Complex processes in the settling of the Americas The expansion into the Americas by the ancestors of present day Native Americans has been difficult to tease apart from analyses of present day populations. To understand how humans diverged and spread across North and South America, Moreno-Mayar et al. sequenced 15 ancient human genomes from Alaska to Patagonia. Analysis of the oldest genomes suggests that there was an early split within Beringian populations, giving rise to the Northern and Southern lineages. Because population history cannot be explained by simple models or patterns of dispersal, it seems that people moved out of Beringia and across the continents in a complex manner. Science, this issue p. eaav2621 Ancient genomes from the Americas show a complex genetic history giving rise to present-day diversity. INTRODUCTION Genetic studies of the Pleistocene peopling of the Americas have focused on the timing and number of migrations from Siberia into North America. They show that ancestral Native Americans (NAs) diverged from Siberians and East Asians ~23,000 years (~23 ka) ago and that a split within that ancestral lineage between later NAs and Ancient Beringians (ABs) occurred ~21 ka ago. Subsequently, NAs diverged into northern NA (NNA) and southern NA (SNA) branches ~15.5 ka ago, a split inferred to have taken place south of eastern Beringia (present-day Alaska and western Yukon Territory). RATIONALE Claims of migrations into the Americas by people related to Australasians or by bearers of a distinctive cranial morphology (“Paleoamericans”) before the divergence of NAs from Siberians and East Asians have created controversy. Likewise, the speed by which the Americas were populated; the number of basal divergences; and the degrees of isolation, admixture, and continuity in different regions are poorly understood. To address these matters, we sequenced 15 ancient human genomes recovered from sites spanning from Alaska to Patagonia; six are ≥10 ka old (up to ~18× coverage). RESULTS All genomes are most closely related to NAs, including those of two morphologically distinct Paleoamericans and an AB individual. However, we also found that the previous model is just a rough outline of the peopling process: NA dispersal gave rise to more complex serial splitting and early population structure—including that of a population that diverged before the NNA-SNA split—as well as admixture with an earlier unsampled population, which is neither AB nor NNA or SNA. Once in the Americas, SNAs spread widely and rapidly, as evidenced by genetic similarity, despite differences in material cultural, between >10-ka-old genomes from North and South America. Soon after arrival in South America, groups diverged along multiple geographic paths, and before 10.4 ka ago, these groups admixed with a population that harbored Australasian ancestry, which may have been widespread among early South Americans. Later, Mesoamerican-related population(s) expanded north and south, possibly marking the movement of relatively small groups that did not necessarily swamp local populations genetically or culturally. CONCLUSION NAs radiated rapidly and gave rise to multiple groups, some visible in the genetic record only as unsampled populations. At different times these groups expanded to different portions of the continent, though not as extensively as in the initial peopling. That the early population spread widely and rapidly suggests that their access to large portions of the hemisphere was essentially unrestricted, yet there are genomic and archaeological hints of an earlier human presence. How these early groups are related or structured, particularly those with Australasian ancestry, remains unknown. Rapid expansion, compounded by the attenuating effect of distance and, in places, by geographic and social barriers, gave rise to complex population histories. These include strong population structure in the Pacific Northwest; isolation in the North American Great Basin, followed by long-term genetic continuity and ultimately an episode of admixture predating ~0.7 ka ago; and multiple independent, geographically uneven migrations into South America. One such migration provides clues of Late Pleistocene Australasian ancestry in South America, whereas another represents a Mesoamerican-related expansion; both contributed to present-day South American ancestry. NA dispersal and divergence over time. Schematic representation of the sampling points included in this study (circles) and our main conclusions (presented geographically and temporally). (A) Population history of the basal AB, NNA, and SNA branches in North America. kya, thousand years ago. (B) Early, rapid dispersal of SNAs across the continent (~14 ka ago). (C) Recent Mesoamerican-related expansion north and south. Arrows do not correspond to specific migration routes. Studies of the peopling of the Americas have focused on the timing and number of initial migrations. Less attention has been paid to the subsequent spread of people within the Americas. We sequenced 15 ancient human genomes spanning from Alaska to Patagonia; six are ≥10,000 years old (up to ~18× coverage). All are most closely related to Native Americans, including those from an Ancient Beringian individual and two morphologically distinct “Paleoamericans.” We found evidence of rapid dispersal and early diversification that included previously unknown groups as people moved south. This resulted in multiple independent, geographically uneven migrations, including one that provides clues of a Late Pleistocene Australasian genetic signal, as well as a later Mesoamerican-related expansion. These led to complex and dynamic population histories from North to South America.

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美洲早期人类的传播

美洲定居的复杂过程 当今美洲原住民的祖先向美洲扩张的过程，除了对当今人口的分析之外，很难梳理清楚。为了了解人类如何在北美和南美分化和传播，Moreno-Mayar 等人。对从阿拉斯加到巴塔哥尼亚的 15 个古代人类基因组进行了测序。对最古老的基因组的分析表明，白令种群内部出现了早期分裂，产生了北方和南方的谱系。由于人口历史不能用简单的模型或散布模式来解释，因此人们似乎以复杂的方式迁出白令岛并穿越各大洲。科学，这个问题 p。eaav2621 来自美洲的古代基因组显示出复杂的遗传历史，导致了当今的多样性。介绍 美洲更新世人口的遗传研究集中在从西伯利亚迁移到北美的时间和数量。他们表明，祖先美洲原住民 (NAs) 在大约 23,000 年前 (~23 ka) 之前与西伯利亚人和东亚人发生了分歧，并且在大约 21 ka 之前，后来的 NAs 和古代白令人 (ABs) 之间的祖先谱系中发生了分裂。随后，北美地区在大约 15.5 ka 前分裂为北北美 (NNA) 和南北美 (SNA) 分支，推测发生在白令岛东部（今阿拉斯加和育空地区西部）以南的分裂。基本原理 在 NA 与西伯利亚人和东亚人发生分歧之前，与澳大拉西亚人有关的人或具有独特颅骨形态的人（“古美洲人”）移民到美洲的说法引起了争议。同样地，美洲人口的增长速度；基础分歧的数量；并且对不同地区的孤立、混合和连续性的程度知之甚少。为了解决这些问题，我们对从阿拉斯加到巴塔哥尼亚的地点回收的 15 个古代人类基因组进行了测序；六个≥10 ka（高达~18 倍覆盖率）。结果 所有基因组都与 NA 最密切相关，包括两个形态不同的古美洲人和一个 AB 个体的基因组。然而，我们也发现之前的模型只是人口形成过程的一个粗略轮廓：NA 扩散导致了更复杂的序列分裂和早期种群结构——包括在 NNA-SNA 分裂之前分化的种群结构——以及与较早的未抽样总体（既不是 AB 也不是 NNA 或 SNA）混合。一到美洲，SNA 广泛而迅速地传播，正如遗传相似性所证明的那样，尽管物质文化存在差异，但来自北美和南美 > 10 ka 的基因组之间存在差异。抵达南美洲后不久，群体沿着多条地理路径分化，在 10.4 ka 之前，这些群体与拥有澳大拉西亚血统的人群混合在一起，这可能在早期南美​​人中很普遍。后来，中美洲相关人口向北和向南扩张，可能标志着相对较小的群体的迁移，这些群体不一定在遗传或文化上淹没当地人口。结论 NAs 迅速辐射并产生多个群体，其中一些在遗传记录中仅作为未采样的群体可见。在不同时期，这些团体扩展到大陆的不同地区，虽然不像最初的人那样广泛。早期人口广泛而迅速地传播表明他们进入半球的大部分地区基本上是不受限制的，但有基因组和考古学的迹象表明更早的人类存在。这些早期群体是如何相关或结构化的，尤其是那些具有澳大利亚血统的群体，仍然未知。快速扩张，加上距离的衰减效应，以及在某些地方，地理和社会障碍，导致复杂的人口历史。其中包括太平洋西北部强大的人口结构；在北美大盆地隔离，随后是长期的遗传连续性，最终在约 0.7 ka 前出现混合事件；以及多次独立的、地理上不均衡的迁徙到南美洲。一次这样的迁徙提供了南美洲晚更新世澳大拉西亚血统的线索，而另一次则代表了与中美洲相关的扩张；两者都促成了当今的南美血统。随着时间的推移，NA 的分散和发散。本研究中包含的采样点（圆圈）和我们的主要结论（在地理和时间上呈现）的示意图。(A) 北美基础 AB、NNA 和 SNA 分支的种群历史。kya，千年前。(B) SNA 在整个大陆的早期快速传播（约 14 ka 前）。(C) 最近与中美洲相关的南北扩张。箭头不对应特定的迁移路线。对美洲人口的研究集中在初始迁移的时间和数量上。人们对随后在美洲境内的传播的关注较少。我们对从阿拉斯加到巴塔哥尼亚的 15 个古代人类基因组进行了测序；六个是≥10,000 岁（高达 ~18 倍的覆盖范围）。所有这些都与美洲原住民关系最密切，包括来自古代白令个人和两个形态不同的“古美洲人”。我们发现了快速分散和早期多样化的证据，其中包括随着人们向南迁移，以前未知的群体。这导致了多次独立的、地理上不均匀的迁徙，包括提供晚更新世澳大利亚遗传信号线索的迁徙，以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。我们对从阿拉斯加到巴塔哥尼亚的 15 个古代人类基因组进行了测序；六个是≥10,000 岁（高达 ~18 倍的覆盖范围）。所有这些都与美洲原住民关系最密切，包括来自古代白令个人和两个形态不同的“古美洲人”。我们发现了快速分散和早期多样化的证据，其中包括随着人们向南迁移，以前未知的群体。这导致了多次独立的、地理上不均衡的迁徙，包括提供晚更新世澳大利亚遗传信号线索的迁徙，以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。我们对从阿拉斯加到巴塔哥尼亚的 15 个古代人类基因组进行了测序；六个是≥10,000 岁（高达 ~18 倍的覆盖范围）。所有这些都与美洲原住民关系最密切，包括来自古代白令个人和两个形态不同的“古美洲人”。我们发现了快速分散和早期多样化的证据，其中包括随着人们向南迁移，以前未知的群体。这导致了多次独立的、地理上不均匀的迁徙，包括提供晚更新世澳大利亚遗传信号线索的迁徙，以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。包括来自古代白令个人和两个形态不同的“古美洲人”的人。我们发现了快速分散和早期多样化的证据，其中包括随着人们向南迁移，以前未知的群体。这导致了多次独立的、地理上不均匀的迁徙，包括提供晚更新世澳大利亚遗传信号线索的迁徙，以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。包括来自古代白令个人和两个形态不同的“古美洲人”的人。我们发现了快速分散和早期多样化的证据，其中包括随着人们向南迁移，以前未知的群体。这导致了多次独立的、地理上不均匀的迁徙，包括提供晚更新世澳大利亚遗传信号线索的迁徙，以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。以及后来与中美洲相关的扩张。这些导致了从北美到南美的复杂而动态的人口历史。