One of the most fascinating topics in evolutionary biology is how and why organisms cooperate with each other. Natural selection works through competition between alleles for representation in the next generation. Yet one sees everywhere organisms actually helping each other, from mutualisms between ants and plants to the altruistic acts of firefighters storming into burning buildings to rescue people. But how can natural selection lead to cooperation? This, of course, is not a new question, and a tremendous amount of work in evolutionary theory in the last 40 years has shown that helping others can frequently be the winning strategy in the struggle for existence. We have a sophisticated theory of social evolution, dealing not only with helping behaviors, but also other behaviors such as policing, spiteful harm-doing, and so on.