Research purporting to demonstrate that trans-identifying individuals’ brains resemble those of the opposite sex often ignores a major confo
By: Colin Wright, Samuel Stagg, Christina Buttons
Published: Mar 14, 2025
Earlier this week, City Journal published the tragic story of Yarden Silveira, a young detransitioner—someone who pursues hormonal and/or surgical “sex change” procedures but then seeks to reverse course—whose life ended abruptly after suffering severe complications from a gender-related genital surgery. What led Yarden to adopt a transgender identity in the first place? In 2014, after encountering the growing wave of pro-trans narratives in popular culture, Yarden told his family that he believed he had a “female brain.” Though initially uncertain, his mother was ultimately convinced by scientific papers that suggested that her son could have a female brain trapped in a male body, and that this mismatch caused him unimaginable distress.
“A trans woman (such as myself) was born with a male body, but she has always had her female brain. Literally born with a female brain,” Yarden wrote in 2016.
This belief was widespread back then—and it still is. On January 31, Wisconsin Public Radio featured an interview with a mother, Carri, concerned about President Trump’s new executive order banning federally funded medical and surgical “sex change” procedures for minors. Carri spoke about her daughter, who identified as transgender at 15 and was allowed to medically transition. She said, “Those hormones really helped match his brain with his body which, to me, that’s just the basic level of care we can provide individuals that identify as trans.”
The power of this narrative in persuading people to pursue, or to allow their children to pursue, irreversible medical procedures cannot be overstated. But the notion that males can have “female brains,” and vice versa, rests on a flawed interpretation of “brain sex” studies that in no way demonstrate or even suggest a definitive biological basis for “gender identity.” Little effort has been made to correct this misleading assertion.
The theory is advanced for relatively straightforward reasons. Civil rights lawyers, activists, and researchers contend that people who identify as transgender possess a “brain sex” misaligned with their physical body, thereby establishing a biological basis for “gender identity” akin to immutable traits like race. This framing carries significant legal weight, as U.S. civil rights law offers strong protections for characteristics considered “innate” or rooted in biology.
In courtrooms, prominent gender clinicians routinely invoke “brain sex” literature to bolster the perceived immutability and innateness of “gender identity.” For example, Daniel Shumer, a pediatric endocrinologist and clinical director of the Child and Adolescent Gender Clinic at Mott Children’s Hospital at Michigan Medicine, provided expert testimony in a case challenging Texas’s prohibition of “gender-affirming care” for minors. He linked “gender identity” to “brain structures,” arguing:
Scientific research and medical literature across disciplines demonstrates that gender identity, like other components of sex, has a strong biological foundation. For example, there are numerous studies detailing the similarities in the brain structures of transgender and non-transgender people with the same gender identity.
Such statements have become standard in legal battles over “gender-affirming care” and other trans-related policies. In Talbott v. Trump, a legal challenge to the president’s executive order barring transgender individuals from military service, Nicolas Talbott—a transgender-identifying female and activist—joined six active-duty service members and two prospective enlistees in arguing that “[s]trong research supports the conclusion that gender identity has a biological basis” and that “transgender women and non-transgender women have similar brain structures, specifically in the volume of the bed nucleus of the stria terminalis.”
Outside the courtroom, the idea of a brain-body mismatch has permeated popular culture, resonating with the “born this way” narrative embraced by many in the LGBT community. Mainstream television and other media have reinforced the concept. For instance, in a 2009 episode of Law & Order: Special Victims Unit, psychiatrist George Huang, played by B.D. Wong, explained that a trans-identified boy had a “female brain”: “For some children, something happens in utero where the brain develops as one gender and the body the other.” Children’s books have reinforced this idea, with the trans-identified protagonist in I Am Jazz declaring, “I have a girl brain but a boy body. This is called transgender. I was born this way!”
There is reason to believe the “brain sex” narrative has influenced many young people’s decisions to pursue medical transition. In a forthcoming survey conducted by coauthor Buttons, 49.2 percent of detransitioner respondents recalled health-care providers framing the respondents’ transgender identity as a brain condition, using phrases like “male brain in a female body,” or vice versa. In total, 85.7 percent of those surveyed said that their providers characterized transgender identity as an inherent, biological trait that required medical intervention.
To bolster these claims, providers often cite a growing body of scientific literature that purportedly validates the brain-body mismatch hypothesis. These studies claim that the neuroanatomy of people identifying as transgender more closely resembles the brain structures typical of the sex with which they identify, relative to non-transgender-identifying controls. Media amplified these findings, often presenting them as definitive proof that trans-identifying people “are who they say they are.” Headlines such as “Science Proves Transgender People Aren’t Making It Up” and “Transgender people are born that way, a new study has found” further entrench the narrative.
Proponents of these studies, however, rarely possess the expertise and background knowledge needed to examine their methods and conclusions critically. And the culturally charged atmosphere surrounding transgender issues means that facts often take a backseat to politically—and legally—expedient narratives.
The central flaw in current research purporting to validate the cross-sex brain hypothesis is an inconsistent—or complete lack of—control for individuals’ sexual orientation. Why does this matter? Because most people who identify as transgender are not exclusively heterosexual, and same-sex attraction has been linked to neuroanatomical differences that reflect a cross-sex shift—or, more broadly, to a reduction in typical sexual dimorphism (i.e., to having more androgynous brain structures). This raises serious methodological concerns about the extent to which sexual orientation might confound or interact with the neurobiological markers that “brain sex” studies routinely attribute to gender dysphoria. It also raises major ethical concerns about the use of “gender-affirming care” as a form of gay conversion therapy or as a maladaptive coping strategy for gay men.
If one properly controls for sexual orientation, the reported neuroanatomical shifts in transgender brain-scan studies diminish greatly or vanish entirely. To illustrate that point, consider three influential studies examining regional gray matter differences between transgender-identifying individuals and controls. These examples, considered together, illustrate a pervasive problem in the “brain sex” literature.
The first study, by Lajos Simon et al. and titled “Regional Grey Matter Structure Differences between Transsexuals and Healthy Controls—A Voxel Based Morphometry Study,” reported that trans-identifying individuals exhibit brain structures more closely resembling those of the opposite sex, relative to controls. This study is frequently cited as evidence supporting the brain-sex hypothesis. However, a different study by Eileen Luders et al. titled “Regional gray matter variation in male-to-female transsexualism,” which used similar neuroimaging techniques, found no significant differences overall in gray-matter volume between male-to-female (MtF) trans-identifying individuals and male controls. In one small brain region, the putamen, the MtFs did exhibit a cross-sex shift, relative to their dataset—i.e., putamen volumes in MtFs were larger and more similar to female controls—but this result is anomalous and incongruent with the findings of large-scale studies and meta-analyses demonstrating that males, not females, have larger putamen gray-matter volumes, on average.
A third study, by Ivanka Savic and Stefan Arver titled “Sex Dimorphism of the Brain in Male-to-Female Transsexuals,” comprehensively analyzed structural brain differences using MRI. While the authors observed some structural differences in the brains of trans-identifying men compared with those of non-trans-identifying male controls, these differences did not align neatly with a feminization pattern. Instead, the variations were distinct from typical male or female brain structures, suggesting a unique neuroanatomical profile rather than a simple cross-sex shift. Importantly, Savic and Arver controlled for participants’ sexual orientation and found that, when they did so, the brain differences attributed to gender dysphoria were much less pronounced.
A clear pattern emerges when comparing these and similar studies: the magnitude of the cross-sex shift reported in trans-identified individuals’ brains correlates with the proportion of homosexuals in the sample. For example, in Simon et al.’s study, all transgender participants were homosexual, potentially amplifying participants’ sex-atypical neuroanatomical features. In contrast, Luders et al.’s cohort had a much lower proportion of homosexual participants, coinciding with null findings overall regarding brain feminization. Savic and Arver’s rigorous control for sexual orientation further demonstrates that some neuroanatomical differences previously attributed to gender dysphoria likely reflect—or are confounded by—sexual orientation-related brain variations.
Popular “transgender brain” studies, in short, often fail to control for sexuality, undermining the claim that people with transgender identities have brains that more closely resemble those of the opposite sex.
What would it mean if the “transgender brain” hypothesis were true, and properly controlled studies did document a statistically significant cross-sex shift in the brains of people who identify as transgender? It would not logically follow that a brain scan can capture a person’s “gender identity”—just as brain scans cannot ascertain a person’s sexuality. Differences in group averages do not mean that every individual within a group shares those characteristics. Populations contain variance; for instance, some straight men exhibit brain structures that skew feminine, while some gay men exhibit brain structures that skew masculine. Brain scans therefore cannot verify whether a person is homosexual; nor could they verify whether a person “is transgender.” Brains, like most physical traits apart from primary sex organs, are not discretely sexed; they simply exhibit average differences between the sexes.
Even if there were compelling evidence for “brain sex,” gender clinicians, though often expressing strong confidence in the hypothesis, would be the last to advocate for the use of objective brain scans to validate their claims. Their hesitancy has roots in the history of sexuality research. When scientists proposed the existence of a “gay brain,” many gay rights advocates strongly objected, citing its potential for eugenic abuse (imagine, for example, a drug company developing a fetal “treatment” to “cure” homosexuality based on such findings). Despite progressives’ deep pessimism about science’s potential for abuse, however, many activists still peddle the “brain sex” narrative.
Notably, even though homosexuality is associated with a cross-sex shift in certain brain structures, activists avoid claiming that gays and lesbians exhibit a brain-body mismatch. This avoidance highlights a striking inconsistency in the application of the “brain sex” narrative. For decades, research has shown that homosexuals exhibit subtle neuroanatomical differences that trend toward patterns typical of the opposite sex. Yet, proponents of LGBT rights have rejected the notion that these differences imply a pathological misalignment requiring medical correction.
The persistence of the “brain sex” narrative has real and sometimes tragic consequences. For individuals like Yarden Silveira, it contributed to life-altering—and ultimately life-ending—medical decisions based on a flawed understanding of the science. The notion that transgender identity is rooted in immutable brain structure has led countless young people to undergo unnecessary and often harmful medical treatments, frequently without fully informed consent or consideration of alternative approaches. Challenging that notion isn’t just an academic exercise—it’s a necessary step toward protecting vulnerable individuals from medical abuse.
Policymakers should mandate rigorous, independent reviews of the scientific claims surrounding transgender identity’s supposedly biological basis. This review should include scrutinizing studies that promote the “transgender brain” hypothesis, and incorporate evidence from desistance and detransition research, which highlight how transgender identities are often transient.
Public-health policies must be grounded in comprehensive and unbiased research. Otherwise, vulnerable young people will continue to face irrevocable and potentially devastating treatments.
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It's funny how there are supposedly no differences between males and females when it comes to sports, and yet there are supposedly MRI-detectable "male brains" and "female brains."
🤔
This ideology is completely incoherent.
It's astonishing how many formerly reputable scientific institutions have embraced abject pseudoscientific gobbledygook.
This is "atheism is a religion." Or "atheists are angry at god/worship the devil/worship themselves." They won't let you just not be part of the thing. Saying you're not part of the thing becomes a way of being part of the thing.
No, I don't accept the underlying premise of your belief, that incorporeal sexed thetans have been incompetently sorted by Xenu's intern into mismatched meat prisons.
I don't know who told you that every mundane thing about your personality deserves its own flag and special day, but you've been wildly misinformed.
The landmark decision has been announced; reality has prevailed.
By: Andrew Doyle
Published: Apr 16, 2025
If the law is an ass, the culture war is a bigger one. How else can one explain the phenomenon of judges at the UK supreme court gathering to determine the definition of a ‘woman’? This landmark case was heard in November, and today the verdict has been reached: ‘The unanimous decision of this court is that the terms woman and sex in the Equality Act 2010 refer to a biological woman and biological sex’.
So there we have it. We now have confirmation that a person’s sex does not change under the Equality Act simply because he or she holds a Gender Recognition Certificate (GRC). It is curious to think that this decision could have gone either way. When the Equality Act was penned fifteen years ago, not a single legal mind in the land would have entertained the notion that its references to ‘sex’ and ‘women’ would one day cause confusion. Surely these most unambiguous of terms could not have been open to challenge?
The casual observer might have assumed that the judiciary has gone mad, but there are good reasons why this case was raised. It has come about because of the Scottish government’s view – enshrined in its guidance on the Gender Representation on Public Boards (Scotland) Act 2018 – that ‘sex’ in the Equality Act refers to ‘gender identity’ rather than, you know, an individual’s potential to produce large or small gametes. From the SNP’s perspective, anyone could be a woman so long as they hold a GRC. But this legal fiction – created in the Gender Recognition Act of 2004 – has created problems, not least that some of those so certificated now seem to believe that this should grant them access to women-only spaces.Upgrade to paid
The court’s decision could never have altered reality, of course. Human beings cannot change sex, no matter what the law says. The legal fiction of ‘gender’ has emboldened various campaign groups over the years to rewrite the law inside their own heads, which is why Stonewall was found to have been representing the law as it ‘would prefer it to be, rather than the law as it is’. As a result of this activist meddling, many organisations and even schools have been operating under the assumption that anyone who claims to be female should have access to women’s toilets and changing areas, but this has never been the case. Nor has it even been true that self-identification exists in law, in spite of claims to the contrary by genderists.
For Women Scotland was able to make this challenge because the Scottish government has a duty to comply with the Equality Act in its guidance and legislation. By arguing that a GRC could make a man a woman for the purposes of the 2018 Act, they were effectively prohibiting women from assembling without men. This is a scenario that has already been playing out in Australia, where lesbians are no longer permitted to hold female-only events, because to exclude any man who believes himself to be a woman would be illegal discrimination. In the recent case of Sall Grover, we even had a judge ruling that ‘sex is changeable’. Reader: it isn’t.
For those in any doubt at the absurdity of this debate, here is an excerpt from the submission by Scottish Lesbians, The Lesbian Project and LGB Alliance:
‘It barely needs stating that lesbians are females who are sexually orientated to the bodies of other females. Again, it barely needs stating that there are anatomical differences between males and females. The defining characteristic of a lesbian is that she is not sexually attracted to male bodies, including penises, testicles, male body mass and shape. Nor is she sexually attracted to certificates.’
Anyone seriously attempting to argue against this is irretrievably detached from reality.
The task of the supreme court was interpretative, and their interpretations of the Gender Recognition Act and the Equality Act should settle many of the more frustrating debates of our times. Ultimately, that we have reached this point at all tells us all we need to know about the careening lunacy of the culture wars. Such has been the power of activists that they have been able to reduce the judiciary to a laughing stock. Their war on women has also been a war on language and reality, and the fact that even the highest judges in the land have been dragooned into the fray is some indication of the extent of their power.
It is reassuring that the supreme court eventually settled on the side of reality, but this war will doubtless continue to rage. Activists have made clear that they consider the law an enemy, and this ruling will not change that. In this most deranging of times, it is worth reiterating the basic facts. No human being has ever changed sex. Men cannot become women and women cannot become men. Trans women are, by definition, male. Trans men are, by definition, female. There is no such thing as a ‘trans child’. ‘Non-binary’ is a fashionable form of self-classification, not an inherent characteristic worthy of protection in law. These are facts that will not bend according to the whims of those who wish to run roughshod over the rights of women and gay people.
Men who wave their GRCs around like magic wands and believe that it transforms them into lesbians are deluded. Thank goodness the judges understood this incontestable truth.
As ever, let’s begin with a story. And, trust me, by the end of this piece, you’re going to know a lot more about creationism than you expected.
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In the 1920s, in concert with many other American states, the Tennessee House of Representatives passed the Butler Act, making it illegal for state public schools to: “teach any theory that denies the Story of the Divine Creation of man as taught in the Bible.” In other words, they banned schools from teaching the theory of evolution.
Three months later, Tennessee science teacher John Scopes was on trial, charged with teaching the theory of evolution, a crime he was ultimately found guilty of. He was fined $100 – about $1500 in today’s money – so it could have been an expensive affair for him, had he not got off on a really boring administrative technicality.
Yet, despite the evidence against him and his own confession, he was an innocent man. Scopes was not guilty of teaching the theory of evolution. He admitted to a crime he had not committed. He even coached his students in their testimonies against him. So why would he admit to this wrongdoing of which he was entirely innocent? Why would he contrive apparent guilt? In protest. In protest against a law he viewed as fundamentally incompatible with the pursuit of scientific truth.
The history of creationism and education laws in the US is turbulent and often opaquely legalese, especially for those of us unfamiliar with US law. Some of the methods of the wider creationist movement, however, will be immediately recognisable as they are employed by a new movement, a new religion, Sex Denialism.
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Method 1. Like Creationists did with “species”, Sex Denialists aim to render human descriptions of the natural world “arbitrary”, and thus, a “social construct” that need not exist if we chose to reject it. Never mind that these “arbitrary” understandings of sex appear to be surprisingly similar classifications across all cultures and civilisations, with people happily churning out babies, perhaps oblivious to the argument that this basic biological function is all in their head.
The deconstruction of established scientific knowledge spotlights tricky “boundary cases.” For Creationists, the “missing links’ in the fossil record are unlikely to have a personal problem with being weaponised in pursuit of stupidity. But this is a very real problem in the modern world for people with disorders of sex development whose sex characteristics are ambiguous or atypical, and who are constantly invoked - even fetishized - as “not males” or “not females” to “prove” that understandings of sex are somehow no more than human whimsy. And, with no obvious explanation, why the existence of DSDs makes it apparently-impossible to identify sex in perfectly-typical newborns.
People with DSDs have complex and often traumatic medical histories, perhaps struggling to understand their bodies, and they deserve more respect than to be casually and thoughtlessly used as a postemodernist “gotcha” by the very people so horribly triggered by a pronoun.
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Method 2. Creationists and Sex Denialists alike lean on the development of sciencey-sounding language to create a veneer of academic rigour. Creationists invented “irreducible complexity” and “specified complexity” to argue that structures like the eye are just too complicated to have evolved. Sex Denialists try to beat people over the head with the dazzling language of “bimodal distributions arranged in n-dimensional space.” Come again?
Creationists, unable to publish in mainstream science journals because they weren’t producing, well, anything that looked like science, established their own “journals”. The lazier Sex Denialists have taken a shortcut and captured existing journals, albeit limited to more news-based ones and to occasional blogs about gender (which is not sex) and - reminiscent of an eye so complex we cannot possibly understand it’s existence without an intelligent God at the helm - about how developmental biology is soooo complicated. It is, you can get a PhD in it and everything, and it’s rather good training for breaking complicated biological systems down to identify fundamental properties and principles (reductionism is not a dirty word for developmental biologists). But this does not mean sex is complicated – the internal combustion engine is complicated but cars still fundamentally go forwards, backwards and, unexpectedly and usually unintentionally, sideways. Occasionally, a journal will remind us that discussing the biology of sex is mean - OK, good luck with that at your doctor’s surgery.
Remarkably, many such blogs and articles are written by scientists who simultaneously deny sex to their captured fanbase while writing academic papers about how female flies make shells for their eggs, about the development of ovaries or testes in fish, about how males make sperm. The dissonance must be hell.
The current editor-in-chief at Nature, the first female to hold this position, studied sex determination in worms for her PhD, and she now presides over a journal with an editorial policy to insert disclaimers about the binary nature of sex into spotlight features about research on, for example, different death rates in male and female cystic fibrosis patients. The authors of the studies are not prevaricating or handwaving about sex, but the editorial team is “bending the knee”. I used to research a genetic disorder that was male-lethal – that is, male human babies died early in gestation. I’d love to know if this disclaimer would be applied there.
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Method 3. Creationists were famous for debate strategies like The Gish Gallop, named for Duane Gish, a prominent creationist who didn’t like the fossil record. What it boils down to is: throw any old argument, regardless of its validity, in quick succession at your opponent and then claim any dismissal or missed response - or even hesitation in response - as a '“score” for your side. In Twitter parlance, we know this as “sealioning”, in political propaganda as the “firehose of falsehood”, although Wikipedia also suggests that it is covered by the term “bullshit”.
Typically: “So, what about intersex people? what about this article about slugs? what about an XY person with a uterus? what about the fa’afafine? what about that article about seahorses? look at this pretty picture of a cuttlefish, what about what about whataboutery what about clownfish clownfish clownfish?” The aim is not to discuss or debate, it is to force submission from frustration or exhaustion.
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Method 4. Creationists don’t like that we are descended form primates, and Sex Denialists also ring fence humans as separate from not just monkeys but the rest of the living world. They employ special pleading for special descriptions that frame humans as the chosen ones, such that the same process of reproducing new individuals - common to humans and asparagus, an observation I chose because it seems superficially silly - requires its own description, one that accounts for gender identity. In this, Sex Denialists come closest to their Creationist cousins, bordering on outright denial of evolution.
In the Scopes trial, which saw discussion of whether Eve was actually created from Adam’s rib and ruminations on where Cain got his wife, Scopes was defended by a legal group who had begun scouting for a test case subject as soon as the Tennessee ban was enacted. This legal group claimed to advocate for:
"Freedom of speech for ideas from the most extreme left such as anarchists and socialists, to the most extreme right including the Ku Klux Klan, Henry Ford, and others who would now be considered more toward the Fascist end of the spectrum."
The legal group so keen to defend the right to speak the truth, in this case a fundamental, observable scientific truth? The American Civil Liberties Union (ACLU), a group whose modern day social media presence promotes nonsense like:
"The notion of biological sex was developed for the exclusive purpose of being weaponized against people."
"Sex and gender are different words for the same thing [that is] a set of politically and socially contingent notions of embodied and expressed identity."
They share articles asserting that biological sex is rooted in white supremacy. I mean, I know the US has a traumatic racial history, but are they saying black people didn’t know what sex was until White Man taught them?
Since the Scopes case, the ACLU have fought against many US laws preventing, or the teaching of evolution. I cannot process the irony of a group of people historically and consistently prepared to robustly defend the truth of evolution now denying one of the most important biological foundations of evolutionary theory.
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How do we fight this current craze of Sex Denialism? A major blow for creationism teaching was delivered in 1986 while the US Supreme Court were considering a Louisiana state law requiring creationism to be taught alongside evolution. The Louisiana law was struck down, in part influenced by the expert opinions, submitted to the court, of scientists who put aside their individual and, as one of them has since described “often violent” differences on Theory X and Experiment Y, to present a unified defence of scientific truth over religious belief. 76 Nobel laureates, 17 state academies of science and a handful of scientific organisations all got behind this single cause, and made a very real change.
Support for creationism has slowly ebbed away and the US is in a much more sensible position these days, although I still meet the occasional student from a Southern state who didn’t learn about evolution until college.
Sadly, one of the Nobel laureates has highlighted how unusual this collective response was and that he could not imagine any other issue that would receive the same groundswell of community support. Although he forged his career listening out for the Big Bang, so maybe I need to go through the list and find the biologists.
Part of the problem petitioning biologists to speak out is not necessarily fear of being cancelled or whatever, but simple lack of awareness of the issue, or incredulity that it is being taken remotely seriously. I’ve been working on a legal document and was discussing with a colleague about my efforts to find a citation for the statement: “there are two sexes, male and female”. He laughed at the idea that this would require a citation, told me to check a textbook, then realised that this statement is so simple that it would not even be included in a textbook.
And he’s right. I can find chapters in textbooks and hundreds of academic papers dedicated to how males and females are made, how they develop, how they differ, yet very few that feel the need to preface any of this with the statement “There are two sexes, male and female”. It is apparently something that biologists do not think needs to be said.
But of course, I think they are wrong, and that we live in a time where it does need to be said, where some aspects of society are being restructured around a scientific untruth, and where females will suffer.
Without recognition of and language to describe our anatomy, and the experiences that stem from that anatomy, mostly uninvited, we can neither detect nor measure things like rates of violence against women, the medical experiences, the social experiences of women and girls.
And, as for creationism, the reality of sex perhaps needs to be said by those with scientific authority, in unambiguous terms. Otherwise, we are living in a society that tolerates nonsense like there is no such thing as male or female, that differences evident to our own eyes are not real, that anatomies readily observable and existing in monkey and man alike do not actually exist. I’m sure this last assertion has the full support of the Creationist community. And perhaps, as for creationism, a true tipping point will be tested when it is our children being taught these scientific untruths, or worse, when it is illegal to say different.
At the end of his trial, the only words Scopes uttered in court were these:
“Your honor, I feel that I have been convicted of violating an unjust statute. I will continue in the future, as I have in the past, to oppose this law in any way I can. Any other action would be in violation of my ideal of academic freedom—that is, to teach the truth as guaranteed in our constitution, of personal and religious freedom.”
I do not exaggerate when I say we are dealing with a new type of religion, a new form of creationism and a new assault on scientific truth. This is the Age of Unenlightenment. I also do not exaggerate when I say it may take a high profile court case to rebalance the public discourse around sex. There is only so far that letters, opinion articles and public statements from eminent scientists about the nature of sex can go.
Two things I predict about such a court case. It will not be defended by the ACLU. And with the recent proposals on hate speech law in Scotland, it will probably involve a Scottish John Scopes,who finds themself in front of a judge for the seditious crime of discussing the sex life of asparagus at their dinner table.
Debunking all five frameworks that claim to refute the sex binary.
By: Colin Wright
Published: Nov 6, 2024
Author’s Note
This essay reproduces in full my Commentary published in Archives of Sexual Behavior as part of its series, “How Many Sexes Are There? How Many Genders Are There?” The commentary systematically debunks all five frameworks that purport to refute the binary nature of sex. Every argument I have ever encountered against the sex binary fits into one or more of these five models—and each collapses under scrutiny.
I explain why biological sex is binary in all anisogamous species, defined strictly by the type of gamete—sperm or ova—that an organism’s reproductive system has the biological function to produce.
I see this commentary, and the broader series it belongs to, as a pivotal moment: a reassertion of empirical clarity in a field long clouded by ideology. The sex binary is storming back, and scientific sanity is being restored to the biology of sex.
If you’re looking for an academic work to cite that rigorously lays out why sex is binary—and why every alternative model either fails or quietly presupposes the gametic definition—this is it.
Why There Are Exactly Two Sexes
Across anisogamous species, the existence of two—and only two—sexes has been a settled matter in modern biology (Lehtonen et al., 2016; Parker et al., 1972). “Male” designates organisms whose biological function is to produce small gametes (sperm), and “female” designates organisms whose biological function is to produce large gametes (ova) (Hilton & Wright, 2023; Minot, 1888; Smith, 1978). This nomenclature reflects two divergent reproductive strategies that recur across a wide range of taxa (Togashi & Cox, 2011). As with the fact of evolution itself, contemporary scientific debates have long moved on from questioning whether the sex binary is a fact to questions about how anisogamy evolved, why it persists, and what its evolutionary consequences are.
In recent years, however, this previously uncontroversial fact has been challenged in popular discourse (Fuentes, 2023; Kralick, 2018; Viloria & Nieto, 2020) and now increasingly in scholarly scientific publications (Ainsworth, 2015; Fuentes, 2025; McLaughlin et al., 2023; Velocci, 2024), seemingly driven by cultural and political debates surrounding the concept of “gender identity” and transgender rights. Popular outlets now routinely publish articles asserting that there are more than two sexes or that sex is a nonbinary “spectrum” conceived as a continuum or as a multivariate cluster of traits. Scholarly articles have amplified this framing by characterizing the sex binary as overly simplistic, outdated, and even oppressive, urging its replacement with broader and putatively more nuanced models (Ainsworth, 2015).
Here I synthesize evolutionary and developmental evidence to demonstrate that sex is binary (i.e., there are only two sexes) in all anisogamous species and that males and females are defined universally by the type of gamete they have the biological function to produce—not by karyotypes, secondary sexual characteristics, or other correlates.
I begin with a concise account of sexual reproduction and the evolution of anisogamy, explaining why two differentiated gamete types evolved from isogamous ancestors and how this functional dimorphism grounds the categories “male” and “female.” I then assess five recurrent arguments used to undermine the binary nature of sex: (1) conflating “mating types” with sexes; (2) treating sex chromosome aneuploidies and karyotype variation as additional sexes; (3) reclassifying differences/disorders of sex development as evidence for a nonbinary “sex spectrum”; (4) recasting sex as a polythetic cluster of traits; and (5) proposing “multilevel” models that attach sex labels not to individual organisms but only to specific traits. Finally, I outline the scientific and societal benefits of definitional clarity, and close by explaining why attempts to decenter gametes are inherently self-defeating because all coherent routes to “male” and “female” remain intelligible only with respect to sperm and ova.
The Evolutionary and Biological Basis of the Sex Binary
What Sex Is and Why It Evolved
Sexual reproduction is the formation of a new organism by the fusion of haploid gametes (syngamy) produced via meiosis (Alberts et al., 2014). By reshuffling genetic variation through recombination and outcrossing, sexual reproduction generates novel genotypes and can reduce the genetic load, which helps explain its persistence despite the costs (Kondrashov, 1988; Otto, 2009).
At the gametic level, sexual reproduction occurs in two broad modes that differ in the size of gametes being fused (Togashi & Cox, 2011). In isogamy, fusion involves gametes of equal size. In anisogamy, fusion involves differently sized gametes (Lehtonen et al., 2016). Anisogamy is thought to have evolved over one billion years ago (Butterfield, 2000) from isogamous ancestors via disruptive selection favoring two distinct gamete types: small, typically motile gametes optimized for quantity and encounter rate (sperm) and large, nutrient-rich gametes optimized for provisioning (ova) (Levitan, 2006; Parker, 2011; Parker et al., 1972). Working in concert, these divergent strategies maximize fertilization success and offspring survival.
The sexes—male and female—refer to these two distinct reproductive strategies in anisogamous species. Males are defined as the sex that produces numerous small gametes (sperm). Females, conversely, are defined as the sex that yields fewer but larger gametes (ova) (Parker, 2011; Williams, 1975). Accordingly, individuals are categorized as male or female based on whether their reproductive system has the biological function to produce sperm or ova, respectively (Bogardus, 2025). Because sperm and ova are the only two gamete classes in anisogamous systems, there are only two sexes. This gametic dimorphism underlies biologists’ reference to sex as a “binary” (Hilton & Wright, 2023).
Common Arguments Against the Binary and Why They Fail
Sexes as Mating Types
Popular and scholarly articles sometimes claim that certain fungi and slime molds have “hundreds” or even “thousands” of sexes (GrrlScientist, 2019; Scharping, 2017). These claims commit a category error by conflating mating types with sexes (Lehtonen et al., 2012). In isogamous taxa, mating types are genetically or molecularly defined compatibility classes that regulate which gametes can fuse; they are not differentiated by gamete size (Hurst & Hamilton, 1992). By contrast, sexes in anisogamous taxa are defined by gametic dimorphism—the production of small gametes (sperm) versus large gametes (ova). Some anisogamous species may also possess mating-type systems layered on top of male and female functions, but isogamous species, by definition, lack sexes.
Claims of hundreds or thousands of sexes thus refer to many mating types in isogamous systems, not to sexes. Where reproduction is anisogamous, the number of sexes remains two—male and female—defined by gamete type (Lehtonen, 2021).
Sexes as Karyotypes
A common line of argumentation used to undermine the binary nature of sex does so by misrepresenting the sex binary as a binary of human karyotypes (XX = female; XY = male) and then citing sex chromosome aneuploidies (e.g., XXY in Klinefelter syndrome; X0 in Turner syndrome) or rare XX males and XY females to claim there must be “more than two sexes” (Ainsworth, 2015; Blackless et al., 2000). How could sex be binary and determined by sex chromosomes, they argue, if there are more viable sex chromosome karyotypes in humans beyond XX and XY?
The fundamental flaw is conflating how sex is determined with how it is defined (Capel, 2017; Griffiths, 2021; Hilton & Wright, 2023). In developmental biology, sex determination refers to the mechanisms that trigger and regulate sexual development. These mechanisms vary widely across taxa (Bachtrog, 2014). Examples include chromosomal (e.g., SRY gene on Y chromosome in mammals), temperature-dependent (e.g., higher temperatures produce males in many reptiles), haplodiploidy (e.g., unfertilized haploid eggs yield males in most Hymenoptera insects), or environmental (e.g., chemical cues in Bonellia viridis).
Yet, regardless of the mechanism by which sex is determined, an individual’s sex—male or female—is universally defined by the type of gamete (sperm or ova) their reproductive system has the biological function to produce (Goymann et al., 2023). Sex chromosome aneuploidies therefore represent variations within the two sexes, not additional sexes.
Sex as a Spectrum
While claims that there are “more than two sexes” are common, the most frequent challenge against the binary nature of sex asserts that sex is a “spectrum” (Ainsworth, 2015; Fuentes, 2025). On this view, “male” and “female” are not distinct biological categories, but theoretical endpoints of a continuous distribution that individuals can only ever statistically approximate. This model entails that individuals can only be described in degrees of maleness and femaleness, rather than strictly male or female. The primary evidence invoked to support the spectrum model is the existence of disorders/differences in sex development (DSDs) (Sax, 2002), including forms of genital or gonadal atypicality, often presented visually along a continuum from “typical female” to “typical male.”
However, the existence of such conditions does not undermine the binary nature of sex, because the sex binary does not entail that every individual can be unambiguously categorized as male or female. Rather, the claim is that in anisogamous organisms there are only two gamete types, sperm and ova, and thus only two sexes. Sexual ambiguity is not a third or intermediate sex because developmental variation does not correspond to producing new gamete types.
Sexes as Polythetic Categories
A polythetic category is one in which members share overlapping characteristics, with no single feature necessary or sufficient for membership. Inclusion is based on “family resemblance”: Each member shares enough traits with others to be recognized as part of the set, even though not all members share the same combination of traits (Needham, 1975; Wittgenstein, 1953).
Proponents of a polythetic sex model draw on this idea to portray sex as multivariate (rather than univariate, as in a simple “spectrum”). On this view, “sex” is an aggregate of traits—chromosomes, gonads, gametes, hormones, neuroanatomy, secondary sex characteristics, and other sexually dimorphic traits—and individuals are assigned degrees of maleness or femaleness according to how their overall profile aligns with what is considered male-typical or female-typical (Dreger, 2000; Fausto-Sterling, 2000).
However, male and female are not polythetic categories. They are reproductive classes defined by a single criterion: The type of gamete (sperm or ova) an organism’s reproductive system has the biological function to produce. All other traits—karyotype, genital morphology, hormone profiles, neurological and somatic dimorphisms—are typically causes, proxies, or consequences of that functional distinction. Treating those correlates as jointly definitional blurs the determinants and downstream effects of sex with sex itself.
Moreover, the polythetic approach is logically self-refuting (Griffiths, 2021). Traits are labeled “male-typical” or “female-typical” because they correlate with males and females already identified independently—ultimately by reference to gametes. In other words, the model presupposes the binary categories rooted in gametes it seeks to replace and then infers those categories back from their correlates. As a descriptive framework for trait variation, a multivariate summary can be useful; as a definition of sex, it is nonsensical.
The Multilevel Sex Model
The multilevel model blends spectrum and polythetic approaches by distributing “sex” across several putative “levels”, commonly including sex chromosomes, internal reproductive anatomy, external genitalia, secondary sexual characteristics, hormone profiles, and behavior, and sometimes extending to “gender identity” (Migeon & Wisniewski, 1998). Rather than classifying organisms as male or female, the model assigns sex labels to traits or levels (e.g., “genetic sex,” “endocrine sex,” “morphological sex,” “behavioral sex,” and so on) (McLaughlin et al., 2023; Sun et al., 2023).
As articulated by McLaughlin et al. (2023), sex is framed as “a constructed category operating at multiple biological levels,” with four focal levels: genetic, endocrine, morphological, and behavioral. This framing conflates the determinants and correlates of sex with sex itself (Bachtrog, 2014; Capel, 2017). Genes and gene networks initiate and regulate sexual differentiation; hormones mediate downstream development and phenotypic dimorphisms; morphology and many behaviors are influenced by an organism’s sex. Yet none of these traits defines sex. Sex is an organism-level reproductive class anchored to the type of gamete that organism has the biological function to produce. Treating upstream regulators (e.g., SRY activity, hormonal milieu) or downstream outcomes (e.g., dimorphic morphology, behavior) as coequal “levels” of sex is a level-of-analysis error.
Moreover, the multilevel account inherits the same circularity as the polythetic model. Traits are labeled “male-typical” or “female-typical” only because they correlate with organisms already identified as male or female—an identification that, in anisogamous species, is made ultimately by reference to gametes. Once that reference is removed, the typology loses its interpretive footing. As a descriptive framework to integrate genetic, endocrine, and morphological findings in clinical differential diagnosis, the multilevel schema has pragmatic value; as a definition of sex, it is incoherent.
Conclusion
This commentary advances a simple claim with broad consequences: In anisogamous organisms, the sexes—male and female—are functional classes defined by the type of gamete an individual has the biological function to produce (Bogardus, 2025). Males have the biological function to produce sperm; females have the biological function to produce ova (Parker et al., 1972). That definition is universal across all anisogamous taxa. Much contemporary confusion arises from conflating how sex is determined (i.e., how sex develops) with how sex is defined (what sex is), and from conflating upstream determinant and downstream correlates of sex with sex itself. On this account, aneuploidies and DSDs describe variation in development or function within the two sexes; “mating types” belong to isogamous systems and are compatibility classes, not sexes; and “multivariate” or “spectrum” depictions quantify trait variation within and between the two sexes without altering the number of sexes.
The scientific value of clear and precise definitions is enormous (Dawkins, 2025). A gamete-based definition prevents error propagation across comparative biology, physiology, ecology, and medicine. It preserves the interpretability of sex-linked phenomena—sexual selection, dimorphism, and life-history trade-offs—and maintains conceptual discipline by keeping determination mechanisms (e.g., SRY pathways, ZW systems, temperature-dependent determination, social cues) in their proper explanatory lane. It also secures cross-taxon coherence: Whether a species is gonochoric or hermaphroditic, and whether determination is chromosomal, environmental, or social, “male” and “female” remain meaningfully comparable because those terms are anchored to reproductive function rather than to a bundle of traits that shift widely from taxa to taxa.
The societal and ethical stakes are also significant. Accurate biology is distinct from questions of dignity, rights, and how we treat one another. Policy disputes should not be adjudicated by redefining—or defining away—the reproductive realities that make sex a useful scientific concept in the first place. When categories are blurred for nonscientific reasons, we invite downstream harms: muddled clinical protocols, compromised epidemiology, eroding and/or conflicting legal protections, and diminished public trust in science.
Across anisogamous taxa, males and females are defined by gametic dimorphism. Proposals to redefine sex in terms of karyotypes, secondary sexual characteristics, behavior, or other correlates are incoherent and invariably presuppose this foundation, because the categories “male” and “female” are intelligible only by reference to sperm and ova.
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LOL. She's basically just an English Lit professor, pretending to lecture biologists about biology, becuase "mUh TrAnS eXpErIeNcE!!"
Why Conflicts Arise with Trans Activists by Pamela Garfield-Jaeger
By: Pamela Garfield-Jaeger
Published: Apr 22, 2025
“There are only two genders.”
“Men can’t be women.”
“Men and women are different.”
“There’s no such thing as a trans child.”
These statements seem obvious to some and many others, yet they still clash with friends and family who believe transgenderism is real. They think, “It’s common sense—what’s going on here?”
I’ll tell you - They are speaking a different language. They assume a certain set of beliefs. They don’t understand the gender religion.
[ A person proudly showcasing their “God is a Transwoman” tattoo ]
Most people who believe in transgenderism recognize men and women exist, but they believe their sexed bodies are inconsequential. They believe their bodies are vessels and their inner gender being is transcendent. This is an element of queer theory.
Via google AI: Queer theory is a field of critical theory that examines and critiques society's definitions of gender and sexuality, challenging traditional assumptions about what is "normal" and exploring the social and power structures that shape our understanding of identity.
They certainly wouldn’t agree that “there’s no such thing as a trans child.” They believe these children possess a special soul requiring affirmation. Without physical and emotional affirmation, they argue, these kids will die—it’s life or death to them. This may sound like hyperbole, but many genuinely believe denying this truth leads to death. Studies “proving” this have been quietly debunked, yet they persist in prominent institutions. For example, the Society for Evidence-Based Gender Medicine (SEGM) cites a retracted study on sex changes, while Sex Matters explains why these studies are flawed and how this misinformation has spread across major organizations.
The Trevor Project
The Trevor Project claims LGBTQ young people with access to “affirming spaces” report lower rates of attempting suicide. Notice this data is self-reported (likely via leading surveys) and doesn’t account for completed suicides—only self-reported attempts. This population is repeatedly told they must be affirmed or harm themselves, so naturally, they report more suicidal thoughts and gestures. This data is meaningless.
Their view of children differs sharply. They believe children know themselves, and adults must listen—children must lead. Some claim this applies even at birth. Psychologist Diane Ehrensaft, PhD, claims babies send “gender messages” by wearing a onesie like a dress or removing barrettes. She elaborates in a 2015 essay on the UCSF website and, in a 2014 video, discusses “gender hybrids” and “gender smoothies” with a straight face:
They argue intersex conditions and clownfish prove multiple genders exist. They overlook that humans still only produce male or female gametes, regardless of rare birth defects. They also cite anomalies like clownfish and seahorses to bolster their case. Yet, despite which fish lays the eggs, these species remain male or female. Plus, trans activists forget a basic fact: humans aren’t fish.
An Orthodoxy of Queer?
Even transexuals—people who surgically alter their bodies to align with the opposite sex—aren’t 'evolved' enough for queer theory adherents. Transexuals and transgenders differ—most transexuals acknowledge a mental health struggle, accept two sexes, and seek to blend in quietly, not challenge norms loudly. The modern trans movement has sidelined them.
Queer theory aims to upend everything “normal.” The notion of male and female is humanity’s most basic truth, yet activists have convinced millions that multiple genders exist—a profound shift.
So, if you’re a logical person and someone you love believes illogical things, what do you do?
Patience is a Virtue
First, you must practice a lot of patience. The reason for that is you will need to remember that your logical, common-sense worldview does not align with a trans believer. If you really want to get through to someone and not butt heads, I recommend that you stop using the phrases above. They only reinforce the wedge this ideology intentionally places between you and the person you are trying to reach.
You must understand that your loved one has joined a new religion, and religions don’t respond well to logical statements. They need facts and truth, but you still must appeal to feelings and strategically poke holes in their faulty belief system. What feelings am I talking about? Consider what feelings might draw the person you care about to reject logic. Some possibilities are feelings of isolation, fear, sadness, and vulnerability. Pay attention to who are talking to. Listen and learn, even though a lot won’t make any sense. Sasha Ayad, LPC just tweeted “Take the distress SERIOUSLY, but not LITERALLY.” While you attempt to be gentle, if you are the parent, you must also remember your authority. You must set limits with internet access and the friend groups that are influencing your child. Your conversations can evolve as more logic penetrates.
There are so many things you can do, especially as a parent of a minor, but this essay aims to help people understand broadly why you can so quickly hit a wall when it comes to having an honest conversation with a person who believes transgenderism is a real inner phenomenon. You must learn their language first before you can communicate yours.
You can learn more about the trans language, including a “Trans/English” dictionary in my book, A Practical Response to Gender Distress: Tips and Tools for Families, available on Amazon. In order to mend this horrible divide in our country, we must first learn how to communicate with people who think very differently, especially those we love.
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Pamela Garfield-Jaeger is a licensed clinical social worker from California. She earned her MSW from New York University in 1999 and has worked in schools, group homes, hospitals, and community-based organizations. She now educates parents and emboldens mental health professionals to challenge the ideological capture of her field.
For more on empowering yourself as a parent and navigating mental health, see the Parents’ Guide to Mental Health. Pamela authored A Practical Response to Gender Distress, available on Amazon.
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Something people still don't seem to grasp is the full-on magical mysticism of a belief in a "gender identity."
When they say "sex and gender are separate," they're not just saying that they're separate concepts, they're saying that your "gender" is a transcendant essence, a property of human experience that's independent from your physical body.
"Born in the wrong body" was always understood as a clumsy way for a miniscule number of people to try to describe the experience of a mental disorder of discomfort with their sexed body. But the gender cult regards that as literally true.
Activists lack solid evidence that trans identity is an inborn condition.
By: Christina Buttons
Published: Nov 14, 2025
Gender-affirming pediatricians don’t offer uncertainty. They offer the confidence of settled science: the young people who enter their clinics are “transgender,” and medical interventions, such as hormone treatments and genital surgeries, will align their brains with their bodies. While no scan or blood test can verify this diagnosis, treatment begins regardless.
In modern medicine, “being transgender” is often portrayed as a condition with biological underpinnings. This belief endures despite decades of unsuccessful searches for an objective biomarker.
Jonni Skinner, a detransitioner who received “gender-affirming” medical care as a child, shows the human cost of that belief. Jonni grew up in a small Michigan town with his mother and brother, moving from place to place amid an unstable home situation. At the age of four, he was diagnosed with Autism Spectrum Disorder. He was a sensitive and empathetic child, which made him a target for bullies.
Jonni had a devout Christian upbringing and took his faith seriously. As adolescence arrived, his emerging same-sex attraction became a monumental source of stress because he believed being gay was a sin. His anxiety quickly turned into depression.
Online and on television, he encountered a different story about boys like him. YouTube personalities Gigi Gorgeous and Stef Sanjati, and reality TV figure Jazz Jennings, were effeminate, same-sex-attracted boys whose transitions played out in public. They appeared happy, successful, and self-possessed. For Jonni, it was easy to believe that following their path might offer the same relief.
The chance to speak with a specialist came through a family friend who tutored Jonni—a lesbian who had begun identifying as a transgender man and taking testosterone. She referred him to the University of Michigan’s pediatric gender clinic at C. S. Mott Children’s Hospital.
Jonni did not walk in at 13 years old convinced he was transgender; he wanted clarity about the distress he was feeling. The clinic supplied that clarity on its own terms. Jonni claims that after a single three-hour intake interview, a clinical social worker affirmed him as “transgender” and placed him on a medical track.
At the clinic, Jonni was seen by Daniel Shumer, a pediatric endocrinologist. According to Jonni, Shumer told him he had a “neurological intersex condition” and that medical treatment was the only effective way to align his brain with his body. Jonni remembers the conversation in explicit detail, because it was pivotal in deciding the course for him and his mother. (Shumer declined a request to comment for this article.)
In the consultation room, Jonni claimed, Shumer used a whiteboard to sketch a prenatal hormone pathway: in the womb, a mistimed androgen signal in early development had “feminized” his brain, while testosterone had masculinized his body later on. Jonni says that his distress was presented as a brain-body mismatch.
The brain-body mismatch story took shape in the 1960s, when researchers first proposed brain-based explanations for transsexuality. By 1980, psychiatry was pivoting toward a biomedical model, anticipating that neuroimaging would reveal biological signatures of mental disorders. The search for a “transgender brain” followed.
In 1995, a Dutch team published a small postmortem study in Nature of six males who identified as women, reporting that their hypothalamic region more closely resembled the typical female pattern. This was widely considered a landmark finding. But later analyses of this study suggested that long-term cross-sex hormone use, known to alter brain structure, was the more likely explanation for the similarities found between trans-identifying people’s brains and those of the opposite sex.
Clinicians nonetheless proceeded to develop clinical guidelines on the expectation that biological evidence would emerge to validate their proposed medical interventions. Within a few years of the Nature study, Dutch clinicians created the first protocol to alter the sex characteristics of gender-dysphoric adolescents, introducing puberty blockers and cross-sex hormones at the onset of puberty. In 2007, Boston endocrinologist Norman Spack imported the “Dutch protocol,” as it came to be known, to the United States when he opened the nation’s first pediatric gender clinic.
This clinic became ground zero for the gender-affirming model of care in the United States. Spack framed transgender identity as a medical condition and described people identifying as trans as having been “born with brains that didn’t fit their bodies.” Shumer trained under Spack, and in 2015, built a program in Michigan for minors on the same “gender-affirming” template.
Dutch researchers continued to pursue biological explanations for transgender identity, even as clear evidence remained elusive. In 2009, they offered a simple account: transsexualism could result from a mismatch between the differentiation of a fetus’s genitalia (which occurs within the first two months of pregnancy) and the sexual differentiation of the fetus’s brain (which occurs in the second half). They claimed “[t]here is no proof that social environment after birth has an effect on gender identity or sexual orientation.” This became the foundation of the script that Shumer allegedly presented to Jonni.
“So, he explained I wasn’t gay, I simply had a female brain in a boy’s body. And how the inverse happens to create a trans man,” Jonni said. He came away convinced that he “was literally in the wrong body,” and that “[a medical intervention] is the only treatment that would work.”
To reinforce what he allegedly told Jonni, Shumer emailed him a 2014 clinician review by pediatric endocrinologist Stephen M. Rosenthal and colleagues, which devoted pages to the “Current Concepts of the Biology of Gender Identity.” It summarized studies on differences of sex development (DSDs), brain structure and function, genes, and twin concordance, which are often invoked to suggest a biological contribution to transgenderism.
DSD studies examine congenital differences in sex development involving chromosomes, gonads, or genital anatomy, usually in patients with complex medical histories. In the transgender research literature, researchers lean heavily on DSD papers and often present them as the strongest evidence that “gender identity is fixed.”
Yet the people in these studies, who have atypical sexual anatomy, are generally not comparable to those who identify as transgender. While the idea of “gender identity” emerged in DSD research and may have utility in that narrow context, it was later applied to transgender research as the basis for biological inquiry. But gender identity is an unfalsifiable construct—it relies entirely on self-report, based on how people say they feel, with no independent way to observe, measure, or disprove it—making it a weak foundation for biological claims.
Studies of brain structure and function report differences between trans-identified groups and non-trans control groups. But when confounding factors such as same-sex attraction and long-term cross-sex hormone use are controlled for, the effects shrink or disappear.
Genetic studies have found small differences in androgen- and estrogen-receptor genes between trans-identified groups and non-trans control groups. Those same variants also appear in the general population and are linked to sex-atypical traits and interests. In plain terms, they reflect normal variation in traits and interests that are less typical for one’s sex. This variation is more common in trans-identified groups, but it is not unique to them and is not a biological marker of “being transgender.”
Twin research is often cited as the strongest evidence for a genetic role in the development of transgender identity. But since these studies often involve twins who were reared together, they cannot reliably separate heredity from the effects of having been raised in a shared environment. In these studies, concordance—which means, in this context, that both twins identify as transgender—is concentrated among same-sex–attracted identical twin pairs. The results are modest for identical twin pairs, and near-zero among fraternal twins, which is out of step with standard genetic expectations for heritability. Identical twins also have closer social bonds and are more likely to imitate each other than fraternal twins, which means that social influence can help explain their higher concordance rates.
Taken together, none of these lines of evidence demonstrates a biological basis for transgender identities per se. But to Jonni and his mother, who trusted physicians and had only a layman’s grasp of biology, the combination of a clinical explanation and a scholarly paper proved persuasive. Reflecting back, Jonni said it was “a very powerful thing to hear from a doctor.”
Jonni’s pursuit of gender clinic services in 2016 coincided with the cultural rise of transgender stories. The year 2015 is often referred to as the “transgender tipping point,” when transgender identification began rising dramatically. The 2010s were saturated with media coverage of studies claiming to support a biological basis for such identities. Subsequent studies that challenged those claims received little media attention.
Follow-ups on early gender-clinic cohorts who did not socially or medically transition—many of them boys who later grew up to be gay men—received far less coverage because they cut against the prevailing narrative. Jonni fits that profile. As a young boy frightened by his emerging sexual orientation, he was looking for an alternative to being gay. The medical story was a way out.
On that basis, Jonni and his mother signed consent forms. Jonni had accepted the modern transgender framework, which holds that even ordinary sex nonconformity—i.e., being a masculine girl or a feminine boy—is potentially proof that a person “is transgender.” Afterward, he began to understand his feminine temperament and preferences as evidence of a female “gender identity.”
Jonni was medicalized before any social transition—before changing his name, pronouns, or clothing—and before any therapy. Intake notes that he provided to City Journal read: “Psychotherapy is not clinically necessary for Jonathon to move forward with medical intervention.”
Jonni’s treatment began immediately. At thirteen, in 2016, he started spironolactone and estrogen, and soon after received a puberty-blocking implant. Throughout the experience, he developed painful muscle spasms, hot flashes, persistent nausea, blood in his urine, a bladder ulcer, urinary incontinence, and fatigue. The depression, insecurity about his appearance, and social isolation he sought help for only worsened. He remained on hormones until 21, when he finally detransitioned.
Today he reports chronic bone and joint pain, reduced adult height, sexual dysfunction, and arrested psychosocial development. None of these risks, he says, were disclosed prior to treatment. Looking back, Jonni believes his distress stemmed from internalized homophobia. “I was just a kid that needed some therapy,” he says. Now 22, he speaks publicly about what he describes as malpractice and fraud in pediatric gender medicine.
Meantime, Shumer has been called to testify as an expert witness in at least 13 cases on behalf of transgender-identifying plaintiffs. He continues to advance a largely biological account of transgenderism. In sworn statements, he has claimed that “gender identity is properly understood to be a naturally occurring source of human biological diversity,” and that such identities have “biologically-rooted, immutable, and unchangeable determinants.” When pressed in a recent deposition, he said a person’s gender identity is “likely . . . innate.”
As of August, after receiving a federal subpoena, the University of Michigan’s medical center has stopped providing puberty blockers and cross-sex hormones to minors. By his own estimate, Shumer has personally evaluated and treated about 400 patients with gender dysphoria.
Asked for comment, Mary Masson, Michigan Health’s senior director of public relations, said “at University of Michigan Health, our gender services care always involves compassionate, individualized support for each patient. We are committed to comprehensive, multidisciplinary care—including mental health services and support-to ensure patients and families can make informed decisions that are right for them.”
The experience that Jonni described is not unique. In an informal 2023 survey that I conducted of 63 detransitioners, many of whom had transitioned as minors, 85.7 percent said a health-care provider told them that being transgender was a biological condition beyond their control. Nearly half recalled being told they had the brain of the opposite sex.
Biomedical explanations for psychological distress can have iatrogenic effects, that is, harm that results from the medical or clinical process itself (including diagnosis, explanation, or treatment). This has been well documented in studies of depression, addiction, and mental-health disorders more broadly.
When people receive biological explanations for mental illness, it diminishes their sense of agency and influences the choices they make. The “chemical imbalance” theory of depression, for example, was long promoted as scientific fact. Yet systematic reviews have found no consistent, high-quality evidence that depression is caused by low serotonin. Studies show that people given biological explanations for the cause of their depression feel less able to manage their emotions, less hopeful about recovery, more likely to choose antidepressant medication, and less confident that therapy or other non-medicalized approaches could help.
Psychologists call this bias psychological essentialism, the tendency to treat social categories as if they were biological. For many decades, people have described a strong desire to live as the opposite sex. That experience is real, but it does not mean that “transgender people” represent a distinct biological type.
Once the transgender framework gained traction, many individuals began interpreting their distress through that lens. The label did not merely describe a preexisting condition; it helped create one. Ian Hacking, a philosopher and historian of science, called this process “making up people”: once a diagnostic category is named and institutionalized, it reshapes how people understand themselves and how clinicians respond to them.
Activists have played a major role in shaping the popular conception of transgender identity. U.S. opinion data show that people who believe that being “transgender” has a biological basis are significantly more supportive of “transgender rights,” with the largest shift among conservatives. As of 2025, 57 percent of Democrats still hold the view that being transgender is “something a person is born with.” Framing transgender identity as innate has proved an effective political strategy—one that endures because it feels scientifically grounded.
Yet after decades of research, evidence for an innate, biologically determined transgender identity has not materialized. Instead, research has identified other factors—childhood sex nonconformity, homosexuality, and autogynephilia—that more plausibly account for the desires and experiences that have been labeled “transgender.” The recent rise of adolescent-onset gender dysphoria further illustrates how cultural influence and peer contagion, rather than biology, can shape identity and distress.
People deserve clear and accurate information about the causes of their distress so they can make informed decisions about how best to address it—and to avoid the potentially life-long consequences of following the wrong advice.
