devils live with angels
"Selfish punishers can invade the population when rare but then limit each other, preventing the altruists from being completely eliminated.Individuals who behave altruistically are vulnerable to exploitation by more selfish individuals within their own group, but groups of altruists can robustly out-compete more selfish groups. Altruism can therefore evolve by natural selection as long as its collective advantage outweighs its more local disadvantage."
"Altruists ‘pay’ the selfish punishers by allowing themselves to be exploited, while the selfish punishers return the favor with their second-order altruism. “That way, no one needs to pay the double cost required of an altruist who also punishes others,” says Eldakar. “If so, then the best groups might be those that include a few devils along with the angels.” "
——————from Science daily
想起小时候，小学里的班长虽然没有人喜欢，我们称他为“奸懒馋猾坏”五毒俱全，但是老师还是喜欢他做班长，大概就是这个原因。 一个集体对外竞争既需要好人，也需要坏蛋。 一个国家既需要忠臣也许要奸臣；这种组合是因也是果。经济学家认为是减少损耗的双赢。
