Pampush James D
Department of Anthropology, University of Florida, Gainesville, FL, USA.
J Hum Evol. 2015 May;82:127-36. doi: 10.1016/j.jhevol.2015.02.005. Epub 2015 Mar 17.
Chins, which are unique to humans, have generated considerable debate concerning their evolutionary origins, yet a consensus has remained elusive. Many have argued that chins are adaptations for chewing stress, speech, or sexual ornamentation. Alternatively, some have suggested that chins are spandrels-byproducts of selection operating elsewhere in the mandible or face. Lastly, chins could be the product of genetic drift. The questions addressed by this study are: [1] whether chins represent an exceptionally derived morphological condition, and [2] if this can be interpreted as the product of natural selection. These questions are important since the chin is one of the features used to define Homo sapiens in the fossil record. Quantitative measures that capture the degree of chin expression were gathered from a sample of 123 primate taxa, and evolutionary rates associated with these measures were reconstructed in the primate phylogeny. The evolutionary rate associated with these measures was reconstructed to be far higher along the Homo tip (∼77 times greater than the primate background rate of evolution) than elsewhere in the primate phylogeny. These results suggest that human symphyseal morphology is exceptionally derived relative to other primates, and selection has been operational in producing the human chin.
下巴是人类独有的特征，关于其进化起源引发了诸多争论，但至今仍未达成共识。许多人认为下巴是对咀嚼压力、言语或性装饰的适应。也有人认为下巴是下颌骨或面部其他部位选择作用下产生的副产物——附带现象。最后，下巴可能是基因漂变的产物。本研究探讨的问题是：[1]下巴是否代表一种异常衍生的形态状况，以及[2]这是否可被解释为自然选择的产物。这些问题很重要，因为下巴是化石记录中用于定义智人的特征之一。从123个灵长类分类单元的样本中收集了反映下巴表现程度的量化指标，并在灵长类系统发育中重建了与这些指标相关的进化速率。结果显示，与这些指标相关的进化速率在人类分支末端（比灵长类进化的背景速率快约77倍）远比灵长类系统发育的其他部位高。这些结果表明，相对于其他灵长类动物，人类联合部形态是异常衍生的，并且自然选择在人类下巴的形成过程中发挥了作用。
