Ethan Watters writes: In the summer of 1995, a young graduate student in anthropology at UCLA named Joe Henrich traveled to Peru to carry out some fieldwork among the Machiguenga, an indigenous people who live north of Machu Picchu in the Amazon basin. The Machiguenga had traditionally been horticulturalists who lived in single-family, thatch-roofed houses in small hamlets composed of clusters of extended families. For sustenance, they relied on local game and produce from small-scale farming. They shared with their kin but rarely traded with outside groups.

While the setting was fairly typical for an anthropologist, Henrich’s research was not. Rather than practice traditional ethnography, he decided to run a behavioral experiment that had been developed by economists. Henrich used a “game”—along the lines of the famous prisoner’s dilemma—to see whether isolated cultures shared with the West the same basic instinct for fairness. In doing so, Henrich expected to confirm one of the foundational assumptions underlying such experiments, and indeed underpinning the entire fields of economics and psychology: that humans all share the same cognitive machinery—the same evolved rational and psychological hardwiring.

The test that Henrich introduced to the Machiguenga was called the ultimatum game. The rules are simple: in each game there are two players who remain anonymous to each other. The first player is given an amount of money, say $100, and told that he has to offer some of the cash, in an amount of his choosing, to the other subject. The second player can accept or refuse the split. But there’s a hitch: players know that if the recipient refuses the offer, both leave empty-handed. North Americans, who are the most common subjects for such experiments, usually offer a 50-50 split when on the giving end. When on the receiving end, they show an eagerness to punish the other player for uneven splits at their own expense. In short, Americans show the tendency to be equitable with strangers—and to punish those who are not.

Among the Machiguenga, word quickly spread of the young, square-jawed visitor from America giving away money. The stakes Henrich used in the game with the Machiguenga were not insubstantial—roughly equivalent to the few days’ wages they sometimes earned from episodic work with logging or oil companies. So Henrich had no problem finding volunteers. What he had great difficulty with, however, was explaining the rules, as the game struck the Machiguenga as deeply odd.

When he began to run the game it became immediately clear that Machiguengan behavior was dramatically different from that of the average North American. To begin with, the offers from the first player were much lower. In addition, when on the receiving end of the game, the Machiguenga rarely refused even the lowest possible amount. “It just seemed ridiculous to the Machiguenga that you would reject an offer of free money,” says Henrich. “They just didn’t understand why anyone would sacrifice money to punish someone who had the good luck of getting to play the other role in the game.”

The potential implications of the unexpected results were quickly apparent to Henrich. He knew that a vast amount of scholarly literature in the social sciences—particularly in economics and psychology—relied on the ultimatum game and similar experiments. At the heart of most of that research was the implicit assumption that the results revealed evolved psychological traits common to all humans, never mind that the test subjects were nearly always from the industrialized West. Henrich realized that if the Machiguenga results stood up, and if similar differences could be measured across other populations, this assumption of universality would have to be challenged.

Henrich had thought he would be adding a small branch to an established tree of knowledge. It turned out he was sawing at the very trunk. He began to wonder: What other certainties about “human nature” in social science research would need to be reconsidered when tested across diverse populations? [Continue reading…]