Some fish—groupers, porgies, bluehead wrasses—live as transsexuals. They change, typically from female to male. All bluehead wrasses, for example, are born female. They stay that way until a resident male disappears or dies. Then, the most dominant females immediately begin acting like males. They battle for preeminence. When one finally takes over, her ovaries degenerate, testes develop, and her brain creates new behaviors. She becomes a he.
