Hypoglossal canal size and hominid speech

The mammalian hypoglossal canal transmits the nerve that supplies the motor innervation to the tongue. Hypoglossal canal size has previously been used to date the origin of human-like speech capabilities to at least 400,000 y ears ago and to assign modern human vocal abilities to Neandertals. These c onclusions are based on the hypothesis that the size of the hypoglossal can al is indicative of speech capabilities. This hypothesis is falsified here by the finding of numerous nonhuman primate taxa that have hypoglossal cana ls in the modern human size range, both absolutely and relative to oral cav ity volume. Specimens of Australopithecus afarensis, Australopithecus afric anus, and,Australopithecus boisei also have hypoglossal canals that, both a bsolutely and relative to oral cavity volume, are equal in size to those of modern humans. The basis for the hypothesis that hypoglossal canal size is indicative of speech hiss the assumption that hypoglossal canal size is co rrelated with hypoglossal nerve size, which in turn is related to tongue fu nction. This assumption is probably incorrect, as we found no apparent corr elation between the size of the hypoglossal nerve, or the number of axons i t contains, and the size of the hypoglossal canal in a sample of cadavers. Our data demonstrate that the size of the hypoglossal canal does not reflec t vocal capabilities or language usage. Thus the date of origin for human l anguage and the speech capabilities of Neandertals remain open questions.