An alternative hypothesis for the evolution of same-sex sexual behavior in animals

An article in The Washington Post presents a new approach to same-sex relationships in animals (and humans, by implication). Researchers argue that heterosexuality is a pretty recent invention, as far as evolution is concerned.

When Procreation is a God

Traditionally homosexual or bisexual practices have been seen as deviations that need to be explained. The premise is that sex is for pro-creation, so same-sex sex makes no sense. Why does not evolution eradicate such behavior, given that it does not lead to offspring?

Ray Blanchard, the man behind the transphobic  autogynephilia theory is, for instance,  deeply anchored in this way of thinking. He has spent a lot of time trying to explain why homosexuals exists. Moreover, he presents both homosexuality and transgender conditions as mental illnesses, again because they – presumably – do not lead to procreation.

(Why “evolutionary psychologists” have decided to make procreation God and the ruler over right and wrong will have to be addressed at another time. It makes little sense to me.)

Same-sex behavior is the starting point

The report presented in the Washington Post takes a completely different approach. Polysexuality might just as well be the natural default, if I understand the researchers correctly. Same-sex behavior has always been there.


In evolutionary terms the development of procreation based on the interaction between two biological sexes is a pretty recent development. Moreover, many species have more than two sexes. In some all (or some) individuals are both male and female. And there are animals that change sex during a lifetime.

Keep in mind that as far as our closest relatives in the animal kingdom, the bonobos, are concerned, anyone can have sex with anyone, independently of biological sex or age.

And there is no reason to think that same-sex sex really reduces the procreation of a specific species. There is far too much sex going around for that to be much of a problem.

In a paper published in Nature the researchers explain:

We argue that the frequently implicit assumption of DSB [different-sex sexual behaviour] as ancestral has not been rigorously examined, and instead hypothesize an ancestral condition of indiscriminate sexual behaviours directed towards all sexes. By shifting the lens through which we study animal sexual behaviour, we can more fruitfully examine the evolutionary history of diverse sexual strategies.

Sex science has been influenced by cultural prejudices

The traditional two gender view of sex, sexuality and gender identity is clearly influenced by social and religious dogma. Up till now many researchers have been culturally programmed to think in the traditional way.

“The idea that same-sex sexual behavior had to be justified at all seemed like a perspective of dominant cultural norms rather than a more holistic view of the actual biology,” Julia Monk, a Ph.D. candidate at Yale and the study’s lead author argues.

“Sometimes there’s a really exclusive view of evolutionary fitness and we can have a more inclusive view,” Monk says. “Variation is the baseline, and that baseline persists to this day.”

These days biology presents a picture of nature as driven by diversity and experimentation, not as a straight journey towards evolutionary perfection.

The researchers have not looked into gender identity, and for obvious reasons: You cannot ask animals about how they experience gender. However, it does not take a leap of imagination to see that variation as regards sexual behavior might also imply that gender is an equally diverse phenomenon.

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An alternative hypothesis for the evolution of same-sex sexual behaviour in animals, by Julia D. Monk, Erin Giglio, Ambika Kamath, Max R. Lambert & Caitlin E. McDonough. Nature, Ecology and Evolution 2019.

More about “gay” animals.  See also my article on “transgender” animals.

Photo: damedeeso