Perspective ARTICLE

Front. Psychol., 20 February 2013 | doi: 10.3389/fpsyg.2013.00071

The emergence of hierarchical structure in human language

  • 1Department of Linguistics and Philosophy, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 2Department of Electrical Engineering and Computer Science and Laboratory for Information and Decision Systems, MIT, Cambridge MA, USA
  • 3Department of Life Sciences, The University of Tokyo, Tokyo, Japan

We propose a novel account for the emergence of human language syntax. Like many evolutionary innovations, language arose from the adventitious combination of two pre-existing, simpler systems that had been evolved for other functional tasks. The first system, Type E(xpression), is found in birdsong, where the same song marks territory, mating availability, and similar “expressive” functions. The second system, Type L(exical), has been suggestively found in non-human primate calls and in honeybee waggle dances, where it demarcates predicates with one or more “arguments,” such as combinations of calls in monkeys or compass headings set to sun position in honeybees. We show that human language syntax is composed of two layers that parallel these two independently evolved systems: an “E” layer resembling the Type E system of birdsong and an “L” layer providing words. The existence of the “E” and “L” layers can be confirmed using standard linguistic methodology. Each layer, E and L, when considered separately, is characterizable as a finite state system, as observed in several non-human species. When the two systems are put together they interact, yielding the unbounded, non-finite state, hierarchical structure that serves as the hallmark of full-fledged human language syntax. In this way, we account for the appearance of a novel function, language, within a conventional Darwinian framework, along with its apparently unique emergence in a single species.

Keywords: human language, birdsong, honeybee, monkey communication, hierarchy

Citation: Miyagawa S, Berwick RC and Okanoya K (2013) The emergence of hierarchical structure in human language. Front. Psychol. 4:71. doi: 10.3389/fpsyg.2013.00071

Received: 20 November 2012; Accepted: 02 February 2013;
Published online: 20 February 2013.

Edited by:

Marcela Pena, Catholic University of Chile, Chile

Reviewed by:

Alan Langus, SISSA, Italy
Francisco Aboitiz, Pontificia Universidad Catolica de Chile, Chile

Copyright: © 2013 Miyagawa, Berwick and Okanoya. 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: Shigeru Miyagawa, Department of Linguistics and Philosophy, Massachusetts Institute of Technology, 32D-886, Cambridge, MA 02139, USA. e-mail:

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