Evolution and Homosexuality
Wed, April 21, 2021

Evolution and Homosexuality

Now, researchers provide two new hypotheses for the evolution of homosexual behavior; one explaining how these behaviors can be advantageous from a natural selection perspective and the other arguing that homosexuality evolved for social reasons rather than reproductive ability / Photo by: lightfieldstudios via 123RF


Under evolution, traits are passed onto children who will then acquire a form of competitive advantage from those traits. Following this logic, it could be argued that homosexuality shouldn't have evolved considering gay sex doesn't produce offspring.

However, same-sex attraction and sexual behavior did evolve and persisted even after millions of years of evolution—both in animals and humans. Evolutionary biologists struggled to explain the so-called Darwin Paradox or why such behaviors are common even when they result in no opportunity for a species to reproduce.

Now, researchers provide two new hypotheses for the evolution of homosexual behavior; one explaining how these behaviors can be advantageous from a natural selection perspective and the other arguing that homosexuality evolved for social reasons rather than reproductive ability.

Part of an Ancestral Condition

There is well-documented evidence that shows over 1,500 species engaging in homosexual behavior. But even with this large body of evidence, it still fails to answer the paradox bugging scientists' minds.

In the journal Nature Ecology & Evolution, researchers from the Yale School of Forestry & Environmental Studies argued that same-sex behaviors were part of animals' ancestral condition and persisted because of some possible benefits.

Instead of looking into the issue as a problem needing a solution, they suggest reframing the question from "why animals practice homosexual behaviors?" to "why not?"

"By shifting the lens through which we study animal sexual behavior, we can more fruitfully examine the evolutionary history of diverse sexual strategies," the researchers wrote, as per British newspaper The Independent.

The researchers further argued that a combination of same-sex sexual behaviors (SSBs) and different-sex sexual behaviors (DSBs) form an original condition for all sexually producing animals and likely evolved in the earliest forms of sexual behavior.

Contrary to the assumption of homosexual behaviors having high costs—individuals spending time and energy on activities that don't offer the potential for reproductive success—these behaviors may provide advantages based on the perspective of natural selection (considering individuals are more likely to mate with more partners), The Independent reports.

Many species try to mate with more than one of its kind, and it can be difficult for these species to recognize the difference between different sexes.

"So, if you’re too picky in targeting what you think is the opposite sex, you just mate with fewer individuals. On the other hand, if you’re less picky and engage in both SSB and DSB, you can mate with more individuals in general, including individuals of different sex," explained co-author Max Lambert.

The Sociosexual Hypothesis

While Lambert and his colleagues focused on explaining homosexuality among animals, Andrew Barron of Macquarie University and Brian Hare of Duke University provided an explanation for the evolution of homosexuality among humans.

Barron and Hare argued that natural selection's leaning towards traits that allowed better social integration (prosociality) became the driver for humans' recent cognitive and behavioral evolution.

Early humans had a strong selective advantage for being able to easily access the benefits of living in a group, which led the researchers to believe that the evolution of traits increased their communication, understanding, social play, and affiliation.

"Species such as the bonobo, that evolved for high prosociality, evolved to use sexual behavior in many social contexts. This results in an increase of sex in general, greater diversity in the contexts of sex, and an increase in gay sex," Barron wrote in The Conversation.

"We believe something similar happened in recent human evolution. Gay sex and attraction may have evolved because individuals with a degree of same-sex attraction benefited from greater social mobility, integration and stronger same-sex social bonds."

He added that their hypothesis predicts bisexuality and people who identify as "mostly straight" as more common than those who exclusively identify themselves as gay. Such is the case given recent genetic analyses confirming the complex ways of genes influencing sexuality.

The fact that each person's genetic makeup is unique makes it nearly impossible for two people to have the same set of genes that influence their sexuality—giving way for variation in which people fall along a wide spectrum from a straight majority to a gay minority.

"Our hypothesis for the evolution of homosexuality would predict this kind of variation in human sexuality and can help explain why it is generally stable across cultures. We believe sexuality is a highly complex trait, interwoven with sociality. Attraction, sexual behavior, social bonds and desire all contribute to its complexity," Barron concluded.

A Counterintuitive Circumstance

Barron and Hare noted that their argument merely addresses the early evolution of human sexuality and not how "relatively recent phenomena like religion and religion-based legal structures" reacted to sexual minorities.

Still, it doesn't diminish the fact that the supposed origin of homosexual behaviors sounds counterintuitive since gay people were socially marginalized, ostracised, and even criminalized—with some societies still putting people from this spectrum in such situations.

This social marginalization comes even as the number of people who identify themselves as part of the LGBTQ community continues to grow. However, persistent stigma and methodological barriers make it difficult to determine the exact number of people who identify as lesbian, gay, bisexual, transgender, or queer.

In Canada, about 3% identify themselves as either a lesbian, gay, or bisexual while the same is seen in 8.9% of Japan's population, 2% of the UK, and 4.5% of the US.  Other countries measure the LGBTQ population on the number of those in a same-sex relationship.

Estimates show 0.9% of all couples in Australia are LGBT, similar to that of Canada, while 0.5% of all German couples are in a same-sex relationship. The US shows the highest percentage (1.5%) of the couple-households being of the same-sex, based on data from global nonprofit company Catalyst.

Moreover, Lambert believes that the assumption that SSB is costly stopped humans from actively studying the frequency and circumstances in which SSB is happening.

"Given our casual observations suggest that SSB seems to happen pretty commonly across thousands of species, imagine what we would have learned if we had assumed this was something interesting and not just a rampant accident."