It is often said that humans’ two closest primate relatives represent opposite aspects of our nature: peaceful bonobos and violent chimpanzees. But a new study published Friday Current Biology, He says it’s not that simple. In fact, male bonobos fight with each other more often than male chimpanzees, and bonobos, the “bad guys” who are killed more often, also have greater mating success.

Lead author Maude Mugino, from Boston University, told AFP that she decided to study aggression among bonobos after previous studies identified “reproductive skew” among males, meaning some produce much more offspring than others.

“So the real question was, if bonobos are so non-aggressive, how can they have such a high reproductive skew?” said.

After bonobos were recognized as a different species from chimpanzees, bonobos began to be romanticized for their freedom-loving nature. Part of their “hippie” reputation stems from their use of sex as a means of conflict resolution and the fact that they frequently had same-sex couples, especially among women. They also share food more often than chimpanzees.

Researchers have previously tried to compare aggression between two species that share 99.6% of their DNA, but these studies were limited because different methods were used in the field. Mugino and his colleagues focused on three communities in the Kokolopori Bonobo Sanctuary in the Democratic Republic of the Congo and two chimpanzee communities in Gombe National Park in Tanzania.

By monitoring the individual behavior of 12 male bonobos and 14 male chimpanzees for two years, the team was able to collect data on such things as how often each engaged in aggressive interactions, who was involved in those encounters, and whether physical contact occurred. such as biting, pushing, or simply attacking the opponent.

Surprisingly, the researchers found that male bonobos display higher levels of aggression than chimpanzees. Specifically, bonobos engaged in 2.8 times more aggressive encounters and three times more physical fights than their chimpanzee counterparts.

“I think this is a great find for the paper,” Mugino said. “And one more thing: We found that more aggressive male bonobos mated more frequently with what we call ‘maximally swollen’ females, that is, females whose genitals are swollen due to ovulation.

Spending more time with women?

While male bonobos hid their aggression almost entirely from other males, male chimpanzees were more likely to be aggressive towards females. Both of these results met expectations. Female bonobos are often the leaders of their groups and form alliances to stop lone males who try to force themselves sexually, so it doesn’t make sense for males to challenge them.

In contrast, chimpanzees are a highly male-dominated society, and it is the males who band together to punish hostile males who force females into sexual intercourse or challenge their authority. The fact that disputes between male bonobos are mostly one-on-one, rather than one-on-one, may explain why they occur more often because the risk is lower, Mougineau said. Bonobos have never killed each other.

Chimpanzee fights, on the other hand, involve multiple males and can be fatal in territorial battles within their own group or against rival groups. For this reason, the high costs of combating chimpanzees may limit the frequency of implementation of this struggle.

As for why “gentler” male bonobos perform worse with females, “it’s also possible that these aggressive males are spending more time with females and winning over rivals,” Mougineau said, but this needs further confirmation.

But Mouzhino, who now focuses his anthropological studies on humans, suspects that the “bad boy” trope in humans—the idea that rule-breaking men tend to attract more women—is directly reflected in bonobos. He emphasized that female bonobos have considerable strength and do not hesitate to suppress male aggression against them. But maybe they might find it attractive when directed at others.