Imitation is thought to be the sincerest form of flattery—even when the mimic and model are unaware of the mimicry. Now, new evidence from a study of capuchin monkeys shows a possible evolutionary benefit to being a clueless copycat (or copy-capuchin, in this case).

"We've known for awhile that we humans imitate each other all the time, unintentionally and unconsciously," says Annika Paukner, a comparative behaviorist at the National Institute of Child Health and Human Development and lead author of the study published online today in the journal Science. "When people start using the same words or the same body language, it seems to help social interaction. People [who are imitated] say they like the other person better. It builds rapport and empathy."

Paukner and her colleagues were interested to see if the same held true for nonhuman primates. "If there is an evolutionary route to this phenomenon, it may well be shared with monkeys," Paukner says, adding that scientists have observed groups of capuchins in the wild synchronizing their behavior—feeding, defending and traveling together.

To test whether or not monkeys respond to imitation with affiliation, the researchers performed a series of experiments—first, using a Wiffle ball filled with food. The idea was to see what the monkeys did with the ball once it was handed to them, and then to mimic that behavior and observe how the primates reacted to the mimicry. Making a monkey imitate another's response to a food-filled Wiffle ball is difficult, however, so the researchers did the imitating instead and waited to see how the monkeys responded.

The capuchins did one of three things when given the plastic ball by a researcher. "They either tried to bite directly into the ball, poke into its holes, or they just banged it on the floor to see if anything fell out," Paukner says. One human mirrored the monkey's behavior, whereas another performed either of the other two ball maneuvers. Then the researchers observed who the monkeys watched: More often than not, it was their mimics.

Of course, looking can mean many things, Paukner notes. "They could be curious or some way attracted, or maybe it just looked a bit odd to him what the human did," she says. "So we tried to find if looking really meant they would show more affiliation."

One clue would be if the monkey chose to spend more time near the human imitator than the nonimitator, after the ball game. "And that’s exactly what we found," Paukner says.

The researchers also played a second, more interactive game with the capuchins. After repeating the Wiffle ball experiment, a monkey was given a token that it could exchange for food from either the mimicking or the nonmimicking researcher. "From a monkey's perspective, it shouldn't have mattered where to go; he would get the same thing," Paukner explains. "But the monkeys consistently chose the imitator."

Mimicking, it seemed, made a human more attractive in the capuchins' eyes. "And monkeys like to spend time with individuals they like," Paukner says. Her team is continuing work to confirm this behavior in monkey-to-monkey interactions. But, so far, evidence suggests that an evolutionary adaptation to subtly imitate may promote the formation of social groups—building cooperation, reducing conflict, and aiding the survival of each individual.

These results may open up a new field of research, Paukner says. "In the past, we looked at imitation as 'What did [the imitator] learn?' But the role of the model has been largely ignored," she says. "Turns out, imitation is not just good for learning something new. It's also beneficial for the whole group—or whole species."