A Wealth of Evidence

So, how prevalent are same-sex sexual behaviors—scientists’ term for this phenomenon—among animals? Research indicates that over 1,500 species engage in such behaviors. A recent study revealed that both male and female animals participate in same-sex activities at nearly equal rates. Eliot Schrefer, in his acclaimed book "Queer Ducks (and Other Animals)," emphasizes that these behaviors are not rare occurrences, stating:

"An explosion of research over the past 20 years has shown significant amounts of same-sex sexual behavior throughout the animal kingdom."

From penguins to sea urchins, the evidence is abundant, but it is particularly notable among non-human primates, with 51 identified species including everything from small lemurs to large apes.

Dolphins are another fascinating example, exhibiting a high frequency of sexual interactions that rarely lead to reproduction. Behavioral ecologist Janet Mann, who studies dolphins in Shark Bay, Australia, has noted:

"The amount of homosexual behavior [in dolphins] is so high. In fact, we see very few heterosexual matings altogether."

We know that there is considerable diversity in heterosexual behavior among humans and animals alike, including monogamy, promiscuity, and polyamory. The same holds true for homosexual behavior, which encompasses more than just intercourse. For instance, female bonobos engage in genital rubbing, believed to foster sharing and reduce stress. Additionally, male bats of the Bonin flying fox species often cuddle in same-sex groups during mating season. In Hawaii, female Laysan albatrosses engage in sexual mounting, share nests, and co-parent offspring.

The diversity of same-sex sexual behavior across species is vast, and it has only been in recent decades that researchers have begun to explore this topic in depth, with over a thousand species documented so far.

While I’m excited about the progress being made, I find it curious that it has taken so long to uncover this information. The field of animal sciences has a long history, predating Darwin, making the delay in awareness perplexing.

Human Bias and Research Delays

Unfortunately, human bias and prejudice have obscured the understanding of same-sex sexual behaviors in animals. A century ago, naturalist Edmund Selous expressed dismay at the behavior of male ruffs in the Netherlands, labeling it as "perverted sexuality." Fast forward to 1986, and we find a butterfly scientist, W.J. Tennent, who disparaged the same-sex behavior of Mazarine blues butterflies, likening it to "horrific sexual offenses" committed by humans.

Fortunately, attitudes toward homosexuality have evolved over the years. The increasing diversity within the United States and its academic institutions has led to more LGBTQ+ researchers in the field, reducing the stigma associated with studying animal homosexuality.

Despite the prevailing notion that reproduction is the sole purpose of sexuality, researchers are intrigued by the evolutionary significance of same-sex sexual behaviors. While definitive answers remain elusive, investigations are actively ongoing.

What Could Be the Reasons?

From an evolutionary perspective, the prevalence of homosexual behavior in animals poses a fascinating question. If heterosexual interactions are primarily for reproduction, what is the purpose of same-sex relations? Moreover, why haven't genes associated with homosexuality faded through natural selection?

Researchers propose various explanations. Firstly, many animals exhibiting same-sex behaviors also engage in heterosexual interactions, leading to offspring. Thus, they may be better described as bisexual rather than exclusively homosexual, which helps explain the persistence of these behaviors in the gene pool.

Secondly, observations suggest that social factors often drive same-sex sexual behaviors in animals. For example, in her studies of dolphins, Mann identified potential reasons such as establishing dominance and enabling young dolphins to practice mating. More often than not, these behaviors appear to serve as a means of fostering relationships and social bonds.

In some cases, same-sex behaviors may even relate indirectly to reproduction. A June 2023 study on male macaques found that such interactions helped establish dominance, alleviate tension after aggression, and provided solutions when opposite-sex partners were scarce.

Repeated Evolutionary Origins?

The aforementioned examples represent only a fraction of the species exhibiting same-sex sexual behaviors. A recent study published in October 2023 in Nature Communications focused on 51 mammal species. Researchers created a database tracking the evolution of same-sex behaviors across these species.

Their findings revealed that male and female mammals display same-sex behaviors equally, but in species where adult males may kill one another, these behaviors are more likely to evolve in males. The researchers suggest that in such cases, these behaviors might help mitigate violence.

They concluded that homosexual behaviors likely have multiple independent origins rather than evolving once and subsequently spreading. José Gómez, an evolutionary biologist and co-author of the study, stated:

"It may contribute to establishing and maintaining positive social relationships. With the current data available, it seems that it has evolved multiple times."

Gómez's conclusions align with the understanding that same-sex sexual behaviors are widespread among mammals, suggesting the trait does not have a singular origin.

An Alternative Perspective

An intriguing concept emerged from an article by the National Wildlife Federation (NWF), discussing research by Julia Monk, an ecologist at UC Berkeley. During her Ph.D. studies at Yale, Monk encountered literature on same-sex animal couplings and noted that past researchers viewed these behaviors as unusual and requiring an explanation. She argued that if such behaviors were widespread, they should not be considered anomalies.

Monk proposed that perhaps the ancestral state for animals was not strictly heterosexual. In her view, early in the evolutionary timeline, animals might have simply engaged in sexual activity without consideration of sex. The differentiation between male and female requires advanced recognition and physical differences, which took time to evolve.

In collaboration with a group of early-career scientists, most of whom identify as queer, Monk published a paper in 2019 proposing an "ancestral condition of indiscriminate sexual behaviors directed towards all sexes." They posited that animals would narrow their sexual targets only after distinct physical differences evolved between sexes.

Max Lambert, a biologist involved in the study, offered a straightforward perspective:

"Things exist, and they don't go away in evolutionary time scales unless they're really, really harmful. They can just persist because they just do."

This implies that since same-sex interactions are not harmful, there is no evolutionary pressure to eliminate them. In fact, they may even provide social benefits.

Human Similarities

While humans share many similarities with the animal kingdom, there are important caveats. Although researchers have documented same-sex behaviors in over 1,500 species, this represents just a small fraction of known species. Our understanding of this topic will continue to evolve as more studies emerge.

Moreover, many researchers caution against using these findings to explain human sexual orientation. Most animals exhibiting same-sex behaviors do so as part of short-term courtship or mating rather than as a long-term sexual preference.

However, it’s worth noting that humans are not the only animals to form long-term same-sex relationships. Male zebra finches, prevalent in Australia, are known for forming lifelong socially monogamous bonds. These finches perform courtship dances for each other and remain together even when females become available.

A Shift in Perspective

While we may not yet fully understand the reasons behind the prevalence of same-sex behaviors in the animal kingdom, it is clear that they exist without any inherent danger. This raises an important point: sex should not be solely viewed through the lens of reproduction.

Research into same-sex sexual behaviors suggests that these interactions are fundamentally about forming connections and relationships. It appears that sexuality encompasses multiple evolutionary purposes, and it's humans who often reduce sexual acts to narrow definitions focused solely on male-female reproduction.

Sexuality, like many aspects of existence, is a spectrum. Ultimately, it is about the desire to connect with others.

This article was initially published in the author's newsletter, Curious Adventure, and later edited and republished on Medium with her permission. Thank you for reading; your support is appreciated.

This video explores the prevalence of homosexuality in wildlife, examining various species and their behaviors in detail.

A comprehensive overview of homosexual behaviors in the animal kingdom, highlighting significant findings and research breakthroughs.