The Grape vs. the Cucumber, or The Wages of Inequity

 …together with Sarah Brosnan, we did a study in which capuchin monkeys received either a grape or a piece of cucumber for a simple task.

If both monkeys got the same reward, there never was a problem. Grapes are by far preferred (as real primates, like us, they go for sugar content), but even if both received cucumber, they’d perform the task many times in a row.

However, if they received different rewards, the one who got the short end of the stick would begin to waver in its responses, and very soon start a rebellion by either refusing to perform the task or refusing to eat the cucumber.

This is an “irrational” response in the sense that if profit-maximizing is what life (and economics) is about, one should always take what one can get. Monkeys will always accept and eat a piece of cucumber whenever we give it to them, but apparently not when their partner is getting a better deal. In humans, this reaction is known as “inequity aversion.”

I actually don’t think the response is irrational at all, but related to the fact that in a cooperative system, one needs to watch what kind of investment one makes and what one gets in return. If your partners always ends up getting a greater share, this means that you’re being taken advantage of. So, the rational thing to do is withhold cooperation until the reward division improves.

This holds an important message for American society which is becoming less fair by the day.

The Gini-index (which measures income inequality) keeps rising and is now more in line with that of third-world countries than of other industrialized nations. If monkeys already have trouble accepting income inequality, you can imagine what it does to us. It creates great tensions within a society, and we know that tensions affect psychological and physical well-being. Some attribute the dismal health statistics of Americans (now #42 in the world’s longevity ranking) to the social frictions of an unfair society (see Richard Wilkinson, 2005: The Impact of Inequality).

interview from Freakonomics.com with primatologist Frans de Waal