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“There are only two sexes.”

At a moment when transgender people face unprecedented visibility and vulnerability, this claim pervades the discourse surrounding our identities. We hear it everywhere: in the media, in our legislatures, and, yes, at our very own university.

Even when it is not being used to categorically deny the existence of trans people, this claim is weaponized to qualify our validity. The argument goes as follows: “Trans people can ask to be called whatever they want, but they can’t change the fact that there are only two sexes.”

The idea that sex is binary is presented as an irrefutable fact of life, the most natural truth in the world. Anyone who dares question this “fact” is quickly discounted as a “radical, woke ideologue” or an agent of the “liberal DEI agenda.”

This line of thinking is dangerous and deeply alarming. The truth of the matter is that sex is not a simple binary. To claim otherwise is overly simplistic, flawed, and harmful.

Let us first clarify what the claim “sex is binary” actually means. This framework organizes the human sex into two distinct categories: male and female. These categories encompass a variety of biological characteristics. Males have a penis, testes, higher levels of testosterone, and XY chromosomes. Females have a vagina, ovaries, higher levels of estrogen, and XX chromosomes.

At least, that’s what they teach you in sex ed.

But this is not the full story. What about people who don’t fit neatly into one of these two categories? What about people with ambiguous genitalia, or those who have the genitalia typical of one sex but the chromosomes and anatomy typical of the other?

These are not abstract what-ifs. As many as one out of every fifteen hundred babies is born with ambiguous genitalia. Many more are born with another type of sex variation, though some are more subtle or late to manifest.

People whose sex falls outside of the binary are known as intersex, and experts estimate that they make up as much as 1.7 percent of the population.

It may feel tempting to dismiss this number as insignificant, but consider: It is almost exactly similar to the number of people born with red hair. Think about the number of redheads you’ve met. You’ve likely encountered a comparable amount of intersex people, even if you don’t know it.

This is where the sex binary fails us. How can it be an undeniable, natural truth that there are only two sexes if we consistently observe a myriad of naturally-occurring variations in sex?

The answer? It isn’t. Saying there is only male and female is like saying there’s only blond and brunette — the sex binary is a social construct, not a biological fact.

This is not to say that sex itself isn’t real. Though sexed traits vary between people, we do all have our own specific and discernable set. However, the labels “male” and “female” only have meaning because we attach specific values to them.

Perhaps the best evidence of the sex binary’s social construction is the fact that it hasn’t always existed. Ancient Greek scholars understood men and women not as members of two distinct sexes, but as variations of a singular sex. Female genitalia and male genitalia were distinguished by location — internal versus external — rather than structure.

It was not until the 18th century that a binary model for sex became prevalent in Western society, and at the time it was deeply connected to eugenics and scientific racism.

The sex binary is a human invention — one that is driven, at least in part, by political motives. As a society, we are deeply invested in this invention, having imbued the binary with immense power and influence. This raises several points of concern.

First, it is bad science. Treating the sex binary as an immutable fact ignores the ample evidence that calls it into question, producing biased research design and results.

Peer-reviewed research contradicts a strictly binary interpretation of sex. We have yet to uncover a precise causal mechanism that definitively and consistently guarantees an individual’s sex. Though many suggest that chromosomes are the determining factor, science supports that sex differentiation is a much more complex process.

Second, in failing to account for the wide range of human variation, it harms anyone who does not fit neatly within it — namely, intersex and transgender people.

The presumed verity of the binary is weaponized to force conformity upon those who are different. This is what allows conservative politicians to pass harmful laws that ban gender-affirming care for trans people (under the guise of protecting children) while maintaining carve-outs allowing damaging “corrective” surgeries on intersex babies.

I am not calling for the complete abandonment of the sex binary, much less its prohibition. While it is a flawed and outdated model for understanding sex, this does not mean it has no utility. The categories of “male” and “female” are certainly still valuable and applicable to broad swaths of the population.

However, we must not accept the binary as an indisputable and restrictive truth. To do so is not only dangerous to those who fall outside of these two categories, it is antithetical to the very spirit of scientific inquiry.

Great scientific breakthroughs have always been outrageous and controversial. But here at Harvard, our motto is simple: Veritas. Truth.

We must never stop striving for truth — even when it is difficult, even when it requires us to challenge the status quo. This should not be any different when it comes to sex.

E. Matteo Diaz ’27, a Crimson Editorial editor, lives in Grays Hall. His column, “Transcriptions,” runs bi-weekly on Thursdays.

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