The Science Behind the Sex Divide in Sports

A new review paper shows that the athletic performance gap between males and females is real, measurable, and matters at every age.

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About the Author

Dr. Colin Wright is the CEO/Editor-in-Chief of Reality’s Last Stand, an evolutionary biology PhD, and Manhattan Institute Fellow. His writing has appeared in The Wall Street Journal, The Times, the New York Post, Newsweek, City Journal, Quillette, Queer Majority, and other major news outlets and peer-reviewed journals.

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The debate over fairness in women’s sports has become a major cultural issue in recent years, as sports organizations and political leaders try to figure out how to handle the participation of transgender women—biological males—in female sports categories. Most Americans support keeping sports divided by sex, but political responses have been deeply split along party lines. President Donald Trump has made this a key issue, recently announcing an executive order called Keeping Men Out of Women’s Sports. The order aims to protect Title IX and ensure that only biological women can compete in female sports. A few weeks later, the Trump administration also cut off $175 million in federal funding to the University of Pennsylvania over how it handled the case of Lia Thomas, a male swimmer who competed on the women’s team after hormone treatment.

Polls consistently show that about 70–80 percent of Americans believe male athletes shouldn’t compete against females, but the Democratic Party has had difficulty separating itself from its more progressive wing on this issue. As a result, many voters—especially women and girls—feel frustrated, since their opportunities, safety, and fairness in competition are directly affected.

In an effort to move beyond politics and focus on facts, a new paper in the Journal of Applied Physiology titled “Evidence on sex differences in sports performance” offers a timely, in-depth look at the biological differences between male and female athletes. Written by experts in physiology and sports medicine, the review examines performance differences before and after puberty and provides a solid foundation for understanding what true fairness in sports means.

One of the paper’s main findings challenges a popular argument made by some inclusion advocates—that male athletes who block puberty before adolescence can compete fairly against females. In reality, the evidence shows that meaningful performance differences between boys and girls exist even before puberty begins. These differences, while smaller than those observed in adulthood, are nonetheless significant—and they demonstrate that blocking puberty does not eliminate the athletic advantage conferred by male biology. The takeaway is this: both men who went through male puberty and those who blocked it still have physical advantages that make competition unfair for females.

The review highlights seven major conclusions about the nature and persistence of sex-based differences in athletic performance. In the sections that follow, I’ll go through each one—explaining the evidence behind them and what they mean for policymakers, sports regulators, and the broader public conversation about fairness and inclusion in sports.