Pure Pedantry

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But do the capuchins actually understand money? Or is Chen simply exploiting their endless appetites to make them perform neat tricks?

Several facts suggest the former. During a recent capuchin experiment that used cucumbers as treats, a research assistant happened to slice the cucumber into discs instead of cubes, as was typical. One capuchin picked up a slice, started to eat it and then ran over to a researcher to see if he could ''buy'' something sweeter with it. To the capuchin, a round slice of cucumber bore enough resemblance to Chen's silver tokens to seem like another piece of currency.

Then there is the stealing. Santos has observed that the monkeys never deliberately save any money, but they do sometimes purloin a token or two during an experiment. All seven monkeys live in a communal main chamber of about 750 cubic feet. For experiments, one capuchin at a time is let into a smaller testing chamber next door. Once, a capuchin in the testing chamber picked up an entire tray of tokens, flung them into the main chamber and then scurried in after them -- a combination jailbreak and bank heist -- which led to a chaotic scene in which the human researchers had to rush into the main chamber and offer food bribes for the tokens, a reinforcement that in effect encouraged more stealing.

Something else happened during that chaotic scene, something that convinced Chen of the monkeys' true grasp of money. Perhaps the most distinguishing characteristic of money, after all, is its fungibility, the fact that it can be used to buy not just food but anything. During the chaos in the monkey cage, Chen saw something out of the corner of his eye that he would later try to play down but in his heart of hearts he knew to be true. What he witnessed was probably the first observed exchange of money for sex in the history of monkeykind. (Further proof that the monkeys truly understood money: the monkey who was paid for sex immediately traded the token in for a grape.) (Emphasis mine.)

Read the whole thing. It's hysterical.

Two things about this:

1) I am super jealous of these guys because this kind of research is too cool for words.

2) The fact that monkeys can perform these operations should not be surprising.

First, S-S conditioning -- where the response associated with stimulus 1 becomes associated with stimulus 2 because of the association of stimulus 1 and 2 -- is not new, and basically that is all money is. (It's been a while since I took a class in classical conditioning, but I think they would call stimulus 2 a secondary reinforcer.) Money is only valuable because of the positive associations attached to things that money can buy. It is essentially a secondary reinforcer. If S-S conditioning is present in even lower animals, than most of them should be able to associate value with money.

Second, I work with rats at the moment, and sometimes they amaze me with the subtle calculations about value even they can make. Let me give you an example. I was running this experiment where I would switch the rats between two different tasks in a maze repeatedly. Basically the rat had to keep switching strategies to achieve a maximum reward. (Sort of like a Wisconsin Card Sorting Task for rats.)

Anyway, I was running this experiment for days and days and days until one day the rat just stopped switching between strategies. Instead he adopted this sort of middle of the road strategy where he would get a moderate reward no matter which task I expected him to do at the time. Annoying as all hell, but tricky that he could even make that calculation. He essentially calculated the highest expected value over a long period that could be expected if he did not change what he was doing (I think he was getting annoyed with switching).

What I am saying is that the mental apparatus in animals for calculating rewards is easily applied to economic calculation. Thus, it should not be surprising that given sufficient training animals can adopt economic behaviors similar to humans. The machinery in humans is more complex and more precise, but it is essentially the same.