On August 25, Texas judge Maria Cantú Hexsel temporarily blocked Senate Bill 14, which limits sex-trait modification procedures—euphemistically called “gender-affirming care”—to adults only. In her decision, Hexsel stated that the law “interferes with Texas families’ private decisions and strips Texas parents . . . of the right to seek, direct, and provide medical care for their children.” In response, the Texas attorney general’s office swiftly filed an appeal with the state’s Supreme Court to halt Hexsel’s injunction, highlighting the “unproven” nature of pediatric sex-trait modification procedures being “pushed by some activists in the medical and psychiatric professions.”
Weeks before the hearing, the Texas attorney general’s office had asked me to serve as an expert witness on the biology of sex. It invited me to respond to a series of false and perplexing assertions made by the plaintiff’s three expert witnesses—including the premise that a person’s sex is comprised of many traits, among them chromosomes, hormones, internal reproductive organs, genitalia, and secondary sexual characteristics, as well as one’s “gender identity.”
In the scientific understanding of sex, only one trait—the type of gamete (i.e., sperm or ova) that someone can, will, or would produce—defines male or female. This is true not only for humans but also for all plants and animals. The other traits mentioned by the plaintiffs’ experts, while related to one’s sex, do not define it. Moreover, the push to include “gender identity” as a defining aspect of being male or female represents an extreme departure from empirical reality in service of a pseudoscientific outlook designed to validate the feelings of people who experience discomfort with their bodies.
Traveling to Austin and appearing before a judge to explain these basic facts was a surreal experience. To my knowledge, this was the first time a biologist has been called to testify in court to defend the material existence of males and females as natural and distinct biological categories. Yet, this isn’t the first time that core principles of biology have been put on trial.
In the 2005 case Kitzmiller v. Dover Area School District, plaintiffs contested a Pennsylvania school district’s policy that mandated teaching the religious concept of Intelligent Design (ID) alongside evolution in biology class. Biologists were summoned to defend the extensive evidence supporting evolution and explain how ID does not meet the fundamental standards of the scientific method: ID is unfalsifiable and relies on supernatural explanations that fall outside the purview of science.
The Kitzmiller case fascinated me, and I followed it closely. In fact, it inspired me to pursue a career as an evolutionary biologist. Over the years, I’ve engaged in debates with numerous creationists and ID supporters. While I didn’t realize it then, confronting these faith-based arguments against the reality of evolution equipped me to handle the current wave of popular anti-science sentiment around the denial of biological sex. Strikingly, the arguments made by sex denialists often mirror those presented by creationists and ID proponents.
In addition to being glaring instances of metaphysics parading as science, both ID and sex denialism rely on a similar “argument from complexity” designed to stun audiences into adopting their perspectives. ID advocates, for instance, contend that biological systems and features are “irreducibly complex,” meaning that they couldn’t have emerged from gradual, unguided processes like natural selection and random mutation and must therefore have been directed by a supernatural “designer” (i.e., God). In a similar vein, gender activists argue that biological sex is so complex and irreducible to any single trait that all efforts to classify individuals as male or female are futile, and people should therefore be allowed to identify as any sex they like.
While both arguments highlight genuine complexities within biology, they misconstrue the actual scientific understanding. In the Kitzmiller case, the presiding judge, a Christian appointed in 2002 by President George W. Bush, saw through the ruse and ruled against teaching ID as science, stating that “ID is a religious view . . . and not a scientific theory.” The denial of biological sex is no different, and its societal impacts are more pervasive and harmful than the denial of evolution.
However, in a twist I could not have anticipated, the same colleagues who once applauded my efforts to defend evolution against creationism and ID now condemn me for challenging the new sex pseudoscience. Evidently, scientists are not the impassive, Spock-like figures that both society and many scientists themselves perceive them to be. They, too, can get wrapped up in ideological and political trends.
Defending the binary nature of sex in court will become increasingly important as more states consider implementing age restrictions on hormonal and surgical sex-trait modification. This is because the depiction of sex as a haphazard collection of sex-related traits—instead of being tied to reproductive function—forms a central tenet of gender ideology. If one determines a person’s sex by tallying various traits, which can range from male-typical to female-typical, it follows that hormonal or surgical modifications can literally shift one’s physical sex along this perceived spectrum to align with that person’s internal “gender identity.” If, however, a person’s sex is immutable, then such interventions lack empirical justification
After I was sworn in and presented my credentials as an expert on the biology of sex, the plaintiff’s lawyers objected that they didn’t understand “the relevance of this witness.” I don’t think they were being insincere: I believe they really did not understand the relevance of natural science to the debate over how to help kids who feel alienated from their bodies. And that, of course, is exactly the problem.
Our Constitution guarantees all Americans the right to direct their lives according to their faith—whether that faith is about a revelation on Mt. Sinai or about sex as a spectrum or about the existence of gendered souls. The Constitution does not, however, immunize doctors from scientific criticism when their own beliefs clash with empirical fact and lead to medical harm. It is essential that scientists find the courage to defend the principles of rationalism and empiricism in the court of law as well as in the court of public opinion to help guide medicine, and our society, back to reality.