Photo: Monkeys Can Subtract, Study Finds



A rhesus macaque presses a touch screen to select its answer to a subtraction problem in a Duke University lab. The dots in the set of three are bigger than those in the set of eight, to ensure that the monkeys are selecting for number of dots rather than the physical size of the group.


The experiments established the monkeys as the first known nonhuman animals with "widespread success" at subtraction, scientists announced at a February 2009 conference.



Photograph courtesy Jessica Cantlon, Ph.D./Duke University


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