“Gay sex is unnatural.”

It’s a phrase that has been echoing across current conservative and religious circles for centuries. Even Saint Thomas Aquinas writing in the 13th century deemed homosexual acts to be “contrary to the natural order.”
But gay sex is, actually, quite natural. As scientists investigate sexual behavior amongst animals, they’ve reported instances of same-sex sexual activity in more than 1500 animal species. Homosexual behavior is seen across all major groups of invertebrates and vertebrates, from nematodes to amphibians. For primates in particular, same-sex activities are observed in more than 51 species out of only a few hundred. It is, therefore, difficult to argue that these tendencies are in any way unnatural when they are so clearly prevalent.
So why are same-sex sexual behaviors so prevalent? How could evolution favor behavior that does not directly contribute to reproductive success, especially if it costs around the same amount of energy as opposite-sex sexual behavior? To some scientists, this represents a “Darwinian paradox,” meaning that it does not appear to offer evolutionary advantages.

What if it’s all just an accident? Maybe it’s just a case of mistaken identity where an animal attempts to mate without realizing its partner belongs to the same sex. Well, this likely isn’t the case, based on a study conducted on termites by researchers at the Bangalore Institute of Science. In their research, scientists focused on a species of termites that engage in lifelong monogamous pairings. Typically, a pair forms through what’s called a “tandem run,” where the male termite follows the female as it searches for a nesting site. These paired termites will groom each other and find food together, and if the pair gets separated during the tandem run, the female will pause while the male actively searches for her. The scientists discovered that not only did same-sex tandem run pairs occur, but the termites involved were actually intentionally choosing to do so. 

Since a male follows a female in a typical tandem run, same-sex tandem runs need a bit of flexibility. In this case, one of the termites will alter its behavior to resemble that of the opposite sex. For instance, in female-female pairings, one of the termites will adopt the behavior of a male, and follow the other. This is a display of “behavioral plasticity,” where the animals are making adaptive responses to changing social environments. Evolutionarily, this likely allowed termites to have a higher chance of survival, as when opposite-sex partners are not available, they still need to establish nests and groom each other for survival. Due to the highly coordinated process of tandem runs, same-sex pairs needed behavioral plasticity, maintained through their homosexual behavior, to ensure their runs are successful until a mate can be found or they reproduce differently. In female-female pairs, parthenogenesis (a form of asexual reproduction) allows them to reproduce without a male, and male-male pairs occasionally raid neighboring termite colonies together, looking for females to mate with. 

The study takes this a step further by exploring the evolutionary origins of termite behavioral plasticity through phylogenetic analysis, a method used to track down the origin and evolution of traits like behavioral plasticity. Researchers found that in early lineages of termites, behavioral roles were actually flexible—both males and females can lead or follow during tandem runs. As termites evolved, they underwent sexual dimorphism (where different sexes developed different characteristics) with female termites leading in most tandem runs. However, within some lineages, that ancestral flexibility remained—resulting in the behavioral plasticity seen in certain species of termites. What this phylogenetic analysis showed was that same-sex behavior, at least for termites, is not a random occurrence, but an adaptive strategy that is useful in responding to changes in the environment.

The species of termites that researchers studied at the Bangalore Institute of Science is only one of many animal species that display same-sex sexual behavior. For termites, such behavior may have explanations rooted in survival, but for other species, like bonobos, same-sex sexual behavior helps to maintain social bonds and reduces conflict. For dolphins and bison, homosexual behavior reinforces group hierarchies. Fundamentally, same-sex interactions provide benefits far beyond reproduction. When people claim that homosexuality is “unnatural,” they often assume that such behavior does not occur in nature. In reality, homosexuality is a vital part of behavioral biodiversity for many species.

Being gay is natural.