Monkey see, monkey do

Paul Wren, from Wanna be an Anthropologist, emailed me this article, “Neonatal Imitation in Rhesus Macaques” the other night. I’m not surprised that John Hawks has already commented on it, but even super-blog Boing Boing has posted on it! The research shows that through several behavioral tests, like infant humans, newborn Rhesus Macaques (Macaca mulatta) learn by imitation. The research influences me to conclude that that this kind of imitation has a purpose, as a form of social learning beyond great apes. Now mimmicry is not limited to apes and humans as previously thought. Rather, it evolved more than 25 million years before the monkey ancestors diverged from the human lineage.

Human newborns have a known capacity to mimic certain specific adult facial expressions, including mouth opening and tongue protrusion. The so-called imitation period lasts up to three months in human infants and two months in chimps. Since newborns cannot see their own faces, they rely on watching adults to learn facial expressions, and mimicry is thought to be crucial to the development of a mother-infant relationship.

The lead author, Pier Ferrari at the University of Parma, Italy, tested 21 newborn macaques by holding each in front of a researcher who made various facial expressions. The abstract reads,

“The emergence of social behaviors early in life is likely crucial for the development of mother–infant relationships. Some of these behaviors, such as the capacity of neonates to imitate adult facial movements, were previously thought to be limited to humans and perhaps the ape lineage. Here we report the behavioral responses of infant rhesus macaques (Macaca mulatta) to the following human facial and hand gestures: lip smacking, tongue protrusion, mouth opening, hand opening, and opening and closing of eyes (control condition). In the third day of life, infant macaques imitate lip smacking and tongue protrusion. On the first day of life, the model’s mouth openings elicited a similar matched behavior (lip smacking) in the infants. These imitative responses are present at an early stage of development, but they are apparently confined to a narrow temporal window. Because lip smacking is a core gesture in face-to-face interactions in macaques, neonatal imitation may serve to tune infants’ affiliative responses to the social world. Our findings provide a quantitative description of neonatal imitation in a nonhuman primate species and suggest that these imitative capacities, contrary to what was previously thought, are not unique to the ape and human lineage. We suggest that their evolutionary origins may be traced to affiliative gestures with communicative functions.”

This picture documents a little macaque mimmicking what I call “sticking out your tongue” test.

At one day old, none of the infants showed any imitation. By day three, however, infants started to copy the researchers’ expressions, including tongue protrusions, mouth opening and lip smacking – all typical macaque expressions. By two weeks, all imitative behaviour had ceased, showing the imitation period in the monkeys is far shorter than for great apes. I wonder if that has to do with some sort of gene expression, or activation of mirror neurons? However, Ferrari notes that macaques may copy other macaques for longer.

Here’s two videos of the macaques immitating. This first one is of a macaque copying tongue poking:


The second of a macaque copying a mouth opening action:


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