A new study by Dirk Helbing at ETH Zurich in Switzerland and colleagues has modeled the emergence of "nice" behavior in idealized human beings. It's done by computer, using the famous "prisoner's dilemma" game, in which a prisoner has to decide between cooperating with a comrade to get a mutual reward or avoiding a punishment by being the first of the two to defect to the other side. The Zurich team found that so long as players in the game stay near their (modeled) parents, the birth of a nice guy predisposed to cooperate can trigger "a cascade" of generous acts.

In...