Haim, I heard about this today on the radio. It sure explains a lot of things...
The researchers spent two years teaching their monkeys to exchange tokens for food. Normally, the monkeys were happy enough to swap pieces of rock for slices of cucumber. However, when two monkeys were placed in separate but adjoining chambers, so that each could observe what the other was getting in return for its rock, their behaviour became markedly different.
In the world of capuchins, grapes are luxury goods (and much preferable to cucumbers). So when one monkey was handed a grape in exchange for her token, the second was reluctant to hand hers over for a mere piece of cucumber. And if one received a grape without having to provide her token in exchange at all, the other either tossed her own token at the researcher or out of the chamber, or refused to accept the slice of cucumber. Indeed, the mere presence of a grape in the other chamber (in the absence of an actual monkey able to eat it) was enough to induce sullen behaviour in a female capuchin.
Dr Brosnan and Dr de Waal report that such behaviour is unusual in their trained monkeys. During two years of bartering prior to these experiments, failure to exchange tokens for food occurred in fewer than 5% of trials. And what made the behaviour even more extraordinary was that these monkeys forfeited food that they could see¡ªand which they would have readily accepted in almost any other set of circumstances.
The researchers suggest that capuchin monkeys, like humans, are guided by social emotions. In the wild, they are a co-operative, group-living species. Such co-operation is likely to be stable only when each animal feels it is not being cheated.
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