Does “science” show that transgender girls who compete as females in a sport have an unfair advantage?

That’s the claim made earlier this month by a Tennessee state legislator who called for a law inflicting career-ruining sanctions on school officials who let trans-student-athletes compete in accord with their gender identities. 

The proposal is neutral on its face: it would apply to both boys and girls. But the specter of trans girls (girls born as boys) gaining an unfair edge on “real” girls animates it and other proposals like it.

People who are physiologically male at birth have myriad advantages on the playing field; the story goes: differences in muscle mass, skeletal structures, and hormonal biology persist after medical and surgical gender transition. 

Trans rights advocates — and many in the medical community — push back by observing that substantial musculoskeletal sex differences don’t emerge until puberty and thus aren’t significant for children who transition from male to female via hormonal treatments beforehand.

They contend, moreover, that trans women who make the shift via hormonal therapy after puberty lose any male muscle-mass advantage within a year. 

Many questions about the impact of sex-at-birth and gender transition treatments upon athletic performance remain without scientific answers. But even an encyclopedic set of answers wouldn’t resolve the separate question of fairness.

Which biological advantages— or disadvantages — should be treated as “talent,” or a “gift,” or lack thereof, and which should be seen as “cheating” or “unsportsmanlike?” 

Myriad influences — environmental, genetic, and mixtures of both — produce differences in athletic capability and performance. Without these differences, sports would be insufferably dull. Every competition would yield a tie — or, worse, a winner decided by dumb luck.

Ditto was we to view all such differences as unfair. Then, the only right and proper sporting result would be a tie; winning would be, by definition, the product of wrongful advantage. 

So we allow some differences in capability to affect sports outcomes without calling out those with an edge as cheaters. Indeed, we admire many of these advantages, whether we believe they’re bestowed by God or good fortune: we praise competitors for their strength, speed, endurance, agility, toughness, discipline, resolve, and more.

And here’s the key: the lines we draw between the competitive edges we accept, even admire, and those we think unfair are the stuff of our culture, not our science. Wrestlers compete in weight classes — we reject a contest between a 125 pounder and a 195 pounder as a mismatch — but we’re OK with a 6’ 4” high-school basketball center’s unequal struggle under the rim against an opposing team’s 7-footer.

Or consider the Houston Astros’ mix of high and low tech (high-res cameras to see opposing catchers’ hand signals from afar, followed by banging on trash cans to tell Astros’ hitters what pitches to expect) to gain a large advantage at the plate. Sign-stealing of this sort is the stuff of baseball lore, going back more than a hundred years 

It’s allowed — when baserunners pick up the catcher’s signals and tell the batter (by coded gesture) what’s coming next. But baseball bans binoculars, cameras, and other technologies that extend the eye’s reach.

To those not steeped in baseball’s mores, this distinction may seem silly: if stealing catchers’ signs is allowed, why should the method matter? The mores, though, are key: they set the sport’s boundaries between cheating and legitimate deviousness.

And mores — and culture — evolve, both within and outside sports. Sometimes, scientific findings influence this evolution: postmortem proof of the high incidence of brain damage in former NFL players has inspired new rules against hits that put the brain at high risk. But science can’t answer the question of how to balance football’s health risks against the audience appeal of ferocity.

People make such judgments: the governing bodies of sports decide what’s fair or clean and what’s not. And social norms guide these judgments since a sport can’t prosper without buy-in from players, fans, and sponsoring institutions like schools and advertisers. 

So cultural change off-the-field has no small impact on understandings of athletic fairness. Movement toward gender equity is driving the dissolution of rules differences between men’s and women’s competitions. And growing acceptance of gender identity as subjectively-experienced, not anatomic, is driving change in understandings of which advantages are and aren’t fair when women and men compete separately.

We should say no to attempts to push back against this acceptance by misusing “science” to brand birth-anatomy difference as “cheating” or otherwise unfair. More broadly, we should recognize that in sports, as in the rest of life, we all have competitive edges and weaknesses — and that judgments about which are and aren’t fair are matters of culture and politics, not biology.

Gregg Bloche, M.D., J.D., @greggbloche, is a professor of law at Georgetown University and co-director of the Georgetown-Johns Hopkins joint degree program in law & public health.