Abstract
Comparative studies of nonhuman communication systems could provide insights into the origins and evolution of a distinct dimension of human language: intentionality. Recent studies have provided evidence for intentional communication in different species but generally in captive settings. We report here a novel behaviour of food requesting from humans displayed by wild bonnet macaques Macaca radiata, an Old World cercopithecine primate, in the Bandipur National Park of southern India. Using both natural observations and field experiments, we examined four different behavioural components—coo-calls, hand-extension gesture, orientation, and monitoring behaviour—of food requesting for their conformity with the established criteria of intentional communication. Our results suggest that food requesting by bonnet macaques is potentially an intentionally produced behavioural strategy as all the food requesting behaviours except coo-calls qualify the criteria for intentionality. We comment on plausible hypotheses for the origin and spread of this novel behavioural strategy in the study macaque population and speculate that the cognitive precursors for language production may be manifest in the usage of combination of signals of different modalities in communication, which could have emerged in simians earlier than in the anthropoid apes.
Highlights
Organised human language is perhaps one of the most important behaviours that distinguish human beings from all other species[1,2], with intentionality lying at the core of this communication system[3,4,5,6]
This approach is practically helpful to identify intentionality in human communication, recent studies have suggested that mental-state attribution may not be a necessary criterion to typify intentional communication, in non-humans[13]. This has given rise to various general behavioural criteria to qualify a communicative signal to be intentional. These criteria include (1) the social use of the communicative act, as indicated by the signal being directed to particular recipients, modified by various factors, such as the presence or composition of the attendant audience; (2) sensitivity of the signaller to the attentional states of the recipients; (3) manipulation of the attentional states of recipients to attract attention, when a mutual attention state between the signaller and recipient is absent or the signaller moves itself into the line of view of a recipient; (4) monitoring the responses of the audience and (5) persistence in the production and/or elaboration of the signal until the desired communicative goal is met[4,14,15]
Our long-term studies on wild bonnet macaques have, revealed food-requesting behaviour towards humans to be an intrinsic component of the behavioural repertoire of several free-ranging individuals in two independent populations of this species, reflecting contexts and situations similar to that in the experiments conducted in captivity[60,61]
Summary
Organised human language is perhaps one of the most important behaviours that distinguish human beings from all other species[1,2], with intentionality lying at the core of this communication system[3,4,5,6]. These criteria include (1) the social use of the communicative act, as indicated by the signal being directed to particular recipients, modified by various factors, such as the presence or composition of the attendant audience; (2) sensitivity of the signaller to the attentional states of the recipients; (3) manipulation of the attentional states of recipients to attract attention, when a mutual attention state between the signaller and recipient is absent or the signaller moves itself into the line of view of a recipient; (4) monitoring the responses of the audience and (5) persistence in the production and/or elaboration of the signal until the desired communicative goal is met[4,14,15] (but see ref.[13] for a recently proposed, simpler framework for intentional communication in animals) The use of these criteria is largely restricted to the great ape communication systems and several studies have revealed that, among various modalities used in primate communication, gestures represent intentional signals[3,16,17,18,19,20,21,22,23,24]. The presence of an elaborate and flexible behavioural repertoire[64,65], complex social interactions mediated by cognitive decision-making[66], innovations in communication behaviour[67] and varied behavioural traditions in different populations of the species[60] provide further evidence of the phenotypic plasticity that characterises this primate
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