Temporal bone anatomy and the evolution of acoustic capacities in fossil humans

The present study is the first comprehensive analysis of taxonomic variation in the anatomical structures of the outer and middle ear in the human fossil record. The results demonstrate that the outer and middle ears are important but unappreciated sources of phylogenetic information within the human lineage. The anatomical variation documented between taxa also has clear auditory implications, and the present study shows that it is feasible to study aspects of sensory perception in fossil specimens.; The analysis of the outer and middle ear anatomy and dimensions has revealed important changes during the course of our evolutionary history. Results suggest that anatomical changes in the tympanic membrane and auditory ossicles may represent one of the first human-like characteristics to appear in the hominid lineage. At the same time, the genus Homo appears to be largely characterized by evolutionary stasis in several anatomical structures of the outer and middle ear. In contrast, the appearance of our own species, Homo sapiens, is associated with a marked change in some middle ear dimensions.; The auditory capacities in the early hominid taxa Australopithecus africanus and Paranthropus robustus are quite similar in showing a peak in sensitivity at around 2.5 kHz followed by a sharp dropoff above this frequency. Although both these taxa clearly resemble the chimpanzee pattern most closely, they do show a somewhat heightened sensitivity compared with chimpanzees between 2.5-5.0 kHz. In contrast, European Middle Pleistocene hominids show only minor differences from living humans in their auditory capacities. In particular, they share a broadened region of heightened sensitivity between 1.0-3.5 kHz and more closely resemble the modern human pattern above this frequency range. The presence of similar patterns in both living humans and in the Neandertal evolutionary lineage suggests that the modern human auditory pattern probably emerged sometime during the Lower Pleistocene.