It would appear that altruistic traits should quickly become rare and go extinct, since altruists always fare worse than their selfish neighbors. They expose themselves to the danger of death while the selfish save their own skins, simultaneously benefiting from the protective behavior of the altruist. But altruism is everywhere. Somehow, evolution bridges the gap between the individual, where altruism dies, and the group, which it vivifies.
For Sloan Wilson, the solution is straightforward: Altruism is advantageous at a larger scale, and that is the scale at which natural selection selects it. Altruism is good for the group; therefore its evolution and persistence are inevitable.