Humans aren't supposed to be monogamous, argues psychologist Christopher Ryan in the new book Sex at Dawn. "[C]ouples are led to believe that waning sexual passion in enduring marriages or sexual interest in anyone but their partner portend a failed relationship, when in reality these things often signify nothing more than that we are Homo sapiens," writes Ryan. "This is a problem because there is no reason to believe monogamy comes naturally to human beings."
