Bonobos, the pacifist chimpanzees, much more aggressive than previously thought

2024-04-17 02:23:59

Bonobos and chimpanzees are the closest living relatives of humans. In terms of genetics we differ very little, just 1.3%, from both species, which are even more similar between them, but while it is said that chimpanzees reflect our aggressive and dominant side, bonobos are known for being peaceful, playful and sexually very active. However, a new study recently published in the journal ‘Current Biology’ suggests that, in reality, bonobos are far from deserving of their ‘peace and love’ reputation.

According to researchers at Boston University, within their own communities, male bonobos show aggression more often than chimpanzees. Contrary to what might be expected, for both species, the more aggressive males had more mating opportunities.

“Chimpanzees and bonobos use aggression in different ways for specific reasons,” says anthropologist and lead author Maud Mouginot. «The idea is not to invalidate the image that bonobos are peaceful; “The idea is that there is much more complexity in both species.”

Although previous studies have investigated aggression in bonobos and chimpanzees, this is the first study to directly compare the behavior of both species using the same field methods. The researchers focused on male aggression, which is often linked to reproduction, but they note that females are not passive either.

Pushing and biting

The team examined rates of male aggression in three communities of bonobos in the Kokolopori Bonobo Reserve (Democratic Republic of the Congo) and two communities of chimpanzees in Gombe National Park (Tanzania). Overall, they examined the behavior of 12 bonobos and 14 chimpanzees by conducting “focal tracking,” which involved tracking an individual’s behavior over an entire day and taking note of how often they engaged in aggressive interactions, who they were with, and how often they engaged in aggressive interactions. these interactions and whether they were physical or not (for example, whether the aggressor pushed and bit or simply chased his adversary).

“You go to their nests and wait for them to wake up and then you follow them throughout the day (from the moment they wake up to the moment they go to sleep at night) and record everything they do,” Mouginot says. .

To their surprise, the researchers found that male bonobos were more frequently aggressive than chimpanzees. Overall, bonobos engaged in 2.8 times more aggressive interactions and 3 times more physical aggression.

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 male “coalitions” (13.2% vs. 1% of bonobo aggression). The researchers believe that these coalitions could be one of the reasons why aggression is less frequent among chimpanzees. Alterations involving groups of males have the potential to cause more injuries, and fights within the community could also weaken the group’s ability to fight other groups of chimpanzees. Bonobos don’t have this problem because most of their disputes are one-on-one, they have never been observed killing each other, and they are not believed to be territorial, leaving their communities free to argue with each other.

Success with females

For both chimpanzees and bonobos, more aggressive males had greater mating success. The researchers were surprised to find this in bonobos, which have a co-dominant social dynamic in which females often outnumber males, compared to chimpanzees, which have male-dominated hierarchies in which coalitions of males force females to mate.

“Male bonobos that are more aggressive obtain more copulations with females, something we wouldn’t expect,” says Mouginot. “It means that females are not necessarily looking for nicer men,” he stresses.

These findings partially contradict a predominant hypothesis in anthropological and primate behavior (the self-domestication hypothesis), which posits that aggression has been selected against in bonobos and humans, but not in chimpanzees.