Science2014-06-10 3:44 PM

关于谁是第一批美洲人有了新线索 Late Pleistocene Human Skeleton and mtDNA Link Paleoamericans and Modern Native Americans 

论文摘要 

破译居住于美洲的第一批人的祖先一直是一个挑战。根据遗传学,现代美洲原住民被认为是西伯利亚人的后裔,他们在2万6000年至1万8000年前进入到白令陆桥的东部。这些人——即最早的美洲人——接着向南部扩散。尽管这一理念得到广泛的支持,然而,最早美洲人的祖先是谁仍然存在争议,因为最早的美洲人骨骼的面部特征与那些现代美洲原住民的面部特征不怎么像。这导致人们猜测,第一批美洲人与美洲原住民也许来自不同的故乡。令这一谜团变得更为复杂的是,人们一直很难找到完整的古美洲人骨骼来做进一步的研究。 

然而现在,James Chatters及其同事报告发现了一具近乎完整的晚更新世时期的人类骨骼,它深藏于墨西哥东尤卡坦半岛上的一个洞穴系统内的一个被水淹没的腔室内,该洞穴系统只有潜水员才能进入。很久之前,人与动物掉入该洞穴并且被困在那里。接着,在大约1万年前,全球冰川开始融化,也让水填满了洞穴。Chatters等人在那里发现的几近完整的骨骼是一个小号的大约15或16岁大的女性骨骼。根据对她的牙釉质的放射性碳年代测定及对她的骨矿物质沉积分析,研究人员推断她的遗骸至少有1.2万年之久。她拥有最早美洲人的独特颅面形态,但为了更多地了解她的祖先以及其与现代美洲原住民可能有的联系,研究人员从她的磨牙中提取了DNA。他们接下来分析了该女孩的线粒体DNA(mtDNA),这是一种检验人群相关性的有用工具。他们的分析揭示了一个与现代美洲原住民相同的单倍体型。 

这一遗传学特征只发生在美洲,可能是在白令陆桥中发展成的。该样本显示,更新世时代的有着源自白令陆桥mtDNA的个体的行迹遍及美洲各地,并一直向南至墨西哥。文章的作者说,至关重要的是,它显示,尽管在颅面形状上与现代美洲原住民存在着差异,这一早期的美洲女性与他们是有关系的;在颅面形状中的差异可能被最好地解释为白令陆桥人与其西伯利亚祖先发生分化之后的进化改变。他们的研究提示,美洲并非由来自欧亚不同地区的独立迁徙事件所拓殖的。相反,最早的美洲人所代表的是从白令陆桥向外扩展的一个人群。这一发现支持古美洲人和美洲原住民源自某个单一来源的人群。

Abstract 

Because of differences in craniofacial morphology and dentition between the earliest American skeletons and modern Native Americans, separate origins have been postulated for them, despite genetic evidence to the contrary. We describe a near-complete human skeleton with an intact cranium and preserved DNA found with extinct fauna in a submerged cave on Mexico’s Yucatan Peninsula. This skeleton dates to between 13,000 and 12,000 calendar years ago and has Paleoamerican craniofacial characteristics and a Beringian-derived mitochondrial DNA (mtDNA) haplogroup (D1). Thus, the differences between Paleoamericans and Native Americans probably resulted from in situ evolution rather than separate ancestry. 

Editor's Summary 

American Beauty 

Modern Native American ancestry traces back to an East Asian migration across Beringia. However, some Native American skeletons from the late Pleistocene show phenotypic characteristics more similar to other, more geographically distant, human populations. Chatters et al. (p. 750) describe a skeleton with a Paleoamerican phenotype from the eastern Yucatan, dating to approximately 12 to 13 thousand years ago, with a relatively common extant Native American mitochondrial DNA haplotype. The Paleoamerican phenotype may thus have evolved independently among Native American populations. 

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