The Bonobo Handshake: Are there Homosexual Animals?

“On the face of it, homosexual behaviour by animals looks like a really bad idea”

- Bruce Bagemih

Until this topic came up in a recent conversation with an Anthropology student at Wits, I didn’t think that I was interested in the nature of Homosexuality - something to be considered with care in some settings, but never something that needed to be investigated. I had certainly learned the theories of sexual selection, of mating efficiency and Natural selection as a science student, and followed the assumption that the evolution of any species could not be furthered by homosexuality in any way.

As the rather reluctant conversation progressed, however, I realized how little I actually understood about homosexuality - a strange human propensity with probable roots in psychology, more so than biology, right? So I did as I had been programmed and scoured the web, textbooks and had a few more conversations. What I found was both embarrassing and enlightening; and here’s the thing, nature has somewhat of a gay flare. Homosexuality in the animal kingdom is common, purpose-driven and interestingly accepted with a record as long as Darwin’s Origin of species. From male killer whales that ride the dorsal fin of another male to female bonobos that rub their genitals together, the animal kingdom tolerates all kinds of sexuality.

Scientists acknowledge incompatible sexual behavior in over 1500 species and the phenomenon has been well described for 500 of them. The occurrence is so common that a first-ever museum display, "Against Nature?" was opened in 2006 at the University of Oslo's Natural History Museum in Norway, presenting 51 species of animals exhibiting homosexuality. In an interview with Livescience Linda Wolfe (head of the Department of Anthropology at East Carolina University) stated that homosexuality is well described for hundreds of species. “The idea, however, is rarely discussed in the scientific community and is often dismissed as unnatural because it doesn't appear to benefit the larger cause of species continuation. I think to some extent people don't think it's important because we went through a time period in sociobiology where everything had to be tied to reproduction and reproductive success."

In the last 10 to 15 years, scientific evidence has started to accumulate indicating that animals do experience a general sensation of pleasure. In 2001, for example, psychologists Jeffrey Burgdorf and Jaak Panskepp discovered that laboratory rats enjoyed being tickled, emitting a chirpy laugh outside the range of human hearing. Also, they would actively seek out the feeling by encouraging the researchers to repeat the motion. Regarding sex for pleasure, one doesn’t have to dig deep. Humans, along with various members of the animal kingdom, engage in sexual activities more than is necessary for reproduction.

Italian researchers Alfonso Troisi and Monica Carosi spent 238 hours observing Japanese macaques, and witnessed 240 individual copulations between males and females. In a third of those copulations, they observed (what they called) female orgasmic responses: "the female turns her head to look back at her partner, reaches back with one hand, and grasps the male". It is reasonable to infer that this behaviour is similar to ecstasy experienced by human females as macaque behaviour is occasionally accompanied by specific physiological changes seen in humans (such as increases in heart rate and vaginal spasms). Interestingly, the female macaques were more likely to experience a response when copulating with males who lived higher-up in their monkey dominance hierarchy, suggesting that there is a social, not just physiological, component to this and not merely reflexive responses to sexual stimulation.

Conversely, ethologist Jonathan Balcombe argues that homosexual sex could have a bigger natural cause than just pure ecstasy: namely evolutionary benefits. Copulation could be used for alliance and protection among animals of the same sex. In situations when a species is mostly bisexual, homosexual relationships allow an animal to join a pack. In bonobos for instance, strictly heterosexual individuals would not be able to make friends in the flock and thus never be able to breed. Males that have engaged in a fight sometimes perform genital-to-genital touching, known as "penis fencing", as a way of reducing tension. More rarely, they also kiss, perform fellatio and massage each other's genitals. It is worth mentioning that Bonobos are often described as our "over-sexed" relatives. They engage in an excessive amount of sex, so much so that it's often referred to as a "bonobo handshake", and this includes homosexual behaviour among both males and females.

There are hundreds of examples of non-reproductive sex among animals, from albatrosses to koalas. In some bird species, that bond for life, homosexual pairs raise young. For the Laysan albatross, which nests on the island of Oahu in Hawaii, 31% of pairings are made up of two unrelated females and have equivalent reproductive success. Similarly almost a quarter of black swan families are parented by homosexual couples. Males sometimes mate with a female just to acquire an egg. Once she lays the egg, they chase her off, hatch it, and raise the chick on their own.

Now new studies of gay sheep appear to confirm the controversial suggestion that there is a biological basis for sexual preference. The research reveals that rams who prefer male sexual partners had small but distinct physiological differences of the brain, when compared with rams that preferred to mate with ewes. Kay Larkin along with colleagues from Oregon Health and Science University found the differences were in a particular region of the hypothalamus – the preoptic nucleus. The region is generally almost twice as large in rams as in ewes, but for “gay” rams was found to be almost identical in size to that of “straight” females. The hypothalamus is known to control sex hormone release and many types of sexual behaviour. Several other parts of the hypothalamus showed consistent differences in size, but only this specific region showed differences that correlated with sexual preference. These differences are similar to those identified from highly controversial studies of the brains of gay men by the neuroscientist Simon LeVay in the early 90’s.

So, animals have been observed engaging in same-sex matings for decades, but viewed mostly as anomalies or curiosities. Bruce Bagemihl's 1999 book Biological Exuberance outlined so many examples from so many different species that it moved the topic to centre stage. Since then, scientists have studied the behaviour systematically and the rather anti-climactic truth about gay nature is that despite the giant roster of examples, homosexual behaviour still seems to be a rarity. We have probably missed some examples, as in many species males and females look pretty much alike. But while hundreds of species have been documented from isolated occasions, only a handful has made it a habitual part of their lives.

Darwin's theory of evolution by natural selection implies that genes have to be passed on to the next generation, or die out. Any genes that make an animal more likely to engage in same-sex matings would be less likely to get passed on than genes pushing for heterosexual pairings, so homosexuality ought to quickly die out? In some cases, however, there is a fairly straightforward evolutionary reason why animals engage in homosexual behaviour. Paul Vasey of the University of Lethbridge in Alberta, Canada holds firm that humans are the only documented case of "true" homosexuality in animals. "It is not the case that you have lesbian or gay bonobos," says Vasey. "What's been described is simply that various animals are happy to engage in sex with partners of either sex."

My opinion about all of this is that biologists should have predicted this. When Darwin was developing his theory of natural selection, one of the things that inspired him was the realisation that animals tend to have far more offspring than they seem to need. In theory a pair of animals need only have two offspring to replace themselves, but in practice they have as many as they possibly can – because so many of their young will die before they manage to reproduce.

It seems obvious that this built-in need to keep reproducing would manifest itself in a powerful sex drive, one that might well spill over into mating while females are infertile, or even to same-sex matings. Victorian scientists saw animals having more offspring than seemed necessary: today we see animals having more sex than seems necessary. "Homosexual behaviour doesn't challenge Darwin's ideas," says Marlene Zuk of the University of Minnesota in Saint Paul, US. “Instead there are many ways it can evolve and be beneficial

We may never find a wild animal that is strictly homosexual in the way some humans are, but we can expect to find many more animals that don't conform to traditional categories of sexual orientation. They use sex to satisfy all sorts of needs, from simple pleasure to social advancement, and that means being flexible. For the moment the mystery of sexual preference and its function is much like like staring at the outlines of an unfinished piece of artwork. We understand the bigger picture well, and that’s great, but without the intricacies of colours and tones (the gay flare if you will) we may never see it come to life.