[hvdijk]

> I thought trans was about changing gender, not changing sex.

Mostly true, but it's confusing. Historically, sex and gender have been used interchangeably. That is slowly changing. There are a lot of places that refer to "sex" where "biological sex", as you put it, is not what is meant. See e.g. how trans people can still get their "sex" updated on documents that refer to sex and not gender, and how many places described as single-sex are actually closer to single-gender.

[whoooooo123]

> Historically, sex and gender have been used interchangeably.

This really isn't true. "Sex" was the only word anyone used for most of history; the idea that there's a distinction between "sex" and "gender" was invented by the sexologist John Money in 1955.

https://en.wikipedia.org/wiki/Gender#History_of_the_concept

"Gender" was originally a term from linguistics that had nothing to do with biological sex.

[hvdijk]

The Wikipedia article you link to also claims that the 1882 Oxford Etymological Dictionary of the English Language said that one meaning of gender was sex. Other dictionaries from well before 1955 also support this. In fact, the 1828 Webster's dictionary, available online, specifically says the meaning of sex came first, the meaning in grammar followed from that. The separation of sex and gender is recent, you're right about that and that's what I was saying too, but you're wrong that sex was the only term used before that.