The Usefulness of Spite

Let’s play the ultimatum game. I’m first player, you’re second player. We have ten bucks to divide, first player gets to propose a division, and second player gets to accept or reject the division—and if the second player rejects, then nobody gets anything. If I’m smart, I’ll propose a fifty-fifty split, because you surely wouldn’t reject that offer, would you? If I’m greedy, I’ll take nine bucks and propose that you only get one—and you’d reject that, wouldn’t you? Even though, rationally, you’re better off getting a dollar than no dollar, you’re likely to cut off your nose to spite your face and reject the offer.

So, what gives? Why on earth would we, as a species, keep this seemingly irrational behaviour, spite, around? Well, a new study from the Proceedings of the Royal Society B has found out what you’ve always suspected: we’re spiteful in order to enforce fairness.

For this study, researchers slightly altered the ultimatum game described above by adding “negative assortment”, which means that players consider that they’re probably not using the same strategy as their competitors. For example, if two players both commit to making fair offers, but one will accept all offers and the other will accept only fair ones, they are negatively assorted. A spiteful strategy would be to only make unfair offers, but also reject unfair offers. We suggest that researchers call this the TTC Union Bargaining Strategy.

Anyway, in the normal version of the game, a spiteful player will always walk away. However, with the negative assortment, spite becomes more common and promotes fairness, because acting fairly protects you from spite, but acting unfairly makes you a target of spite.

How? Well, consider another strategy, that of the “gamesman”. A gamesman is someone who only makes unfair offers, but accepts all offers, because a gamesman is rational, unfair, and attempting to maximize profits. Unfortunately for the gamesmen, they become targets of the spiters, because a spite-driven player will always reject a gamesman’s terrible offer, eventually killing off the gamesman. Players making fair offers do just fine, because by making fair offers they won’t provoke the spiteful players in to walking away.

Of course, you’ll note that people who adopt fair play as a strategy do the best, on average, over time. Interacting with spiteful players is probably non-to-pleasant, especially when a spiteful player is making an offer, but the silver lining is that spiteful players mostly reserve their bile for people who really deserve it. Never thought we’d say this, but: thank goodness for spite.