You can spot the problem with this study a mile away: were the gay brains LeVay studied born that way, or did they become that way? LeVay himself pointed this out to Discover Magazine in 1994: “Since I looked at adult brains, we don't know if the differences I found were there at birth or if they appeared later.” Further, the brains LeVay studied belonged to AIDS victims, so he couldn’t even be sure if what he was seeing had something to do with the disease.

Another landmark paper on the origins of homosexuality was published in 1993 by a geneticist named Dean Hamer, who was interested to learn whether homosexuality could be inherited. Beginning from his observation that there are more gay relatives on a mother’s side than a father’s, Hamer turned his attention to the X chromosome (which is passed on by the mother). He then recruited 40 pairs of gay brothers and got to work. What he found was that 33 of those brothers shared matching DNA in the Xq28, a region in the X chromosome. Hamer’s conclusion? He believes there’s about “99.5% certainty that there is a gene (or genes) in this area of the X chromosome that predisposes a male to become a heterosexual.”

A 2015 study sought to confirm Hamer’s findings, this time with a much larger sample: 409 pairs of gay brothers. Researchers were pleased with their findings, which they claimed “support the existence of genes on… Xq28 influencing development of male sexual orientation.”

But not everyone finds the results convincing, according to Science. For one thing, the study relied on a technique called genetic linkage, which has been widely replaced by genome-wide association studies. It’s also noteworthy that Sanders himself urged his study to be viewed with a certain caution. “We don’t think genetics is the whole story,” he said. “It’s not.”

And as Allen points out, there have also been studies that found no “X-linked gene underlying male homosexuality.” Perhaps predictably, these studies haven’t received as much media coverage.

Besides the individual critiques leveled against each new study announcing some gay gene discovery, there are major methodological criticisms to make about the entire enterprise in general, as Grzanka points out: “If we look at the ravenous pursuit, particularly among American scientists, to find a gay gene, what we see is that the conclusion has already been arrived at. All science is doing is waiting to find the proof.”

The other problem with Born This Way science is summed up nicely by Simon Copland: “Scientists are asking whether homosexuality is natural when we can’t even agree exactly what homosexuality is.”

Grzanka agrees. “If you know anything about social constructionism, then you know these sexual categories are very recent. How then could they be rooted in our genome?” Our desires may express themselves in many different ways that do not all conform to existing notions of ‘gay’, ‘straight’ or ‘bisexual’.

This is one of the best takeaways of Ward’s Not Gay, a penetrating analysis of sex between straight white men. Gay men make up only a fraction of the US population — yet Ward says that there are many men not included in that number who engage in homosexual behavior. Why, then, do some men who have sex with men identify as gay, and others identify as heterosexual? This question interests her far more than ‘how were they born?’.

Ward stresses that not all straight-identifying men who have sex with men are bisexual or closeted, and we do a disservice if we force those words on them. That’s because terms like ‘heterosexual’ and ‘straight’ and ‘bisexual’ and ‘gay’ come with all sorts of cultural baggage attached. Crucially, she argues, “whether or not this baggage is appealing is a separate matter altogether from the appeal of homosexual or heterosexual sex.”

Even if you accept that sexual desire may exist on a kind of spectrum, the predominant idea is still that these desires are innate and immutable – but this runs counter to what we know about human taste, says Ward. “Our desires are oriented and re-oriented based on our experiences throughout our lives.”