Should I stay or should I go? Initiation of joint travel in mother-infant dyads of two chimpanzee communities in the wild.

Marlen Fröhlich,Roman M Wittig,Simone Pika

doi:10.1007/s10071-015-0948-z

Abstract

It is well established that great apes communicate via intentionally produced, elaborate and flexible gestural means. Yet relatively little is known about the most fundamental steps into this communicative endeavour—communicative exchanges of mother–infant dyads and gestural acquisition; perhaps because the majority of studies concerned captive groups and single communities in the wild only. Here, we report the first systematic, quantitative comparison of communicative interactions of mother–infant dyads in two communities of wild chimpanzees by focusing on a single communicative function: initiation of carries for joint travel. Over 156 days of observation, we recorded 442 actions, 599 cases of intentional gesture production, 51 multi-modal combinations and 80 vocalisations in the Kanyawara community, Kibale National Park, Uganda, and the Taï South community, Taï National Park, Côte d’Ivoire. Our results showed that (1) mothers and infants differed concerning the signal frequency and modality employed to initiate joint travel, (2) concordance rates of mothers’ gestural production were relatively low within but also between communities, (3) infant communicative development is characterised by a shift from mainly vocal to gestural means, and (4) chimpanzee mothers adjusted their signals to the communicative level of their infants. Since neither genetic channelling nor ontogenetic ritualization explains our results satisfactorily, we propose a revised theory of gestural acquisition, social negotiation, in which gestures are the output of social shaping, shared understanding and mutual construction in real time by both interactants.Electronic supplementary materialThe online version of this article (doi:10.1007/s10071-015-0948-z) contains supplementary material, which is available to authorized users.

Highlights

Across cultures and languages, human children enter language hands first
Are gesture types employed to initiate joint travel due to learning between mothers and infants or can their production be explained as a result of genetic channelling? Since it is impossible to observe developmental processes as they unfold over time under natural conditions, a window approach onto gesture acquisition was applied: We investigated the degree of variability in gestural production to initiate joint travel within dyads within communities and between communities (Pika et al 2003, 2005)
The main aim of the present study was to gain a better understanding of the complexity and variability of communicative exchanges in chimpanzee mother–infant dyads in natural environments and to shed light on gestural acquisition

Summary

Introduction

Human children enter language hands first. It has been hypothesised that this brief period in human ontogeny recapitulates phylogeny, with gestures being the modality out of which human language may have blossomed (for an overview, see Hewes 1973). Pioneering work has been carried out by Plooij (1978, 1979) 40 years ago, who investigated gestural ontogeny in mother–infant communication in chimpanzees at Gombe, Tanzania He showed that, similar to communicative development in human children, interactions between chimpanzee infants and their mothers slowly progress, with a shift around the ages of 9–12 months from acts without social–communicatory intention to intentional acts. Byrne and colleagues (Genty et al 2009; Hobaiter and Byrne 2011) challenged the idea that learning plays a role in great ape’s gestural production and suggested that to vocal production and facial expressions, gestures appear hard-wired and can be explained as a result of genetic channelling during development alone This hypothesis is in contrast to great apes’ high degree of manual flexibility in other behavioural domains such as food processing and tool use, and considerable inter-site variability (Byrne et al 2011; van Schaik et al 2003; Whiten et al 1999). Since systematic quantitative comparisons of gestural signalling in wild populations are still lacking, the absence of evidence might merely reflect a paucity of data, rather than a lack of gestural complexity on behalf of the apes

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