When people learn just a little about game theory, decision theory, economics, or even evolutionary theory, they sometimes come away thinking that altruism is somehow “irrational” or that rational agents are selfish. Here are a number of reasons why altruism is often rational: I. People can value altruism for its own sake: 1. Intrinsic values: as a psychological fact, most humans intrinsically value at least some things as ends (not merely as means to other ends) that are not about...