The Sex Binary is Not ‘High School Biology’

A biologist breaks down an activist's arguments against biological reality.

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Yesterday, conservative commentator Matt Walsh from the Daily Wire shared a video on Twitter from a Q&A session at a Young America's Foundation (YAF) event where he gave a talk about gender ideology. During the Q&A, a trans-identified male gender activist was given the microphone and asked Walsh the age-old question: “How would you define a woman?” As expected, Walsh replied promptly, “An adult human female.” The questioner followed up with, “And how doesn’t a transgender woman fit that definition?” to which Walsh replied, “Because they’re not female.”

Matt Walsh @MattWalshBlog

A trans EMT tried to use his medical training to prove that sex is not binary. He ran into trouble when I asked him how he’d respond to a patient with a penis who claims he’s having a miscarriage.

After these initial questions, a back-and-forth discussion about biological sex ensued between Walsh and the activist. The activist employed several tricks and made false claims to throw Walsh off track, such as citing intersex conditions, dismissing the sex binary as amateurish “high school biology,” and insisting that sex is now universally regarded as a “spectrum” by expert researchers.

Walsh did a commendable job responding and keeping the discussion on topic. However, as a biologist, I would like to scrutinize each of the activist’s claims in detail and explain why they are inaccurate.

One of the first tricks the activist used when Walsh asked him whether he was “biologically male” was to deflect the question by bringing up intersex conditions: “I said I’m transgender. I might be intersex for all we know. Almost as many people in the world are transgender as intersex, and a lot of people don’t know.”

As I explained in a recent article, this strategy is called the “intersex trap,” and it works by attempting to steer discussions about people who are unambiguously male and merely “identify” as women toward a debate about various complex intersex conditions. This tactic is effective because it can cause people to hesitate and struggle to give straightforward answers, making them appear foolish, and shifts the subject away from something simple (stating the plain fact that transwomen are male) to something complex (making endless judgment calls on complicated intersex conditions). The Intersex Trap is, in other words, a red herring.

Fortunately, Walsh saw through this attempt to derail the conversation and asked the activist directly whether he believed a transwoman is female. The activist responded, “By the definitions I’m familiar with, yes.” Walsh then asked the obvious follow-up, “So how would you define female?” And the activist provided an answer:

Through my training, in healthcare, there are several different categories for how we define sex. People bring up chromosomes. People also bring up hormone levels. People bring up all sorts of other categories. Lots of people don’t fit neatly into a gender binary. Even people we don’t consider to be intersex. [confusing sex and gender here] It’s a complicated spectrum.

Walsh pointed out that the activist failed to define “women” or “female” in his response. So he asks again: “What is a woman? What is a female? What do these words mean?”

It’s complicated. And I know you’re not going to like that answer, but that’s because there are no simple answers in human biology. You guys like to bring up high school-level biology classes a lot. I get that a lot, but people who go on to more complicated biology classes will talk about sex as a spectrum.

When Walsh rejects the claim about sex being a spectrum, the activist retorts that, “biological researchers would disagree with you.”

The activist made several false claims that require addressing. The first claim pertains to a person’s sex being determined by a combination of various factors such as chromosomes, hormone levels, and “all sorts of other categories.” This claim is unfortunately common and even appears in top science and medical journals. However, it is based on a fundamental misunderstanding about the definition of sex, which is rooted in the binary distinction of having the function of producing either sperm or ova. While it is true that males and females in humans and many other species differ on several axes, it is essential to understand that not all sex differences are differences of sex.

In mammals and birds, for instance, chromosomes play a mechanistic role in “determining” whether an embryo develops into a male or female. However, chromosomes do not define what a male and female is. This fact is evident by the existence of many species that have male and female sexes but do not have sex chromosomes, such as many reptiles that use temperature to guide sex development.

Hormones are also a trait that differs between human males and females, yet they do not factor in when categorizing people by sex. Rather, hormones like testosterone and estrogen guide the development of secondary sexual characteristics that emerge during puberty. For males these traits include facial hair, deeper voices, an Adam’s apple, and more upper body muscle, and for females, they include breasts, wider hips, and so on. However, these traits are downstream consequences of one's sex and do not individually or collectively define a person’s sex. Some females may have deep voices, and some males may develop breasts. Although these traits are atypical for females and males, respectively, they do not have any bearing on a person's sex, which is always defined by the type of gamete (sperm or ova) that a person has the function of producing.

Moving on, the activist appears to conflate sex and “gender roles” when stating, “Lots of people don’t fit neatly into a gender binary. Even people we don’t consider to be intersex.” This is false for two reasons. The first is that the existence of intersex conditions does not undermine the sex binary because all the sex binary means is that there are only two sexes. Being sexually ambiguous is not a third sex. The second reason is that the so-called “gender binary” in Gender Studies refers to the social roles and expectations placed on individuals because of their sex. It should not be confused with the sex binary, which refers strictly to the binary distinction between sperm and ova. Activists often use the words “sex” and “gender” interchangeably in order to sow confusion and further their agenda.

The activist also claimed that “there are no simple answers in human biology.” This is not correct. Although development, including sex development, is a very complex process, this does not entail that the end products are equally complex. Variation among individuals exists, but it almost always falls within the bounds of people being clearly and unequivocally either male or female. Intersex people, defined by the appearance of sex ambiguity, occur only in 0.018 percent of humans. See the figure below for a visual representation of this.

For the overwhelmingly vast majority of humans, the answer regarding their sex is very simple.

The activist’s final attempt to win the argument relied on likening the sex binary as “high school-level biology” and insisting that “biological researchers” now all agree that sex is a “spectrum.” Walsh was correct in describing researchers who would say that as being “full of shit,” though I would also add “extremely ignorant” as another option given the sheer amount of propaganda out there on the biology of sex.

It’s ironic that the activist criticized the sex binary as “high school-level biology” while promoting the unproven concept of the sex spectrum, which is often popularized in unreviewed science magazines and cartoon teaching aids aimed at children like the Genderbread Person and the Gender Unicorn.

People can easily be misled when something appears complex, mistaking it for being scientific or nuanced. This is why concepts like the “sex spectrum” and multivariable models of biological sex can seem attractive. It’s also useful in debates because presenting complex models allows one to portray themselves as having a colorful and sophisticated view of biology, while their opponents are stuck in the past viewing the world in simplistic black and white. However, this is merely ideological rhetoric designed to make you doubt your own eyes.

In reality, the fundamental concept of biological sex is very simple. Yet this simplistic binary at the root of sexual reproduction gives rise to endless and complex forms. Far from limiting our ability to see nature’s complexity, the fundamental binarity of sex serves as a central organizing principle that affords us a much deeper understanding into patterns of evolved sex differences in nature than would be possible by looking at individual traits in isolation.

Ignoring the fundamental causes underlying general patterns will sacrifice true understanding and turn science into a collection of random unrelated facts.