanzees, as their altercations involving have the potential to cause more injuries and could weaken the group’s ability to fight off other groups of chimps.
More aggressive males also had greater mating success. This is an unsurprising finding in the male-dominated hierarchies of chimpanzees, in which male coalitions coerce females into mating.
“Male bonobos that are more aggressive obtain more copulations with females, which is something that we would not expect,” says Mouginot.
Bonobos have a co-dominant social dynamic in which females often outrank males and males rarely use coercive mating strategies.
“It means that females do not necessarily go for nicer males,” says Mouginot.
The researchers note that they focused on male aggression, which is often tied to reproduction, but female bonobos and chimpanzees are not passive, and their aggression warrants its own future research.
