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).
Women with complete Androgen Insensitivity Syndrome are less “masculinized” in their muscles and brains than the average woman, because the average woman makes and “hears” some androgens. Want to tell women with Androgen Insensitivity Syndrome they have to compete as men, just because they have a Y chromosome? That makes no sense.
So, some say, just look at genitals. Forget the genes — pull down the jeans! The I.A.A.F. asks drug testers to do this. But because male and female genitals start from the same stuff, a person can have something between a penis and a clitoris, and still legitimately be thought of as a man or a woman.
Moreover, a person can look male-typical on the outside but be female-typical on the inside, or vice versa. A few years ago, I got a call from Matthew, a 19-year-old who was born looking obviously male, was raised a boy, and had a girlfriend and a male-typical life. Then he found out, by way of some medical problems, that he had ovaries and a uterus.
Matthew had an extreme form of Congenital Adrenal Hyperplasia. His adrenal glands made so many androgens, even though he had XX chromosomes and ovaries, that his body developed to look male-typical. In fact, his body is mostly male-typical, including his muscle development and his self identity.
O.K., you say, if chromosomes and genitals do not work, how about hormones? We might assume that it is hormones that really matter in terms of whether someone has an athletic advantage.
Well, women and men make the same hormones, just in different quantities, on average. The average man has more androgens than the average woman. But to state the obvious, the average female athlete is not the average woman. In some sports, she is likely to have naturally high levels of androgens. That is probably part of why she has succeeded athletically.