Chimpanzees and bonobos demonstrate why sex is not just for reproduction

Bonobos and chimpanzees are our closest relatives. And, therefore, their behavior is often viewed as reminiscent of ancestral human nature. Both species are very similar. However, in the effort to discover more about ourselves, bonobos are often attributed with our more benevolent and cooperative inclinations, while chimpanzees are defined by our more violent and competitive ones. As if they — unlike us, who can be Jain monks, or industrial-scale genocidaires — are just one thing.

One of the most popular traits of bonobo societies is their tendency to resolve conflicts with sex. Chimpanzees — more inclined to settle disagreements with their fists — also use this resource. Now, a group of scientists led by researchers from Durham University, in the UK, have compared how the two species use sex beyond the reproductive function. This has been done, in part, to explain the origins of a practice that also occurs among humans.

The scientists, who published their findings in the journal Royal Society Open Science, observed the behavior of bonobos at the Lola ya Bonobo sanctuary in the Democratic Republic of the Congo, while observing chimpanzees at the Chimfunshi sanctuary in Zambia. They found that both species use sex to relieve tensions caused by confrontations or disagreements, or quarrels that occur before meals. Bonobos — true to their reputation — did so more frequently. Chimpanzees — among whom conflicts are more dangerous — have a broader repertoire of gestures and clearer signals for calming down and restoring social bonds. After a confrontation, chimpanzees commonly kiss the other’s body or place their fingers in their mouths. Showing vulnerability to a rival in a dangerous situation fosters trust and tests social bonds.

There were also differences observed in the use of sex as a tension-reliever between species, by gender and depending on age. Homosexual contact was observed in both bonobos and chimpanzees. Genital rubbing is known as a practice that improves social bonds and cooperation among females, but it has also been observed among males, who sometimes mount each other, with the more dominant male positioning himself on top. Genital rubbing, or rear-to-rear contact, was also observed among chimpanzees during moments of social tension. However, differences were also noted in this regard, with less genital contact between male chimpanzees than an opposite-sex pair.

Scientists also wonder whether these types of practices are transmitted from older to younger chimpanzees. This is because, as observed by the researchers, while bonobos and immature chimpanzees engaged in touching or rubbing after conflicts, in the moments before feeding, it was the older apes who initiated the sexual approach. And, when it came to sex, females tended to make the first move among bonobos, while males tended to make the first move among chimpanzees. It was also observed that, although interactions involving genital contact between relatives did occur, they were more frequent when there was no kinship.

“In contrast to the assumption that bonobos are pacifist and sex-crazed, while chimpanzees are aggressive, we found that both species use sex in similar ways [during stressful situations], including [via] same-sex pairings,” says Zanna Clay, a researcher at Durham University and lead author of the study. “This study highlights that, beyond reproduction, sex plays an important role in their societies… and probably also did for our ancestors,” she adds.

The study authors point out that — even when referring to our closest relatives — it’s crucial to analyze the variation in the expression of sexual behavior within groups. This is because primates can also have different responses and different contexts when faced with stressful situations.

Among humans, studies have found more than 200 reasons for why people have sex. The most common — at least, of the reported ones — are those related to physical attraction, love, affection, or pure curiosity. But there are also cases in which sex serves to achieve social status, or even to exact revenge, or simply to survive. Among humans, sexual differences have also been found, with men demonstrating a greater tendency to have sex for physical reasons, while women utilize it to express love or feel loved. As is the case among chimpanzees and bonobos, these are mere tendencies: not everyone has sex all the time for the same reasons.

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