Who could have dreamt of reading, in an order signed by the President, that “it is the policy of the United States to recognize two sexes, male and female”? Governing institutions are not in the habit of affirming widely known scientific truths. Perhaps the last time that happened was in 1992, when the Catholic Church officially acknowledged—more than 350 years after Galileo’s trial—that the Earth orbits the Sun. And yet, those were the words of Donald Trump’s Executive Order (EO) of January 20, 2025, “Defending Women from Gender Ideology Extremism and Restoring Biological Truth to the Federal Government.”
The EO defines each sex in terms of the size of “reproductive cells,” and defines a woman as an “adult human female” (with similar definitions for men, girls and boys). But why was it felt necessary to define “male” and “female” at all, let alone in terms of “reproductive cells”? “Male” and “female” are common words in everyday speech. The same goes for “woman” and “man,” which are ubiquitous. And where did the EO’s defining phrase “adult human female” come from?
The answers lie across the Atlantic, in that drizzly sceptered isle, known affectionally to its gender-critical inhabitants as TERF Island. “British feminists,” Susanna Rustin writes in her fine history of British feminism, Sexed, “are at the heart of the movement to resist the philosophy or ideology that says every human being has an inner gender.” Some of these feminists may not wish to admit it, but Trump’s Executive Order owes much to them.
“Female” vs. “Woman”
It’s often difficult to trace the passage of words and ideas, but for the EO’s phrase “adult human female,” there’s little doubt about its origin. In 2018, the phrase briefly appeared in September on a billboard in Liverpool, put there by the activist Kellie-Jay Keen-Minshull, reproducing Google’s (then) definition of “woman.”
One consequence of the ensuing fuss over Keen-Minshull’s stunt was that “adult human female” caught on with British feminists who opposed reforms to the 2004 Gender Recognition Act, which would have ushered in a form of gender self-identification. The opposition succeeded: the reforms were dropped in England and Wales in 2020, limping on in Scotland before being finally crushed in 2023. (Keen-Minshull would later become a controversial figure in gender-critical circles, partly because of her association with the religious right.)
The background to the definition of sex in Trump’s Executive Order is fascinating, albeit less straightforward. But before getting to that, a striking asymmetry in the critical responses to the EO is worth pointing out. Almost without exception, critics attacked the definitions of “female” and “male,” which were:
“Female” means a person belonging, at conception, to the sex that produces the large reproductive cell.
“Male” means a person belonging, at conception, to the sex that produces the small reproductive cell.
The definition of “woman” as “adult human female” received almost no resistance. The news coverage gave the impression that experts on biology resoundingly rejected the EO’s definition of “female” and “male,” while no experts of any kind disputed the definition of “woman” and “man.”
If you know anything about this subject, you’ll realize that this is rather odd. The EO’s definition of sex is close enough to orthodoxy, at least among evolutionary biologists and philosophers of biology. The EO’s definitions of “woman” and “man,” on the other hand, are almost universally rejected by academics in gender studies and philosophers of sex and gender.
According to the renowned feminist legal theorist Catharine MacKinnon, to think that a woman is a mature female of our species, the human equivalent of ewes, lionesses, and peahens, is to be guilty of “biological essentialism.” “Women are not simply adult (human) females” concludes a recent paper in Hypatia, the leading journal of feminist philosophy. The title of another recent philosophy paper couldn’t be more explicit: “Women are not adult human females.”
Experts love being quoted as authorities in popular media, pontificating in op-eds, and generally having their expertise recognized. Why have no prominent experts patiently explained why the EO’s definition of “woman” is—as MacKinnon maintains—philosophically naïve and seriously mistaken? If the biologists can dumb things down, why not professors of philosophy or gender studies? If there really are powerful objections to the EO’s definition of “woman,” then prizes and plaudits await the scholar who can clearly make the case to the public. Every incentive is in place, and yet no one is prepared to speak up.
Perhaps the reason for the radio silence is that any objections will seem rather strained when stated in plain English. Be that as it may, the kerfuffle over sex is more interesting. Let’s start with some biology.
Sex: A Brief History
Female and male organisms first got together at least a billion years ago, so the two sexes have been around for a very long time. Humans have always noticed this division among themselves, and it’s easy to generalize to numerous other animals, and even plants.
People can distinguish between females and males, as they can between lumps of gold and iron, while only having a superficial understanding of the items they are distinguishing. The ancient Egyptians knew that gold and iron were different, but had no inkling of modern chemistry, metallic bonding, the periodic table, and all that. We now know the fundamental constituents of gold and iron; the ancient Egyptians did not.
Likewise, the ancient Egyptians knew that cats come in female and male varieties, despite being clueless about modern biology. The female cats are the ones that give birth and suckle the kittens, so that’s an easy way of telling them apart from males. But that doesn’t work in all cases: the female ibis produces her young by laying eggs. She nourishes them, not by suckling, but by regurgitating food, which the male ibis does as well. Date palms were grown in ancient Egypt: the female is the one that produces dates, which contain seeds that grow into new date palms. No birthing or suckling there either. Perhaps the “females” of these different organisms only resemble each other in some vague analogical way.
Sexual reproduction remained something of a mystery for the next five millennia, until the German physician Theodor von Bischoff hypothesized in the mid-nineteenth century that it involved the fusion of (in the EO’s language) two “reproductive cells”—one sperm and one ovum, or egg. The sperm is small and relatively simple, the egg large and much more complicated. When von Bischoff’s theory was later confirmed, it was a short step to uncovering the deep distinction between females and males: females produce large reproductive cells (or gametes), males produce small ones. What about producing both? Some animals (and many plants) do just that: they are hermaphrodites—female and male.
Here’s Robert Payne Bigelow, a biology professor from my own university, writing in 1903:
The ability to produce a macro- or microgamete constitutes the essential distinction of sex. The individual which produces the latter is said to be of the male sex, the individual producing the former is said to be of the female sex. In most of the higher plants and in a few of the lower animals both sexes are included in a single individual, which is then said to be hermaphrodite.
The French philosopher Simone de Beauvoir noted that the sexes are “defined primarily … by the gametes which they produce—sperms and eggs respectively” in The Second Sex, published in 1949. Yet in her 2023 book Beyond the Binary: Thinking About Sex and Gender, the feminist philosopher Shannon Dea tells us that “papaya trees come in three sexes—male, female, and hermaphroditic.” That is wrong, as Bigelow made clear 120 years earlier. Hermaphroditic papaya trees are both male and female, not a third sex.
Although blissful ignorance reigns in some parts of the academy, it’s not as if the definition of the sexes in terms of gamete size remained an esoteric secret carefully guarded by biologists. For instance, in Richard Dawkins’ The Selfish Gene—published in 1976 and once voted the most influential science book of all time—we learn that females are the ones with “large sex cells,” while males have the small kind.
Since there are no intermediate-sized gametes, there are exactly two sexes. For the same reason, sex is not any kind of “spectrum,” although of course males and females can differ on various “spectrum-like” traits. Male stag beetles have large mandibles, but some males have larger mandibles than others. Pregnant human females have high levels of the hormone prolactin, but some females have higher levels than others. Some sex-related traits are on a spectrum, but sex itself is not.
“Shockingly out of step with what we know from science”
In short, the EO’s definitions of “female” and “male” are right, or at least substantially on the right lines. (On February 19, the Department of Health and Human Services issued a memo with improved versions.) So why the furor? What were the experts’ main complaints?
Some struggled with reading comprehension. The Director of the Centre for Indigenous Initiatives at Carleton University criticized the claim that there are “two genders” as “ignorant,” evidently thinking of so-called “third genders” in some traditional North American societies. But the EO pronounces on the number of sexes, not on the special cultural arrangements that have sometimes been made to accommodate homosexual men. In any case, even if the EO had said there were only two “genders,” it would have used the word as a synonym for “sex.”
Others were just painfully muddled. A biological anthropologist at the University of Urbana-Champaign declared that sex has multiple definitions, each valid for different purposes. One definition “is around typical hormone ranges. [For instance, people with] polycystic ovary syndrome end up having androgen levels that are very different from those of most people that we might put in the sex category of female.” The suggestion seemed to be that on one acceptable definition of “female,” people with polycystic ovary syndrome aren’t female because they have (relatively) high androgen levels. (The clue is in the name: polycystic ovary syndrome.)
Any acceptable definition of sex needs to get the right results for cats, ibises, and date palms, and one based on circulating hormones won’t. A definition based on chromosomes works for cats and date palms: they both employ the XX/XY sex determination system, with the males being XY. But ibises have it the other way round: the lady ibis is the one with different sex chromosomes. And what about other animals known to the ancient Egyptians, such as the Nile crocodile and the honeybee? The sex of a baby croc is determined not by chromosomes, but by the temperature of the nest, and male bees develop from unfertilized eggs, with half a set of chromosomes.
There is no definition of sex other than the standard gamete one that classifies female humans, cats, ibises, date palms, crocodiles, and bees correctly. That did not stop the anthropologist from saying that the EO “misunderstand[s] basic human biology.”
Anthropologists can be flaky. Still, one might have expected the Presidents of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biologists to get basic biology right. However, according to them, in a letter to Trump and members of Congress, sex is a spectrum, a “continuum of male to female.” This “continuum” apparently has something to do with “chromosomes, hormonal balances, … gonads, external genitalia,” although the three presidents declined to spell out the details. Presumably, on this account, women with polycystic ovary syndrome are mostly-but-not-entirely female—perhaps a slight improvement on the anthropologist’s position. The biologist Jerry Coyne dissected the letter on his blog, writing in an email, “I used to be President of the Society for the Study of Evolution. Now it embarrasses me.”
The British Gender Wars
Since plenty of academics will be stumped to explain what female cats, ibises, date palms, crocodiles and bees have in common, we shouldn’t expect people with proper jobs to do any better. Still, there’s more public awareness of the gamete definition of sex than one might have guessed. This is surely due to the British gender wars, which started to heat up around 2018.
Emma Hilton, a developmental biologist from the University of Manchester, bravely volunteered for the Gender-Critical Twitter Regiment. She began tweeting anonymously, using the handle @fondofbeetles, an allusion to a quip attributed to the biologist J. B. S. Haldane (who mused that the Creator must have an “inordinate fondness for beetles”). In a February 2018 tweet, Hilton identified females as belonging to “the sex that produces ova.” Along with some other gender-criticals, she was an early “adult human female” adopter, tweeting in August 2018 (a month before Keen-Minshull’s billboard) that “woman” is a word “referring to an adult human female.”
In May 2019, Hilton tweeted a classic thread illustrating why the gamete definition is the only one in town. Later that year, she broke her cover with the hashtag #fuckfear—a blunt reminder that the gender wars inflicted real damage to careers and reputations. “Thinking of Magdalen,” she wrote in the next tweet in the thread, a reference to Magdalen Berns, a legendary gender-critical YouTuber who had died of cancer that very day, aged 36. In 2020, Hilton wrote a Wall Street Journal article with the US biologist Colin Wright, “The Dangerous Denial of Sex.” Not quite beetlemania, but Hilton certainly influenced both sides of the pond.
One bunker buster bomb dropped by the gender-critical side was J. K. Rowling’s tweet (322,000 likes to date), at the end of 2019:
Dress however you please. Call yourself whatever you like. Sleep with any consenting adult who’ll have you. Live your best life in peace and security. But force women out of their jobs for stating that sex is real? #IStandWithMaya #ThisIsNotADrill
“Maya” was the British researcher Maya Forstater, who had lost a consulting contract due to her gender critical opinions, primarily expressed on Twitter. Forstater had taken her employer, the Centre for Global Development (CDG), to an employment tribunal, and the day before Rowling’s tweet, the tribunal judge had ruled that Forstater’s beliefs were “not worthy of respect in a democratic society.” (“This Is Not a Drill” is the title of an essay dashed off immediately after the judgment, by the philosopher Kathleen Stock.)
Forstater’s witness statement (October 2019) prefigured Trump’s EO on both “female/male” and “woman/man”:
Males are people with the type of body which, if all things are working, are able to produce male gametes (sperm). Females have the type of body which, if all things are working, is able to produce female gametes (ova), and gestate a pregnancy.
Women are adult human females. Men are adult human males.
With “all things are working” Forstater even anticipated the (facile) objection that males or females might lack the capacity to produce gametes, due to immaturity, disease, old age, and so on.
Forstater knew Emma Hilton, but she didn’t learn the gamete definition from her. As a teenager, Forstater had read The Selfish Gene. The night before the employment tribunal hearing, Forstater phoned Hilton to check some facts about “intersex” conditions, which she anticipated would be mentioned. Sure enough, they were brought up by CDG’s barrister, who referred to a 2016 expert declaration written by Dr. Deanna Adkins, a gender specialist at Duke University in the US. In her recitation of the gender identity catechism, Adkins dissolved sex away, replacing it with gender identity: “From a medical perspective, the appropriate determinant of sex is gender identity.” In a saner age, an employment tribunal judge would have raised an eyebrow at this pronouncement. Not Forstater’s judge, who made no objections.
After Forstater lost her case, and Rowling tweeted her support, there was a huge public outcry. Forstater appealed, the judgment was reversed, and in 2023 she was awarded more than £100,000 in compensation and aggravated damages. Closing a circle that began with a youthful reading of The Selfish Gene, in 2024 Forstater hosted Richard Dawkins in the House of Lords on behalf of Sex Matters, a human-rights charity she co-founded with Emma Hilton and two lawyers.
Last April, Rowling tweeted, “I believe a woman is a human being who belongs to the sex class that produces large gametes.” Gametes were in the air—as they literally are when flowers bloom. Some of them drifted from TERF Island to America.
The house of genders has begun tumbling down. One (impractical) lesson from this fiasco is that it’s useful to have J. K. Rowling as an ally. However, looking back, it’s hard to believe that “gender identity ideology” could have carried on for much longer without collapsing under the weight of its own absurdities. The gender-critical women of TERF Island would have eventually triumphed without Rowling’s help, because they had the plain truth on their side.
Trump’s EO does not rest with the biological facts; it also sets a raft of policies. Among other things, government officials are directed “to require that government-issued identification documents, including passports, visas, and Global Entry cards, accurately reflect the holder’s sex.” It is understandable that someone seeking peace of mind by living as a member of the other sex would want a sex marker to match, especially when traveling to the less tolerant parts of the world. We should hope that the EO does not make life more difficult for such people than it already is. That hope is undoubtedly in vain, but the problem with pushing the pendulum too far in one direction is that it will tend to swing too far in the other. The activists who—predictably—have produced an equal and opposite reaction have only themselves to blame.
