On Monday, the so-called Supreme Court of Sport ruled that 19-year-old Indian sprinter Dutee Chand, as well as all other female athletes who test positive for naturally high levels of testosterone, cannot be excluded from competing in female athletic competitions.
Chand was banned from competing last July, after winning two gold medals at the Asian Junior Athletics Championship in Taipei. Although she tested negative for doping, the Athletic Federation of India asked that her hormone levels be tested after growing suspicions around her "masculine build" and athletic ability.
Chand's tests showed that her blood possessed very high levels of natural testosterone, a hormone that helps with things like muscle strength, bone density, and the production of red blood cells — possibly giving her an advantage on the track.
According to rules adopted in 2011 by the International Association of Athletics Federations (IAAF), track and field's global governing body, as well as the International Olympics Committee, female athletes must have testosterone levels under 10 nanometers per liter — the lower bound of what's considered normal for males — in order to compete.
The regulations stated that women who exceeded this limit must undergo hormonal treatments or surgeries to lower their bodies' natural production of testosterone, or otherwise be excluded from competing.
Chand, whose blood testosterone exceeded IAAF's limit, chose to do neither. "I want to remain who I am and compete again. I have lived my life as a girl," Chand told the Indian Express last year.
Last September, she appealed her case and also sought a much bigger target: overturning the international rules dictating which women can compete.
On Monday, a three-member panel on the Court of Arbitration for Sport in Lausanne, Switzerland, ruled in Chand's favor, on the grounds that limiting female competitors based on testosterone has not been shown as necessary for ensuring fair competition.
The CAS has given the IAAF two years to compile scientific evidence establishing that high testosterone is enough to confer a significant advantage to female athletes as compared to their peers.
But for now, the ruling means that all women — regardless of their natural hormone levels — will be allowed to compete.
"Dutee took a huge and courageous risk with her decision to challenge a policy she felt was unfair to her and to all women athletes," Katrina Karkazis, a bioethicist at Stanford University who studies gender and athletics, told BuzzFeed News by email. "It's a policy that affected all women so [its] suspension is an historic victory for women's equality in sport."
Chand is not the only person who was angry about the rules restricting which female athletes could compete.
"Testosterone certainly matters biologically in the performance of athletes," Alice Dreger, a bioethicist at Northwestern University, told BuzzFeed News by email.
"That said, to limit women to a certain level of testosterone, and not men, is to act as if testosterone naturally belongs to men and not women," Dreger added. "That's weird. And I'm not sure why it isn't also sexist."
Things get murkier in the case of elite athletes, where extraordinary biology is the norm. For example, although just 1 in 20,000 women in the general population are born with a Y chromosome (typically the marker of a man), in elite female athletes that number is closer to 1 in 420, according to Eric Vilain, a medical geneticist who researches disorders of sex development at UCLA.
As scientists learn more and more about the many ways in which biological sex is a messy spectrum rather than a tidy binary, it's become increasingly difficult to determine where — and whether — to draw a gender line in sports.
The problem has been around since the 1930s, when female athletes were subjected to physical inspections in the nude, to root out so-called sex impostors.
In the late 1960s the IOC began a "more dignified" testing for sex based on chromosomes, but perplexingly, XY females cropped up all over the place, and the protocol was ditched in 1999. Since 2011, testosterone was the only marker used to differentiate between the two sexes in sports.
"It is an imperfect marker in the sense that it does not explain all the sex differences in performance," Vilain told BuzzFeed News via email, citing other physiological differences, such as skeletal shape, that can confer an athletic advantage. But, he says, "it is one of the best markers we have that is both relevant to athletic performance and very different between men and women."
For Vilain, who advised the IOC on its testosterone policy, the rules are there to help the majority of women trying to compete on a fair playing field. "Separating men and women in sports competition allows women to win," he said.
Chand's win will "push authorities to rely on declaration of gender," Vilain added. "And that would be a disservice to the vast majority of women who want to compete on a fair basis."
But others have argued that the international regulations pushed female athletes with high levels of testosterone to surgically alter what is just a feature of their normal biology.
A 2013 report in the Journal of Clinical Endocrinology & Metabolism described four female athletes, all from developing countries, who received surgical treatment after testing for high testosterone. Each had surgery to remove internal testes and also underwent hormonal therapy, but doctors also recommended other surgeries such as clitoris reduction. All four also consented to the additional procedures, and were allowed to compete within one year.
"The [old] policy that requires women athletes with hyperandrogenism to undergo therapy or surgery if they want to compete again is encouraging genital mutilation in an institutionalized way," Payoshni Mitra, a research consultant on gender and sports who worked with Chand to fight the policy, told the Indian Express.
With the verdict in her favor, Chand will immediately be able to race again. "What I had to face last year was not fair. I have a right to run and compete," she said in a statement released Monday.
"I was humiliated for something that I can't be blamed for. I am glad that no other female athlete will have to face what I have faced."