What is desire? Why does libido decline when couples spend years together? Scientists the world over are deciphering the essence of desire. They are investigating the extent to which the love-life of monkeys corresponds to that of people, and are exploring whether the alleged lack of interest on the part of women is really due to a pathological problem. The amazing result of their research: in monogamous relationships, women get bored considerably sooner than men. Evolutionary psychologist Dietrich Klusmann questioned almost 2,000 students and discovered that the longer a relationship lasted, the further apart the sexual interests of the male and female partners grew. At the outset of the relationship, each wanted sex equally often. After three years, this was true of only a quarter of the women. At the same time, the desire for sex with someone else grew. From the evolutionary perspective, this lack of fidelity is quite explicable, for it promotes genetic diversity if women have children by different partners and men spread their genes around as far as possible. But what was normal behaviour over the millennia of human existence has run up against its limits in the age of romantic love. The imperative of sexual exclusivity – desire for just one person, all one’s life – leads inexorably to frustrations; jealousy, lovesickness and high divorce rates. Are polyamorous relationships an alternative? And how helpful are desire-promoting drugs for women, research into which the pharmaceutical industry is pursuing with great energy? This documentary also accompanies a couple through a therapy course, and shows surprising experiments on the subject of female desire. Recognized experts in the field give their views, including anthropologist Helen Fisher, medical journalist Werner Bartens, sexologist Ulrich Clement and the New York best-selling author Daniel Bergner.