The Evolution of the Auditory System: A Tutorial

Abstract

A respectable body of work exists on the evolution of speech production, but little has been published on the evolution of the auditory system. Salient points in the evolution of the auditory system are presented here based on a review of the literature in paleontology, embryology, and comparative studies of extant organisms. Structural changes in the vertebrate ear are the central issue. Research methods and interpretive caveats are examined, followed by a discussion of evolution in relation to audition and the emergence of the auditory system. Findings from the fossil record, pertinent to aural structures, are noted, with comparative investigations of extant organisms in the evolution of the inner ear and central auditory structures. Discussion focuses on changes in structure and their benefits for evolutionary selection, with an overview of theories associated with these changes. In conclusion, the implications of ongoing evolution of the auditory system in higher primates are considered. lthough the understanding of evolution may not play an obvious part in the day-to-day functioning of the clinical speech-language pathologist or audiologist, deeper knowledge of the role of audition in humans, and of human auditory capabilities relative to other species, may serve as a basis for more informed practice in assessing and treating what we know as speech-language and hearing deficits. Little work has been published on the evolution of the auditory system until very recently, and most of this is highly specialized, focusing on very narrow aspects of evolutionary study. This relatively brief tutorial is intended to provide an overview of the evolution of the auditory system. The emphasis here reflects the weight of the literature on evolution with regard to hearing and the function of hearing in human evolution: The structural changes to the middle ear and associated changes in hearing are discussed in relative depth, with less attention to development of the outer and inner ear. The evolution of the ear as vertebrates emerged and moved from water onto land has been the central issue in this area. The study is approached through paleontology, embryology, and comparative studies of organisms that are alive today. This tutorial will begin with a brief discussion of evolution, theory and methods, and will proceed to an overview of recent research on evolution of the structure of the ear, based heavily on the fossil record and comparative anatomy. The discussion will proceed from peripheral to more central structure, with a brief look at auditory perception.