Are Trans Women 'Biologically Male'? The Answer is Complicated

A History of Changing Sex

In the modern era, the scientific concept of transgender – that there could be a perceived or felt difference between one's psychological sex and their biological sex – dates back to at least the late 19th century. At that time, the very definition of sex itself was changing.

For centuries prior, sex was commonly determined through a simple visual inspection of anatomy: does a person have a penis or a vulva?

By the 1870s, however, scientific advancements in dissection and the study of intersex conditions led some researchers to posit a new definition of biological sex: one based on gonads – internal reproductive anatomy such as testes or ovaries – rather than external genitalia.

Herculine Barbin is an example of this shift. Assigned female at birth, Barbin was raised in 19th-century France as a girl. In her teenage years, a doctor discovered hidden testicles adjacent to her vaginal canal. Based on this internal anatomy, a court ruled Barbin's sex must be reassigned to male. Her "true sex," the court resolved, was gonadal.

As transgender medicine emerged as a field of study in the 1920s and 1930s, the gonadal view of sex reigned. Eugen Steinach, an Austrian scientist, conducted studies demonstrating that a guinea pig's sex could be changed by removing its gonads and replacing them with the gonads of the opposite sex.

Transgender advocates such as the German physician Magnus Hirschfeld realized that human sex functioned in a similar way to Steinach's guinea pigs. If the hormonally induced characteristics many people consider "male" and "female" – such as facial hair, breast growth or the pitch of one's voice – are largely determined by gonads, then a person can change their sex by changing gonads. Therefore, the most common surgeries for trans women at this time consisted of orchiectomies – the removal of testes.