Rapid facial mimicry in geladas.

Rapid facial mimicry (RFM) is an automatic response, in which individuals mimic others' expressions. RFM, only demonstrated in humans and apes, is grounded in the automatic perception-action coupling of sensorimotor information occurring in the mirror neuron system. In humans, RFM seems to reflect the capacity of individuals to empathize with others. Here, we demonstrated that, during play, RFM is also present in a cercopithecoid species (Theropithecus gelada). Mother-infant play sessions were not only characterized by the highest levels of RFM, but also by the fastest responses. Our findings suggest that RFM in humans have homologous not only in apes, but also in cercopitecoids. Moreover, data point to similarities in the modality in which mother-infant synchronous behaviours are expressed among primates, suggesting a common evolutionary root in the basic elements of mother-infant affective exchanges.