Same-Sex Behavior Common Among Animals—And Humans Are No Exception

Same-sex sexual behavior has been documented in over 1,500 animal species. It occurs across virtually all major groups—from insects and worms to reptiles, birds, and mammals.

Bonobos use SSSB to reconcile after conflicts, and dolphins form alliances through such behaviors.

While it’s not the norm, it’s also not particularly rare. Around 4% of all mammalian species exhibit this behavior, and that’s likely a conservative estimate. It often goes unnoticed or is hard to confirm in the wild, Mihai Andrei reported for ZME Science.

Interestingly, this behavior appears in both wild and semi-wild populations and shows up in both male and female mammals at nearly equal rates.

Things get even more interesting when we look at our closest animal relatives.

“Same-sex sexual behavior (SSSB) is particularly prevalent in nonhuman primates, where it has been observed in at least 51 species—from lemurs to apes,” write the authors of a recent study on homosexuality in animals.

The behavior seems to be common in species that are more intelligent and social. For instance, bonobos use SSSB to reconcile after conflicts, and dolphins form alliances through such behaviors.

Same-sex sexual behavior is also common in humans. Historical and anthropological evidence suggests it likely existed throughout human history and across a wide range of societies and cultures.

Why would this type of behavior evolve in nature? Researchers from the University of Granada in Spain found some interesting clues. To get answers, a team of researchers led by José M. Gómez turned to evolutionary biology.

Using phylogenetic tools—methods that reconstruct the evolutionary relationships between species—they traced the origins of same-sex behavior across mammals.

They found that this trait likely evolved multiple times independently, rather than being inherited from a single common ancestor. In other words, it’s a classic case of convergent evolution, where unrelated species develop similar traits under similar selective pressures.

The study, The Evolution of Same-Sex Sexual Behavior in Mammals, was published in Nature Communications.