Chimpanzee with a head for figures revealed by researchers

A clever chimpanzee named Ai has learned to use numbers at a level comparable to a pre-school child and can readily memorise five random numbers, according to a report in today's science journal, Nature.

The 23-year-old west African chimpanzee has been at the Primate Research Institute at Kyoto University, Japan, since 1977. She can count from zero to nine and can recognise numbers.

Her usual routine is to use a touch-sensitive screen to order numbers in ascending sequence with near 100 per cent accuracy, according to her teachers, Dr Nobuyuki Kawai and Dr Tetsuro Matsuzawa.

Now she can remember numbers easily, handling up to five in any sequence, "the same as, or even more than, pre-school children", according to researchers.

Humans readily memorise strings of codes such as phone numbers and postcodes, so long as they contain no more than seven items. Above this our memory skills tend to falter, creating what is known as the "magic number seven effect".

The researchers at Kyoto wanted to see if there was an equivalent magic number for chimps, which made Ai a perfect subject, given her numerical achievements.

Instead of simply being challenged to order the numbers, a sequence of numbers was shown one by one to the chimpanzee and then covered. This meant that in order to be correct in a trial she had to memorise all the numbers and then order them in their respective positions.

She scored 90 per cent accuracy with four items and 65 per cent with five items, significantly above chance in each case.

The research team was doubly impressed when, during a test, a fight broke out among a group of chimpanzees outside the room, accompanied by loud screaming. Ai abandoned her task and listened to the fight for about 20 seconds before returning to the screen and completing the trial without error.

It might not be enough to get her a job in the bank but it did demonstrate a rudimentary form of numerical competence in non-human primates, the researchers pointed out.