 An ejaculate of sperm swim through a uterus. At the branches of the Fallopian tubes, half go one way and half the other. Down one tube toward the sperm bounces a female head, singing, happily on her way. Four sperm zero in; she panics but can t avoid them. Pow! they hit her full force and disappear into her. The decision she makes and what she does next change the course of her life in a major way.