levels of oxytocin, a hormone linked to pleasure and happiness. Apparently the trusting gesture of the first player, by offering some money, elicits a positive hormonal response. “It tells us that people are very much responsive to their environment,” Zak told me when I visited him at Claremont. “People who got a positive signal had a nice positive happy hormone response, and their behavior reflects that.”12

Zak believes that the relationship between trust and oxytocin is central to understanding many of the world’s economic ills. Oxytocin is linked to happiness, and the countries where people report high levels of happiness are also countries where people report high degrees of trust. Trust levels, in turn, are a good indicator of a country’s economic well-being. “Trust is among the biggest things economists have ever found that are related to economic growth,” Zak said.

HOMO NEUROECONOMICUS

For all of its intriguing findings, neuroeconomics doesn’t excite everybody, like the economist who perplexed Montague by not caring about the brain. From the perspective of economists like that one, neuroeconomics probably doesn’t have much to offer. To them, it only matters what people do; it doesn’t matter which part of the brain is busy when they do it.

Neuoreconomists, though, want more than a mere description of economic decision making. They want the Code of Nature, the scientific understanding of humanity sought by 18th-century thinkers such as David Hume and Adam Smith. “The more ambitious aim of neuroeconomics,” writes neuroeconomist Aldo Rustichini, “is going to be the attempt to complete the research program that the early classics (in particular Hume and Smith) set out in the first place: to provide a unified theory of human behavior.”13

Rustichini, of the University of Minnesota, points out that Adam Smith’s great works—Theory of Moral Sentiments and Wealth of Nations—were part of a grand plan to codify the nature of



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