Fair and square among monkeys
( 2003-09-28 16:56) (Agencies)
Everybody loves a fat pay rise. Yet pleasure at your own can vanish if you
learn that a colleague has been given a bigger one. Indeed, if he has a
reputation for slacking, you might even be outraged. Such behaviour is regarded
as “all too human”, with the underlying assumption that other animals would not
be capable of this finely developed sense of grievance. But a study by Sarah
Brosnan and Frans de Waal of Emory University in Atlanta, Georgia, which has
just been published in Nature, suggests that it is all too monkey, as well.
The researchers studied the behaviour of female brown capuchin monkeys, which
have all the necessary ingredients to capture the public imagination. They look
cute. They are good-natured, co-operative creatures, and they share their food
readily. Above all, like their finicky female human counterparts, they tend to
pay much closer attention to the value of “goods and services” than males
(although why this is so remains a mystery).
Such characteristics make them perfect candidates for Dr Brosnan's and Dr de
Waal's study. 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—and 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. Feelings of righteous indignation, it seems, are not the preserve
of people alone. Refusing a lesser reward completely makes these feelings
abundantly clear to other members of the group. However, whether such a sense of
fairness evolved independently in capuchins and humans, or whether it stems from
the common ancestor that the species had 35m years ago, is, as yet, an
unanswered question.
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