Imitation may be the sincerest form of flattery, but it's also a good way to make friends. People warm up to us when we unconsciously mimic them. Now, it turns out that capuchin monkeys also favor people who "flatter" them with imitation--the first time the behavior has been seen in nonhumans. "This work is really important because it shows that human social interaction ... [is] rooted in very implicit evolutionarily ancient processes," says Laurie Santos, a psychologist at Yale University.
Researchers speculate that, because imitation seems to foster friendship in humans, it helps maintain the peaceful relationships that have been essential to the success of our species. Humans aren't the only social animal, however, and psychologist Annika Paukner wondered whether other primates share the imitation-friendship connection.
Paukner and colleagues at the National Institute of Child Health and Human Development in Poolesville, Maryland, focused on capuchin monkeys, which live in highly social groups of 30 to 40 animals. They placed a monkey in the middle of three interconnected cages, while a person stood in front of each of the end cages. The monkey and the two people each had a small ball: One person poked, mouthed, and pounded the ball randomly; the other mimicked whatever the monkey did with the ball.
Like humans, the monkeys seemed drawn to the imitation. After watching the two people for just a few minutes, the capuchins spent twice as much time looking at the imitator and almost 38% of the test period sitting directly in front of the imitator, compared with 27% in front of the other person. When the people switched places, the monkey tended to shift cages as well, showing a greater affiliation for the imitator.
Imitated monkeys also interacted more with their mimickers. Later in the experiments, the volunteers who had stood near the cages gave the capuchins pieces of marshmallow in exchange for small plastic chips, which the monkeys had been trained to turn over to get a food reward. On average, out of 10 chances, the monkey offered tokens to the imitator six times, versus about five times for the nonimitators. These interactions indicate that the monkeys feel more comfortable with the imitator, says Paukner, whose team reports  its findings online today in Science.
It is not clear how these results translate into natural behavior of capuchins, Paukner says. But in the wild, the monkeys will synchronize certain behaviors--traveling en masse to a food source, eating at the same time, and so on--which may help keep the group harmonious as well as provide safety in numbers. "I think that imitating others unintentionally and unconsciously is a mechanism that is exploited by us humans and capuchin monkeys to regulate social relationships," says Paukner. "Of course, humans are vastly more complex and might use this mechanism in many more ways."