The claim that transgender status is immutable and biologically based was raised in the recent case of Talbott v. Trump. Eight plaintiffs—six active-duty service members and two individuals seeking to enlist—are challenging President Trump’s January 27 executive order barring transgender individuals from military service. The plaintiffs’ filings refer to “gender identity” as a deeply ingrained and involuntary characteristic with a biological basis—language that can be used to claim constitutional protections. The plaintiffs allege that the ban amounts to unlawful discrimination under the equal protection clause of the Fifth Amendment.
During hearings in February 2025, U.S. District Judge Ana C. Reyes pressed Department of Justice attorneys on the administration’s justification for the order. She instructed both parties to brief the court on “questions of biology,” prompting the plaintiffs to submit a five-page brief arguing that transgender identity is both innate and immutable.
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This claim carries implications far beyond military recruitment. Activists have used it to justify medical interventions for minors, inform education policies, and establish civil rights protections for “gender identity” comparable with those for race and sexual orientation. There’s just one problem: the plaintiffs’ brief—and the immutability argument more broadly—doesn’t withstand scientific scrutiny.
Though the plaintiffs’ filing never defines gender identity—commonly understood by its proponents as a person’s “internal sense of being male, female, both, or neither”—it nonetheless describes it as “innate,” “deep-seated,” and “impervious to change through external influences.” The brief also claims that a “scientific consensus” exists supporting the biological basis of transgender identity and asserting that transgender individuals constitute “a discernible class.”
The brief’s claim that transgender identity is both innate and immutable appears to rely on a misreading of the evidence. While “innate” typically refers to traits present at birth, “immutable” implies that they cannot be changed. Even early researchers who believed gender dysphoria might be innate did not consider it immutable—particularly in children. Decades of desistance research suggest that 85 percent to 90 percent of children with gender dysphoria who do not undergo medical transition eventually outgrow those feelings, with most going on to become gay or lesbian adults. The growing visibility of detransitioners—individuals who once identified as transgender but later reversed course—further challenges the idea that transgender identity is invariably fixed.
Even if biology plays a role, transgender identification does not arise from a single cause. The heterogeneity within trans-identified populations makes it unlikely that one universal explanation applies across the board. Research instead points to several developmental pathways: a homosexual pathway, historically seen primarily in boys and linked to childhood gender nonconformity and same-sex attraction; an autogynephilic pathway, primarily in adult men, involving sexual arousal at the thought of being female; and rapid-onset gender dysphoria, a pattern that has recently emerged mainly among adolescent girls and shaped by social and psychological factors. These distinct profiles challenge any effort to define transgender identity as a singular, biologically determined condition.
To a layperson, the plaintiffs’ brief may appear persuasive. It employs technical language, cites scientific studies, and references earlier court rulings that treated transgender status as immutable.
But none of this holds up under closer scrutiny. The rulings cited failed to examine the underlying evidence, instead reinforcing a kind of circular legal logic. The studies—focused on brain structure, twin concordance, genetics, and fetal hormone exposure—can give the illusion of a solid scientific foundation, but they are fraught with limitations. They often rely on small, non-representative samples, produce inconsistent results, fail to control for key confounding variables, and lack reliable replication. What remains is a patchwork of inconclusive findings, frequently overstated to support broad claims.
To assess the plaintiffs’ scientific claims properly, it helps to understand that, while sex itself is binary, many sex-related physical and psychological traits exist along a continuum. Some individuals naturally display traits more commonly associated with the opposite sex—often referred to as gender or sex nonconformity. Evidence suggests that prenatal hormone exposure can shape such traits in both boys and girls. Childhood gender nonconformity, a term used in clinical research, has also been strongly associated with same-sex attraction.
Social and cultural influences shape how these traits are understood and expressed. For some, these traits may cause distress, leading to a diagnosis like gender dysphoria. In today’s environment, where transgender identity is often conflated with gender nonconformity, individuals who don’t conform to traditional sex stereotypes may interpret their experiences as an internal “mismatch,” rather than as natural variations in behavior, personality, or sexual orientation.
Sex-based differences in brain structure are well-documented, and, as neuroimaging techniques advanced in the early 2000s, researchers began searching for neurological correlates of gender dysphoria. This sparked a wave of transgender brain studies, many of which received enthusiastic media coverage. Many have referenced these studies to support the idea of a “neurological sex”—that the brain possesses an internal sex separate from the body.
Building on this idea, the brief claims that “research shows transgender women and non-transgender women have similar brain structures,” citing five studies. But these findings are complicated by confounding variables. The use of cross-sex hormones—commonly used among those who medically transition—can alter brain anatomy. And sexual orientation can independently influence brain structure. When studies control for these factors, the results often show that the brains of trans-identified individuals more closely resemble those of their biological sex.
The brief also cites a review of numerous twin case studies to suggest a genetic basis for transgender identity. While identical twins in the review were more likely than fraternal twins to identify as transgender, this does not constitute strong evidence of genetic causation. The research relies on case reports of twins raised together, making it difficult to separate genetic influence from environmental and social factors. Identical twins often share closer emotional bonds, which can influence belief systems and reinforce shared identities.
In nearly every case where both twins identified as transgender, both were also homosexual. The one exception involved a pair of identical twins described in the literature as exhibiting “transvestic fetishism”—a condition now more commonly referred to as autogynephilia. This raises the possibility that the studies are not capturing a genetic basis for transgender identity, but rather a shared predisposition for same-sex attraction.
The study’s findings also diverge from what would be expected if transgender identity were strongly heritable: concordance rates between identical twins—that is, how often both twins in a pair identified as transgender—were modest, while fraternal twins showed no concordance at all. For comparison, twin studies on homosexuality show a more typical genetic pattern, with fraternal twins exhibiting about half the concordance rate of identical twins.
The brief references a study of genetic variants—differences in DNA sequences—related to sex-hormone pathways. These pathways influence how the body produces or responds to hormones like testosterone and estrogen, which may in turn affect behavior patterns traditionally associated with masculinity or femininity. Atypicality in these traits reflect gender nonconformity—not transgender identity itself. While these variants may be more common in trans-identified populations, they are neither unique to, nor predictive of, transgender identity. The authors of the study explicitly caution that “none of the studied variants could hence be assumed to be a primary cause of this condition.”
The brief also cites research on congenital adrenal hyperplasia (CAH), a disorder of sex development in which female fetuses are exposed to elevated levels of testosterone due to adrenal gland dysfunction. This excess androgen can lead to masculinized physical traits and more traditionally male-typical behaviors in childhood. While the brief interprets this as evidence that prenatal hormones shape “gender identity,” what the research actually shows is an association between prenatal androgens and masculinized behaviors or interests—that is, gender nonconformity, not identity rejection. Most girls with CAH continue to identify as female, despite these biological effects.
Taken together, the studies cited in the immutability brief do not establish that transgender identification is biologically determined. Instead, they more consistently reflect patterns of gender nonconformity and same-sex attraction. Ultimately, transgender identification is an individual choice made in response to gender-related distress—not the result of a hardwired biological condition.
Misinterpreting the findings of these studies as evidence of a fixed transgender identity risks narrowing society’s understanding of gender nonconformity. Rather than encouraging individuals to alter themselves to fit a prescribed identity, we should create space for a broader range of expression—recognizing that many gender-nonconforming children grow up to be gay or lesbian adults.
As courts and policymakers weigh the arguments in Talbott v. Trump and similar cases, they should treat claims of scientific certainty with skepticism. Decisions with profound personal and social consequences demand clear evidence, honest interpretation, and restraint in drawing conclusions that the research cannot support.
Photo: Nicolas Talbott, the plaintiff in the case of Talbott v. Trump (Photo by JIM WATSON/AFP via Getty Images)
