Ignacio Martínez Mendizábal
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One of the big problems when studying the evolutionary history of the human beings is the origin of language. From the point of view of Paleontology, and considering that words cannot be fossilized, the aim is knowing when, in what specie, and under which circumstances did the anatomical structures supporting our most usual way of communication -speech- appeared. For this, along the las half century, there have been two different ways to address the problem: one of them focused on the reconstruction of the throat anatomy of the different fossil hominids, while the other focused in the study of intracranial molds. Neither of these ways has obtained convincing results.

A novel line of research has been established by studying the audition patterns (audiograms) of the current and fossil species. The audiograms of most species of platyrrhines (New World monkeys) and catarrhines (Old World monkeys and apes) are characterized by "peaks" of maximum sensibility around 1 and 8 kHz respectively, separated by a range of less sensibility in the "intermediate frequencies" around 2 and 4 kHz. In opposition to the rest of "anthropoids", us humans have our maximum sensibility precisely in the "intermediate frequencies", in which the human voice resonates.

Using computed axial tomographies of the temporal bone region (more than 100 tomographies per individual), it has been possible to digitally reconstruct the cavities of the external and middle ear from five individuals of the Mesopleistocene deposit in the site Sima de los Huesos (Atapuerca Sierra) assigned to the species Homo heidelbergensis. A number of anatomical variables have been measured over these reconstructions, based on which a circuit model reproducing the function of the external and middle ear has been built to test the acoustic filtration of sounds along the external and middle ear. That acoustic filter is the determining factor of the auditive pattern in each species: the position and bandwidth of maximum sensibility. The results obtained are unequivocal and show that the individuals of Sima de los Huesos had an auditory pattern similar to that of the modern human populations (in both, the position of the area of maximum sensibility, and in the magnitude of the bandwidth) and very different from the one of chimpanzees.  

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