London: Researchers have taught three rhesus monkeys to do simple addition using the numbers 1 through 25, a feat which provides the best evidence yet that the primates can perform basic arithmetic.
Researchers led by neurobiologist Margaret Livingstone at Harvard Medical School in Boston set out to test how well monkeys can represent and manipulate numbers in their brains.
Scientists had their subjects perform thousands of calculations with a system of written symbols, including the numerals 1 through 9 and letters of the alphabet.
The monkeys were taught to recognise the symbols for each of the numbers when they correctly linked a symbol to its corresponding number, they were rewarded with the same number of drops of water or juice.
Then they were faced with a series of choices on a computer screen: A single symbol on one side versus a combination of two symbols on the other.
The monkeys were rewarded as before, which should have motivated them to pick the larger value, `New Scientist` reported.
Researchers found that the monkeys chose the larger number between 70 and 90 per cent of the time. They were even able to repeat the success after learning a second, totally new set of symbols.
Past studies have hinted at primates` quantitative abilities but have been limited to numbers less than 10, or were unable to prove that the animals were performing addition.
This latest work provides clear evidence that monkeys can indeed perform basic arithmetic, researchers said.
"The data in my opinion are quite convincing, because it is really unlikely that the monkeys remembered each combination of symbols," said Elsa Addessi at the Institute of Cognitive Sciences and Technologies in Rome.
The study was published in the journal Proceedings of the National Academy of Sciences.
