— Counting monkeyhttp://www.youtube.com/watch?v=qeATUaOiGwM
It takes a smart monkey to do mathematics, and although Elsa Addessi insists her 10 capuchins aren't quite doing sums, she admits they must be pretty clever to be able to pass the tests that she has put them through. One can even handle multiplication.
Addessi, a researcher at the Institute of Cognitive Sciences and Technologies in Rome, Italy, tested whether her capuchins could understand the value of monkey money, and then use it to buy the greatest amount of food.
First, all ten capuchins successfully learned that a blue token would "buy" them one piece of peanut whereas a yellow token would get them three, and if offered the choice between one of each token, they would be better off choosing a yellow one.
But things became more difficult when they were asked to choose between one yellow and up to five blue tokens.
Two monkeys went for quantity, always choosing the larger stack of tokens on offer, regardless of the token's colour. Another four preferred colour over quantity, always choosing yellow tokens over blue, however many blue tokens were on offer.
Addessi thinks this may be due to the design of the experiment: the monkeys were given three peanuts all in one go in exchange for a yellow token, whereas they had to hand over five blue tokens one by one before they received five peanuts. "I think waiting for their reward made them upset, frustrated," she says.
However, "four capuchins were able to maximise their payoff," says Addessi. These monkeys could work out that four blue tokens bought more food than a single yellow token, whereas two blue tokens were of lesser value.
Addessi and her colleagues then tested the four "smart" capuchins and two others further. This time they were allowed to choose between two yellow tokens, worth six peanut pieces, and four or five blue tokens, worth four or five peanut pieces respectively.
One of the monkeys didn't understand the test at all. Three stuck to yellow tokens regardless, leaving just two monkeys that were able to maximise their payoff.
Addessi says the monkeys are not actually doing maths, but roughly estimating which lot of tokens is worth more. If they were doing maths, they would find it just as easy to discriminate, say, between six and five pieces of nut as between six and four pieces.
But the monkeys were better at discriminating between numbers further apart, for instance when they could choose between six and four pieces, represented by two yellow tokens and four blue, rather than between six and five, represented by two yellow tokens and five blue.
The ability to discriminate between "less" and "more" is important for most animals. Figuring out which tree has more berries on it, for example, or determining whether there are more friends than enemies in an area, are matters of life and death (see Number of the beasts).
What is unique about Addessi's study is that the monkeys didn't just choose between quantities but also showed they were able to represent them using symbols much as humans use coins to represent value.
"I find this quite surprising coming from an animal that diverged from us 35 million years ago," Addessi told New Scientist
Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2007.0774)
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