[uion]

No it's more fundamental than that. Sex is based around reproductive role - in particular, which type of gametes are produced.

If we look at other species this is perhaps more obvious, rather than focusing on sex-specific differences just in humans and other mammals.

[CuriousCosmic]

While technically yes in the strict biological definition, it's a measurably less useful definition in humans since we generally don't consider a man who can't produce sperm as "not male" and a woman who doesn't have eggs as "not female".

Point being that while sex is certaintly more fundamental than gender, I don't know if the formal biology definition of sex is sufficiently nuanced for the way we perceive sex in humans. Especially since of the primary sex characteristics, having eggs or sperm is arguably the characteristic that humans care the least about when determining sex.

[uion]

True, a male can develop with malformed testes or a woman with non-functioning ovaries, but can we still understand the difference between the sexes. For gonochoric species like humans it's the whole body plan that develops separately for each reproductive role.

It's not just hormone levels measured at any one point in time, but the result of a long and specialised developmental process. For instance, females and males end up having different skeletal structure which we can observe as accommodating childbirth in the former.