Gender is one of the fundamental ways in which the social life of human beings is organized. Indeed, one of the fi rst questions people ask when they hear of a birth is whether the child is a boy or a girl. From infancy onwards, parents often think that boys and girls are very different. For example, a few years ago, a newspaper columnist wrote about his young son (Weasel, 2001). His son is messy, leaves grape juice stains on the counter, and has Oreo rings around his mouth. He doesn’t like to take afternoon naps, he plays with “boy stuff,” and is obsessed with monster trucks. Weasel noted that his daughters have very different interests and behaviors than his son. More than likely many readers found the column charming, and agreed that boys and girls really do seem like different kinds of beings.