Using a naturalistic video database, we examined whether gestures scaffold the symbolic development of a language-enculturated chimpanzee, a language-enculturated bonobo, and a human child during the second year of life. These three species constitute a complete clade: species possessing a common immediate ancestor. A basic finding was the functional and formal similarity of many gestures between chimpanzee, bonobo, and human child. The child’s symbols were spoken words; the apes’ symbols were lexigrams – non-iconic visual signifiers. A developmental pattern in which gestural representation of a referent preceded symbolic representation of the same referent appeared in all three species (but was statistically significant only for the child). Nonetheless, across species, the ratio of symbol to gesture increased significantly with age. But even though their symbol production increased, the apes continued to communicate more frequently by gesture than by symbol. In contrast, by 15–18 months of age, the child used symbols more frequently than gestures. This ontogenetic sequence from gesture to symbol, present across the clade but more pronounced in child than ape, provides support for the role of gesture in language evolution. In all three species, the overwhelming majority of gestures were communicative (i.e., paired with eye contact, vocalization, and/or persistence). However, vocalization was rare for the apes, but accompanied the majority of the child’s communicative gestures. This species difference suggests the co-evolution of speech and gesture after the evolutionary divergence of the hominid line. Multimodal expressions of communicative intent (e.g., vocalization plus persistence) were normative for the child, but less common for the apes. This species difference suggests that multimodal expression of communicative intent was also strengthened after hominids diverged from apes.
Keywords: gestural theory of language evolution, language-enculturated apes, symbolic development, cross-species comparisons, gesture, communication development, language development
Citation: Gillespie-Lynch K, Greenfield PM, Feng Y, Savage-Rumbaugh S and Lyn H (2013) A cross-species study of gesture and its role in symbolic development: implications for the gestural theory of language evolution. Front. Psychol. 4:160. doi: 10.3389/fpsyg.2013.00160
Received: 18 December 2012; Accepted: 14 March 2013;
Published online: 06 June 2013.
Edited by:Aaron P. Blaisdell, University of California Los Angeles, USA
Reviewed by:Leslie Phillmore, Dalhousie University, Canada
Copyright: © 2013 Gillespie-Lynch, Greenfield, Feng, Savage-Rumbaugh and Lyn. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: K. Gillespie-Lynch, Department of Psychology, 4S-234, College of Staten Island, CUNY, 2800 Victory Boulevard, Staten Island, NY 10314, USA. e-mail: email@example.com