Abstract
Increasing our understanding of primate gestural communication can provide new insights into language evolution. A key question in primate communication is the association between the social relationships of primates and their repertoire of gestures. Such analyses can reveal how primates use their repertoire of gestural communication to maintain their networks of family and friends, much as humans use language to maintain their social networks. In this study we examined the association between the repertoire of gestures (overall, manual and bodily gestures, and gestures of different modalities) and social bonds (presence of reciprocated grooming), coordinated behaviors (travel, resting, co‐feeding), and the complexity of ecology (e.g. noise, illumination) and sociality (party size, audience), in wild East African chimpanzees (Pan troglodytes schweinfurthii). A larger repertoire size of manual, visual gestures was associated with the presence of a relationship based on reciprocated grooming and increases in social complexity. A smaller repertoire of manual tactile gestures occurred when the relationship was based on reciprocated grooming. A smaller repertoire of bodily gestures occurred between partners who jointly traveled for longer. Whereas gesture repertoire size was associated with social complexity, complex ecology also influenced repertoire size. The evolution of a large repertoire of manual, visual gestures may have been a key factor that enabled larger social groups to emerge during evolution. Thus, the evolution of the larger brains in hominins may have co‐occurred with an increase in the cognitive complexity underpinning gestural communication and this, in turn, may have enabled hominins to live in more complex social groups.
Highlights
Understanding the evolution of language is one of the most important questions in establishing whether or not humans are truly distinct from other animals
We examine the associations between gestural repertoire size, sociality and ecological factors in wild East African chimpanzees (Pan troglodytes schweinfurthii) living in Budongo Forest, Uganda
Previous studies of gestural communication of primates have identified different patterns of response specificity to gestures overall, and across manual and bodily gestures. We extend these findings to show that the repertoire size of manual and bodily gestures of wild chimpanzees is differentiated in the nature of its association with social relationships and ecology
Summary
Understanding the evolution of language is one of the most important questions in establishing whether or not humans are truly distinct from other animals. Non-human primates (hereafter primates), and great apes, have an extensive repertoire of gestures, defined as voluntary movements of the arms, head, body postures and locomotory gaits (Liebal et al 2004; Nishida et al 2010; Liebal & Call 2012) While other species such as ravens (Pika & Bugnyar 2011), elephants (Moss et al 2011) and black bears (Kilham 2013) use forms of gestural communication (Palagi et al 2016), there has been an intensive research focus on great ape communication because of the importance of understanding primate communication in developing theories of human language evolution (Fitch 2010; Byrne et al 2017; Corballis 2017). The repertoire size of communication signals is a key aspect to human communication and is part of what characterizes social relationships among humans as complex
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