Spend Like a Monkey

At least one monkey species learns quickly the joys of shopping

• Hannah Schardt
• Oct 01, 2005

WHEN IT COMES to shopping, capuchin monkeys act all too human. A new study from Yale University found that capuchins demonstrate the exact same rational and irrational behavior as humans when they are given the power to buy.

The Yale researchers--a behavioral economist and two psychologists--set out to see whether capuchin monkeys would follow classical economic theories. But before they could conduct their experiments, the researchers had to teach the monkeys the value of a dollar--or, in this case, the value of a shiny metal token. Research assistants spent hours with the monkeys, training them to recognize the tokens as having a value. Once the capuchins realized that the tokens could be exchanged for treats such as grapes or apple chunks, they resorted to some very human behaviors, including stealing the tokens from other monkeys.

"The important thing is that the monkeys understood that exchanging the tokens was not just like pulling a lever: You pull the lever and food falls into the cage," says Keith Chen, the economist involved in the study. "Instead, they understood that it's not automatic--that the token can be worth any number of things."

In the first experiment, the monkeys were given a budget of 10 tokens and allowed to exchange those tokens for a variety of treats. Research assistants played shopkeeper, each offering a different food. As the monkeys "shopped," researchers would change the value of the tokens. A token might be worth one grape one day but two grapes the next. Chen says that the monkeys' reaction to price fluctuation was perfectly rational--and quite human. When prices went up for one food, the monkeys bought less of it. When prices went down, they bought more.

But also like humans, the capuchins were not always rational. In the second experiment, researchers presented the monkeys with a sort of economic gamble. They were given a number of discs and offered a choice: exchange a disc for one visible piece of food, with a 50 percent chance of getting a bonus piece of food, or exchange a disc for two visible pieces of food, with a 50 percent chance of having one taken away. With either choice, the monkeys had an equal chance of receiving either one or two pieces of food. But the animals overwhelmingly went for the single piece of visible food, demonstrating their reluctance to "lose out"--even though they ended up with the same chance of two treats no matter what choice they made. Chen says that the monkeys' preference demonstrates the economic principle of "loss aversion," a preference for security over risk that humans share.

"Loss aversion is a classic economic phenomenon," says Chen. Humans demonstrate loss aversion when they invest in low-return retirement plans or hold onto a losing stock for too long, reluctant to sell at a loss. Chen says his team's research could give an idea of just how primitive and deeply ingrained loss aversion is to human--or primate--behavior.