stances, even those never previously encountered. “There must have been a transition in evolution,” Nowak said, that allowed humans to develop this “infinite” communication system. Such a flexible language system no doubt helped humans evolve their other distinction—widespread cooperation. “Humans are the only species that have solved the problem of large-scale cooperation between nonrelated individuals,” Nowak pointed out. “That cooperation is interesting because evolution is based on competition, and if you want survival of the fittest, this competition makes it difficult to explain cooperation.”13

Charles Darwin himself noted this “altruism” problem. Behaving altruistically—helping someone else out, at a cost to you with no benefit in return—does seem to be a rather foolish strategy in the struggle to survive. But humans (many of them, at least) possess a compelling instinct to be helpful. There must have been some survival advantage to being a nice guy, no matter what Leo Durocher might have thought. (He was the baseball manager of the mid-20th century who was famous for saying “Nice guys finish last.”)

One early guess was that altruism works to the altruist’s advantage in some way, like mutual backscratching. If you help out your neighbor, maybe someday your neighbor will return the favor. (This is the notion of “reciprocal altruism.”) But that explanation doesn’t take you very far. It only works if you will encounter the recipient of your help again in the future. Yet people often help others whom they will probably never see again.

Maybe you can still get an advantage from being nice in an indirect way. Suppose you help out a stranger whom you never see again, but that stranger—overwhelmed by your kindness— becomes a traveling Good Samaritan, rendering aid to all sorts of disadvantaged souls. Someday maybe one of the Samaritan’s beneficiaries will encounter you and help you out, thanks to the lesson learned from the Samaritan you initially inspired.

Such “indirect reciprocity,” Nowak told me, had been mentioned long ago by the biologist Richard Alexander but was generally dismissed by evolutionary biologists. And on the face of it, it

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