Monkeys wise up and get the hang of money
When primates were taught to use currency, an age-old deal took place
Long ago Adam Smith, the founder of classical economics, observed: “Nobody ever saw a dog make a fair and deliberate exchange of one bone for another with another dog. Nobody ever saw one animal by its gestures and natural cries signify to another, this is mine, that yours; I am willing to give this for that.”
Smith was certain that humankind alone had a knack for monetary exchange. But was he right? Keith Chen, an associate professor of economics at Yale, asked himself: what would happen if I could teach a bunch of monkeys to use money?
His monkey of choice was the capuchin, which, he says, “has a small brain” and is “pretty much focused on food and sex”. Chen went to work with seven capuchins, which, in the tradition of monkey labs everywhere, were given names — in this case derived from characters in James Bond films. Felix, named after the CIA agent Felix Leiter, was Chen’s favourite.
The monkeys lived together in a large, open cage with a testing chamber at the end. For currency, Chen settled on a 1in silver disc with a hole in the middle.
The first step was to teach the monkeys that the coins had value. If you give a capuchin a coin, he will sniff it and, after determining he can’t eat it (or have sex with it), he’ll toss it aside. So Chen and his colleagues gave the monkey a coin and then showed a treat. Whenever the monkey gave the coin back to the researcher, it got the treat. It took many months, but the monkeys eventually learnt that the coins could buy the treats.
Chen now introduced price shocks to the monkeys’ economy. Let’s say Felix’s favourite food was Jell-O, and he was accustomed to getting three cubes of it for one coin. How would he respond if one coin suddenly bought just two cubes?
To Chen’s surprise, Felix and the others responded rationally. When the price of a given food rose, the monkeys bought less of it, and when the price fell, they bought more. The most basic law of economics — that the demand curve slopes downward — held for monkeys as well as humans.
Other experiments confirmed the parallels between human beings and these monkeys. And then, as if Chen needed any further evidence, the strangest thing happened in the lab.
Felix scurried into the testing chamber, gathered up all the coins that had been placed there, flung them back into the communal cage and dashed after them — a bank heist followed by a jailbreak.
There was chaos in the big cage, with 12 coins on the floor and seven monkeys going after them. When Chen and the other researchers went inside to get the coins, the monkeys wouldn’t give them up. After all, they had learnt that the coins had value. So the humans resorted to bribing the capuchins with treats. This taught the monkeys another valuable lesson: crime pays.
Out of the corner of his eye, Chen saw something remarkable. One monkey, rather than handing his coin over to the humans for a grape or a slice of apple, gave it to a female monkey. Chen had done earlier research in which monkeys were found to be altruistic. Had he just witnessed an unprompted act of monkey altruism?
Then — bam! — the two capuchins were having sex. As soon as the sex was over — it lasted about eight seconds; they’re monkeys, after all — the female brought the coin over to Chen to purchase some grapes.
What he had seen wasn’t altruism but the first instance of monkey prostitution in the recorded history of science.