Monkey Business

Levitt and Dubner end the second book of their Freakonomics series, Super Freakonomics, with a little story about two researchers and seven Capuchin monkeys. Can monkeys learn to use money? Keith Chen and Venkat Lashminarayanan selected the Capuchin monkey because as Keith Chen observed, “The Capuchin has a small brain, and it’s pretty much focused on food and sex. You should really think of a Capuchin as a bottomless stomach of want. You can feed them marshmallows all day, they’ll throw up, and then come back for more.”

It sounds to me like they would make perfect additions to our American consumer society.

All the monkeys, four females and three males, lived together in one large cage. At the end of this cage was a smaller cage set up so the researchers could interact with one monkey at a time. Chen selected small silver discs with a hole drilled through the center as currency. Teaching the monkeys that these coins could be used in exchange for food treats was a long and tedious process, but finally the Capuchins got the idea. At the beginning of each experiment the monkey was given twelve coins that could then be exchanged for different food treats controlled by different researchers.

Once Chen and his associates determined the food preferences of the different monkeys they would raise and lower the price of a favorite food. The law of supply and demand works with the monkey mind as well as with us highly rational examples of homo-economicus. As the price for a particular treat increased the demand decreased.

Chen then experimented with monkey gambling. They were given a choice between two games. In the first game the researcher offered the monkey one treat. Then, if a coin flip favored the monkey, he was given two treats. In the second game the researcher offered the monkey two treats. If the monkey lost the coin flip he would only receive one treat. Although the two games are statistically identical in outcome, the monkey, like humans, proved to be risk adverse. They greatly favored the game with the potential of gaining a second, unearned treat.

Then one day Felix, the alpha male monkey, decided to take control of the experiment. When offered a tray containing the usual twelve coins. He grabbed the tray and threw it and the coins into the communal cage. He then escaped from the smaller experimental area to the larger cage where the monkeys were fighting over the money. When the researchers tried to get the money back, the Capuchins were having none of it. They continued to hold onto the stolen coins.

At first Chen thought that he had just witnessed an example of monkey altruism. However he noted that soon after the bank heist, one of the male monkeys gave his coin to one of the female monkeys. After a few seconds of grooming the pair engaged in sex. After finishing the first recorded act of monkey prostitution in the history of science, the female Capuchin brought her coin over to a researcher to buy a food treat.

At this point the Yale New Haven Hospital, owner of the Capuchin tribe, decided that enough was enough. They shut down the experiment, fearing that the love of money would hopelessly corrupt their monkeys. Too bad; one can only imagine what could have happened next. Perhaps we would have seen the rise of monkey governments, monkey taxes, monkey slavery, and monkey wars. Perhaps as the monkey economy became more sophisticated they would begin to issue monkey currency from monkey banks. Perhaps, we would have even seen monkey stock exchanges where shares in monkey corporations were bought and sold by monkey day traders.

It sounds like the basis for a good sequel for the Planet of the Apes movie franchise.