“Sex therapists haven’t known which interests are common and which are rare,” Ogas says. “We probably now know more than ever before.”Among their more surprising findings: Straight men enjoy a wider variety of erotica than imagined, including sites devoted to elderly women and transsexuals. Foot fetishes aren’t a deviance; men are evolutionarily wired to look for small feet, which are a sign of high estrogen production, which itself is a sign of fertility. Gay men and straight men have nearly identical brains, and their favorite body parts, in order of preference, line up exactly: chests, buttocks, feet. Straight men prefer heavy women to thin ones. Straight women enjoy reading about and watching romances between two men — it’s not about the sex, which is downplayed, but the emotion, which is the focus. (The largest audience for “Brokeback Mountain,” says the book, was straight women.) Straight men have a fascination with other men’s penises, which may be conscious or unconscious.“The research, as far as I can tell, is pretty damn sound,”