Chimps and bonobos relieve social tension by rubbing their genitals

Some chimpanzees seem to use sexual behaviour like genital rubbing to manage stressful situations, which shows they aren’t as different from hypersexual bonobos – our other closest living ape relatives – or, indeed, people as we thought.

Jake Brooker at Durham University, UK, and his colleagues have investigated the sexual behaviour of non-human primates at the Lola ya Bonobo Sanctuary in the Democratic Republic of the Congo and the Chimfunshi Wildlife Orphanage Trust in Zambia. Both sanctuaries include a mix of wild and captive-born apes that can roam and forage freely within them.

The researchers observed 53 bonobos (Pan paniscus) across three groups at Lola ya Bonobo and 75 chimpanzees (Pan troglodytes) across two groups at Chimfunshi in the course of feeding events that involved a swing distributing a limited supply of peanuts over a particular area.

“Bonobos and chimpanzees both live in very complex social structures with very rich social interactions that they have to navigate on a daily basis,” says team member Zanna Clay, also at Durham University. Anticipating such feeding events can be stressful because of competition over who gets to the food first.

The researchers observed 107 instances of genital contact in the bonobos and 201 in the chimpanzees in the 5 minutes before 45 feeding events across the five groups.

“This is either putting a hand or foot onto another primate’s anogenital region and it also might involve the genitals touching each other, like the genital rubbing behaviour that bonobos are very famous for,” says Brooker.

The study also revealed differences between the species: “We found the frequency of sex in these situations was more common in female bonobos with other females, whereas it was more common among males in chimps,” says Clay. That may be linked to the fact that bonobos live in matriarchal groups, while chimpanzees live in patriarchal ones, she says.

“Using sex as a social tool to navigate all sorts of social problems has given bonobos a bit of a reputation as a sort of sexy, hippie ape,” says Clay. “This work shows us that the differences between the two species are maybe not as big as was previously assumed. Chimpanzees, although they’re known to be aggressive and violent, actually have a really rich repertoire of behaviours that they use to manage their social lives.”

“Chimps have definitely drawn the PR short straw by comparison to bonobos,” says Matilda Brindle at the University of Oxford.

The chimps use sex in a way that goes beyond reproduction and although it is different from sexuality in humans, we also don’t just have sex for reproduction, says Clay. For instance, stress reduction has been given as a reason people have sex.

Kit Opie at the University of Bristol, UK, wonders whether the same level of behaviour would be seen in wild settings rather than sanctuaries.

The work may also shed light on our last common ancestor, which lived some 5 million to 7 million years ago, before humans diverged from chimps and bonobos, he says.

“Given that all three species use sexual behaviours to navigate social relationships, the common ancestor we share likely did too,” says Brindle.