"Have you ever purposely slowed down while driving in order to punish the person tailgating you? Maybe it inconvenienced you, but didn't it feel good? This is spite: hurting ourselves so that we can hurt someone else. Spite seems perfectly needless, evolutionarily speaking. Scientists have long struggled to understand why it exists at all. Unlike cooperation, selfishness, or altruism, spite is a zero-sum game. When Warren Buffet invested in a failing...