In fact, studies have shown that people are more likely to help their imitators, and under appropriate circumstances, even leave them more generous tips. Such imitation is thought to provide the basis by which human beings ultimately form lasting social groups.

Before the current study, however, no one had ever determined if non-human primates were also predisposed to bond with individuals who imitated them.

The researchers chose capuchin monkeys because they are a highly social species that forms strong social groups. For the study, each monkey was given a wiffle ball.

Paukner explained that the monkeys commonly displayed three behaviours: poking the ball with their fingers, putting it in their mouths, or pounding it on a surface, says an NICHD release.

In sequence, each monkey was paired with two human investigators, each of which also had a wiffle ball. One investigator would mimic the monkey's behaviour, poking, mouthing, or pounding the ball, as appropriate. The other investigator would adopt a different behaviour, for example, pounding the ball when the monkey poked it.

After the imitation sequence, the monkeys consistently spent more time near the investigator who imitated them than with the investigator who did not -- which the researchers interpreted as a sign that the monkeys felt a sense of affiliation toward their imitator.

The study appeared in the Friday edition of Science.