DeGusta D, Gilbert W H, Turner S P
Laboratory for Human Evolutionary Studies, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 1999 Feb 16;96(4):1800-4. doi: 10.1073/pnas.96.4.1800.
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 years ago and to assign modern human vocal abilities to Neandertals. These conclusions are based on the hypothesis that the size of the hypoglossal canal is indicative of speech capabilities. This hypothesis is falsified here by the finding of numerous nonhuman primate taxa that have hypoglossal canals in the modern human size range, both absolutely and relative to oral cavity volume. Specimens of Australopithecus afarensis, Australopithecus africanus, and Australopithecus boisei also have hypoglossal canals that, both absolutely 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 was the assumption that hypoglossal canal size is correlated with hypoglossal nerve size, which in turn is related to tongue function. This assumption is probably incorrect, as we found no apparent correlation between the size of the hypoglossal nerve, or the number of axons it 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 reflect vocal capabilities or language usage. Thus the date of origin for human language and the speech capabilities of Neandertals remain open questions.
哺乳动物的舌下神经管传输为舌头提供运动神经支配的神经。舌下神经管的大小此前已被用于将类人语言能力的起源追溯至至少40万年前，并将现代人类的发声能力赋予尼安德特人。这些结论基于这样一种假设，即舌下神经管的大小表明了语言能力。然而，这里发现了众多非人类灵长类分类群，它们的舌下神经管在绝对大小以及相对于口腔容积的相对大小方面都处于现代人类的范围，这一发现证伪了该假设。阿法南方古猿、非洲南方古猿和鲍氏傍人的标本也具有舌下神经管，其绝对大小以及相对于口腔容积的大小都与现代人类的相等。认为舌下神经管大小表明语言能力这一假设的依据是，假定舌下神经管大小与舌下神经大小相关，而舌下神经大小又与舌头功能有关。但这一假定可能是错误的，因为在一组尸体样本中，我们未发现舌下神经的大小或其所含轴突数量与舌下神经管大小之间存在明显关联。我们的数据表明，舌下神经管的大小并不能反映发声能力或语言使用情况。因此，人类语言的起源时间以及尼安德特人的语言能力仍然是悬而未决的问题。
