Does sex have a history? Almost any teenager coping with a parent who still lives in the dark ages will assure you that it does. But the history of sex is surprisingly difficult to study. Why? Lack of evidence. Most people keep their sex lives to themselves. What people write down, publish, and circulate may be sexual fantasy or invention, with plotlines designed to sell copy. This evidence can tell us a lot about what people like to read or watch or imagine, but little about what they actually do. Ironically, the most reliable evidence for a history of sex is the mass of material (by government officials, religious leaders, parents, doctors, and so on) telling people what not to do. We can be certain that some people were doing some of that.