Understanding the meaning and use of a communicative signal

What is it about?

Chimpanzees have a repertoire of communicative gestures, and many previous studies have focused on providing evidence that the gestures are intentional and/or communicative, i.e., purposefully sending a message about something to particular social partner(s). Here we take a bottom-up approach to investigate the meaning and use of the gesture Touch. For each of the 581 instances of Touch found in this study of 3 chimpanzees, from 15 to 60 months of age, we documented the form of the gesture, the target location, the context in which it occurred, and whether the infant initiated or received the gesture. We found that Touch was used flexibly across contexts, with diversity in form and target locations. There were significant differences when infants initiated and when they received Touch but this did not lead developmentally to increasing specificity of particular patterns of form within specific contexts. We conclude that there was not a single, specific communicative meaning of Touch within or across contexts.

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Why is it important?

These findings are important for two reasons related to the evolution of communication. First, this gesture is used very flexibly, with 36 forms (from single finger to whole hand with an action), with 70 target locations (from head to toes of the social partner), and across 26 contexts (attention-getting to dominance /submission). Such flexibility provides strong evidence that there is not a fixed or rigid coupling of form and function in this gesture, supporting claims that nonverbal gesture shows some of the properties of linguistic communication, e.g., generativity/productivity. Secondly, the analyses of form, uses, and development provide evidence to argue against some theoretical explanations for how gestures emerge. The theories of genetic channelling and imitation are refuted as mechanisms to explain the emerge of the gesture Touch, because of the extraordinarily high number of different forms. Counter to the ontogenetic ritualization hypothesis, the gesture Touch did not become more precise or narrower in form with development, nor did particular forms become more tightly linked with particular contexts as the infants developed into juveniles or when infants and adults were compared. At the very least, we can conclude that not all gestures are created via the same developmental mechanisms.

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