Humans do it. Chimps do it. Why shouldn't monkeys do it, too? Mimicry exists throughout the animal kingdom, but imitation with a purpose--matching one's behavior to others' as a form of social learning--has been seen only in great apes. It's generally believed that monkeys do not imitate in this way. However, the discovery that rhesus monkeys have "mirror neurons"--neurons that fire both when monkeys watch another animal perform an action and when they perform the same action--suggests they possess the common neural framework for perception and action that is associated with imitation.
In a new study in the open-access journal PLoS Biology, Pier Ferrari, Stephen Suomi, and colleagues explored the possibility that imitation evolved earlier in the primate tree by studying neonatal imitation in rhesus monkeys, which split from the human lineage about 25 million years ago. They found that rhesus infants can indeed imitate a subset of human facial gestures--gestures the monkeys use to communicate. The first investigation of neonatal imitation outside the great ape lineage, their study suggests that the trait is not unique to great apes after all.
Ferrari et al. tested 21 baby rhesus monkeys' response to various experimental conditions at different ages (one, three, seven, and 14 days old). Infants were held in front of a researcher who began with a passive expression (the baseline condition) and then made one of several gestures, including tongue protrusion, mouth opening, lip smacking, and hand opening.
Day-old infants rarely displayed mouth opening behavior, but smacked their lips frequently. When experimenters performed the mouth opening gesture, infants responded with increased lip smacking but did not increase any other behavior. None of the other stimuli produced significant responses. But by day 3, matched behaviors emerged: infants stuck out their tongues far more often in response to researchers' tongue protrusions compared with
Contact: Natalie Bouaravong
Public Library of Science