Rhesus monkeys correctly read the goal-relevant gestures of a human agent

Abstract

When humans point, they reveal to others their underlying intent to communicate about some distant goal. A controversy has recently emerged based on a broad set of comparative and phylogenetically relevant data. In particular, whereas chimpanzees (Pan troglodytes) have difficulty in using human-generated communicative gestures and actions such as pointing and placing symbolic markers to find hidden rewards, domesticated dogs (Canis familiaris) and silver foxes (Urocyon cinereoargenteus) readily use such gestures and markers. These comparative data have led to the hypothesis that the capacity to infer communicative intent in dogs and foxes has evolved as a result of human domestication. Though this hypothesis has met with challenges, due in part to studies of non-domesticated, non-primate animals, there remains the fundamental question of why our closest living relatives, the chimpanzees, together with other non-human primates, generally fail to make inferences about a target goal of an agent's communicative intent. Here, we add an important wrinkle to this phylogenetic pattern by showing that free-ranging rhesus monkeys (Macaca mulatta) draw correct inferences about the goals of a human agent, using a suite of communicative gestures to locate previously concealed food. Though domestication and human enculturation may play a significant role in tuning up the capacity to infer intentions from communicative gestures, these factors are not necessary.

Figure 1

Schematic of the rhesus monkey's recruitment gesture used to recruit allies in a coalition. Here, animal A attempts to grab B's attention by quickly jutting his head towards B (arrow 1). Once A attracts B's attention, A rapidly juts his head towards C (arrow 2).

Figure 2

Results showing the number of subjects that selectively inspected the box targeted by the experimenter's action (black bars) versus the box that the experimenter did not act towards (grey bars). P-values represent binomial probabilities with an α-level set to 0.05 (one-tailed predictions).

Figure 3

Proportion of subjects (n=10) picking the gestured (correct) box across trials.