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Quantity counts for baboons

Peanut experiment shows that monkeys roughly compare numbers of nuts using logic similar to humans

9:00am, May 17, 2015
monkey portrait

COUNTER INTELLIGENCE  An olive baboon named Pearl, shown here, and one of her troopmates could keep tabs on approximate quantities of peanuts placed one at a time in containers. Researchers say this counting-like logic, which humans use to count exact amounts, comes naturally to monkeys.

Monkeys can’t count. But they can mentally keep track of and compare approximate quantities that increase one item at a time. That shows that monkeys use a kind of reasoning that also underlies human counting, researchers report May 7 in Psychological Science.

In a series of trials, two baboons watched from behind a barrier as one to eight peanuts were placed one by one into a container. Researchers then began singly dropping varying numbers of peanuts into a second container. The animals continually updated and compared that second inexact amount to the first quantity, enabling them to choose the larger cache of nuts as a snack an average of 68 percent of the time, psychologist Jessica Cantlon of the University of Rochester in New York and colleagues report.

If the number of peanuts in the second container reached about the same amount as in the first container, both

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