Rats contain the spinal nucleus of the bulbocavernosus (SNB) is a group of motor neurons that innervate the muscles that control the penis, meaning that while males have about 200 of these cells, females have far less and the muscles die at birth. This follows the organizational hypothesis as androgens given at birth can spare SNB cells and their muscles and castration causes them to die. To the androgen-insensitive the muscles also die, meaning aromatization is not a factor.