They are better than us at climbing trees, they have a more impressive bite and they would make a formidable opponent in a fight. But the brain is one area where humans have come to regard themselves as superior to the great apes.
No longer. Japanese researchers have found three young chimps that can beat people at a numerical memory task. The performance of the best chimp did not drop off even when it was given a fraction of a second to remember where the numbers were - suggesting it has an ability akin to photographic memory.
"There are still many people, including many biologists, who believe that humans are superior to chimpanzees in all cognitive functions," said Tetsuro Matsuzawa, of Kyoto University, who led the study. "No one can imagine that chimpanzees - young chimpanzees at the age of five - have a better performance in a memory task than humans.
"Here we show for the first time that young chimpanzees have an extraordinary working memory capability for numerical recollection - better than that of human adults tested in the same apparatus, following the same procedure."
The team began by testing three pairs of mothers and young on a game that involved touching numbers from 1 to 9 in the correct order. The numbers were randomly scattered across a computer screen. To make things harder the team then changed the task so that some digits were missing. The chimps had to realise that if there was no 3 for example, then 4 was the next in the sequence after 2.
To make things harder still, the researchers changed the game so that once the chimp had hit the first number in the sequence, the rest would disappear and be replaced by blank squares. To complete the task correctly, the chimps had to remember the locations of the numbers behind the squares and hit them in the right order. Again the chimps were up to the task.
Finally, the researchers made the experiment even tougher by steadily reducing the amount of time the chimps had to memorise the sequence of numbers.
When the team compared the chimps' performance with student volunteers they found they left the humans standing. The difference was most noticeable when the chimps and human volunteers had least time to memorise the numbers. Top of the class among the chimps was Ayumu, who got the number order correct 80% of the time when the digits appeared on screen for just two tenths of a second. That compared with a 40% success rate for the humans. He also did no worse at this speed than when he had more time to memorise the positions.
The team report their results in the journal Current Biology.
Ayumu has had the advantage of playing this game for most of his seven years of life - and receiving a treat each time he did the task. But the researchers do not think training is the only reason he is so good. Three of Matsuzawa's students received six months of training and never approached his abilities.
Ayumu and the other young chimps' abilities are reminiscent of "eidetic imagery", an ability to retain a detailed and accurate image of a complex scene or pattern. This memory ability is present in some children, but declines with age. The experiment compared the chimps with human adults, but not children and the performance of Ayumu's mother, Ai, was not as good as the humans. Ai, now 31, was the first chimp to be taught the meaning of Arabic numerals in counting.