There’s Good Reason for Sports to Be Separated by Sex

If the practice stopped, top-level women’s sport as we know it might cease to exist.

A man and a woman racing each other.
Erik Carter/The Atlantic; Getty

My wife and I are lifelong runners. It’s the sport we fell in love with, and ended up excelling at—during our wedding, every speaker from the preacher to the best man mentioned some variation of “Can you imagine how fast their future kids are going to be?” My wife, Hillary, is by far the more accomplished athlete. I made the NCAA championship; she was an All-American. I had dreams of qualifying for the Olympic trials; she actually did it. By many measures, she’s simply better. But not by all of them.

We both got our start in middle school. When Hillary was in seventh grade, she ran a 5:42 mile. At the same age, my best was virtually identical at 5:40. If we had lined up for a race, there would have been a close dash to the finish line. Fast-forward to ninth grade, and we were both ranked among the top freshman runners in Texas. But a clear difference had emerged: Her time had steadily decreased to 5:13, while mine had shot all the way down to 4:22. At the end of our collegiate running careers, the massive gulf remained: She ran 4:43 and I ran 4:01. I didn’t train more, care more, or possess more grit. She surpasses me on all of those things. I just had an inherent advantage: my biology.

It’s no secret that sports-performance differences between sexes are a flashpoint in an American culture war that goes beyond athletics into ideology and identity. I’m not here to tackle the tough and important questions of sport and sex, such as how to include trans athletes and people who have differences of sexual development in a sporting world that is mostly divided along binary lines. What I am here to address is one of the simplest debates. Over the past few years, some cultural commentators and sociologists have minimized the impact of sex-based biological differences on sporting performance. Some claim that men’s biological advantages in speed, strength, or endurance are scientifically debatable. (This magazine recently published such arguments in an article about youth sports.)

Here is what the facts say. Sport for women is generally undervalued and under-resourced in America, and this can affect women’s performance levels. Coed sports at recreational and youth standards—played as part of living a good life, not to develop elite athletes—can be both fun and competitive. But at the highest, rarefied levels of many professional sports, men and women appear to have different performance ceilings.

The research is clear: The difference in my wife’s and my athletic progression is not unusual. With young kids, the best boys tend to be only a hair better than the best girls. We can see this in age-group records: The boys’ and girls’ records for the 9-to-10-year-old 100-meter-sprint are nearly identical (12.73 versus 12.85). But in the 15-to-16-year-old records, the gap has gone from a crack to a gulf (10.51 versus 11.34).

A study by Mike Joyner and his colleagues at the Mayo Clinic found the same trend when analyzing the top 100 freestyle-swimming times of boys and girls from ages 5 to 18. Before the age of 10, both sexes are remarkably similar in performance, with the best young girls actually tending to swim faster than the best boys. But after 10, the boys get ahead. By 17, the average difference is 8.4 percent. Researchers found the same trend when evaluating more than 400,000 ordinary kids in the P.E.-class shuttle run: similar speeds early on, but an ever-widening gap starting at about age 10.

The reason for this is simple: puberty. The overwhelming driver for the sudden jump in male performance seems to be the surge, at this specific time of an athlete’s life, in the steroid hormone testosterone. This hormone influences muscle size and strength as well as the amount of oxygen-carrying red blood cells in our body. A large analysis on running, jumping, and swimming found that the rise in testosterone during puberty in males coincided with a steep improvement in performance. When puberty occurs, girls, on average, continue steadily improving their sporting performance into their teens. But boys get a rapid shift upward in their trajectory.

When looking at elite runners—whether sprinting 100 meters or racing many miles—once athletes hit physical maturity, the best men have anywhere from a 9 to a 12 percent advantage over the best women. A significant gap can be seen in cycling, swimming, speed skating, high-jumping, and a variety of other athletic feats. The gap is even larger in sports that depend highly on strength. For example, when looking at elite weight lifters in the same weight class, the performance gap is about 24 to 30 percent.

It’s important to note a few caveats. First, most of the best research is on sports that are easily quantifiable. For example, there’s no way to directly compare the skill levels of elite tennis players to measure for tiny performance differences unless they play one another. What we know is that the less a sport relies on speed, power, or endurance, and the more it relies on skill, the smaller the gap is. In sports like shooting and archery, the difference between men and women is negligible at best. Second, the performance gap of course doesn’t mean that all men will triumph over all women all the time. My comparatively unathletic brother would get beaten by thousands of women in a mile-long race. And if my wife showed up to a local turkey trot, she’d likely decimate all the men. Third, because there is significant overlap between males and females in performance, female outliers can shine, particularly in niche sports with a small number of competitors (e.g., ultrarunning).

But at the top of the top of the athletic world, in widely played sports with elite coaching, the gap between the sexes seems almost insurmountable. Take the queen of track and field, Allyson Felix. The 11-time Olympic medalist’s best 400-meter time ever is 49.26. In just the 2022 season, that would have put her 689th on the boys’ high-school performance list.

None of this is meant to disparage the phenomenal women athletes at the top of their game. But if we stopped dividing sport by sex, elite women’s sport as we know it could cease to exist. We might miss out on Megan Rapinoe at the World Cup or the spectacle of Sydney McLaughlin effortlessly gliding over hurdle after hurdle. Acknowledging the performance differential should encourage us to do everything possible to make sure female athletes can keep competing at these levels.

But how do we know that the gap between the sexes isn’t sociological, like we’ve seen in fields such as math, where research suggests that social factors explain much of the gender gap in average performance? The history of sport is rife with sexism that has held back women. Take, for example, the 1928 Olympics, where Knute Rockne, the famed Notre Dame football coach (and newspaper columnist), reported in The Pittsburgh Press that after the 800-meter final, five women collapsed and that “it was not a very edifying spectacle to see a group of fine girls running themselves into a state of exhaustion.” Following public outcry, the 800-meter was removed from the Olympics for 32 years. But the reports were false—women weren’t collapsing left and right. The top-three women actually broke the former women’s world record that day.

Women today still face inequality in sport. Many professional sports have a significant pay gap, limiting the ability of women to focus solely on it as a career. Media attention for women’s sport is severely lacking, with 95 percent of sports TV coverage in 2019 going to men, according to a USC/Purdue University study. In some colleges, a significant difference in funding and severe lack of female coaches—who act as both a role model and an advocate for women’s sport—can impact participation rates. Yet even in sports where sexist sociological barriers have been lowered, a performance gap can persist.

Women were barred from major marathons for much of the 20th century. The Boston Marathon, for example, didn’t allow women to compete until 1971. At that point, the women’s unofficial world record was about 2 hours and 45 minutes. At the same time, the men’s record stood at 2:08:34. That’s a massive 30 percent performance gap. By the summer of 1984, when women were finally able to run the marathon in the Olympics, they’d massively cut into the men’s lead, leaving only a 11 percent gap. These kinds of gains bred a sense of optimism. “We’re nearer and nearer the men now,” said the second-place female finisher of the 1983 Boston Marathon. But the trend faltered. In the nearly four decades since then, women have kept improving, but the current gap still stands at 10.7 percent.

Every sport is different. Some are still like 1970s marathoning—the chasm between men and women is caused in large part by discrimination. Those gaps need shrinking. But the same trajectory we saw in the marathon occurs in most women’s sports that remove sexist barriers. For example, a 2010 study traced the progression of male and female performance across the prior decades in 38 athletic events in five different sports: swimming, cycling, speed skating, weight lifting, and track and field. It found that the gender gap had been fairly stable for more than two decades, and concluded, “After a significant narrowing of gender gaps, women and men now evolve in parallel, in the same direction.”

The upside of acknowledging that sex differences in performance exist is that we can discuss the vital, knotty debates that emerge from this biology. For example, would creating more coed sporting opportunities before, say, age 10, keep girls in sport longer? How should schools and clubs handle a young female athlete who wants to play football even though there’s no girls’ team? Should we get rid of sex-based divisions in sports like shooting, where the performance gap is minimal? We certainly need to figure out better answers for trans athletes and people like Caster Semenya, who, because she has differences of sexual development, is allowed to compete in the 5K but not the 800-meter race.

To solve these questions, we need to first accept the premise that puberty can create unequal sporting ability. Doing so doesn’t mean that we stop fighting inequality or dismiss tricky edge cases. It actually should free us from arguing over what should be a noncontroversial claim. We can then shift our focus to making sure women have the space, resources, and opportunities to show their talents. We can acknowledge that though I might have run faster at my peak, my wife’s performance and achievements are undoubtedly more impressive. We can stop judging female athletes against their male counterparts and enjoy their athleticism on its own accord.