Jungers William L, Pokempner Amy A, Kay Richard F, Cartmill Matt
Department of Anatomical Sciences, School of Medicine, Stony Brook University, Stony Brook, NY 11794-8081, USA.
Hum Biol. 2003 Aug;75(4):473-84. doi: 10.1353/hub.2003.0057.
The relative size of the hypoglossal canal has been proposed as a useful diagnostic tool for the identification of human-like speech capabilities in the hominid fossil record. Relatively large hypoglossal canals (standardized to oral cavity size) were observed in humans and assumed to correspond to relatively large hypoglossal nerves, the cranial nerve that controls motor function of the tongue. It was suggested that the human pattern of tongue motor innervation and associated speech potential are very different from those of African apes and australopithecines; the modern human condition apparently appeared by the time of Middle Pleistocene Homo. A broader interspecific analysis of hypoglossal canal size in primates conducted in 1999 has rejected this diagnostic and inferences based upon it. In an attempt to resolve these differences of opinion, which we believe are based in part on biased size-adjustments and/or unwarranted assumptions, a new data set was collected and analyzed from 298 extant hominoid skulls, including orangutans, gorillas, chimpanzees, bonobos, siamang, gibbons, and modern humans. Data on the absolute size of the hypoglossal nerve itself were also gathered from a small sample of humans and chimpanzee cadavers. A scale-free index of relative hypoglossal canal size (RHCS) was computed as 100 x (hypoglossal canal area(0.5)/oral cavity volume(0.333)). No significant sexual dimorphism in RHCS was discovered in any species of living hominoid, but there are significant interspecific differences in both absolute and relative sizes of the hypoglossal canal. In absolute terms, humans possess significantly larger canals than any other species except gorillas, but there is considerable overlap with chimpanzees. Humans are also characterized by large values of RHCS, but gibbons possess an even larger average mean for this index; siamang and bonobos overlap appreciably with humans in RHCS. The value of RHCS in Australopithecus afarensis is well within both human and gibbon ranges, as are the indices computed for selected representatives of fossil Homo. Furthermore, the size of the hypoglossal nerve itself, expressed as the mass of nerve per millimeter of length, does not distinguish chimpanzees from modern humans. We conclude, therefore, that the relative size of the hypoglossal canal is neither a reliable nor sufficient predictor of human-like speech capabilities, and paleoanthropology still lacks a quantifiable, morphological diagnostic for when this capability finally emerged in the human career.
舌下神经管的相对大小已被提议作为一种有用的诊断工具，用于在人类化石记录中识别类似人类的语言能力。在人类中观察到相对较大的舌下神经管（根据口腔大小进行标准化），并假定其对应于相对较大的舌下神经，即控制舌头运动功能的颅神经。有人提出，人类舌头运动神经支配模式及相关的语言潜能与非洲猿类和南方古猿有很大不同；现代人类的这种情况显然在中更新世的智人时期就已出现。1999年对灵长类动物舌下神经管大小进行的更广泛的种间分析否定了这一诊断及其基于此的推论。为了解决这些我们认为部分基于有偏差的大小调整和/或无端假设的意见分歧，我们收集并分析了来自298个现存类人猿头骨的新数据集，这些类人猿包括猩猩、大猩猩、黑猩猩、倭黑猩猩、合趾猿、长臂猿和现代人类。还从一小部分人类和黑猩猩尸体样本中收集了舌下神经本身绝对大小的数据。计算了一个无尺度的舌下神经管相对大小指数（RHCS），其计算方式为100×（舌下神经管面积（0.5）/口腔体积（0.333））。在任何现存类人猿物种中均未发现RHCS存在显著的性别二态性，但舌下神经管的绝对大小和相对大小在种间均存在显著差异。从绝对值来看，除了大猩猩外，人类拥有比其他任何物种都显著更大的神经管，但与黑猩猩有相当大的重叠。人类的RHCS值也较大，但长臂猿的该指数平均均值更大；合趾猿和倭黑猩猩的RHCS与人类有明显重叠。阿法南方古猿的RHCS值处于人类和长臂猿的范围内，为选定的化石智人代表计算的指数也是如此。此外，以每毫米长度神经质量表示的舌下神经本身的大小，并不能区分黑猩猩和现代人类。因此我们得出结论，舌下神经管的相对大小既不是类似人类语言能力的可靠预测指标，也不是充分的预测指标，古人类学仍然缺乏一种可量化的形态学诊断方法来确定这种能力最终在人类发展历程中何时出现。
