Observations of rapid facial mimicry (RFM) in the gelada, a species of Old World monkey, are published in the journal Scientific Reports this week. This rapid, automatic response has been observed in humans and orang-utans but not in non-ape primates, and this study suggests that another primate species is capable of such sophisticated emotional exchanges.

RFM is a rapid, involuntary response in which an individual mimics the facial expression of another individual. RFM is common in humans, where it seems to reflect a person’s capacity to empathize with others, and it has also been observed in the orang-utan. Given the importance RFM is thought to have in social interactions, Giada Mancini, Pier Francesco Ferrari and Elisabetta Palagi examined whether the phenomenon is also present in the gelada (Theropithecus gelada), focusing on facial expressions performed in playful interactions. The authors show that geladas exhibit RFM during play, and that RFM varies depending on the genetic and emotional closeness of the individuals. The highest levels of RFM and the fastest response times were seen in interactions between mothers and their infants.

The results hint that the evolutionary origins of human RFM may potentially stem from early mother-infant relationships of our primate relatives.