Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans

摘要

The origins of the First Americans remain contentious. Although Native Americans seem to be genetically most closely related to east Asians, there is no consensus with regard to which specific Old World populations they are closest to. Here we sequence the draft genome of an approximately 24,000-year-old individual (MA-1), from Mal'ta in south-central Siberia, to an average depth of 1×. To our knowledge this is the oldest anatomically modern human genome reported to date. The MA-1 mitochondrial genome belongs to haplogroup U， which has also been found at high frequency among Upper Palaeolithic and Mesolithic European hunter-gatherers, and the Y chromosome of MA-1 is basal to modern-day western Eurasians and near the root of most Native American lineages. Similarly, we find autosomal evidence that MA-1 is basal to modern-day western Eurasians and genetically closely related to modern-day Native Americans, with no close affinity to east Asians. This suggests that populations related to contemporary western Eurasians had a more north-easterly distribution 24,000 years ago than commonly thought. Furthermore, we estimate that 14 to 38% of Native American ancestry may originate through gene flow from this ancient population. This is likely to have occurred after the divergence of Native American ancestors from east Asian ancestors, but before the diversification of Native American populations in the New World. Gene flow from the MA-1 lineage into Native American ancestors could explain why several crania from the First Americans have been reported as bearing morphological characteristics that do not resemble those of east Asians. Sequencing of another south-central Siberian, Afontova Gora-2 dating to approximately 17,000 years ago, revealed similar autosomal genetic signatures as MA-1, suggesting that the region was continuously occupied by humans throughout the Last Glacial Maximum. Our findings reveal that western Eurasian genetic signatures in modern-day Native Americans derive not only from post-Columbian admixture, as commonly thought, but also from a mixed ancestry of the First Americans.%最早的美洲人是从哪里来的，他们是谁？在这两个问题上，对遗传和考古证据的解读都会引起争议。来自中南西伯利亚Mal'ta的一个24,000年前的人体标本的基因组草图（迄今所报告的最早的现代人类基因组序列）的发表，也许能帮助澄清问题。Eske Willerslev及同事发现，来自Mal'ta的这个人与当今的美洲土著人和最初至当今的西方欧亚人在遗传上密切相关，但与东亚人关系不大。这意味着，与西方欧亚人有关的人群过去的分布要比人们普遍认为的更偏向东北。作者估计，14%至38%的美洲土著人祖先起源于古代这—Mal'ta人群，因此他们的祖先不是东亚人、而是西方欧亚人，这也许可解释为什么最早美洲人的几个头盖骨都曾被报告说具有非东亚人特征。