Born This Way? The Whole Truth About ‘Gay Genes’

Born This Way? The Whole Truth About ‘Gay Genes’

There is a thought that gay guys share a ‘gay gene’ caused a furor in the ‘90s.

There is a thought that gay guys share a ‘gay gene’ caused a furor in the ‘90s.

But new study two decades on supports this idea – and adds another candidate gene. To the evolutionary world, the hypotheses that an individual’s genetic makeup affects his mating preference aren’t new. We can see it in the animal world all the time. There are perhaps lots of genes that influence human sexual orientation.

But rather than thinking of them as ‘homosexual genes’, probably we should suppose them to be ‘male-loving genes.’ They may be general because these variant genes, in a female, predispose her to mate more often and earlier, and to have more kids. Likewise, it would be astonishing if there were not ‘female-loving genes’ in lesbian girls that, in a male, predispose him to mate earlier and have more kids.

Proof of ‘gay genes’ existence

It is possible to detect genetic variants that provide differences between persons by tracking traits in families that show differences. Examples of inheritance show variants of genes called ‘alleles’ that influence normal differences such as hair color or illness states such as sickle cell anemia. Quantitative traits, such as height, are influenced by lots of various genes, as well as environmental factors.

It’s difficult to use these techniques to detect genetic variants connected with male homosexuality, while lots of gay guys prefer to stay in the closet about their sexuality. It’s even more difficult because twin researches display that shared genes are just a part of the story; hormones, environment and birth order play roles too.

In 1993, American geneticist Dean Hamer discovered families with a few gay guys on the mother’s side, supposing a gene on the X chromosome. He showed that pairs of brothers who were openly homosexual shared a little region at the tip of the X, and offered that it contained a gene that predisposes a man to homosexuality.

Hamer’s conclusions were completely controversial. He was challenged at every turn by persons unwilling to realize that homosexuality is at least partly genetic, rather than a ‘lifestyle choice.’ Homosexual guys were divided: it vindicated the oft-repeated ideas that ‘I was born gay’ but also opened frightening new opportunities for discrimination and detection. Similar researches brought to different results. A later study found associations with genes on three other chromosomes.

Past year, a larger research of homosexual brothers, using lots of genetic markers now available through the Human Genome Project, proved the unique finding, and also detected another ‘homosexual gene’ on chromosome 8. This has unleashed a new stream of comment. But why such a furor if we know about gay gene variants in species from flies to mammals? Homosexuality is rather general throughout the animal kingdom. For example, there are variants that impact mating preference in mice and a mutation in the fruit fly makes males do other males instead of females.

Is ‘homosexual gene’ is a ‘male-loving’ allele?

The question isn’t whether ‘homosexual genes’ exist in people, but why they are so common (estimates from 5% to 15%). We know that homosexual guys have fewer kids on average, so shouldn’t these gene variants disappear? There are a few theories that account for the high frequency of homosexuality. A decade ago we wondered if homosexual gene variants have another impact that boosts the chances of leaving offspring, and passing the homosexual allele on.

This is a familiar situation called ‘balanced polymorphism’ in which an allele is advantageous in one situation and not in another. The classic example is the blood disease sickle cell anemia, which leads to disease and death in case you’ve got two alleles, but to malaria resistance in case you’ve got only one, making it general in malarial regions.

A special category is ‘sexually antagonistic genes’ which increase genetic fitness in one gender, but not in the other; some are even lethal. We’ve got a lot of examples across lots of species. Perhaps, the homosexual allele is just another of these. Probably ‘male-loving’ alleles in a female predispose her to mate earlier and have more kids. If her sisters, aunts and mother have more children who share some of their genes, it would make up for the fewer kids of gay boys.

And they do. A lot more kids. An Italian group displayed that the female relatives of homosexual guys have 1.3 times as many kids as the female relatives of heterosexual guys. This is an immense selective benefit that a male-loving allele confers on girls, and offsets the selective disadvantage that it confers on guys. We’re surprised that this work isn’t better known, and its explanatory force is neglected in the entire argue about the ‘normality’ of gay behavior.

Are gay alleles normal or not?

We still don’t know whether these genetic researches identified ‘homosexual alleles’ of the same or various genes. It’s interesting that Hamer detected the unique ‘homosexual gene’ on the X, because this chromosome has more than its fair share of genes that influence reproduction, but we would expect that there are genes all over the genome that contribute to mate choice in people (female-loving as well as male-loving).

In case there are female-loving and male-loving alleles of tens or hundreds of genes battling it out in the population, everybody will inherit a mixture of various variations. Mixed with environmental impacts, it will be difficult to detect personal genes. It’s a bit like height, which is affected by variants in thousands of genes, as well as the environment, and provides a ‘continuous distribution’ of persons of various heights. At the two extremes are the very tall and the very short.

In the same way, at each end of a continuous distribution of individual mating preference, we would expect the ‘very female-loving’ and the ‘very male-loving’ in both genders. Homosexual guys and lesbian girls may simply be the two ends of the same distribution.

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