Young chimps can beat adult humans in a task involving remembering numbers, reveals a new study. It is the first time chimps – and young ones, at that – have outperformed humans at a cognitive task.
And the finding may add weight to a theory about the evolution of language in humans, say the researchers.
Three adult female chimps, their three 5-year-old offspring, and university student volunteers were tested on their ability to memorise the numbers 1 to 9 appearing at random locations on a touchscreen monitor.
The chimps had previously been taught the ascending order of the numbers. Using an ability akin to photographic memory, the young chimps were able to memorise the location of the numerals with better accuracy than humans performing the same task.
During the test, the numerals appeared on the screen for 650, 430 or 210 milliseconds, and were then replaced by blank white squares.
While the adult chimps were able to remember the location of the numbers in the correct order with the same or worse ability as the humans, the three adolescent chimps outperformed the humans.
The youngsters easily remembered the locations, even at the shortest duration, which does not leave enough time for the eye to move and scan the screen. This suggests that they use a kind of eidetic or photographic memory.
In rare cases, human children have a kind of photographic memory like that shown by the young chimps, but it disappears with age, says Tetsuro Matsuzawa, at the primate research institute at Kyoto University, Japan, who led the study. (See a video library of chimp cognition.)
He suggests that early humans lost the skill as we acquired other memory-related skills such as representation and hierarchical organisation. “In the course of evolution we humans lost it, but acquired a new skill of symbolisation – in other words, language,” he says. “We had to lose some function to get a new function.”
The finding challenges human assumptions about our uniqueness, and should make us think harder about ourselves in relation to other animals, says anthropologist Jill Pruetz of Iowa State University, Ames, US.
“Observing that other species can outperform us on tasks that we assume we excel at is a bit humbling,” she says. “Rather than taking such findings as a rare example or a fluke, we should incorporate this knowledge into a mindset that acknowledges that chimpanzees – and probably other species – share aspects of what we think of as uniquely human intelligence.”
The results are “absolutely incredible” says Frans de Waal, at the Yerkes Primate Center at Emory University, Atlanta, Georgia, US. He says that chimp intelligence is chronically underestimated, and one reason is that experiments stack the deck against the chimps.
In the wild, this memory skill might be useful for memorising fruit locations at a glance, or making a quick map of all the branches and routes in a tree, he says.
Matsuzawa emphasises that the chimps in the study are by no means special – all chimps can perform like this, he says. “We underestimate chimpanzee intelligence,” he says. “We are 98.77% chimpanzee. We are their evolutionary neighbours.”