Structure and Functions of Gesture Sequences in Wild Bonnet Macaques (Macaca radiata)

Abstract

Compositionality, a hallmark of human language, involves generating novel meaning by combining existing units. Nonhuman primates (mostly apes) are known to combine gestural units in non-random ways, but they do not make novel meaning with these combinations. What could, however, be the functional roles of these gesture sequences and whether they bear any significance to language evolution is still unclear. Moreover, studies on gesture-sequences in non-ape primate species is almost non-existent. Here, we investigated for the first time, the structure and functions of gesture sequences in the naturally occurring communication of wild bonnet macaques (Macaca radiata), using analyses akin to ape gesture studies (Genty & Byrne, 2010; Hobaiter & Byrne, 2011). Bonnet macaque gesture sequences exhibit non-random combinations of gestures and non-gesture units - certain gestures are significantly more common in sequences, they associate preferentially with specific other components and certain components are more likely to appear either at the beginning or at the end of a sequence. Interplay of these sequences form distinct gestural clusters, corresponding to affiliative/play and agonistic contexts. Although, the overall functions of bonnet macaque gesture sequences remain obscure, as in apes, we found that gesture sequences were specifically used as a persistence strategy, after the initial single gestures have failed to initiate and sustain social interactions. We discuss our findings in the light of a possibility that primate gesture sequences, coordinating the flow of social interactions, may be evolutionary precursors to pragmatic gestures in human language.