Human beings can be tenderly compassionate and yet also shockingly cruel. What if there was a master control for human behaviour? Nurture it and people are loving and generous. Ignore it and they revert to violence and greed. Pioneering neuroeconomist Paul Zak has discovered just such a master switch: a molecule in the human brain. He and his research team have travelled far and wide, taking blood from people active in a wide range of situations. Their experiments to measure a chemical in the bloodstream called oxytocin reveal the answers to those mysteries about why we make the decisions we do. He shows how, once we understand the moral molecule, we can consciously use it to live more enlightened lives.