Published online 3 December 2007 | Nature | doi:10.1038/news.2007.317

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Young chimpanzee can recall number placement better than people can.

Remember this: even if the numbers flash up for only an instant, this chimp can remember where they were. Courtesy of the researchers

A particularly cunning seven-year-old chimp named Ayumu has bested university students at a game of memory. He and two other young chimps recalled the placement of numbers flashed onto a computer screen faster and more accurately than humans.

“It’s a very simple fact: chimpanzees are better than us — at this task,” says Tetsuro Matsuzawa, a primatologist at Kyoto University in Japan who led the study.

The work doesn't mean that chimps are 'smarter' than humans, but rather they seem to be better at memorizing a snapshot view of their surroundings — whether that be numbers on a screen or ripe figs dangling from a tree. Humans may have lost this capacity in exchange for gaining the brainpower to understand language and complex symbols, says Matsuzawa.

“I work with some pretty smart chimps, but they're not going to do your calculus homework” Michael Beran



Quick as a flash

Two decades have passed since Matsuzawa’s team first taught a female chimp, Ai, to recognize and order Arabic numerals1. Later, he and Nobuyuki Kawai trained her to memorize the location of numbers as they flashed onto a computer screen. The numbers would be quickly covered with white squares, and Ai could then touch those squares in order of the numbers concealed beneath them2. After much training, chimps can be remarkably good at this task (see video, in real time).

Matsuzawa and Sana Inoue went on to train three pairs of mother chimps and their infants to recognize and remember numerals, as Ai had done. The kids outmatched their mothers most of the time, and Ai's son Ayumu was head of the class, they report today in Current Biology.3

When Ayumu went head-to-head against university students in the game, he made them look like dunces. This was most noticeable when the numbers appeared on the screen for just two tenths of a second - too brief for humans to get a good grip on them. Here, Ayumu correctly ordered the numbers in 80% of trials, while the students scored an average of just 40% (see video).

It's unclear how long Ayumu’s memory of the number placement lasts after seeing them flash on the screen. When a sound across the room caught his attention, he paused in the middle of a game for ten seconds before finishing the puzzle (see video). Matsuzawa plans to test how much longer chimps can remember the numbers.

Mental trade-off

Could the chimps' superiority come from simply having had more practice? Ayumu had been playing the game throughout his seven years of life, and got a treat after each run. But the researchers think this practice wasn't Ayumu's only advantage. “We trained university students for six months and their accuracy did not reach this level,” says Matsuzawa.

He suggests that humans made a mental trade-off as they diverged from their common ancestor with chimps some 5 to 6 million years ago. In gaining brawnier brains that can process language and other complex symbols, we may have dulled our ability to take quick mental snapshots.

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To find that chimps are better than humans at some specific tasks is not surprising, says Michael Beran, a psychologist at Georgia State University in Atlanta. Chimps and humans are in some ways very similar, he points out. The key to uncovering a chimpanzee's inner Einstein is to put them to the right kind of test, he says.

There are limits, however. “I work with some pretty smart chimps, but they're not going to do your calculus homework,” says Beran.