Gay penguins and bisexual bonobos: sexual diversity in the animal kingdom

Carol O’Brien discusses how homosexuality fits in the theory of evolution and observed sexually diverse relationships between some animal species.

For a long time same-sex relationships were thought not to exist in nature outside of humans. This is a powerful thought that still exists in the minds of many recent referendum ‘no voters’, but one that is in fact, not true. If we look to the animal world, it is filled with examples of colourful and diverse expressions of both gender identity and non-heterosexual relationships. It only takes a little exploration to see that human homosexuality is neither an aberration nor unnatural, as some would have us believe.

In light of Darwin’s theory of evolution, it can become difficult to explain homosexuality. In a Darwinian context, homosexual relations are considered maladaptive, because they do not result in reproduction, and natural selection favours those who can pass their genes to the next generation. Examples of homosexual interactions in animals have certainly not disappeared however, and much research now focuses on whether this behaviour in animals has other advantages. Such advantages can vary greatly across different species according to particular social and mating systems. For animals, non-reproductive sexual activity can play important roles in forming social bonds and influencing survival, and the importance of these aspects should not be overlooked.

Bruce Bagemihl, a former researcher at the University of British Columbia is a noted expert on the subject. His 1999 book, Biological Exuberance, has emerged as something of a landmark celebration of sexual diversity among animals. In it, he claims that over 1,500 species have exhibited homosexual or transgender behavior, and details almost 200 of them. He draws extensively on zoological research to give a comprehensive account of non-reproductive sexual behavior in animals, to show that we live in, as he eloquently put it, “a polysexual, polygendered world”.

Homosexual behaviour exhibited in the animal kingdom is diverse, ranging from short mating rituals and casual sex to to lifelong partnerships. Then there are many animals that seem happy to mate with members of both sexes, in a kind of happy-go-lucky, ‘try-enough-holes-and-I’ll-get-someone-pregnant’ approach. Fruit flies, flatworms, and deep-sea squid all engage in this type of indiscriminate mating. It’s important to bear in mind that when we observe a same-sex animal couple, it’s problematic to assume they will remain exclusively homosexual for life. We simply do not know if they will avoid all heterosexual encounters in the future. In this sense, we can talk of homosexual behaviour, but in most cases cannot really generalise this to talk of ‘gay’ or ‘straight’ animals.

Bonobos are one of our closest relatives in the primate world, and they are well known for their close-knit societies and frequent sexual exploits. Frans de Waal of Emory University, a primatologist and expert on bonobos has described how the vast majority of bonobos seem to be bisexual and enjoy frequent gay sex. In their matriarchal society, female bonobos assemble into groups of unrelated individuals. A newly arrived female with a low social status will often engage in genital rubbing, apparently until orgasm, with other females in an attempt to integrate into the group and move up the social order. The females frequent sexual behaviour may help to cement formation of an alliance. For male bonobos, so-called ‘penis-fencing’ after a fight is a way to diffuse tension. What observations of bonobos shows us is that they engage in sex for reasons not just associated with reproduction. In fact, bonobos seem to be a promiscuous and peaceful species, having sex for any reason at all.

Bottlenose dolphins are another species with a high rate of homosexual behaviour. Adolescent and young males usually live in all male groups. They form male-male pairings which they then keep for life. The two companions not only keep watch over each other and defend each other from attacks, but they also engage in sexual activity. Later at around 20 years old, they will engage in heterosexual encounters, but still keep their male partner close by. Female dolphins also engage in homosexual behaviour, again thought to strengthen social bonds.

One of the most famous gay animal couples was undoubtedly Roy and Silo, a pair of male chinstrap penguins at New York City’s Central Park Zoo. Together they raised a chick called Tango, and inspired a best selling children’s book. They have however, since split up, after being driven out of their nest by two more aggressive penguins. Silo then found love with a new female, while their daughter Tango also went on to pair up with a female. Clearly, there are many incidences of homosexual and bisexual behaviour in animals, yet much rarer is life-long monogamous bonding between two animals of the same-sex.

Laysan albatross are known for their lifelong coupling, and two parent cooperation to raise their chicks. A 2008 study in Biology Letters on female laysan albatross on the island of Oahu, Hawaii, showed that 31% of pairings were actually female-female. The authors do suggest however, that this may have occurred due to a shortage of males on the island, as a female pairing with another female to raise offspring is better than going it alone as a single mother.

Also quite rare, are animals that are exclusively homosexual for life. However, about 8% of domestic male sheep, rams, do appear to be just that. They show a sexual preference for males even when females are present. Additionally, some seem to be bisexual and others asexual. A group of researchers in Oregon led by Charles Roselli, are particularly interested in this field, and their research has focused on exploring hormonal and brain structure differences between gay and straight rams. They were able to identify a region in the sheep’s brains, a part of the hypothalamus, which was smaller in rams with a sexual preference for males than rams with a preference for females, which interestingly mimicked a 1991 study in humans. In 2007 their research hit the news, spawning excellent headlines such as “Brokeback Mutton” and “He’s just not that into ewe”.

Naturally, all animal behaviour we observe is filtered through our own anthropomorphic lens, and interpreted in light of our own social constructs and biases. Although we might draw inspiration from the love story of two penguins in captivity, it is not a particularly wise way of trying to understand the science of human sexuality. Nevertheless, it is clear now that animal same-sex sexual behaviour not only exists in both wild and captive animals, it is likely to have a biological basis, and can be important for non-reproductive means such as conflict resolution, social integration and advancement, expression of social dominance and even just plain and simple pleasure.