Usage and comprehension of manual gestures in wild chimpanzees

Abstract

An important element in understanding the evolutionary origin of human language is to explore homologous traits in cognition and communication between primates and humans (Burling, 1993, Hewes, 1973. One proposed modality of language evolution is that of gestural communication, defined as communicative movements of hands without using or touching objects (de Waal, 2003). While homologies between primate calls and language have been relatively well explored, we still have a limited understanding of how cognitive abilities may have shaped the characteristics of primate gestures (Corballis, 2003). In this Ph.D. research, I investigated the cognitive skills underlying gestural communication in both wild and language trained chimpanzees, with a special focus on the repertoire and the intentionality of production and comprehension. The study of cognitive skills underlying the production of the repertoire and the role of intentionality is important because these skills are cognitively demanding and are a prerequisite in human infants for their ability to acquire language (Baldwin, 1995, Olson, 1993. My research suggests that chimpanzee gestural communication is cognitively complex and may be homologous with the cognitive skills evident in pre-verbal infants on the cusp of language acquisition.Chimpanzees display a multifaceted and complex signal repertoire of manual gestures. These gestures are the prototypes, within which there is variation, and between which the iv boundaries are not clear-cut, but there is gradation apparent along several morphological components. Both wild and language trained chimpanzees communicate intentionally about their perceived desires and the actions that they want the recipients to undertake. They do not just express their emotions, but they communicate flexibly by adjusting their communicative tactics in response to the comprehension states of the recipient. Whilst chimpanzees communicate their intentions flexibly, the messages conveyed are specific. However, recipients comprehend gestures flexibly in light of the signaller"s overall intentions.Whilst wild and language trained chimpanzee gestural communication revealed similar cognitive characteristics, language trained chimpanzees outperformed wild apes in that they had ability to use signals which made distinctions that human deictic words can make. Whilst these differences between wild and language trained chimpanzees may be due to the different methodological approaches used, it is conceivable that language training may have influenced captive ape cognitive skills in the representational domain. These results from wild and language trained chimpanzees indicate that chimpanzees possess some form of cognitive skills necessary for language development and that cognitive skills underlying repertoire and use in chimpanzees are a shared capacity between humans, other apes and a common ancestor. These findings render theories of the gestural origins of language more plausible.v

A structure-based repertoire of manual gestures in wild chimpanzees: statistical analyses of a graded communication system

“…However, perceived morphological variation is often considered to lack communicative function, and subsequently, gesture variants are lumped together (Hobaiter & Byrne, 2011; but see Roberts et al, 2012). The underlying assumptions are that a human observer can identify and classify meaningful units (in a similar manner to the animals themselves) and also that similar morphological properties reflect similarities in function.…”

“…Moreover, not all studies investigated whether the observed signals are intentional, as determined from the signaller directing gestures to recipients in flexible, goal-directed ways (see e.g. Roberts et al, 2012). However, it is important to determine whether the observed behaviours are voluntary because the distinction between simple behavioural actions, which may be used by others to infer intentions and meaningful gestural communication, lies in determining whether the action is used intentionally (Bates, Benigni, Bretherton, Camaioni, & Volterra, 1979).…”

“…Chimpanzee gestural behaviour has been studied in a few wild (Goodall, 1986;Hobaiter & Byrne, 2011;van LawickGoodall, 1968;McGrew, Marchant, Scott, & Tutin, 2001;Nishida, 1970;Nishida, Koichiro, Takahisa, Agumi, & McGrew, 2010;Plooij, 1978Plooij, , 1979Reynolds, 1963;Roberts et al, 2012;Sugiyama, 1969) and captive populations (van Hooff, 1971;Tomasello, Call, Nagell, Olguin, & Carpenter, 1984;Liebal, Call, & Tomasello, 2004;Pollick & de Waal, 2007). Gestures are used flexibly across a diverse range of contexts, including agonism, mating, grooming, and play (Pollick & de Waal, 2007;Roberts et al, 2012); in motheroffspring interactions, gestures are pivotal in negotiating nursing and food sharing, and coordinating travel (Plooij, 1978).…”

“…However, it is important to determine whether the observed behaviours are voluntary because the distinction between simple behavioural actions, which may be used by others to infer intentions and meaningful gestural communication, lies in determining whether the action is used intentionally (Bates, Benigni, Bretherton, Camaioni, & Volterra, 1979). For example, activities that regularly precede a particular event, such as those that indicate changes in activity state (i.e., between resting and locomotion), can become communicative to the receiver even though this signal is unintentional from the sender's perspective (Roberts, 2010;Roberts et al, 2012).…”

“…Gestures are used flexibly across a diverse range of contexts, including agonism, mating, grooming, and play (Pollick & de Waal, 2007;Roberts et al, 2012); in motheroffspring interactions, gestures are pivotal in negotiating nursing and food sharing, and coordinating travel (Plooij, 1978). While these studies provide important insights into overall repertoire, manual gestures have been mostly studied within the broader framework of all communicative bodily movements.…”