War and Peace and War: The Rise and Fall of Empires

by Peter Turchin

One kind of experiment, which has now been conducted by a number of investigative teams, is called “the public goods game.” Subjects are divided up in groups of four and given an initial endowment of $10 each. The game is played in 10 rounds. Every round each participant can contribute any part, from 0 to 10 dollars, to the group project. The experimenters first double the total amount contributed to the common account, and then divide it up equally among all participants. Thus, for each dollar contributed to the common pot, a participant gains back only 50 cents. On the other hand, he or she also gains 50 cents for each dollar contributed by others. If all participants contribute the maximum amount ($10), they would end up with $20 each, doubling their initial endowment. Clearly a rational, self-interested player will contribute nothing to the common pot, keeping the initial stake plus whatever gains come from the cooperative behavior of the others. In the best case, when the other three all contribute the maximum, the “free-rider” would get $15 in addition to the initial stake, for a total of $25. However, others will make the same calculation and also contribute nothing, so everybody is left with $10, instead of the maximum cooperative payoff of $20. Thus, the rational choice theory predicts that there will be no cooperation. Real people did not behave in the way predicted by the self-interest hypothesis. The average contribution to the common pot in the early rounds wa...