Biology is under siege from activists trying to undermine our long-established, universal understanding of what constitutes male and female organisms. These are not merely cloistered academic debates; this ideologically motivated pseudoscience is having a profound impact on society. It affects the existence of female-only spaces such as bathrooms, dressing rooms, rape shelters, and jails/prisons, as well as the safety and fairness of female-only sports leagues and events. It also shapes the debate over “gender-affirming care,” which seeks to alter the bodies of sex-nonconforming children so that their physical features align with their self-proclaimed “gender identity.”

Biological science, however, is firmly on the side of the sex realists. The setbacks this side has experienced in recent years owe not to the weakness of its arguments but to the climate of fear pervading academia, which silences dissent. Those who challenge gender ideology’s prevailing narrative—namely, that biological sex is a social construct or exists on a spectrum—are often targeted, harassed, and publicly branded as “transphobic” bigots. Proponents of gender ideology understand that the biggest threat to their movement is open and honest debate. This is why, for the past five years, I have dedicated myself to educating the public on this topic, and openly engaging with gender ideologues whenever possible.

Last month, such an opportunity presented itself. Ian Copeland, who describes himself as a “Ph.D.-level geneticist,” though he has not published any peer-reviewed scientific work, announced that he would host an event on X Spaces to defend the view that “sex is not binary.” Copeland made this announcement after posting various misleading statements about sex biology on X. For instance, he asserted that “Sex (like all traits) is not binary” and that “All traits are on a spectrum.” He seemed to think that a BBC Earth article discussing the sex-changing abilities of a species of fish, the Asian sheepshead wrasse (Semicossyphus reticulatus), supported his claims. He also stated that “sex is a genotype classification,” arguing that the existence of sex chromosome aneuploidies (atypical combinations of sex chromosomes other than XX and XY) proves the nonbinary nature of biological sex.

The X Spaces event, titled “Bring the Facts: Sex Is Not Binary, Sorry to Burst Your Bubble . . . ,” was scheduled for January 19 at 3:45 p.m. I joined the moment that it opened to request a speaking slot, ensuring I was not far back in the queue. My promptness paid off: I was the first to address Copeland’s deep misunderstandings about the biology of sex.

My primary goal in public debates like these is not necessarily to convince my opponents of their error, though such an outcome would be welcome. Rather, my aim is to demonstrate to the audience what honest truth-seeking sounds like by presenting my arguments as honestly, clearly, and calmly as possible. I believe that observing the stark contrast between a genuine academic and a radical activist can be a powerful means of persuading the openminded.

I began the debate by explaining the biological perspective on why “sex is binary,” and what this phrase signifies. In essence, “sex is binary” refers to there being only two sexes, which are defined by the type of gamete an organism has the function to produce. Males have the function of producing sperm, and females, ova. Sex ambiguity (that is, “intersex” conditions) does not constitute a third sex, as these conditions do not lead to the production of a third type of gamete.

Copeland did not dispute any of this. Yet he insisted that “genetic sex” is not binary, citing the existence of other sex chromosome compositions beyond XX (female) and XY (male), such as X0 (Turner syndrome), XXX (Triple X syndrome), XXY (Klinefelter syndrome), XYY (Jakobs syndrome), and so on. He claimed that if an organism’s “genetic sex” is defined by their sex-chromosome composition, then there must be more than two sexes.

This argument, seemingly logical on its face, stems from a common yet fundamental misunderstanding of what sex is and what geneticists mean by “genetic sex.”

Put plainly, “genetic sex” is a misnomer. While the term is frequently used in medical and scientific papers, government health websites, medical centers, and even by popular human-ancestry companies like 23andMe, “genetic sex” is not a distinct type of sex at all; it is a convenient term or shorthand to denote that a person or cell contains the sex chromosomes that typically cause a male or female to develop. For a geneticist, knowing this about a cell or cell culture might be useful if he is investigating sex differences or wants to control for cellular sex differences as a potential confound in an experiment. Medical professionals often describe sex in multifaceted terms because examining a person’s chromosomes, hormones, genitals, and gonads, and their alignment, aids in diagnosing potential issues along this biological chain. For example, if you’re a male suddenly stricken with abnormally low testosterone, this may be indicative of hypothalamic or pituitary abnormalities, or even testicular cancer. Conversely, abnormally high testosterone in females may by indicative of ovarian cysts. The use of terms like “genetic sex,” “hormonal sex,” and “genital sex,” is driven by practicality, not because they represent legitimate, separate types of sex.

“Genetic sex” is not an alternative type of sex. “Sex” refers only to the type of gamete an organism has the function to produce. This becomes obvious when we look at other animals, such as turtles, that do not use chromosomes to guide their sex development. The sex of green sea turtles (Chelonia mydas) is determined by temperature. Eggs incubated below 27.7°C develop into males, and eggs incubated above 31°C develop into females.

Discussing humans as having a “genetic sex” that’s equivalent to their sex based on gametes is as illogical as referring to turtles as having a “temperature sex” distinct from their actual sex. We may use terms like “male temperatures” for those under 28°C and “female temperatures” for those over 31°C as shorthand for “temperatures that typically lead to male or female development,” but there’s nothing inherently “male” or “female” about these temperatures. A turtle’s sex is ultimately defined by the gamete it has the function to produce, not the temperature of its early days in the egg. For instance, if a female turtle popped out of an incubator set below 28°C, we wouldn’t say that she has a female “gametic sex” and a male “temperature sex.” She would simply be female, and the researchers would likely be intrigued to learn how she developed at a temperature typically associated with male development.

In a similar vein is the Blue Groper (Achoerodus viridis), a fish species characterized by blue males and brown females. In the field, it may be useful for researchers to use color as a quick and accurate proxy when recording a fish’s sex. But it would be incorrect to claim that Blue Gropers have a “color sex,” as there is nothing inherently “male” about being blue or “female” about being brown. Being male or female causes color dimorphism in Blue Gropers, not the other way around. 

Chromosomes in humans and color in fish can serve as operational definitions of sex, but they are neither the essence of sex nor an alternative type of sex. The association of Y chromosomes with human males and the link between color and sex in Blue Gropers are known precisely because sex is a trait distinct from chromosomes or color.

The philosopher of science Paul E. Griffiths makes the same point in a 2021 paper titled “What Are Biological Sexes?”

Biologists know which chromosome pairs are “male” or “female” because they know which animals are male or female, using the gametic definition. . . . The same problem defeats any attempt to define sex in terms of phenotypic characters. . . . Something gets to be a “male” or “female” characteristic in a particular species because it is common in males or females in that species: sexual characteristics are defined by sexes, not the other way around. Like chromosomal definitions of sex, phenotypic definitions are not really “definitions”—they are operational criteria for sex determination underpinned by the gametic definition of sex and valid only for one species or group of species.

This is the fundamental point that Copeland and many others who use the term “genetic sex” fail to grasp. “Genetic sex” is nonsensical because it requires the primacy of the gametic definition of sex.

Despite my efforts to guide Copeland through this logical reasoning, he ultimately refused to acknowledge it. His only defense was that certain medical bodies use the term “genetic sex,” so it must be legitimate. However, this is simply an argument from authority. Furthermore, the popularity of a term is irrelevant to the truth. My reference to Griffiths above is not to counter Copeland’s authority with another authority; that’s not how science operates. Anyone can find a peer-reviewed scientific paper, or a Ph.D. holder, to support his desired beliefs. Instead, we must make arguments and cite sources rooted in evidence and that make the most logical sense.

The prevalence of the term “genetic sex” among scientists, medical organizations, and in genetics textbooks does not establish its validity as a type of sex on par with the gametic definition. I hope this helps put the “genetic sex” myth to rest.

Photo: by_Djenka/iStock/Getty Images Plus


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