The “ultimatum game” is a fiendish invention of economists to test people’s selfishness. One player is asked to share a windfall of cash with another player, but the entire windfall is cancelled if the second player rejects the offer. How much should you share? When people from the Machiguenga tribe in Peru were asked to play this game, they behaved selfishly, wanting to share little of the windfall. Not far away, the Achuar in Ecuador were much more generous, offering almost half the money to the other player — which is roughly how people in the developed world react.
What explains the difference?