Social learning of vocal structure in a nonhuman primate?

Alban Lemasson,Eric J Petit,Karim Ouattara,Klaus Zuberbühler

doi:10.1186/1471-2148-11-362

Abstract

BackgroundNon-human primate communication is thought to be fundamentally different from human speech, mainly due to vast differences in vocal control. The lack of these abilities in non-human primates is especially striking if compared to some marine mammals and bird species, which has generated somewhat of an evolutionary conundrum. What are the biological roots and underlying evolutionary pressures of the human ability to voluntarily control sound production and learn the vocal utterances of others? One hypothesis is that this capacity has evolved gradually in humans from an ancestral stage that resembled the vocal behavior of modern primates. Support for this has come from studies that have documented limited vocal flexibility and convergence in different primate species, typically in calls used during social interactions. The mechanisms underlying these patterns, however, are currently unknown. Specifically, it has been difficult to rule out explanations based on genetic relatedness, suggesting that such vocal flexibility may not be the result of social learning.ResultsTo address this point, we compared the degree of acoustic similarity of contact calls in free-ranging Campbell's monkeys as a function of their social bonds and genetic relatedness. We calculated three different indices to compare the similarities between the calls' frequency contours, the duration of grooming interactions and the microsatellite-based genetic relatedness between partners. We found a significantly positive relation between bond strength and acoustic similarity that was independent of genetic relatedness.ConclusionGenetic factors determine the general species-specific call repertoire of a primate species, while social factors can influence the fine structure of some the call types. The finding is in line with the more general hypothesis that human speech has evolved gradually from earlier primate-like vocal communication.

Highlights

Non-human primate communication is thought to be fundamentally different from human speech, mainly due to vast differences in vocal control
What are the biological roots of vocal production learning in humans, a key capacity for the development of spoken language? Paradoxically, some cetaceans, songbirds and bats are more similar to humans in their vocal learning skills than any of the nonhuman primates, in the sense that all require social models to acquire functionally adequate vocal behavior [1]
We focused on contact calls, which are exchanged between group members during friendly social interactions according to temporal and organizational rules [21,23]

Summary

Introduction

Non-human primate communication is thought to be fundamentally different from human speech, mainly due to vast differences in vocal control. In terms of call morphology, the default assumption has always been that nonhuman primate calls develop under strong This stance has become more controversial, largely due to a diverse body of evidence for vocal plasticity in non-human primates in the form of acoustic convergence at the group level (mouse lemurs [7], Japanese macaques [8], chimpanzees [9]) and individual level (marmosets [10], Campbell’s monkeys [11]), as well as cases of apparent vocal innovation (Campbell’s monkeys [12], chimpanzees [13]). We were interested in the relative influence of social factors on these acoustic differences

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