Monkey Prostitution

By - August 1, 2011

It isn't a topic that I ever anticipated writing about, but monkey prostitution is not just a joke. It has actually been observed, as I discovered when I was recently was reading Super Freakonomics, by Steven D. Levitt and Stephen J. Dubner. It all started with some economics research using... monkeys, of course.

Economist Keith Chen wondered what would happen if he taught monkeys to use money, so he designed an experiment to do just that. Using Capuchin monkeys, he kept them in a large enclosure with a small chamber they could enter at one end. In that chamber one monkey at a time could interact with the handlers. For money he use small shiny discs.

When the monkeys were given the coins they usually threw them aside after inspecting them. If they couldn't eat it or have sex with it, they weren't interested in much. But when they gave it back to the handlers, they were given something good to eat. Thus, with time and difficulty they learned that the coins had value: they could buy tasty treats with them.

Once they knew that the coins had value, Chen and colleagues experimented with prices. A monkey might be given a dozen coins, for example, and normally could trade one for three sweet gelatin cubes or an three apple slices (and they each had their preferences). But when they started getting just one or two gelatin cubes for a coin, the monkeys did as humans do: they bought less of the snacks. This is considered rational behavior by economists.

Then irrational behavior was tested with gambling games. Two scenarios were created. First, a monkey was shown a grape and a coin was tossed. If it landed showing heads, another grape was added. Another researcher presented them with a different game in which two grapes were shown to the monkey, but if the coin flip was lost one was removed and the monkey just got the remaining one. (Don't worry, we'll get the monkey prostitution soon.)

The games were the same statistically speaking, but the monkeys eventually strongly preferred the first game. Getting a bonus versus suffering a loss was more palatable, even if the net outcome was the same. This is referred to as "loss aversion" in behavioral economics, and has been noted in humans in many experiments. We are as irrational as the monkeys, in other words.

The most interesting discovery was made by accident. One day a monkey threw all of his dozen coins into the large enclosure instead of spending them. Chaos erupted as the other monkeys grabbed them. As the researchers bribed the monkeys with treats to get the coins back, they saw one of the male monkeys approaching a female. He gave a coin to her and soon they were having sex. This is believed to be the first recorded instance of monkey prostitution. As soon as they were done (about eight seconds for capuchins), the female brought the coin to a researcher to buy some grapes.

And some people think economics is a boring subject.

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The Adorkist

Steve Gillman's Books

Windows for President




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