SCOTT DETROW, HOST:

Last week saw a flurry of activity in the ongoing debate about transgender athletes competing in school sports.

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UNIDENTIFIED REPORTER #1: Breaking news - transgender athletes will soon be banned from playing in women's sports in Kansas schools.

UNIDENTIFIED REPORTER #2: The Biden administration has proposed a new rule. This plan essentially bars blanket bans of trans athletes, but it leaves wiggle room for schools to place some restrictions at more elite levels.

UNIDENTIFIED REPORTER #3: The U.S. Supreme Court has denied West Virginia's request to let it fully enforce a state law that bans women who are transgender and girls from participating on public school sports teams consistent with their gender identity.

DETROW: The debate is heated, highly politicized, and it's taking place all across the country. According to the ACLU, 19 other states have enacted similar bans over the past three years. They generally state that only those who are assigned biologically female at birth will be allowed to compete on girls' and women's sports teams within the state. In Kansas and elsewhere, supporters say these bans are all about fairness, ensuring an even playing field for girls in particular.

So what does fairness mean really, and what is the extent that it can be measured? What do we know? We decided to ask a doctor to speak with us, an MD PhD who advises sports organizations on the issue of transgender athletes. Dr. Eric Vilain is a pediatrician and geneticist at the University of California, Irvine. Dr. Vilain, thanks for joining us again on ALL THINGS CONSIDERED.

ERIC VILAIN: Always a pleasure to be here.

DETROW: Let's start just a little bit with those headlines. There was that new law in Kansas, then the Biden administration's proposed rule change to Title IX, which would outlaw broad bans against transgender athletes but give schools discretion to ban specific athletes. Do you think that strikes the right balance?

VILAIN: Well, on one hand, not having an indiscriminate ban suggests that the baseline for eligibility for all athletes, including trans athletes, should be inclusion. And I think that's a good thing. And that's actually what the International Olympic Committee has done in creating a framework for inclusion and fairness that's based on the principle of no presumption of advantage. And if a category is going to be excluded, it needs to be based on evidence. The problem here with the exclusion on a case-by-case basis is that it is likely not to be based on evidence. Who's going to undertake all the necessary research to demonstrate a disproportionate advantage, sport by sport, at so many different ages? Who will fund this? Likely not the school systems.

And the other problem is that the proposed rule will likely create a quite inequitable patchwork of inclusion and exclusion throughout the country, with some states or some cities more likely to include and others not. And the same trans athlete may be eligible in one school and, if they move, may not be in another school, which doesn't make much sense. And finally, all the schools that will ban participation will also prevent the collection of any data on trans athletes, which will further even more the inability to make policy supported by data.

DETROW: Is there a way - I mean, if you put the politics out of it, which, at this point, is a naive view and increasingly impossible because it's an incredibly political issue, but is there a balance that could take people and assess them on an individual basis, like you're saying is important, but also be equitable? Because if we're making different policies for specific people and specific places, it feels hard to have a broader policy in place.

VILAIN: The issue is we lack a lot of data, so we, in fact, know very little about advantages of trans girls and women athletes over their cisgender peers. That's true in elite competitions. That's true in school sports. What we know is that boys and men have an advantage in performance over girls and women, and that disadvantage increases after puberty. So the answer of competitive advantage will vary by class level, and the difference will be much smaller, of course, in elementary school, before puberty, than in high school. So it's a complicated debate. Some are making the argument that the difference between boys and girls should translate directly into concluding that there will be the same difference between trans and cisgender girl athletes. But there is no good evidence for this, in part because many cases are going to be different, some having undergone blocking of puberty at different ages.

I'll end by saying that the larger question really goes beyond a simple competitive advantage. It's whether there is a disproportionate competitive advantage between trans and cis athletes. So there are all sorts of advantages coming into play for athletic abilities - their genetic advantages, metabolic differences, physical characteristics, height, for example, and all the socioeconomic access to better nutrition, better coaching, better training equipment. Does all of these differences that provide some advantage are dwarfed by the fact of being trans athlete? We simply don't know.

DETROW: A lot of people say they're worried about inclusion. A lot of other people say they're worried about protecting female athletes. You're an expert in this field. What are you worried about?

VILAIN: I'm worried that outright bans will prevent inclusion. And it's especially worrying at the school level because there are already so much inequity of sports participation that comes from all sorts of other issues, such as socioeconomic status, access to sports, which are not addressed. So adding layers of exclusion is just not helpful.

DETROW: Dr. Eric Vilain is a pediatrician and a geneticist at the University of California, Irvine. Thanks so much for coming on ALL THINGS CONSIDERED.

VILAIN: Thank you. Transcript provided by NPR, Copyright NPR.