In certain economic experiments, some participants willingly pay a cost to punish peers who contribute too little to the public good. Because such punishment can lead to improved group outcomes, this costly punishment has been conceived of as altruistic. Here we provide evidence that individual...

One of the key scientific challenges is the puzzle of human cooperation. Why do people cooperate? Why do people help strangers, even sometimes at a major cost to themselves? Why do people want to punish people who violate norms and undermine collective interests? This book is inspired by the...