Colin Wright, an evolutionary biologist and fellow at the Manhattan Institute, and Samuel Stagg, a Ph.D. student in neuroimmunology, respond to a recent article by English professor Jennifer Finney Boylan published in The Washington Post that purports to claim that the brain and not one’s sex organs is what determines a person’s biological sex. Wright and Stagg first observe the two main pillars of transgender ideology that contradict one another.

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.

They then address a common objection that is raised against the transgender claim: chromosomes that determine one’s sex, namely the XX and XY pairing. They observe that both transgender proponents and those opposed to the erasure of biological sex get the issue wrong.

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.

Wright and Stagg then address Boylan’s primary claim: that the brain is the primary determiner of an individual’s biological sex.

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).

However, they note that Boylan ends up conveniently leaving out significant factors such as sexual attraction that play an outsized role in these differences.

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.

They conclude:

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

Read the whole article here.