Monday, July 15, 2019

Homosexuality Among Animals

Animals have been observed engaging in same-sex matings for decades. 

But for most of that time, the documented cases were largely seen as anomalies or curiosities. 

The turning point was Bruce Bagemihl's 1999 book Biological Exuberance, which outlined so many examples, from so many different species, that the topic moved to center stage. Since then, scientists have studied these behaviors systematically. 

On the face of it, homosexual behavior by animals looks like a really bad idea. 

Darwin's theory of evolution by natural selection implies that genes have to get themselves passed on to the next generation, or they will 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. 

But that evidently isn't what's happening. For some animals, homosexual behaviour isn't an occasional event – which we might put down to simple mistakes – but a regular thing. 

That was the findings of Paul Vasey of the University of Lethbridge in Alberta, Canada, who studied Japanese macaques (Scientific name: Macaca fuscata) for over 20 years. When Vasey first observed the females mounting each other, he was "blown away" by how often they did it. In a 2006 study, he had proposed that the females were simply seeking sexual pleasure. 

But for all the homosexual pairings the females indulge in, Vasey is clear that they are not truly homosexual. A female may engage in female-female mounting, but that doesn't mean she isn't interested in males. Females often mount males, apparently to encourage them to mate more. Once they had evolved this behavior, it was easy for them to apply it to other females as well. 

The bonobo (Scientific name: Pan paniscus), also historically called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee is very much into engaging in homosexual behavior among both males and females. 

Like the macaques, they seem to enjoy it, according to Frans de Waal of Emory University in Atlanta, Georgia, US. Writing in Scientific American in 1995, he described pairs of female bonobos rubbing their genitals together, and "emitting grins and squeals that probably reflect orgasmic experiences". 

But bonobo sex also plays a deeper role: it cements social bonds. Junior bonobos may use sex to bond with more dominant group members, allowing them to climb the social ladder. Males that have had 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. Even the young comfort each other with hugs and sex. 

In some cases, there is a fairly straightforward evolutionary reason why animals engage in homosexual behavior. 

Consider the fruit fly (Scientific name: Drosophila melanogaster). In their first 30 minutes of life, the males will try to copulate with any other fly, male or female. After a while, they learn to recognize the smell of virgin females, and focus on them. 

Male red flour beetles (Scientific name: Tribolium castaneum) use a distinctly sneaky trick. They often mount each other, and go so far as depositing sperm. If the male carrying this sperm mates with a female later, the sperm might get transferred – so the male which produced it has fertilized a female without having to court her. 

In both cases, the males are using homosexual behavior as a roundabout way to fertilize more females. So, it's clear how these behaviors could be favored by evolution. But it's also clear that fruit flies and flour beetles are a long way from strictly homosexual. 

As humans use sex to gain all sorts of advantages, so can animals. 

For instance, among bottlenose dolphins (Family: Delphinidae; Genus: Tursiops), both females and males display homosexual behavior. This helps members of the group form strong social bonds. But, in the end, all concerned will go on to have offspring with the opposite sex. 

All these species might be best described as "bisexual". 

Like the Japanese macaques and the fruit flies, they switch easily between same-sex and opposite-sex behaviors. They don't show a consistent sexual orientation. 

Homosexual behaviors are not as queer as we think they are.

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