In February this year, the Idaho House of Representatives passed a bill declaring that there are only two sexes and genders. 

Disregarding the problematic nature of politicizing gender identification, the bill is fundamentally wrong, simply on a biological basis. Not only does it disregard intersex people—those with sexual characteristics that don’t neatly fit into male or female—it makes the false assumption that sex is equivalent to gender. 

Sex and gender are not the same: sex refers to biological characteristics like chromosomes, genitalia, and hormones, whereas gender refers to social and psychological constructs.

Indeed, gender and biological sex are two separate concepts that can, on occasion, contradict one another. Some transgender and genderqueer people may experience gender dysphoria, a real psychological condition that is caused by their perceived misalignment between gender identity and sex assigned at birth. Gender dysphoria is a well-documented phenomenon, first being described in 1869 by German psychiatrist Karl Westphal. In fact, the now politically targeted Hormone Replacement Therapy (HRT) is one of the commonly recommended treatments for gender dysphoria that psychologists recommend based on decades of research. 

Therefore, it should be abundantly clear that there are scientific bases to gender identities and that the psychological conditions associated with them are real. But what might be difficult to figure out are the origins of these gender identities. Why do some people experience gender dysphoria?

Scientists aren’t entirely sure yet, but they have some clues. For some research groups, their investigation into the neurobiology of gender identity begins with the concept of sexual differentiation in the brain. From early in the fetal development, hormones such as testosterone play a critical role. As studies have shown, testosterone has what is known as "organizational effects" on the brain, shaping its structure in ways that influence behavior long after birth. In cases where testosterone levels diverge from typical patterns—such as in Congenital Adrenal Hyperplasia (CAH), a condition that exposes female fetuses to high levels of androgens—the brain may develop differently from what we would expect given the individual’s chromosomal sex​. 

For some, this early hormonal influence leads to a brain that aligns with their chromosomal and physical sex, but for others, there can be a mismatch. One prominent hypothesis as seen in studies on gender dysphoria, suggests that certain brain regions in transgender individuals resemble the typical structures of their experienced gender, rather than the gender assigned at birth. This was pointed out in research by Swaab and colleagues, which found structural similarities between trans women and cisgender women in areas like the hypothalamus​. The hypothalamus, involved in hormone production and regulation, shows subtle but significant structural variances across genders, contributing to gendered traits and behaviors. These findings align with what neuroscientist Melissa Hines described as “organizational influences” where early exposure to hormones sets up neural patterns that remain throughout life, even when the body’s hormone levels change after birth.
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Neuroimaging studies have provided further insight, revealing that transgender individuals may exhibit brain structures that diverge from cisgender norms but don’t necessarily fit neatly into the binary male-female spectrum. As one study on transgender adolescents observed, these individuals might possess unique neural signatures, suggesting that transgender brains represent a distinct phenotype. Recently, this has prompted some researchers to argue that gender identity is less about fitting into a strict binary and more about existing along a continuum, a concept that is currently reshaping scientific discourse.

So what really makes someone transgender, nonbinary, or any gender identity? How much of a spectrum exists for gender? As science continues to answer these difficult questions through neuroimaging and hormonal studies, it is important to step back and remember that these conditions impact the lives of millions at a time when their very identity is questioned.