As in, not all women attempt suicide, & not all men never attempt suicide?

Right, an individual can claim not to meet the specific determinations of the gender. It's defined by general standards. Sex is not general, everyone has the same standard that anyone can tell as soon as the baby is born (or a doctor can tell even before, now).

Wha? Why would we re-name 'nurture' 'nature', why would we erase social determinism, by calling it biological determinism? How are we meant to talk about class then – it's not biologically determined? Culture is relevant.

Look, I'm not necessarily disagreeing with you, only saying that this is a whole gigantic complicated discussion rather than a simple fact, and what's important at the moment is getting the facts right.

They are incorrectly identified as female & so receive our culture's designated gendered upbringing accordingly. They end up walking, talking, sounding, acting, moving like women, despite being male – now that's how you do transitioning.

Mm, well maybe I am disagreeing with you... so if someone could be incorrectly identified as female early enough they could become the other sex?

I mean, in any case, I'm not arguing over whether something is determined by biology or culture. I'm only arguing over whether biology or culture is absolute. What it results in is not the point. Sure, maybe all people raised as female have certain things in common, maybe not, maybe all people with female hormones have things in common, maybe not: that isn't what I'm focused on here. All I am asking is that we categorize people correctly. People can have male or female reproductive systems, period. Those are physically distinct types of human beings who have different growth charts, puberty experiences, health risks, and bodily capacities. That is just a fact.

We can argue about whether some things should be co-ed but it makes no sense to argue whether some things should be gender-based instead of sex-based. "Gender" is too indeterminate a concept to base a category on. Either it is as you say, directly based on sex anyway, or it is some kind of vague notion of selfhood that we cannot agree to. So, let's use sex as the basis for the categories (like sports teams, prisons, changing rooms, crime statistics & so on)