Monkeys Count

Monkeys can match the number of faces they see to the number of voices they hear.

Monkey see, monkey hear, monkey count.

Rhesus monkeys can match the number of faces they see to the number of voices they hear, a new study shows. This finding suggests that monkeys can keep track of small numbers, and they don’t need language to do it.

Elizabeth Brannon of Duke University was one of the leaders of a study showing that monkeys can match the number of voices they hear to the number of faces they expect to see.

Jim Wallace, Duke University

For the study, researchers at Duke University in Durham, N.C., and their colleagues worked with 20 male monkeys that live at a research institute. Each monkey sat in front of two video monitors. On one monitor, they could watch the faces of two monkeys making noises for a minute. The other monitor showed the faces of three monkeys, also making noises for a minute.

As the animals watched the screens, they heard recordings of either two or three monkeys making loud, cooing sounds. The results showed that monkeys looked longer at the screen that showed the same number of faces as the number of voices that they heard.

Such a response shows that the monkeys could tell the difference between “two” and “three” across two senses—vision and hearing, the researchers say. The animals seemed to understand that “two” and “three” are concepts that cross categories.

The research adds to growing evidence that a wide range of animals have a strong sense of numbers. Some can even add and subtract.

It’s still probably not a good idea, however, to ask a monkey for help with your math homework!—E. Sohn

Going Deeper:

Bower, Bruce. 2005. Monkeys keep track of small numbers. Science News 168(July 2):14. Available at .

You can learn more about research on counting in monkeys and see a video of monkeys in action at (Duke University).

Sohn, Emily. 2004. Fair play. Science News for Kids (Oct. 6). Available at .

______. 2004. An inspiring home for apes. Science News for Kids (July 14). Available at .

______. 2003. It’s a math world for animals. Science News for Kids (Oct. 8). Available at .

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