Why cooperate? This may be the most important scientific question we have ever, and will ever, face. The science of cooperation tells us not only how we got here, but also where we might end up. Cooperation explains how strands of DNA gave rise to modern-day nation states. It defines our extraordinary ecological success as well as many of the most surprising features of what make us human: not only why we live in families, why we have grandmothers and why women experience the menopause, but also why we become paranoid and jealous, and why we cheat. In this book, Nichola Raihani also introduces us to other species who, like us, live and work together.