US:A mental arithmetic challenge between two monkeys and 14 university students almost ended in an embarrassing draw, it was revealed yesterday.
The pair of female rhesus macaques, called Feinstein and Boxer, were as quick at working out sums as the students and nearly as accurate, scientists in the US found. Both followed a strikingly similar pattern, finding certain problems more difficult than others in the same way.
The ability to perform simple mental arithmetic may be part of the shared evolutionary past of humans and other primates, predating the emergence of language by millions of years, the researchers believe.
It was already known that some animals can discriminate between larger and smaller groups of objects. The new study showed for the first time that, like humans, monkeys can add numbers together in their heads.
In the experiments conducted at Duke University in Durham, North Carolina, Feinstein and Boxer were first trained to use a computer touch-screen by being offered food rewards.
They were then shown a display containing a variable number of dots. These were removed and after a delay of 500 milliseconds replaced by a different dot array.
Finally, a third display appeared with two boxes, one containing a number of dots equal to the first two sets added together, and the other an incorrect number of dots. Touching the right box earned the monkeys a fruit juice reward.
Over hundreds of trials involving 40 different addition problems the monkeys had an average accuracy of 76 per cent. In comparison, 14 Duke University students with an average age of 23 who carried out similar tests were correct 94 per cent of the time.
However, response times for monkeys and students choosing their answers were not that different - 1,099 milliseconds compared with 940 milliseconds respectively.
Feinstein and Boxer's ability to pick the correct answer was significantly better than that expected by chance, irrespective of whether the "wrong" number of dots was larger or smaller than the "right" one. The scientists reported their findings in the online journal PLoS Biology.
The way humans dealt with mathematical concepts had been strongly influenced by language and writing, said the scientists. But basic mental arithmetic ability appeared to be an ancient skill dating back to the ancestors of both monkeys and humans.
"Much of adult humans' mathematical capacity lies in their ability to represent numerical concepts using symbolic language," said Dr Elizabeth Brannon, a member of the research team.