Studing audition in fossil hominins: a new approach to the evolution of language?

Abstract

The evolution of human language is one of the oldest questions inpaleoanthropology. Nevertheless, many previous attempts to approachthis question have not yielded informative results since they are oftenbased on anatomical features whose role in speech production in modernhumans is unclear or whose functional implications in fossil specimensare difficult to assess. We take a new approach to this question bystudying the evolution of audition. Human hearing differs from that ofchimpanzees and other primate taxa in maintaining a widened bandwidthof heightened sensitivity between 1-8 kHz, a region that contains relevantacoustic information in spoken language. Comparative analysis ofprimate audiograms suggests that this represents a unique derived featurein modern humans. Knowledge of the auditory capacities in our fossilhuman ancestors could greatly enhance the understanding of when thishuman pattern emerged during the course of our evolutionary history.Here we present a comprehensive approach to this question, onlyrarely addressed in human evolutionary studies. We have analyzed theauditory capacities in five fossil human specimens from the MiddlePleistocene site of the Sima de los Huesos (SH) in the Sierra deAtapuerca of Spain. The results demonstrate that the Atapuerca (SH)hominins resemble modern humans in showing a widened bandwidth ofheightened sensitivity between 1-5 kHz, a frequency range whichoverlaps the range of frequencies emitted during spoken language. At thesame time, both modern humans and the Atapuerca (SH) hominins differfrom chimpanzees in showing a heightened sensitivity to the highconsonant area (approximately 3-5 kHz) of the so-called "speechbanana", a frequency range associated with consonant production inhuman spoken language.The presence of a modern human auditory pattern in the Atapuercahominins suggests that these Middle Pleistocene humans alreadypossessed the anatomical features of the outer and middle ear that supportthe perception of human spoken language. Given the intuitive, butdifficult to quantify, link between sound perception and vocal productionin animals, the study of auditory capacities may have implications for theemergence of language in our fossil human ancestors. Although the studyof audition is an indirect approach to the question of speech capacity infossil specimens, the results of the present study are consistent with otherrecent suggestions for the presence of some form of spoken language inthe genus Homo prior to the appearance of our own species, Homosapiens.