With the Summer Olympics set to begin July 27 in London, the International Olympic Committee (IOC) has ruled that women with hyperandrogenism — a condition in which the body produces excessively high levels of androgens, “male” hormones with performance-enhancing effects — may be declared ineligible for competition.

Prompted by several high-profile cases of gender ambiguity in international athletic competition — among them the controversy surrounding South African middle-distance runner Caster Semenya, the 2009 world champion at 800 meters who was later found to have unusually high levels of testosterone and both male and female organs — the IOC’s ruling has frustrated intersex activists who advocate for an identity-based, rather than biology-based, classification of athletes. People who identify as women, such advocates have suggested, ought to be allowed to compete as women, regardless of their physical characteristics. As Barbara King wrote at npr.org, “Excluding athletes who have trained and competed as women from the Olympics on the basis of naturally occurring hormones in their blood inappropriately reduces athletic ability to hormone levels, and gender to biology.”

This type of argument makes some excellent points. First, the IOC ruling held that androgen levels falling into the “male range” might render hyperandrogenic female athletes ineligible. Androgens, however, occur naturally in both males and females, and just as some women are taller than some men, some women have higher androgen levels than some men. It is therefore unclear precisely why the term “male range” should be used to describe androgen levels, any more than heights between 5-foot-8 and 6-foot-5 should be called the “male range.”

Furthermore, the ruling appears discriminatory on its face — male athletes with abnormally high but naturally occurring levels of testosterone are not subject to expulsion from the Games. Why should women with abnormally high levels of androgens be subject to regulations while men with similarly unusual levels are not?

But I ultimately disagree with the idea that gender classifications in competitive sport should be made on the basis of self-defined identity rather than biological indicators. Reasons unique to the nature of athletic competition dictate that we decide otherwise.

First and most simply, there is a very important purpose for drawing lines — yes, sometimes arbitrary and sometimes apparently irrational — between men and women in the arena of sports that do not exist in society at large. That purpose is ensuring that women have a safe, productive and fruitful arena in which to compete on an equal playing field, just as men do.

Completing the fight began with Title IX. Without a distinction between men and women on the playing field — in other words, in a world in which the only deciding factor was absolute performance — there would not be a single woman at the Olympics, and few in college or professional sports, today.

If we accept the necessity of drawing some sort of line, it also follows that there will be some people — hopefully as few as possible — who fall unfairly on the wrong side of it, much as some teenagers are mature enough to drink at 17 and some 30-year-olds are not, or some 15-year-olds are intelligent and well-informed enough to vote and some 50-year-olds are not. Our goal should therefore be minimizing the error zone of a clearly necessary line, not eliminating it altogether.

Last, unlike matters of human rights or political equality, athletic competition is a zero-sum game. Gains for one — at least in terms of places, medals and points, the primary indicators of Olympic success — are necessarily made at the expense of another. If Athlete A wins gold, Athlete B by definition cannot. While allowing intersex or high-androgen individuals to, for example, participate fully in society, to vote and to hold jobs on the basis of their self-identity expands the pie of rights and abilities available to all, allowing intersex individuals with abnormally high levels of male hormones to compete as women unfairly disadvantages other women.

Ultimately, changes to IOC policy should certainly be made. The science behind the logic needs updating, more thought should be given to defining a “normal male range” and the IOC should consider what to do with hyperandrogenic men.

But that is insufficient reason to do away with the concept of a line between men and women in sports — a line that works to the benefit of both women and the athletic world at large.

Miles wants to hear what you think about gender lines at the Olympics. Email him your views at milesu1 “at” stanford “dot” edu.