Social antecedents of rhythmic behaviours in chimpanzees (Pan troglodytes)

Recently there has been a growing interest in the rhythmic abilities of nonhuman animals, as a way of tracking the evolutionary origins of human musicality. Emerging evidence suggests that a handful of avian and mammalian species can (be trained to) align rhythmic actions to an auditory rhythm. This evidence has spurred an effervescence of speculations and debates regarding the origins of musicality, currently divided between theories that postulate the emergence of rhythmic abilities as the result of audiomotor neural adaptations that enabled flexible vocal learning and language evolution, and theories that view their evolutionary emergence as an essentially social phenomenon, primarily expressed in social bonding contexts, where it enabled individuals to move together in time, thereby allowing precisely timed cooperation. Extant empirical evidence from non-human species however, is insufficient to substantiate any of these theories. In particular, there is a scarcity of data from our closest genetic relatives - the chimpanzees (Pan troglodytes) - and a lack of studies tracking the presence and potential functions of rhythmic behaviours in the (social) contexts in which they occur. To address this limitation, we conducted an observational study in which we documented the range of rhythmic behaviours exhibited by chimpanzees across solitary activities and social interactions. Data collection was carried out at two sites - Furuvik Zoo in Sweden (N=6) and MONA Foundation in Spain (N=14) - totalling 120 hours. Preliminary results show that rhythmic behaviours are frequent in a variety of social contexts (initiation of social interaction, play, grooming, courtship, display) and relatively absent in solitary contexts, with the exception of object play. Given their high frequency in social contexts, it is plausible that rhythmic behaviours accomplish a communicative function, which in turn corroborates social theories on the evolutionary origins of rhythmic abilities.