The evolutionary genetics of homosexuality (GWAS)

Tom Whipple, science editor at The Times, has this piece today.

Sexuality genes linked to sex appeal

The genes that make some people gay could also help straight people to have more sex, according to a study that may help to explain the evolutionary paradox of homosexuality.

Although there is no “gay gene”, scientists have long known that there is a strong genetic component to homosexuality. This leads to a conundrum: given that gay people have fewer children, the genes linked to homosexuality might be expected to be less likely to survive.

A leading theory of why this does not happen has now received its clearest validation. US scientists scoured the genomes of 400,000 people and compared their DNA to surveys about their sex lives. They identified a whole suite of genetic variants associated with people having had a same-sex partner.

They also looked at the sex lives of those who had those genes but who had never slept with someone of the same sex — and found an intriguing result.

According to the results, presented by an international team of researchers to the Human Behaviour and Evolution Society, straight people with the gay genetic variants had more sexual partners and were seen as more attractive. This fits with the “gay genes hypothesis”: that the genes that make some people gay persist in the population because they have reproductively beneficial effects in others.

It's been clear for a while (see lead author Brendan Zietsch's paper from 2008) that female relatives of gay men (such as their sisters) tended to have more children than the female relatives of men with fewer gay characteristics, and that heterosexual men with more alleles for feminised traits were also more reproductively successful. This has been called the Johnny Depp effect. The novelty here is the size of the sample, 400,000, and the use of genomic data.

Whipple did not give a reference and it took me a little while to track down the actual paper, from here.

HUMAN BEHAVIOR AND EVOLUTION SOCIETY
30th Annual Meeting
July 4th – July 7th, 2018

The evolutionary genetics of homosexuality

Brendan Zietsch, Andrea Ganna, Karin Verweij, Felix Day, Michel Nivard, Robert Maier, Robbee Wedow, Abdel Abdellaoui, Benjamin Neale, John Perry

Homosexual behaviour in humans is genetically influenced and is associated with having fewer offspring. This presents a Darwinian paradox: why have genes that predispose to homosexual behaviour been maintained in the population despite apparent selection against them?

Here we show that genes associated with homosexual behaviour are, in heterosexuals, associated with greater mating success. In in a genotyped sample of more than 400,000 individuals from the UK and USA, we for the first time found genome wide-significant association of specific variants with ever having had a same-sex partner, and hundreds of additional variants were significantly associated in aggregate.

Among men and women who had never had a same-sex partner, these same aggregate genetic effects were significantly associated with having more lifetime sexual partners and, in an independent sample, with being judged more physically attractive. Our results suggest that genes that predispose to homosexual behaviour may have been evolutionarily maintained in the population because they confer a mating advantage to heterosexual carriers.

The paper is gated of course, and I haven't been able to find an open-access version. But you get the idea. I suspect we're well down the road to putting Gregory Cochran's 'gay germ' theory to rest.