Testosterone’s effects start early-really early. At conception, every embryo is female and unless hormonally altered will remain so. you need testosterone to turn a fetus with a Y chromosome into a real boy, to masculinize his brain in the body.

men experience a flood of testosterone twice in there lives: in the womb about 6 weeks after conception and at puberty. The first fetal burst primes the brain and the body, endowing male fetuses with the in instinctual knowledge of how to respond to later testosterone surges.

The second, more familiar adolescent rush- squeaky voices, facial hair and all-completes the process. Without testosterone, humans would always revert to the default sex, which is female. The Book of Genesis is therefore exactly wrong. It isn’t Women who are made out of men. It is men who are made out of Women.

Testosterone, to stretch the metaphor, is Eve’s Rib…

Andrew Sullivan, “the he hormone”