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Karl also had plenty of anecdotes to underline why indirect reciprocity is just as relevant to everyday life as the direct version of reciprocity. He pointed out that the Rothschild family had protected the investments of their English clients during the Napoleonic Wars. They were under intense pressure to give them up, but they kept the interests of their English clients at heart. Afterward, of course, the Rothschild family became extraordinarily rich. Their fortune was a direct result of the power of indirect reciprocity: because they had behaved impeccably, everybody now knew that they could be trusted.

Then there was the story of the American baseball player Yogi Berra, who was famous for his pithy comments and witticisms known as Yogi-isms. One of them was a perfect summary of indirect reciprocity: “Always go to other people’s funerals, otherwise they won’t come to yours.” Berra was counting on the fact that his acts of kindness would not be returned by the recipients, but by third parties who were moved by his public mourning.

The idea is also wonderfully summarized in musical form by Tom Lehrer, the American singer-songwriter, satirist, pianist, and mathematician. In “Be Prepared,” Lehrer’s spiky salute to the Boy Scouts, he sings: “Be careful not to do / Your good deeds when there’s no one watching you.” German speakers even have a saying with the same gist, Milinski notes: Tue Gutes und rede darüber. (“Do good and talk about it.”)

Excerpted from page 61of ‘Super co-operators ’ by Martin Nowak