Essay
Olivier Morin/Agence France-Presse — Getty Images 
The fact is, sex is messy. This is demonstrated in the I.A.A.F.’s process for determining whether Caster Semenya is in fact a woman.
By ALICE DREGER
The only thing we know for sure about Caster Semenya, the world-champion runner from South Africa, is that she will live the rest of her life under a cloud of suspicion after track and field’s governing body announced it was investigating her sex.
Why? Because the track organization, the I.A.A.F., has not sorted out the rules for sex typing and is relying on unstated, shifting standards.
To be fair, the biology of sex is a lot more complicated than the average fan believes. Many think you can simply look at a person’s “sex chromosomes.” If the person has XY chromosomes, you declare him a man. If XX, she’s a woman. Right?
Wrong. A little biology: On the Y chromosome, a gene called SRY usually makes a fetus grow as a male. It turns out, though, that SRY can show up on an X, turning an XX fetus essentially male. And if the SRY gene does not work on the Y, the fetus develops essentially female.
Even an XY fetus with a functioning SRY can essentially develop female. In the case of Androgen Insensitivity Syndrome, the ability of cells to “hear” the masculinizing hormones known as androgens is lacking. That means the genitals and the rest of the external body look female-typical, except that these women lack body hair (which depends on androgen-sensitivity).
Family/Reuters
The I.A.A.F.’s process for determining whether Caster Semenya, second from left, is a woman will involve at least a geneticist, an endocrinologist, a gynecologist and a psychologist.
NY Times for more