The bonobo (Pan paniscus) is one of the great apes least known to humans. For decades they were confused with their closest relatives the chimpanzees due to their small populations, which survive mainly in the dense jungles of central Africa.
An international study led by experts from Boston University now indicates that, contrary to what was believed, bonobos are no more peaceful than common chimpanzees and do not always resolve their disputes with sexual acts; one of the characteristics - promiscuity - that has so far caught the attention of (human) researchers. In particular, male bonobos are as aggressive as their cousins, chimpanzees, when it comes to obtaining reproductive material, according to the results of this new study published in the journal Current Biology (April 12).
"Chimpanzees and bonobos use aggression in different ways for specific reasons," explains now the anthropologist and lead author of the study, Maud Mouginot, from Boston University. "The idea is not to invalidate the image that bonobos are peaceful; the idea is that there is much more complexity in both species," says the researcher.
Although previous studies have investigated aggression in bonobos and chimpanzees, this is the first study to directly compare the behavior of the species using the same field methods. The researchers focused on male aggression, which is often linked to reproduction, but note that female bonobos and chimpanzees are not passive, and their aggression warrants its own future research.
To compare the aggression of bonobos and chimpanzees, 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," details the Professor Mouginot in statements released by her university.
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 common 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.
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, which is something we wouldn't expect," Mouginot said. "It means that females don't necessarily seek out gentler males."
These findings partially contradict a predominant hypothesis in anthropological and primate behavior (the self-domestication hypothesis), which posits that aggression has been separated from reproduction in bonobos and humans, but not in chimpanzees.
The researchers were not able to assess the severity of the aggressive interactions in terms of whether they resulted in wounds or injuries, but this is data they hope to collect in the future. They also want to compare aggressive behavior in other groups of chimpanzees and bonobos, since it is possible that behavior varies between communities and subspecies.
"I would love to complement the study with comparable data from other field sites so that we can gain a broader understanding of the variation within and between species," says Maud Mouginot.
