Scientists have suggested that bisexual mating habits were the “original condition” for all animals that have sex, and that gay sexual behaviours in animals are here to stay.

Same-sex behaviour is seen in more than 1,500 animal species, a fact that has always confused scientists because it appears not to have any evolutionary benefits.

But an article from the Yale School of Forestry and Environmental Studies suggests that approaches to animal sexuality have historically been too “traditional”.

The general idea is that more sex is always a good thing. If animals mate with other animals of the same and opposite sexes they can display mating potential and will be more likely to reproduce.

In this way, being bisexual is not disadvantageous for the species and is unlikely to be lost through natural selection.

Co-author of the study Max Lambert said: “So far, most biologists have considered same-sex behaviour as extremely costly and, consequently, something that is aberrant.

“This strong assumption has stopped us as a community from actively studying how often and under what conditions same-sex behaviour is happening.

“Given our casual observations suggest that same-sex behaviour 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.”

“We’re excited to see how relaxing traditional constraints on evolutionary theory of these behaviours will allow for a more complete understanding of the complexity of animal sexual behaviours.”

Monk added that one of the reasons it has taken scientists so long to consider the benefits of same-sex behaviour in animals is judgement and discrimination against gay people in the human world.