Declarative referential gesturing in a wild chimpanzee (Pan troglodytes)

Abstract

Humans are argued to be unique in their ability and motivation to share attention with others about external entities-sharing attention for sharing's sake. Indeed, in humans, using referential gestures declaratively to direct the attention of others toward external objects and events emerges in the first year of life. In contrast, wild great apes seldom use referential gestures, and when they do, it seems to be exclusively for imperative purposes. This apparent species difference has fueled the argument that the motivation and ability to share attention with others is a human-specific trait with important downstream consequences for the evolution of our complex cognition [M. Tomasello, Becoming Human (2019)]. Here, we report evidence of a wild ape showing a conspecific an item of interest. We provide video evidence of an adult female chimpanzee, Fiona, showing a leaf to her mother, Sutherland, in the context of leaf grooming in Kibale Forest, Uganda. We use a dataset of 84 similar leaf-grooming events to explore alternative explanations for the behavior, including food sharing and initiating dyadic grooming or playing. Our observations suggest that in highly specific social conditions, wild chimpanzees, like humans, may use referential showing gestures to direct others' attention to objects simply for the sake of sharing. The difference between humans and our closest living relatives in this regard may be quantitative rather than qualitative, with ramifications for our understanding of the evolution of human social cognition.

Keywords: chimpanzee; declarative gesture; referential communication; shared attention; showing.

Fig. 1.

Photo series of Fiona (on the right) showing the leaf to Sutherland (on the left; the red circle shows the location of the leaf). (A) Fiona leaf grooming while Sutherland sits next to her, not paying visual attention to the leaf grooming. (B) Fiona holds the leaf toward Sutherland, and Sutherland shifts her gaze toward it. (C) Fiona fully extends her arm and holds the leaf directly in front of Sutherland. Sutherland noticeably moves her head and gaze to look directly at the leaf. Fiona then resumes leaf grooming.