Ichim Ionut, Kieser Jules, Swain Michael
Department of Oral Sciences, Faculty of Dentistry, Otago University, Dunedin, New Zealand.
Med Hypotheses. 2007;69(1):20-4. doi: 10.1016/j.mehy.2006.11.048. Epub 2007 Feb 5.
One of the most fundamental yet unanswered questions of human evolution is that of the development of the chin. Whereas it is known that the chin, or mentum osseum, is an unique anatomical feature of modern humans that emerged during the Middle and Late Pleistocene, its origin and biomechanical significance are the subjects of intense controversy. Theories range from the suggestion that the chin evolved as a result of progressive reduction of the dental arch, which left it as a protrusion, to the hypothesis that it provided resistance to mandibular bending during mastication. Until now however, no accepted functional explanation of the human chin has emerged. Here, we develop the hypothesis that the actions of the tongue and non-masticatory orofacial muscles may have played a significant role on the development of the human chin. We report numerical simulations of the forces and resultant stresses developed in hypothetical chinned and non-chinned mandibles. Using empirical data and estimates of the forces generated by the human tongue during speech, our hypothesis suggests that the chin might in fact have developed as a result of the actions of the tongue and perioral muscles, rather than as a buttress to withstand masticatory induced stress. This provides a new perspective on the generation of the chin and importantly, suggests that its appearance may be causally related to the development of the human language.
人类进化中最基本却尚未得到解答的问题之一是下巴的发育问题。虽然已知下巴，即骨性颏，是现代人类独有的解剖学特征，出现在更新世中晚期，但其起源和生物力学意义仍是激烈争论的主题。理论范围从认为下巴是由于牙弓逐渐缩小而进化成一个突出物，到认为它在咀嚼时为下颌弯曲提供阻力的假说。然而直到现在，还没有出现关于人类下巴被广泛接受的功能解释。在此，我们提出一个假说，即舌头和非咀嚼性口面部肌肉的作用可能在人类下巴的发育中起到了重要作用。我们报告了对假设有下巴和无下巴下颌骨中产生的力和由此产生的应力的数值模拟。利用经验数据以及对人类说话时舌头产生的力的估计，我们的假说表明，下巴实际上可能是舌头和口周肌肉作用的结果，而不是作为承受咀嚼引起的应力的支撑结构。这为下巴的形成提供了一个新视角，重要的是，表明其出现可能与人类语言的发展有因果关系。
