dirty rag

The Ultimatum Game and de Waal - Dan Dreifort

The ultimatum game is the unlikely progeny of neuroeconomics and game theory. In the game, two players are told they’re to split a sum of money. One person is put in a position of power; able to set the sharing terms. The other player either accepts or rejects the offer. There is no second offer. If the players don’t agree, there is no payout. Game theory and classical economics forecast that the player making the offer will propose a split wherein she receives a greater portion of the prize. E.g. in a $7 to $3 split each player goes home with something. However, ultimatum game results don’t follow this forecast. Instead, most power players suggest an equal split. Offers that are not mutually beneficial are usually rejected.

Ultimatum Game
it's all about money, son. (oh, and power)

Recent fMRI studies of the ultimatum game by Alan Sanfey showed “brain areas associated with strong emotions, like the anterior insula,” are active when a player is presented with an imbalanced offer (Lehrer, 2007). When the peeved player then mulls over the decision, areas of the brain associated with reason (dorsolateral prefrontal cortex) compete with emotions. As we know, contrary to what several theories suggest, emotional centers almost always win the battle and snubbed subjects stab their own wallets to spite their partner.

In a variation called the dictator game, the power player making the offer gets to keep his share even if the other player rejects the deal. Needless to say, the offers in this version are far more lopsided. In human studies of the dictator game, the second players always accepted their meager consolation and never rejected it. Frans de Waal played a similar game with capuchin monkeys and other primates in which he offered unequal rewards to pairs of subjects. The subjects receiving the lesser award (cucumber) almost always rejected the prize if their pair received something of greater value (grapes) (de Waal & Brosnan, 2003).

De Waal’s experiment differs from the dictator game in that a third party set the exchange rates, but human and non-human reactions to unequal (read: unfair) exchanges are interesting and relevant nonetheless. Humans always took the prize while other primates usually did not. However if one considers de Waal’s experiments more akin to the ultimatum game then perhaps we’re not so different. Both humans and non-humans reject inequality in this pairing.

The unknown Intent of rejections is one of the main problems with de Waal’s game. We don’t know why primates snub unfair offers. Are the subjects trying to manipulate the scientists in the hopes of receiving a greater prize? We don’t know. We also don’t know what parts of the brain are used in non-human unfair exchanges. Others suggest that we can’t like de Waal conclude humans and primates react similarly to unfair exchanges because, “humans do not behave like capuchins in similar [experiments],” and “the available evidence does not suggest that inequity aversion is cross-culturally universal” (Heinrich, 2004).

If both humans and non-human primates are able to someday participate in a suitable study, we might be able to determine to what degree rational and emotional reactions to economic exchanges correspond between species. Surely the results could be parlayed into the primate morality discussion. Regardless, it’s remarkable that we’re just now beginning to understand that popular notions of human rationality are flawed in part because studies ignore emotional factors. As we understand more about ourselves, we’ll be able to know how we’re like and unlike non-human primates.

Works Cited

  • de Waal, F., & Brosnan, S. F. (2003, September 18). Monkeys Reject Unequal Pay. Nature , pp. 297-299.
  • Heinrich, J. (2004). Animal Behaviour. Nature , 428 (6976), 139.
  • Lehrer, J. (2007, March). The Truth Seekers. Seed , pp. 73-85.