Fairness and the Ultimatum Game

by | Jun 21, 2018


A recent IFOD discussed the SCARF model of human social interaction which can be found here: SCARF A Model for Explaining Social Interactions. The “F” in SCARF stands for fairness and posits that humans experience a strong threat response from perceived unfairness.

We humans have a highly defined sense of fairness and we can react strongly, even to our own detriment, when confronted with a situation we perceive as unfair.  A great example of this is the “ultimatum game” which has been performed all over the world with similar results.  Here’s how the game works:

In the ultimatum game there is a “proposer” and a “responder”.  The proposer is given an amount of money and told that they must offer some of it to the responder.  The responder then either accepts or rejects the offer.  If the offer is accepted, both parties get to keep their respective amounts of money.  If the offer is rejected then neither gets to keep any of the money.

Economic theory states that the responder should accept whatever amount offered, as long as it is more than zero, no matter how paltry. The responder is better off with anything above zero – its money for nothing. There is no rational reason why the responder wouldn’t accept any split of the money.  But this is NOT what happens.

What happens is that on average, responders do not accept offers for less than 20% in order to punish the proposer for being unfair.  This result is true across cultures and religions.  The results do vary by individuals, and studies of twins have shown that how a person plays the game is determined by more by genetics than upbringing or culture.

Studies on other species like chimps have shown that they don’t have the same sense of fairness – a chimp will take whatever offered (which is the rational choice) when playing the ultimatum game.

It is theorized that this human sense of fairness allowed us to form and live in groups. Without an underlying sense of fairness creation of societies with rules and acceptable interactions might not have formed.   And the rise of human groups and societies, in turn, led to greater survival and our eventual world dominance. In fact, some theorists have called our innate sense of fairness and willingness to punish unfairness even to our own detriment as humanity’s “killer app.”


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