The Colchester Zoo in England is home to a community of mandrills, the largest of the monkeys. One of these mandrills, a female named Milly, began covering her eyes with her hand when she was three. A dozen years later Milly and her zoo mates continue to perform this gesture, which appears to mean “do not disturb.” The signal is the first gesture with cultural roots reported in monkeys.

Culture accounts for behavioral differences that are geo­graphic, rather than genetic or environmental. Gestures—nonvocal, communicative actions—are often cultural in humans and sometimes in apes, notes Mark E. Laidre, an evolutionary biologist now at the University of California, Berkeley. Laidre observed the Colchester mandrills for a total of 100 hours during the summers of 2007 and 2008. As re­ported in PLoS ONE in February, he found that mandrills performing the eye-covering gesture were approached and touched by other mandrills significantly less than when they were not using the gesture. “Animals who didn’t want to be bothered used it,” Laidre says.

Laidre and other researchers studying mandrills have not seen the eye-covering gesture in other populations, indicating it is a local phenomenon. Laidre also ruled out alternative explanations for the gesture’s appearance. Milly does not have any medical issues with her eyes that might have prompted her to cover them, nor is the gesture more com­-mon on sunny days. It is also unlikely that human activity influenced the mandrills because monkeys—in contrast to apes, dolphins and dogs—do not mimic human behavior, Laidre says. All this evidence suggests that the eye-covering gesture arose naturally and that it conveys information within the mandrill community.

Having brought attention to the Colchester mandrills’ gestural abilities, Laidre expects researchers will now find other monkeys using cultural gestures. If gesturing is per­formed more broadly among primates than previously thought, Laidre says, “the capacity to communicate with the hands in a meaningful way may have existed a long time before humans came on the scene.”