[blinkedup]

> We already do: we determine the sex of babies at birth, and each others' sex as adults, by looking at external genitalia and at secondary sex characteristics.

> Why would knowledge of chromosomes now change that?

If we look again at the case of Caster Semenya, who was reportedly assigned female at birth, with a birth certificate to match, but for whom later tests showed XY chromosomes, this was a strong indication of Semenya actually being male. Then further investigation revealed that Semenya has 5-ARD, a male-only DSD condition in which the penis does not develop as normal due to a mutation in an enzyme responsible for transforming testosterone to DHT. The testes are present and caused Semenya to go through male puberty. There is no female reproductive system: no uterus, no cervix, no fallopian tubes, no ovaries. But there is a male reproductive system, albeit a broken one: testes and an underdeveloped penis. On this basis, Semenya is male, not female.

Knowledge of sex chromosomes was the starting point for confirming that Semenya is a male.

> Also note that some athletic associations, e.g. World Athletics, consider athletes with Y-chromosome DSDs to be eligible for competition in women's categories as long as they reduce their testosterone to [fe]male levels medically.

That's true but it's also controversial. The female category can only coherently exist if the eligibility criteria excludes the male physical advantage acquired by males during male sexual development. And there's no evidence that this advantage is wholly removed when these males suppress testosterone. Only evidence of some weakening. The male body remains.

> As an aside, note in the same article that World Athletics now completely bans transgendered women _who have gone through male puberty_ from competing in the women's category so even having one's sex determined as male as birth is not recognised as an absolute advantage in women's sports; the cutoff is having gone through a male puberty, which a genetic test alone cannot determine.

I think this is an important aside to mention. The male physical advantage is equivalent between the cohorts of males with a trans identity and males with an androgen-sensitive DSD (like 5-ARD). In terms of fair competition, it doesn't really make sense to permit eligibility via testosterone suppression for one group but not the other.

> Yes, but I'm claiming that someone whose sex was determined to be female at birth, and lived their whole life as a woman, and experienced everything that every other woman experiences, is not a male.

Does this apply to the athletes we're discussing though? Having testes and going through male puberty, as Caster Semenya did, is not a female experience.