Are Animals Gay?

What do dragonflies, bottlenose dolphins, and mallard ducks have in common? How about sea stars, bats, and pigeons? They’re all gay! Well, not exactly. Not only would that be an oversimplification, but it would also anthropomorphize animals, an act that is best avoided in animal behavior science. These six animals are among the over 1,500 different species that display same-sex sexual behavior. Same-sex sexual behavior (SSB) is any behavior typically performed at a stage of reproduction with a member of the opposite sex that is instead being aimed toward a member of the same sex. These behaviors have a wide range, including courting rituals, raising young, and mounting.

It’s clear that our history of homophobia led to a scarcity of research on this topic until the second half of the 20th century. For a while, the little that was published on SSB was laden with bias. Take, for instance, the British entomologist W. J. Tennent’s observations on same-sex mating in butterflies. His study, titled “A Note on the Apparent Lowering of Moral Standards in the Lepidoptera,” was published in 1987. Even though signs of SSB in animals are everywhere, they were kept out of the scientific spotlight.

Public awareness of “queerness” in the animal kingdom began with Roy and Silo, two male chinstrap penguins born in the Central Park Zoo in the same year that Tennent published his study. In 1998, zoo staff noticed that they were participating in mating rituals such as intertwining their necks. They were found trying to incubate a rock and were later given an abandoned egg to hatch and raise. This female chick, named Tango, later mated with a female penguin. This story garnered international attention and was adopted into the children’s book “And Tango Makes Three,” which stirred up controversy. According to the American Library Association, the book was the sixth most challenged (challenges being requests to ban the book) from 2010 to 2019.

Studies on SSB in the early 2000s expanded and explored some of the reasons behind its abundance. One study was conducted in 2008 on a group of Laysan albatrosses in Oahu. Same-sex pairings in this colony were first noticed because several nests had two eggs, even though females can only lay one egg per year. Because male and female Laysan albatrosses are nearly indistinguishable, genetic testing was used to reveal that the two birds in those nests were female. This study found that 31 percent of pairs were female-female. Evidently, some female albatrosses copulated with males who likely already had mates so they could have a fertile egg to raise with their same-sex partners.

While about half of the female-female nests started with two eggs, albatrosses can only incubate one egg at a time. In all of these same-sex pairs with two eggs, one of the eggs was either buried in the nest or rolled out. However, in nearly all female-female pairs that mated for multiple years (and thus had multiple chicks), at least one offspring was related to each bird, meaning that both females had the chance to successfully reproduce. The study suggested that female-female pairing was an advantage given the community’s uneven gender distribution with 59 percent of the birds being female.

While skewed gender ratios is a reason for why same-sex pairing is so common in albatrosses, this cannot explain the prevalence of SSB in the animal kingdom as a whole. Under the traditional Darwinian mindset, SSB should not exist because, unlike intercourse between two members of different sexes, it does not directly lead to reproduction. For this reason, SSB has been viewed as an “evolutionary paradox.” The likely reason for how SSB arose is that early animal species did not have many sex-specific traits such as size, color, or body shape. In fact, it can be evolutionarily costly to develop these traits and the ability to recognize them. Without distinguishing traits, animals may have mated indiscriminately with regards to the sex of their partners. Essentially, “gay” sex evolved coincidentally with “straight” sex. Even after sex-specific traits developed, SSB was likely not costly enough for it to lead to decreased fitness, so it persisted.

In many cases, SSB benefits social animals by establishing bonds between members of the same sex. Male chimpanzees have sex after fights in order to reconcile. In bottlenose dolphins, roughly half of all sexual interactions for males are with members of the same sex, a practice thought to establish trust and, in some cases, dominance.

Besides, it is well established that animals experience arousal and sexual pleasure. Sexual activity of any kind can make animals feel good or even reduce cortisol, a stress hormone. Bonobos, well known for frequent same-sex mating, will engage in more non-reproductive sexual contact during stressful events such as encounters with other groups of bonobos that are unfamiliar to them.

In addition to incorrectly implying that SSB does not have benefits, classifying SSB as an evolutionary paradox assumes that animals that solely partake in different-sex sexual behavior (DSB) will have more progeny than animals that perform SSB. However, DSB frequently does not result in reproduction anyway, with animals mating numerous times to have just a few offspring. In other words, DSB is not necessarily efficient at creating babies, so the supposed benefits of DSB compared to SSB are not as clear as one would expect. Furthermore, animals that participate in SSB will often also participate in some amount of DSB, with means that many animals that seek out members of the same sex still have offspring.

Lack of open-mindedness toward the diversity of sexual identity in humans has undoubtedly led to similar bias in the study of SSB in animals. The default assumption that SSB is an evolutionary paradox exemplifies this because it promotes the inaccurate concept that it somehow goes “against nature” and is detrimental to the survival of a species. Even with advances in recent decades, our knowledge of SSB is far from comprehensive, and studies are still ongoing. Animal behavioral and evolutionary science has a lot of catching up to do when it comes to same-sex sexual activity, and it remains unclear what, if anything, this science can tell us about the complexities of sexuality in humans.