Caster Semenya of South Africa competes in the women’s 800 meters in Rome on June 2.

Tiziana Fabi/AFP/Getty Images

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Tiziana Fabi/AFP/Getty Images

Caster Semenya of South Africa competes in the women’s 800 meters in Rome on June 2.

Tiziana Fabi/AFP/Getty Images

One story simmering at the Rio de Janeiro Olympics has to do with gender: specifically, the controversy over intersex athletes, who are anatomically and genetically ambiguous.

At issue: is it fair to allow these athletes, who often have high levels of testosterone, to compete with women?

Much of the attention has been on South African runner Caster Semenya, the favorite to win gold in the women’s 800 meters on Saturday. Semenya has been identified as intersex in numerous media outlets, although she has never confirmed this or spoken about it.

She exploded onto the world stage in 2009, when she was just 18 years old. She destroyed the 800 meters field at the world championships in Berlin, winning with a time of 1:55:45, more than two seconds faster than her closest competitor in the final.

Hazel Clark of the United States ran against Semenya in the semifinals that year and missed the final by one spot.

“There was so much talk around her,” Clark recalled. “Everybody kinda said, ‘Something’s wrong with her. God, have you seen her? “

It wasn’t just Semenya’s stunning performance that raised questions. This was also what she looked like: she has broad shoulders, narrow hips and a prominent Adam’s apple. His voice is deep and masculine.

After the race, two other competitors openly questioned Semenya’s gender.

“Just look at her,” complained Russian Mariya Savinova.

Elisa Cusma Piccione from Italy said emphatically, “For me, that’s not a woman. … It’s pointless to compete with that, and it’s not fair.”

Test results leaked

In 2009, Semenya was subjected to gender verification tests after winning the world championship in Germany.

U.S. runner Hazel Clark (second from left) vies with Caster Semenya (right) during a women’s 800 meters semi-final at the World Championships in Athletics in Berlin August 17, 2009.

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U.S. runner Hazel Clark (second from left) vies with Caster Semenya (right) during a women’s 800 meters semi-final at the World Championships in Athletics in Berlin August 17, 2009.

Anja Niedringhaus/AP

The results were supposed to be confidential, but reports have surfaced that she had testosterone levels three times higher than most women.

Other intimate details about his anatomy have also been reported.

Semenya has been the target of abuse on social media.

Ross Tucker, professor of exercise physiology at the University of the Free State in South Africa, said: “I’ve seen comments from people in response to his performance where they very quickly called him ‘he ‘ and ‘him’. And some of them are even crueler than that. They call Caster Semenya ‘it’, like she’s some kind of weird monster. And that stuff is just awful.

Tucker wrote a lot on the issues raised by intersex athletesand he points out that sex testing on female athletes has a long history.

In the 1960s, Olympic officials attempted to identify men pretending to be women.

Female athletes were subjected to infamous “nude shows”, where they were examined by a panel of doctors. If they “succeeded”, they received a certificate.

“It’s amazing they called it that,” Tucker says. “They used to call it the ‘Certificate of Womanhood.’ And that’s what female athletes had to take with them.”

Tucker notes that there are racial overtones to this controversy. Semenya is black.

“People say the only reason she’s being questioned is because she doesn’t conform to the Western perception of what a woman should look like.”

High levels of testosterone

But for Tucker, the real problem is biological.

He says there is a proven reason why male and female athletes compete separately.

Testosterone gives men a distinct advantage: a performance boost of around 10-13%.

“That’s basically the crux of the matter,” he says. “Do intersex athletes who compete as women have an advantage through testosterone that is unfair, even compared to other obviously recognized advantages in sport?”

Tucker thinks the answer to that question is clear: they have that advantage.

He accepted new rules set in 2011 by the International Association of Athletics Federations, the international governing body for athletics.

The IAAF has ruled that women with high testosterone levels should bring those levels below the normal range for men, either by taking testosterone-suppressing drugs or having their inner testicles surgically removed.

Tucker says, “I thought it was a compromise that balanced the requirement of human rights against that of the performance rights of other athletes in the sport.”

But last year, the Court of Arbitration for Sport suspended this IAAF rulewriting that he “was unable to conclude that hyperandrogenic female athletes can achieve such a significant performance advantage that it is necessary to exclude them from competition in the female category”.

The court gave the IAAF two years to provide more scientific evidence linking high testosterone levels and improved athletic performance.

This means that for these Olympics, at least, there is no upper testosterone limit for intersex athletes.

“It’s the most complicated issue in sports,” Tucker says, “because there are so many layers. Some of those layers are nasty, like the issue of racism and sexism. Some of those layers are really Fascinating, like biology. It’s so packed. It’s like every subject here is a landmine.”

For Clark, Semenya’s former competitor, who has stayed in touch with her via social media, this is uncomfortable territory.

“I have a lot of respect for her,” Clark said in an interview at the Rio Athletes’ Village. “I think she was born the way she was born, and it’s up to us to figure out how to regulate her and make her as fair as possible for everyone. That includes her.”

Clark continues, “I can only imagine how she felt as a young woman, the way people talked about her, scrutinized her and attacked her. I had a lot of compassion for her, and that is always the case.”

Semenya will hit the track at Rio’s Olympic Stadium for her first 800-meter qualifying run on Wednesday.

This week, she tweeted an image of a poster that read, “I truly believe my enemies are my motivators.”

Back in South Africa, Semenya defenders are using social media to show their support. The hashtag “HandsOffCaster” is trending as its run nears.