No Gay Gene, No bron this way, No gay orientation - just political agenda!

There are two ways to challenge politically correct orthodoxies. One is to toss off outrageous remarks designed to épater les bourgeois. This requires little and accomplishes less. The other is to take the commanding orthodoxy, put it under a microscope, and dismantle it piece by piece. This is what Lawrence Mayer, an epidemiologist trained in psychiatry, and psychiatrist Paul McHugh have just done to the regime of gender and sexuality politics.

In a lengthy report for the journal the New Atlantis, Mayer and McHugh survey a broad expanse of the scientific literature on gender and sexuality and demonstrate that much of what has been foisted on the culture in recent years in the name of science has little solid basis in scientific research. Their conclusions: (1) "The understanding of sexual orientation as an innate, biologically fixed property of human beings—the idea that people are 'born that way'—is not supported by scientific evidence." And (2) "The hypothesis that gender identity is an innate, fixed property of human beings that is independent of biological sex—that a person might be 'a man trapped in a woman's body' or 'a woman trapped in a man's body'—is not supported by scientific evidence."

It may sound modest, but this is earth-rumbling stuff.

The Mayer-McHugh report is important for a number of reasons, beginning with what it is not. It is not a political document. "This report is about science and medicine," Mayer writes in the preface. "Nothing more and nothing less." If anything, the authors' primary concern is to serve the non-gendered and non-heteronormative: "I strongly support equality and oppose discrimination for the LGBT community," Mayer writes before dedicating his work on the report "to the LGBT community, which bears a disproportionate rate of mental health problems compared with the population as a whole."

It is also not a prescription. Mayer and McHugh are primarily concerned with establishing the boundaries of scientific knowledge—with making clear what we know and what we do not yet know. And to the extent that they offer suggestions, these are almost exclusively about where more research is needed and how such work might be more effectively focused.

The dominant mode in the report is humility rather than authority—of winching in extrapolations and interpretations and reminding readers that science doesn't always say what you want it to.

For instance: In 2014, Mark Joseph Stern wrote in Slate that "homosexuality, at least in men, is clearly, undoubtedly, inarguably an inborn trait." But this isn't true. For one thing, it can be hard even to define "homosexuality" in a scientifically rigorous manner. And once you work your way out of that cul-de-sac, the scientific evidence—as distinct from the political projections—is incredibly tangled. In 1991 neuroscientist Simon LeVay demonstrated some brain differences between homosexual men and heterosexual men. But even he cautioned, "It's important to stress what I didn't find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn't show that gay men are 'born that way,' the most common mistake people make in interpreting my work."

Here is how Mayer and McHugh stress humility: There is enough research (especially from twin studies) to suggest that "genetic or innate factors may influence the emergence of same-sex attractions." But inferring more than that is a mistake. There is evidence that environmental factors (such as prenatal hormone exposure) and experiential factors (such as being the victim of sexual abuse) also play some role. And beyond that? No one knows. And anyone who insists that they do know is likely to be selling you a political agenda.