Gestenerwerb: Überprüfung der Social Negotiation-Hypothese
Evolution, Anthropologie
Zusammenfassung der Projektergebnisse
Language, one of humans’ most distinctive traits, still remains a ‘mystery’ for evolutionary theory. Investigating the mechanisms underlying human and non-human primate intentional communication systems may, however shed light on the similarities and hence the evolutionary roots of language. Many studies have shown that gestural communication plays a crucial role in human and non-human primates’ communication. In addition, non-human primates’ and particularly great apes’ gestural systems share several characteristics with human language, in particular intentionality, referentiality and conversational rules that are necessary for learning and using communication signals correctly. Studying great apes’ gestural communication should thus provide valuable clues to deeper investigate the evolutionary roots of language. In my project, I clarified 1) the (multicausal) origins of gestures and language, 2) the social cognitive abilities of great apes and 3) the role of key characteristics in the acquisition and development of great apes’ gestural communication. To carry out these 2nd and 3rd points, I considered a rarely studied species but by no means least, the gorillas (Gorilla gorilla gorilla). Recently, much research attention has focused on the origins of gestures and three main hypotheses have been proposed: (1) the phylogenetic ritualization hypothesis supporting the biological inheritance in the gesture acquisition of non-human primates, (2) the ontogenetic ritualization supporting the ontogenetic basis of the gestural acquisition process, and recently (3) learning via social negotiation supporting the role of social exposure and interactional experience in the gestural acquisition process. So far fine-grained analyses of human and non-human primates’ gestural signalling focusing specifically on gestural forms and linkages between morphological features and demographic and social matrices of interactants, were non-existent. Here, I addressed this issue for the first time by performing an unprecedented and finegrained analysis of gestural form during spontaneous intraspecific social-play interactions of subadult gorillas living in two separate captive groups. I focused on four most frequent gesture types (BEAT CHEST, SLAP BODY, SLAP GROUND and TOUCH BODY) and twelve main morphological gesture characteristics (e.g. horizontal and vertical hand trajectories, thumb and fingers flexion and spread). My multifactorial investigation showed that signaller’s sociodemographic characteristics (group and kinship), signaller’s behavioural characteristics (body posture) and context-related characteristics (recipient’s sex, attentional state and position in the signaller’s visual field) influenced morphological characteristics of the four study gesture types differently. This was particularly true for the two auditory gestures, BEAT CHEST and SLAP GROUND, and, to a lesser extent, the tactile gestures (SLAP BODY and TOUCH BODY). Furthermore, the results revealed (1) the existence of "accents” in gestural communication in the Animal Kingdom (including humans), and (2) a highly variable adjustment of gestural form to different conspecifics and interactional characteristics. The revised social negotiation hypothesis postulating that gestures show flexibility in their usage and their form was previously supported for gesture use, it is now also verified for gesture form. Bringing together the most detailed investigation and results of gestural morphology in humans and non-human animals and relevant literature about the evolutionary origins of gesture and language in a concise way, my co-authors and I think that our articles will have wide implications and will be of importance for scientific disciplines dealing with humans and non-human animals such as Behavioural Biology, Linguistics, Comparative Psychology, Anthropology, Biopsychology as well as Social and Cognitive Sciences.
