Clever chimps can outsmart monkeys.© PunchstockA survey of primate IQ has cemented apes' reputation as our most intelligent cousins. An analysis of a slew of studies designed to spot smartness has concluded that orang-utans and chimps are the chief eggheads, with monkeys and lemurs trailing in their intellectual wake.
The study has produced a league table of overall cognitive ability among primates. Previous research had attempted to compare different primates' abilities at specific tasks, but no one had ever combined this data into an overall measure of intelligence.
The researchers compiled results from dozens of problem-solving puzzles given to different types of primates by researchers. These included tests of ability to navigate mazes, to untangle a jumble of differently coloured threads to find food, and to spot the odd-one-out in a series of images. They ranked each species and calculated the overall average intelligence of each.
Orang-utans emerged at the top of the heap, just edging out chimpanzees. Both species share a prodigious ability to use tools and impart traditional wisdom to their young. "Orang-utans are more patient and deliberative," says Robert Deaner, who led the research while at Duke University Medical Center in Durham, North Carolina. "And they're the master escape artists from zoos."
“Orang utans are more patient and deliberative. And they're the master escape artists from zoos.”
Robert Deaner
Grand Valley State University, Michigan
The results reinforce the pecking order of apes at the top, followed by Old World monkeys such as macaques, and New World monkeys such as marmosets, the researchers report in the journal Evolutionary Psychology1. "We can have quite a bit of confidence that great apes do a whole lot better than other animals," says Deaner, now at Grand Valley State University in Allendale, Michigan.
Overall, intelligence seems to be correlated with absolute brain size, rather than brain size relative to body size, or the relative sizes of different brain regions, Deaner says. Previous theories had suggested that a critical factor may be the size of the brain's neocortex, a region that seems to vary in size depending on the size of the social groups in which an animal lives, and that might therefore reflect cognitive skills.
Top of the tree
One surprise is the third place achieved by spider monkeys (Ateles), which marginally beat gorillas. "It's not a significant difference," Deaner says, nor does he know why this might be.
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It's perhaps to be expected that the smartest species are those that are closest to our own branch of the evolutionary tree. The result underlines the fact that humans sprang from a group that already possessed formidable cognitive powers, which were then honed still further in our own evolutionary development.
What seems certain is that humans are the masters of intelligence. Although several of the tests given to the primates — such as the ability to unlearn and relearn arbitrary rules — are similar to those used to identify developmentally impaired humans, a normal adult would ace every test.
It seems unlikely, however, that anyone will ever pit man against even the smartest of primates. "You generally don't set humans tests that don't involve language," Deaner says. "If you sat them in front of a computer and gave them a grape every time they did something right they'd probably walk out of the room."
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Grand Valley State University, Michigan
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