I was reading a book the other day, a book on feminism written for men by a man, which casually states that the notion of gender as a set of behaviours (we might say identity now, but this was written in the 90s) wasn't in usage until the 70s. Until then, gender was a grammatical concept associated with some European languages. It was expanded as a way of describing conditioning sexed people into a way of behaving that was naturalized as sex but newly theorized by feminists at the time to be not natural but constructed (like language: the table isn't inherently male or female but constructed by language as such).
I found this really interesting. I hadn't fully got a grip on the way that gender as a set of behaviours wasn't even a thing in living memory.
Now, we are supposed to believe that such behaviours are an innate part of natural identity that are unrelated to the sexed part of the body, but some how emanate from an unsexed but independently gendered organ - the brain. It's all very confused. It requires a certain ahistoricity in the idea of gender itself, a lack of recognition about where an idea of gender comes from, to accept trans ideology.