Rules on testosterone levels for women athletes have kept star runner Caster Semenya out of the Tokyo Olympics. At the heart of this heated debate: Who should be considered a woman in sport?

Transcript

AILSA CHANG, HOST:

Track and field competition gets underway tomorrow at the Tokyo Olympics. You will not see one of the sport's brightest stars, two-time Olympic gold medalist Caster Semenya of South Africa. She is the fastest woman in the world in the 800 meters. And under new rules, Semenya and other female athletes who refuse to lower their naturally high testosterone levels have been barred from competing in some events. As NPR's Melissa Block reports, those rules have raised heated debate about fairness and inclusion.

MELISSA BLOCK, BYLINE: In defense of Caster Semenya, one of her sponsors, the beauty brand Lux launched a #StandWithCaster (ph) video campaign. It opens with a cascade of voices doubting Semenya's fundamental identity.

(SOUNDBITE OF YOUTUBE VIDEO)

UNIDENTIFIED PERSON #1: I have to say, it's hard to believe Caster's a woman.

UNIDENTIFIED PERSON #2: Identifying as a woman doesn't make you one.

UNIDENTIFIED PERSON #3: There's nothing feminine about her.

UNIDENTIFIED PERSON #4: That's not a woman. She is a he.

BLOCK: But the narrator says Caster was simply born this way, with special gifts.

(SOUNDBITE OF YOUTUBE VIDEO)

UNIDENTIFIED NARRATOR: Lux believes that women should not be judged for how they look, that no woman should ever be stripped of being a woman.

BLOCK: This battle has been waged in court for years. Should women athletes with what's called a difference of sexual development, or DSD, who have XY chromosomes and elevated testosterone levels, be allowed to compete in the female category? Or does their genetic makeup as intersex athletes give them an unfair advantage in a world of sport that's divided along binary lines of sex? Semenya, who was raised female and is legally female, took her case to sports' highest international court and lost. She claims the rules from track's governing body, World Athletics, are specifically designed to keep her out.

(SOUNDBITE OF ARCHIVED RECORDING)

CASTER SEMENYA: When you're the best in the world, people get obsessed, you know, with what you do.

BRUCE KIDD: I don't think it's unfair to call this the Caster rule.

BLOCK: That's Bruce Kidd, a former Olympic racer himself. He's a retired professor at the University of Toronto and a long-time advocate for gender equity in sport. In his view, the Tokyo Games are an asterisk Olympics, since some of track's best female middle-distance athletes will be excluded.

KIDD: Simply because of a very narrow definition of their gender. And I think because the Olympic movement prides itself on its support of human rights, we have to call their exclusion a stain on the Tokyo Olympics.

BLOCK: In order to compete in events from 400 meters to one mile, athletes like Semenya are required to suppress their testosterone with birth control pills, hormone shots or surgery. To all that, Semenya has said...

(SOUNDBITE OF ARCHIVED RECORDING)

SEMENYA: No freakin' way. For who? No.

BLOCK: So what should determine who can race as a woman? And who draws that line? Those are questions on the mind of Tlaleng Mofokeng, a doctor in Johannesburg who focuses on sexual and reproductive health. She also serves as the U.N. Special Rapporteur on the Right to Health.

TLALENG MOFOKENG: There is a definite history of people seeing certain women as not women enough, this idea - right? - that some women are more women than others.

BLOCK: Consider that the women who have publicly run afoul of the gender verification rules are all from the global south. In the Tokyo Games, along with Semenya, it's other runners from Africa, from Kenya, Burundi, Niger and Namibia, who have said they're affected by the rules. That includes all three women who won medals in the 800 meters at the 2016 Rio Olympics. For Dr. Mofokeng, the conclusion is clear.

MOFOKENG: It's racism. It's racism. It's a visceral problem, you know? I agreed to do this interview, but I know how angry it makes me and it will make me, you know, the issues of femininity - right? - who owns femininity and who gets to decide what that looks like.

DORIANE COLEMAN: To suggest that the rules are racist when they're not, when we know they're not - it's really disturbing.

BLOCK: Doriane Coleman is a law professor at Duke and a former elite runner. She was an expert witness testifying in support of the current eligibility rules. Coleman says they preserve competitive space and podium opportunity for women, a protected class in sport that is divided by sex for good reason. As a biracial woman, she says the racism charge especially rankles.

COLEMAN: We know - you know, Black women know, just like all other people, that without sex-segregated sport, whether you're a Black woman or a white woman, you don't have a chance.

BLOCK: World Athletics declined an interview for this report, but sent a lengthy statement, saying in part, quote, "Our female eligibility regulations do not target any single athlete or race." And it continues, "There is copious evidence that Black women are thriving and being celebrated in our sport."

Caster Semenya attempted to qualify for the Tokyo Games in a longer-distance event exempt from the testosterone rules, but she fell short. So no Tokyo for Semenya, no medal around her neck this time. Still, says Dr. Mofokeng, Semenya is a hero.

MOFOKENG: Absolutely. She is. She was. She will always be. She will have a whole chapter in our history.

BLOCK: She says Caster still has the heart of many of us.

Melissa Block, NPR News. Transcript provided by NPR, Copyright NPR.