Expectations are soaring for 25-year-old South African runner Caster Semenya, who races next week in the 800 meters. She’s favored to clinch a gold medal. She might even shatter the longest-running world record for track and field. And if she does, it could affect much more than the pride of her competitors. A big win for Semenya would likely add fuel to an already-fiery debate about gender and sports, and whether women like her should be allowed to race at all. For decades, the International Association of Athletics Federations (IAAF), the world’s governing body for track and field, has sought to preserve the male-female division in its sport through variations of sex testing—gynecological exams, chromosome tests, or hormone tests to make sure female competitors aren’t actually men trying to pass as women, or intersex women with masculine traits that might give them an unfair boost. Since 2011, sex testing has focused on testosterone. Women like Semenya whose functional levels of the hormone are within “the male range,” or higher than 10 nanomoles per liter of blood, have been barred from international competitions like the Olympics. But not this year. For the first time in more than half a century, female Olympians will not be subject to any form of sex testing in Brazil, which means intersex track athletes will be allowed to compete with their natural testosterone levels.
Now, as scientists struggle to determine how testosterone affects performance, thousands of athletes are converging on Rio de Janeiro for what some have described as a total “free-for-all,” as far as gender boundaries go. If Semenya dominates, will it be fair? What does the science say?