Peanut experiment shows that monkeys roughly compare numbers of nuts using logic similar to humans
Adam Fenster/University of Rochester Photography
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.