Gestural Imitation by a Gorilla: Evidence and Nature of the Capacity.

We report the results of an opportunistic experiment on the capacity for gestural imitation in a zoo-housed, female western lowland gorilla (Gorilla g. gorilla). Taking advantage of her temporary disposition to copy humans, we presented 7 non-species-typical gestures, without training or rewards. The gorilla's behaviour was filmed and subsequently rated for gestural imitation by 20 naïve coders, controlling for general demeanour by comparing pre- and post-demonstration segments. For several gestures, behaviour that closely matched the demonstration was seen only or more often after demonstration: gestural imitation was therefore reliably detected. Nevertheless, as in previous studies of great ape gestural imitation, none of the gorilla copies was a perfect match. We suggest that gestural imitation in great apes is based on facilitation of rare behaviours in their extensive and often idiosyncratic gestural repertoire (e.g. by mirror neurons), rather than on acquiring novel behaviours by imitation. [ABSTRACT FROM AUTHOR]