Abstract
To test the role of gestures in the origin of language, we studied hand preferences for grasping or pointing to objects at several spatial positions in human infants and adult baboons. If the roots of language are indeed in gestural communication, we expect that human infants and baboons will present a comparable difference in their pattern of laterality according to task: both should be more right-hand/left-hemisphere specialized when communicating by pointing than when simply grasping objects. Our study is the first to test both human infants and baboons on the same communicative task. Our results show remarkable convergence in the distribution of the two species' hand biases on the two kinds of tasks: In both human infants and baboons, right-hand preference was significantly stronger for the communicative task than for grasping objects. Our findings support the hypothesis that left-lateralized language may be derived from a gestural communication system that was present in the common ancestor of baboons and humans.
Highlights
One of the keys to understanding language evolution is the issue of hemispheric specialization in the communicative behaviors of non-human primates
While left lateralization for language is classically linked to right-handedness for manipulative actions in humans, a different approach [1] suggests that handedness for gestural communication may constitute a better predictor of hemispheric specialization for language
Our study aims to overcome this deficit by testing human infants and nonhuman primates using a similar experimental setup
Summary
One of the keys to understanding language evolution is the issue of hemispheric specialization in the communicative behaviors of non-human primates. While left lateralization for language is classically linked to right-handedness for manipulative actions in humans, a different approach [1] suggests that handedness for gestural communication may constitute a better predictor of hemispheric specialization for language. This view is supported by the existence of strong links between speech and gestures in humans [2]. Our study aims to overcome this deficit by testing human infants and nonhuman primates using a similar experimental setup For this purpose we adapted a test initially designed to quantify hand preference in humans [8], so it could be used to investigate both human infants and adult baboons. This experimental paradigm allowed us to assess handedness in both species in a communication task versus a simple (manipulative) grasping task, while controlling spatial and postural factors
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