Many intractable controversies in today’s culture wars relate to issues of sex and gender. Americans disagree, for instance, about whether marriage is limited to a man and a woman, who can use which bathrooms, and whether we should hope that mothers should take care of children—at least in their formative years. These controversies are emblematic of the inability to say what a man is, what a woman is, or even whether stable sexual identities are linked to our bodies.