Why does a “gay gene” paper still cause a stir? A similar paper on any other topic would probably have passed unnoticed. But this is sex research – where public interest is huge but real funds and real science are very scarce and stories get recycled.
A study which is not even yet a paper was presented in preliminary form on Valentine’s Day by sex researcher Mike Bailey at a conference in Chicago saying that there is a genetic component to homosexuality. In fact, their study of 400 pairs of brothers, where at least one was gay, confirmed a smaller controversial study from 20 years before, and several twin studies in between. The 1993 study led the Daily Mail to run one of its most infamous headlines: “Abortion hope after gay genes finding”.
The Bailey paper claims to have found large segments of chromosomes containing hundreds of genes that are common in gay men. The researchers admitted they couldn’t find any specific “gay genes”.
Last year, a paper in a relatively obscure journal also caused a public stir for saying just the opposite. The authors came up with a complicated biological explanation for why gay men have more female relatives, tend to have older brothers and why it involves testosterone in the womb and runs in families. Controversially, they said it wasn’t due to their genes, but to small chemical signals that alter the genes (called epigenetics) which can pass from one generation to the next, and had some (unclear) evolutionary advantage.
The study was undoubtedly clever and involved high-powered maths, but was purely theoretical, didn’t involve real people and made false assumptions leading to fatal flaws.
This latest round of reporting following the Bailey research has led to perhaps inevitable criticism that we have an obsession with male homosexuality.
One reason people react so violently to these studies is a lack of understanding of basic biology and science, and realising that homosexuality is for a scientist just another human characteristic or trait, like sporting ability, obesity, optimism or depression.
Almost all human traits studied have some genetic (heritable) component, usually in the range of 30-70%. Homosexuality in males and females has a heritability in most studies of around 30-40% with plenty of room for environment. And there is no single gene for any of these traits.
We have around 20,000 genes (about the same as worms) and thousands of genes influence each behavioural trait to tiny extents. So whether you believe it or not – the “gay gene” is a joke. No genes have actually been found to consistently influence homosexuality solely because genetic studies have been far too small; it took more than 34,000 people and 20 labs to find one little gene variantthat influenced 0.1% of blood pressure – wow.
More controversial still
While researching Identically Different, my book on the effect of epigenetics on twins, I interviewed several sets of identical twins where one was gay and one straight (which is more common that than both being gay). All pairs were puzzled by their eventual differences which often didn’t emerge until well after puberty. In these genetic clones, genes might explain their increased susceptibility but clearly was not enough to be in any way “deterministic”.
Importantly, while genes couldn’t explain the differences, the relatively new mechanism of epigenetics – which can differ between twins – was the probable reason. When I discussed these results last year on the radio, gay rights activists seemed to get even more upset at the idea of epigenetics rather than plain genetics. They were worried that as these changes were theoretically reversible, epigenetic drugs might become a future anti-gay treatment in oppressive societies.
The complexity and randomness of possible epigenetic changes combined with the biology and multiple influences on sexual preferences makes this fear unfounded.
So we could (if someone wanted to pay for it) do a large study of thousands of subjects, and find hundreds of “gay genes” of tiny influence, but what would we do with them? As we see from the many identical twin pairs who differ in sexual preferences – they would be useless for prediction. If we found subtle epigenetic changes associated with homosexuality this would certainly be interesting from a science perspective, but wouldn’t alter the political debate – although it would certainly guarantee you great publicity for years to come.
Tim Spector, The Conversation