Since the dawn of humanity we've been mystified by desire, love and the compulsion to bond with others. What force keeps people together, and, if it's so powerful, how can anybody ever cheat? Neuroscientists like Young are at last able to peer inside living brains to discover how chemicals acting on circuits drive such seemingly complex behaviours. It turns out that on a molecular level, love is not so mysterious after all. The authors explain the mechanisms behind bonding, physical attraction, jealousy, infidelity and the essence of what it means to be human.