A new study has suggested that male homosexuality is much more genetically determined than previously thought, and is directly related to the fecundity of female relatives.

New research, undertaken at the University of Padova, also seems to suggest that while female sexuality is more fluid, male homosexuality is a strongly genetic trait, and is therefore inborn and unalterable, Lifes Little Mysteries, a media organisation, reports through the Huffington Post.

Significantly, the study suggests that mothers and maternal aunts of gay men tend to have significantly more offspring than corresponding relatives of straight men, thus linking female fecundity to male homosexuality. In effect, this favours the so-called ‘balancing selection hypothesis,’ which attempts to explain why, in evolutionary terms, gay men have not been ‘selected out’ by evolution.

The preponderance of homosexuality in nature, now documented in hundreds of species around the world, has puzzled evolutionary biologists, as it does not square with the tendency of natural selection to favour those genes which aid in procreation. Current research adds weight to the hypothesis that those genes which promote reproductive ability in women also favour male homosexuality in some of their offspring, as a ‘trade-off’ for the reproductive success.

Although no so-called ‘gay genes’ have yet been identified, and sexuality at large is thought to be a multi-gene trait, at least one of those genes appears to be located on the X-chromosome, of which females have two and males have one. The lead author of the study, Andrea Camperio Ciani, has suggested that doubling of that gene might increase attractiveness to men.

“High fecundity, that means having more babies, is not about pleasure in sex, nor is it about promiscuity. The androphilic pattern that we found is about females who increase their reproductive value to attract the best males,” Ms Camperio Ciani told Life’s Little Mysteries.

This does not make the search for ‘gay genes’ any more fruitful however, as research suggests that pre-natal exposure to certain hormones also has a strong role in determining male (and possibly female) sexuality. That said, the research would put nature vs. nurture debate firmly on the first camp.

The study will be formally published in a forthcoming issue of the Journal of Sexual Medicine.