Gender ideology rests upon two main pillars. The first proposes that the two sexes are not distinct and immutable categories, but rather correspond to a collection of many traits that one can plot along a spectrum. Male and female, in this view, exist only in a statistical sense. The second asserts that every human brain contains an unchangeable “gender identity” that is knowable from a very young age, physically detectable, and may conflict with one’s biological sex. The practical aspirations of gender ideologues depend on the truth of both claims: if male and female are not arbitrary or mutable, then there would be no basis for allowing males in female sports, prisons, or female-only spaces; if sex is binary, and no innate and fixed gender identity exists, then one cannot be “mismatched” from one’s sex—and “gender affirming” treatment is unjustified. Put another way, the belief in the sex spectrum provides the assurance of the ability to materially change one’s sex, while the belief in an innate and fixed gender identity that can be “mismatched” from one’s sex (i.e., a person can be “born in the wrong body”) provides the ethical justification or even obligation for hormonal or surgical intervention.

These gender-ideology pillars lack empirical support and are buttressed entirely by politically motivated wishful thinking. Consider a recent Washington Post article by English professor Jennifer Finney Boylan, which tried to establish the validity of both. Boylan does not seem to understand the well-established universal property that defines all males and females in nature, displays confusion about the difference between how sex is defined versus how it is determined, and demonstrates a tenuous grasp of the research of so-called “brain sex” that purports to ground “gender identity.”

We agree with Boylan that policy must ultimately be rooted in material reality. A scientist’s job is to describe the natural world as clearly and accurately as possible; society can collectively decide what, if anything, to do with those facts. But scientists also have a duty to combat falsehoods on topics they know well, especially when such falsehoods have real-world consequences. Misleading and incorrect claims about gender identity are being used to justify invasive, permanent medical procedures on minors and adults and to eliminate sex-based distinctions in law. Boylan’s claims, representative of progressive defenses of gender ideology, deserve serious scrutiny.

Boylan begins by outlining some general questions about biology. “So what, then, is a biological male, or female? What determines this supposedly simple truth? It’s about chromosomes, right?” Boylan then purports to debunk the chromosomal notion of sex by highlighting exceptions to the general rule that males have XY chromosomes and females are XX, noting that “not every person with a Y chromosome is male, and not every person with a double X is female,” and that “the world is full of people with other combinations: XXY (or Klinefelter Syndrome), XXX (or Trisomy X), XXXY and so on.”

The notion that males and females are defined by their chromosomes, with males always being XY and females always XX, is a frustratingly common misconception that occurs on both sides of the political divide. Gender activists use this misconception to provide exceptions that they believe refute the notion that there are only two sexes. Conversely, some opponents of the erasure of biological sex tout the XY and XX concept of males and females as proof that sex is binary and etched into our DNA.

Neither depiction is accurate. The central error, not obvious to those unfamiliar with biology, is made explicit in Boylan’s second question: What “determines” whether an individual is male or female? For what determines an individual’s sex is different from what defines it. “Sex determination” refers to the processes that set an embryo on the developmental pathway of becoming male or female. But the mechanisms responsible for triggering male and female development do not define the male and female sexes themselves. Humans and other mammals use genes located on chromosomes to trigger sex development; some animals, like many reptiles, use temperature. Just as chromosomes do not define an individual mammal’s sex, temperature does not define an individual alligator’s sex. Rather, one’s sex is defined by his or her primary reproductive anatomy, indicating the type of gamete (sperm or ova) he or she can or would produce.

The different chromosomal combinations Boylan highlights, such as XXY, XXX, and XXXY, are not examples of new sexes beyond male or female. Instead, they represent chromosomal variation within the two sexes. Assuming a properly functioning SRY gene (the gene that triggers male development) on the Y chromosomes, the hypothetical XXY and XXXY individuals would be unambiguously male, and the XXX individual unambiguously female.

Moving on, Boylan mentions complete androgen insensitivity syndrome (CAIS), describing it as “a condition that keeps the brains of people with a Y [chromosome] from absorbing the information in that chromosome.” This description is not even remotely correct. CAIS is a condition in which a person’s cells are completely unresponsive to androgens, such as testosterone. This prevents the genitals in a developing male fetus from masculinizing, and further prevents the development of male secondary sexual characteristics during puberty, despite the presence of functioning internal testes.

Boylan then displays confusion regarding the distinction between primary sex organs (gonads) and secondary sex characteristics (traits that differentiate between males and females during puberty). Boylan questions whether women who have had mastectomies or men with “enlarged breasts” are still female and male, respectively. Breasts are called “secondary sex characteristics” for a reason: they are related to sex, but do not define it. Just as painting stripes on a lion does not turn it into a tiger, augmenting a man’s breasts does not make him a woman.

After concluding that the basis for being male or female cannot be reduced to anatomy or genetics, Boylan turns to the brain, writing: “It might be that what’s in your pants is less important than what’s between your ears.” The concept of “brain sex” has been of special interest to gender activists and medical professionals who seek to root “gender identity” in something immutable and innate. That would allow them to draw upon existing legal precedents and civil rights laws, as Leor Sapir, an expert in this domain, observes:

Another reason for the medical professionals’ insistence is that “brain sex” resonates with a legal culture shaped by the civil rights movement. The Supreme Court has long recognized that a trait’s immutability is relevant to its eligibility for constitutional protection. In the final stages of the Gloucester litigation, the Fourth Circuit based its equal protection analysis on the claim that gender identity is, like race, an “immutable characteristic.”

Boylan does not claim that the brains of transgender “women” (in other words, natal males) resemble those of natal females. Instead, Boylan claims that they are “something distinct,” citing a recent study. The study in question recruited 72 participants (24 males, 24 females, and 24 transgender women) who all underwent magnetic resonance imaging (MRI). The images were then subjected to a multivariate machine-learning algorithm designed to predict sex, which it did reasonably accurately. From the machine-learning data, a “brain sex index” (BSI) was created, with a BSI of zero being standardized to represent a totally female brain and a BSI of one representing a totally male brain. When applied to the transgender women, the BSI indicated a shift of 25 percent toward the female end (though still remaining much closer to typical male brains).

A closer examination casts doubt on the utility of the study for Boylan’s claim. Six out of the 24 transgender participants were attracted to members of the same sex. Why would this be important? As it turns out, several lines of evidence suggest that homosexual individuals have less sexually dimorphic brains than heterosexuals (or even a tendency for a reversed sex pattern, on average). Whether these differences are causal to homosexuality or not is irrelevant. What is important is that sex-atypicality within the brain is associated with sexual orientation.

In an effort to show exactly how sexual orientation can affect research on gender dysphoria, one study scanned the brains of 24 heterosexual male-to-female transsexuals (i.e., males, identifying as women, who are attracted to females; also known as “gynephilic”) and compared them with male and female heterosexuals. When it came to the former group, the authors found no signs of brain “feminization,” but instead found (in relation to both males and females) larger gray matter volume in the temporo-parietal junction, an area involved in body perception and recognition and out-of-body experiences.

In fact, studies claiming that the brains of transgender-identifying individuals are shifted toward the opposite sex routinely do not control for homosexuality. And when they do, they fail to demonstrate any such shift. Consider two studies that assess regional gray matter differences between transsexuals and controls. The first, by Simon and colleagues, concluded that transsexuals have brains resembling that of the opposite sex. However, the second, by Luders et al., found no difference between male-to-female transsexuals and control males.

What caused these dramatically different findings? The transsexual participants in Simon et al. were all homosexual, whereas only one-quarter of the transsexual participants from the Luders study were homosexual. Across all studies, the percentage of homosexuality in the transgender cohort appears to correlate with the degree of sex-atypicality within the brain. The study Boylan cites is consistent with this trend, as the BSI cross-sex shift and the percentage of homosexuality match perfectly (25 percent).

Next, Boylan references a Scientific American blog post to explain a 2014 functional MRI (fMRI) study on the effects of smelling androstenedione (AND)—a precursor in the biosynthesis of testosterone and estrogen that increases throughout puberty and acts as a pheromone in human sweat—in a group of prepubescent children and adolescents with and without gender dysphoria. In both pre-pubertal and adolescent controls, males showed a desensitizing effect to smelling AND (in technical terms, their hypothalamic activational response decreased significantly over time), while females demonstrated increased hypothalamic activation over time. In contrast, adolescent girls and boys with gender dysphoria exhibited responses to AND that more resembled those of the opposite sex. No sex-atypical response was found in the pre-pubertal children.

Once again, it might appear on its face that dysphoric adolescents show atypical responses in the brain, which could explain a feeling of being “trapped in the wrong body.” However, as with the BSI study, the vast majority of the adolescent cohort—the only cohort to find an atypical result—were homosexual. (When asked “Have you ever been in love?” and, if so, “Was this person a boy or a girl?” all girls with gender dysphoria and 70 percent of boys with gender dysphoria answered with a person of the same natal sex.) Why would sexuality be important? An atypical response to smelling AND has been reported in both homosexual men and lesbian women within the hypothalamus. Since the sexual orientation of the prepubescent children was considerably more varied (and perhaps why the results were, according to Boylan, less clear), it seems far more likely that this atypical reaction was not a result of gender dysphoria but rather the participants’ sexuality.

Finally, Boylan briefly discusses a study on click-evoked otoacoustic emissions (CEOAEs)—echo-like sound waves produced by the inner ear in response to transient clicking stimuli. The study focused on children and young adolescents who all met the DSM-IV criteria for gender identity disorder (GID) and were of the “early onset” typology (typically homosexual). CEOAEs, a byproduct of the cochlear amplification mechanism, exhibit sexual dimorphism—females tend to show a higher amplitude compared with males from birth, suggesting a role for the pre-natal hormonal environment. In GID subjects, boys showed an atypical response (i.e., increased mean amplitude CEOAE) in the right ear, whereas GID girls did not. The authors suggest their findings support the “hypo-masculinization” of GID boys through decreased exposure to androgens during early development, but do not support the hypothesis of an increased exposure to androgens in girls with GID. However, research has shown that bisexual and homosexual females exhibit a partial “masculinization” of their CEOAE amplitude, implicating pre-natal androgens in modulating female-atypical responses. Thus, the atypical CEOAEs may indeed relate to the pre-natal environment, however, this is intertwined with the subjects sexual orientation (early on-set type). Further, the adolescent GID participants in the study had a wide age range, which could have affected the results since many were at different pubertal stages and thus differentially affected by circulating pubertal hormones. Indeed, trans-identifying adolescent females who received puberty blockers and cross-sex hormone treatment showed significantly weaker mean CEOAE amplitudes in the right ear compared to control girls. This could partly explain the differences observed in the GID adolescent cohort.

Boylan misinterprets science throughout the piece, which culminates to the following statement:

What does it mean, to respond to the world in this way? For me, it has meant having a sense of myself as a woman, a sense that no matter how comfortable I was with the fact of being feminine, I was never at ease with not being female. When I was young, I tried to talk myself out of it, telling myself, in short, to “get over it.”

Boylan had previously claimed that transgender brains are neither male- nor female-typical, but rather “something distinct,” and provided several lines of evidence for sex-atypical responses in transgender individuals. Nonetheless, Boylan makes the common mistake of assuming that having a brain resembling that of the opposite sex is a causal mechanism of gender-dysphoric feelings, without considering confounding variables such as sexual orientation.

“All the science tells us,” Boylan writes, “is that a biological male—or female—is not any one thing, but a collection of possibilities.” No: an individual’s sex is based on the type of gamete (sperm or ova) his or her primary sex organs are organized around, through development, to produce. Males have primary sex organs organized around the production of sperm, and females, ova. Brains do not define an individual’s sex. Brains, like any other part of one’s body, exhibit average differences between males and females. A brain, like any other organ, does not have its own sex, separate from the body. The terms “male brain” and “female brain” simply refer to the brains residing in the bodies of males and females, respectively. It is not possible to be “born in the wrong body.”

If Boylan’s essay demonstrates anything, it’s how it is far easier to make a mess of the truth than to clarify it.

Photo: Atlas Studio/iStock


City Journal is a publication of the Manhattan Institute for Policy Research (MI), a leading free-market think tank. Are you interested in supporting the magazine? As a 501(c)(3) nonprofit, donations in support of MI and City Journal are fully tax-deductible as provided by law (EIN #13-2912529).

Further Reading

Up Next