Controversial New Genetic Test Can (Kind Of) Predict Sexual Orientation

Illustrated by Ly Ngo.
Even with research on the topic building for decades now, science still has a hard time finding a definitive biological basis for sexual orientation. But according to researchers at UCLA, a new test can predict someone's sexual orientation with 67% accuracy, BuzzFeed reports. However, there are some pretty big problems with the study.

We know that genetics play some part in our sexuality, thanks to twin studies. In men, if one identical twin is gay, some research suggests there's about a 50% chance that the other twin is also gay. But if the twins are fraternal (and thus have only half their DNA in common), that chance is much lower.

This suggests that genes are important, but there's also something else going on. The UCLA team wanted to find that something else. So, rather than looking at specific genes, they looked at chemical epigenetic markers that can determine whether or not those genes are actually expressed.

In the study, presented last week at the annual meeting of the American Society of Human Genetics, the researchers found that five epigenetic markers in particular — out of the 400,000 they looked at — could predict if male participants were straight with 50% accuracy, or if they were gay with 83% accuracy. So, overall, the test is 67% accurate. But there's no obvious reason why the epigenetic markers identified here (which help regulate the immune system and proteins in the brain) would be involved in sexual orientation.

On one hand, wouldn't it be great to convince everyone — once and for all — that sexual orientation has a very real genetic basis? But on the other hand, identifying people in this way could come with opportunities for discrimination and some other pretty dark implications.

Indeed, the ethical concerns were so great that Tuck Ngun, PhD, lead researcher on the project, told BuzzFeed that he's already left academia. “It kind of, honestly, became a little bit troubling to me, what I was actually doing," he said. “Having done this now, I could sort of foresee a not-so-happy outcome.”

Still, as The Atlantic points out, many other scientists are skeptical about just how useful the test is in its current form and whether or not it will truly ever be an accurate genetic test for sexual orientation. For one thing, the area of epigenetics is extremely complex, and we're only beginning to really understand how our biology and environment interact with each other in this way.

There's also the design of the study itself. John Greally, PhD, has already criticized it in a blog post for the Albert Einstein College of Medicine. When analyzing epigenetic markers in this way, thanks to statistics, you're pretty much guaranteed to find some kind of association between those markers and the thing you're interested in. Inherent flaws like this need to be corrected for in researchers' analyses. So, for this and several other reasons, Dr. Greally calls the UCLA study's results "uninterpretable."

These skeptics aren't denying a genetic basis for sexual orientation. But, obviously, there's plenty of work left to do if we want to continue down this path of study. So the skeptics want to see that the work is done with the extreme care it deserves.
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