Scientists have come up with a surprising new equation. Monkeys plus arithmetic equals college students.

NPR's Jon Hamilton has more on the math skills of various primates.

JON HAMILTON: Humans are really good at precise calculations. Monkeys aren't. But Jessica Cantlon, a brain researcher at Duke University, says monkeys are good at something called fuzzy math.

Dr. JESSICA CANTLON (Duke University): It's much more like estimating than the verbal mathematics that you learn in school.

HAMILTON: Cantlon wanted to know how monkeys' fuzzy math stacks up against humans. First, she tested two female rhesus monkeys named Boxer and Feinstein, after the senators. The monkeys watched the video screen.

Dr. CANTLON: They would see one set of dots and there would be a little delay. They would see a second set of dots and then they'd be given two choices and their task was to press the choice that represented the sum of those two sets of dots.

HAMILTON: When Boxer and Feinstein were right, they got Kool-Aid. And they were right about 75 percent of the time. That's pretty good.

Dr. CANTLON: Then what we did was we gave college students the same exact task.

HAMILTON: Duke students, to be precise. They got cash instead of Kool-Aid, and they were right about 90 percent of the time - only a bit better than the monkeys. Cantlon says the students would have been much better if they had been given enough time to count the dots out loud or in their heads and then add up the numbers.

Dr. CANTLON: When you take away language from a human during a math task like this, they end up looking just like a monkey. You see these remnants of these more primitive mathematical abilities that are still kicking around in humans.

HAMILTON: Monkeys don't count. Cantlon says they are probably good at this sort of estimating because they often need to assess quantities in a hurry, like whether they're outnumbered by an enemy. Cantlon says young children probably do something very similar before they learn formal arithmetic. The study appears in the journal Public Library of Science Biology.

Jon Hamilton, NPR News.

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