Homosexual and bisexual activity between animals has been well documented, with more than 1,500 species recorded in engaging in same-sex sexual behaviour. But despite the large body of evidence, evolutionary biologists have struggled to explain what has become known as the “Darwin Paradox” – why are these behaviours so common when they result in no opportunity for species to reproduce.

And why, when animals have evolved over millennia, has same-sex sexual behaviour repeatedly evolved and persisted?

Researchers from the Yale School of Forestry & Environmental Studies suggest instead of examining the issue as a conundrum in need of a solution, the question ought to be reframed from “why do animals engage in same sex behaviour” to “why not?”

Writing in the journal Nature Ecology & Evolution, the authors suggest that these behaviours may actually have been part of the original, ancestral condition in animals and have persisted because they have few — if any — costs and perhaps some important benefits.

“We argue that the frequently implicit assumption of [different-sex sexual behaviour] as ancestral has not been rigorously examined, and instead hypothesise 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.”

Lead author and F&ES doctoral candidate Julia Monk said: “We propose a shift in our thinking on the sexual behaviours of animals. Read more via Independent