Those who claim that sex is determined by chromosomes must not realize that sex is assigned at birth not by chromosomes, not even by gonads, but by genitals. In fact, the vast majority of us never learn what our sex chromosomes are. Sex isn’t something we’re actually born with, it’s something that doctors or our parents assign us at birth. So if sex is determined by genitals, they must be clearly binary and unchangeable, right? Wrong. Genitals can be ambiguous at birth and many trans people get gender confirmation surgery to change them. Neither chromosomes nor genitals are binary in the way that “biological sex” defenders claim they are, and the vast majority of measures by which we judge sex are very much changeable.

While it is true that gender and sex are different things, and that gender is indeed a social construct, sex isn’t the Ultimate Biological Reality that transphobes make it out to be. There’s nothing intrinsically male about XY chromosomes, testosterone, body hair, muscle mass or penises. If an alien civilization found earth, they wouldn’t look at a person with a penis and say “Oh, that must be a male, sex based on genitalia is the One Universal Constant.” Sex, like gender, is indeed socially constructed and can be changed.