What is more, altruism sometimes evolves without selfish punishment. In a software simulation, Eldakar and Wilson have found that as the cost of punishing cheaters falls, so do the number of selfish punishers. "When punishment is cheap, lots of people punish," Wilson explains. And among humans, there is no shortage of low-cost ways to keep others in line from outright ostracism to good old-fashioned gossip.
Editor's Note: This story was originally published with the title "Thriving on Selfishness"