Human hearing differs from that of chimpanzees and most other anthropoids in maintaining a relatively high sensitivity from 2 kHz up to 4 kHz, a region that contains relevant acoustic information in spoken language. Knowledge of the auditory capacities in human fossil ancestors could greatly enhance the understanding of when this human pattern emerged during the course of our evolutionary history. Here we use a comprehensive physical model to analyze the influence of skeletal structures on the acoustic filtering of the outer and middle ears in five fossil human specimens from the Middle Pleistocene site of the Sima de los Huesos in the Sierra de Atapuerca of Spain. Our results show that the skeletal anatomy in these hominids is compatible with a human-like pattern of sound power transmission through the outer and middle ear at frequencies up to 5 kHz, suggesting that they already had auditory capacities similar to those of living humans in this frequency range.K nowledge about the sensory capabilities of past life forms could greatly enhance our understanding of the adaptations and lifeways in extinct organisms. Audition is the most readily accessible in fossils because it is based primarily in physical properties that can be approached through their skeletal structures (1). Recently, the possibility to analyze auditory capacities in fossil species has been highlighted as one of the major challenges in modern vertebrate paleontology, particularly since the advent of computed tomography (CT)-based analyses (2).The recent publication of a detailed comparison of the human and chimpanzee genomes has highlighted several genes involved with hearing that appear to have undergone adaptive evolutionary changes in the human lineage (3). The authors have suggested that these changes could be related with the acquisition of hearing acuity necessary for understanding spoken language, and they emphasize the importance of further research into hearing differences between humans and chimpanzees (3). At least one of the human genes mentioned as having undergone adaptive evolutionary change (EYA1) is related to the development of the outer and middle ear (4, 5). These results are compatible with the known differences in the anatomical structures of the outer and middle ear in chimpanzees and ourselves (6, 7).As might be expected from these genetic and anatomical data, the empirical studies of chimpanzee hearing capabilities also show clear differences with human hearing. Chimpanzee audiograms (8, 9) show a W-shaped pattern characterized by two peaks of high sensitivity at Ϸ1 kHz and 8 kHz, respectively, and a relative loss of sensitivity in the midrange frequencies (between 2 and 4 kHz). Of course, this relative loss does not mean that chimpanzees cannot hear in the midrange frequencies, but rather that they are adapted to hear best at Ϸ1 kHz and 8 kHz. It is interesting to note that the species-specific pant-hoots regularly emitted by wild chimpanzees to communicate with conspecifics over long distances concentrate the acoustic ...

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Hearing in early hominins may have facilitated an increased emphasis on short-range vocal communication in open habitats.