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Intro Bio Psy
Monkeys like to know the odds

Risk aversion is a well known feature of human decision making. It refers to our tendency to choose a certain payoff over an uncertain, but potentially higher payoff. For example, most people prefer getting E500 over a 50/50 chance of getting E1000. A more abstract form of risk aversion, usually called ambiguity aversion, is our tendency to avoid situations in which we don't know the odds of a good outcome at all, in favor of risky situations in which we do know the odds. For example, we like a 50/50 chance of getting E1000 better than an unknown chance of receiving E1500. In other words, we don't like risks, but we like unknown risks even less.

In a forthcoming paper in Biology Letters, Rosati and Hare show that chimps and bonobos are ambiguity averse as well. They let monkeys choose between a piece a food that they could have for sure (but wasn't always very tasty) and two pieces of food, of which they would get one (but they didn't know which). On some trials the monkeys could see these two pieces of food and on some trials they couldn't. The “sure thing” piece of food was always visible to the monkeys. What they found was that monkeys tended to stick to the sure thing if they weren't able to see the other two pieces of food, even if the sure thing wasn't very tasty.

Another cool finding was that this ambiguity aversion lasted only very briefly and was gone by the second testing session. Presumably, the monkeys picked up on the fact that the average payoff was the same, regardless of whether some pieces of food were hidden. Smart animals.

Photo: Wikimedia Commons


Rosati, A. G., & Hare, B. (2011). Chimpanzees and bonobos distinguish between risk and ambiguity. Biology Letters, 7(1), 15 -18.