smart and receptive brains. Indirect reciprocity relies on what others think of us. Making a reputation has been shown to engage much of the same reward circuitry in the brain as making money. By being helpful, I obtain the reputation of being a nice, obliging, and considerate person. My behavior toward you, of course, now depends on your reputation and thus what you have done to others: if you have been a cad and a rotter, I am less likely to trust you to deliver. Then again, if we know nothing about someone, we are often willing to give them the benefit of the doubt for the sake of our own reputation.
There is a clear link between this mechanism of cooperation and the evolution of empathy. We need to have a good idea of what is going through the mind of another person in order to understand and appreciate the motivation of a Good Samaritan. “Even though he was rushing home to see his ill mother, he stopped to help that injured man,” “If I had been lying there, bleeding at the curbside, I would have been so grateful for the help of a stranger,” “I could see she was in pain and felt I had to help,” and so on. We require, in the parlance of the psychologists, a “theory of mind,” that remarkable capacity that enables us to understand the desires, motivations, and intentions of others. This mind-reading ability allows us to infer another’s perspective—whether emotional or intellectual.
One can easily envisage how the mechanism of indirect reciprocity can stimulate the evolution of moral systems. The quotation from Luke at the start of this chapter has a direct corollary, known as the Golden Rule, that transcends all cultures and religions: “Do unto others as you would have them do unto you.” The rule pops up in Greek philosophy (“What you wish your neighbors to be to you, you will also be to them,” Sextus the Pythagorean), Buddhism (“Putting oneself in the place of another, one should not kill nor cause another to kill”), Christianity and Judaism (“Love your neighbor as yourself ”), in the Mahabharata of Hinduism (“One should never do that to another which one regards as injurious to one’s own self ”) in the Farewell Sermon of Muhammad (“Hurt no one so that no one may hurt you ”) and in Taoism too (“He is kind to the kind; he is also kind to the unkind”).
The Golden Rule interlinks several ideas: it binds empathy with the idea of reciprocity along with an ironclad faith in the power of indirect reciprocity—if I am good to another person today, somebody will be good to me in the future. In this way, indirect reciprocity has played a central role in the development of our brains, of our ability to lay down memories, and of our language and moral codes. This remarkably potent ingredient of cooperation is at the heart of what it means to be human.
KAHLENBERG
I first came to appreciate the power of indirect reciprocity on a walk with Karl Sigmund in the summer of 1996. We were hiking around the Kahlenberg, a forested hill north of Vienna. The ridge is blessed with breathtaking views of the great city, being part of the Wienerwald, the Vienna woods. We were negotiating a chain of tree-covered hills northeast of the city, bounded by rivers, including the Danube. There are villages here and there, such as one where Beethoven lived (Nussdorf), and taverns (Heurige) are dotted all about, where we could sit down to sip the local wines.
Although this does not sound a likely birthplace for a scientific breakthrough, there is plenty of evidence that the networks of paths that crisscross the forested hills of the Wienerwald are steeped in creative magic. Mahler would walk from the Kahlenberg into the city to conduct opera. Johann Strauss the Younger composed his “Tales from the Vienna Woods” in waltz time. Franz Schubert and Beethoven were also moved by its rolling Arcadian landscapes. A green meadow on a plateau high above the city where the skies open wide is called Himmel (Heaven). There, the young Sigmund Freud managed to convince himself that he had understood the nature of dreams.
During our long meander though heaven, Karl mentioned something that made me stop in my tracks. He suggested that we should extend our work on cooperation to take a close look at indirect reciprocity. I had never heard that expression before but so many thoughts gushed into my mind that I found it intoxicating. I told him that I did not want him to explain too many details. I did not want to know what work might have been done before on this subject, so I could follow through my own line of thinking. I knew exactly what he meant and how the perfect clarity of mathematics could bring this idea into sharp focus. I stopped everything else that I was doing. In my mind a rolling landscape of new possibilities for cooperation beckoned.
I fell in love with this work, which I felt would take our research in a new direction. I was almost consumed by the feeling. Amour did seem to be in the air. For one thing, I was reading The English Patient (“In love, there are no boundaries”). For another, Karl and I had made a poignant discovery during our walk in the lush greenery of the Wienerwald. We stumbled across a little cemetery, where there was an overgrown grave. The headstone was carved with poems and stories to celebrate the memory of Caroline Traunwieser, apparently the greatest beauty of the Vienna Congress of 1815.
Among the many dedications to Caroline was a tribute from the founder of the Austrian Academy of Sciences, Freiherr von Hammer-Purgstall, an Orientalist scholar who supplied Goethe with Persian poetry. He recounted his first heart-skipping encounter with her in a salon: “Never before and never afterwards in my life was I so overwhelmed by the appearance of beauty.” She was adored by all, from poets to officers to the director of the Viennese China Factory (Wiener Porzellanmanufaktur). Her grave revealed that she died young and that no portrait of her survived. In a strange way, Karl and I felt bereft after reading these moving tributes to her lost beauty. My melancholy was a faint reflection of Caroline’s radiant glow that had illuminated Vienna long ago, a testament to her reputation.
FROM REPUTATION TO COOPERATION
The most incomprehensible thing about the universe is that it is comprehensible.
—Albert Einstein
By the time my flash of inspiration came in the Wienerwald, my confidence in my ability to crack problems was growing. Deep in my brain a geyser bubbled and sent a torrent of thoughts skyward. I knew I had to work fast. Nearby was my parents’ house, on the northern slope of the Kahlenberg. In my little bedroom, which I have used since I was eight years old, I sat down and began my research on indirect reciprocity.
Usually when you begin a new project you immediately run into difficulties. There’s one unforeseen problem, then another. Often there are many. You need time to wrestle with them and, only if you are very lucky, resolve them. Usually you fail. Not this time, however. Everything I attempted worked, and first time too. After three weeks, I had an almost complete story, a mathematical picture of indirect reciprocity and, most important, how it helps cooperation to bloom. I was driven on by the excitement of trying and succeeding at something new. I was proud of the lightning speed with which I managed to knit my intuitions into a mathematical theory.
After three weeks I saw Karl again to discuss my findings. Once again, we met in the forest. This time, the weather was grey, the air damp and raw. We had arranged to meet in a little inn and, once we had sat down together at a wooden table, I presented my results to him. Even though we were friends, I felt nervous as though I were revealing a secret for the first time. Karl liked the approach and immediately saw the implications.
I began with a computer model that described a population of people. In that population, any one encounter involves two people. One of them is offered a choice—whether or not to help the other. When a Good Samaritan does something nice for someone else, this altruistic act confers a benefit on the recipient at a cost to the Samaritan. That could be when you have to sacrifice your time to help another, whether giving a hand to that doddery old lady to help get her safely across a street or taking a moment to point out the nearest car park to a motorist.
If the cost is smaller than the benefit then the act of charity, once returned, leaves both individuals
