The Evolution of Generosity in the Ultimatum Game
A study by Arend Hintze of Michigan State University and Ralph Hertwig from the Max Planck Institute for Human Development conducted many trials of the one-shot anonymous ultimatum game described in section 12 of the textbook, particularly when factoring kinship between participants. In this game, two anonymous individuals must decide how to share 1.0 units of a desired resource according this pattern: one individual, the proposer, proposes a fraction of the resource to give to the other individual, the responder, who can decide to accept the proposal or reject it, in which case neither individual gets any of the resource. This game has been used as an example of the flaws of rational, Nash equilibrium-based logic in predicting human behavior in extreme circumstances. The responder is expected to accept any offer (besides 0.0 in which the responder should be indifferent, rationally), as the amount of resource gained through accepting the offer will be higher than 0.0, the amount of resource gained by rejecting it. The textbook explains this difference by factoring humans’ desires for fairness, and the negative emotions that could result from accepting such an unfair offer.
This study offers another explanation: humans’ behavior is rational, when factoring in kinship. If one assumes that players are not only motivated by self-interest, but by “familial interest” (much like some seemingly altruistic behavior evolved, as that behavior aided others with similar genes even at the cost of the individual performing it). The researchers found that with non-kin, the results were similar to those of previous UG experiments–players rejected poorer deals, even if they were not the “rational” decision. However, with kin, players behaved optimally as designated by the Nash equilibrium. With both of these strategies, players who played with both kin and non-kin would maximize the amount of resource afforded to kin by denying unfavorable trades only with non-kin, as these trades would cause the responding family to lose resource, relative to the proposing family. Humans are often considered “irrational” beings, whose emotions get in the way with optimal thinking and behavior. This study offers a different conclusion: humans are rational, but the strict, formulaic ways we analyze them is not.
http://www.nature.com/articles/srep34102