Return of the brother of the gay gene

From the Herald (from the Telegraph)

Factors ranging from exposure to certain chemicals to childhood abuse, diet and exercise may affect the DNA controlling sexuality, according to research being presented at a US conference on genetics.

…

They believe they can predict with 70 per cent accuracy whether a man is gay or straight, simply by looking at those parts of the genome.

[There’s a slightly better story in Nature News.]

70% accuracy doesn’t seem all that impressive. Using the usual figures on the proportion of men who are gay, the approach of assuming everyone is straight unless you are told otherwise is better than 90% accurate, and doesn’t need expensive genetics.  Presumably they mean something different by 70% accuracy, but we don’t know what.

More importantly, this is research in identical twins.  If you take pairs of people who are genetically identical, had the same environment in the womb, and then very similar environments in infancy and childhood, you’ve stripped out nearly all the other factors that could affect sexual orientation. That’s the point of doing the research this way — you get a clearer view of potentially-small differences — but it’s a limitation when you’re trying to make claims about people in general.

Also, there’s an important difference between genetics and epigenetics here. The epigenetic markers, as the story says, can be affected by things that happen to you during childhood. But that means we can’t necessarily assume the correlations between epigenetic differences and sexual orientation are causal.  The “factors ranging from exposure to certain chemicals to childhood abuse, diet and exercise” that can affect epigenetic markers could also affect sexual orientation directly — especially since the epigenetic markers were measured in cells from the lining of the mouth, not in, say, the brain.

On top of all that, this is another annoying example of research being publicised before it’s published. It’s not at all impossible that the claims are true,  but there isn’t enough public information to tell. The research was presented at the conference of the American Society for Human Genetics. People at the conference would have been able to see more detail, and maybe ask questions. We can’t. We won’t be able to until there’s a published research paper. That would have been the time for publicity.

And finally, there’s an interesting assumption revealed in the headline “Boys ‘turned gay by childhood shift in genes’“. The research looked at differences between identical twins. It says absolutely nothing about which twin changed and which one stayed the same — you could equally well say “Boys turned straight by childhood shift in genes”.