Abstract
The Americas were the last continents to be populated by humans, and their colonization represents a very interesting chapter in our species' evolution in which important issues are still contentious or largely unknown. One difficult topic concerns the details of the early peopling of Beringia, such as for how long it was colonized before people moved into the Americas and the demography of this occupation. A recent work using mitochondrial genome (mtDNA) data presented evidence for a so called “three-stage model” consisting of a very early expansion into Beringia followed by ∼20,000 years of population stability before the final entry into the Americas. However, these results are in disagreement with other recent studies using similar data and methods. Here, we reanalyze their data to check the robustness of this model and test the ability of Native American mtDNA to discriminate details of the early colonization of Beringia. We apply the Bayesian Skyline Plot approach to recover the past demographic dynamic underpinning these events using different mtDNA data sets. Our results refute the specific details of the “three-stage model”, since the early stage of expansion into Beringia followed by a long period of stasis could not be reproduced in any mtDNA data set cleaned from non-Native American haplotypes. Nevertheless, they are consistent with a moderate population bottleneck in Beringia associated with the Last Glacial Maximum followed by a strong population growth around 18,000 years ago as suggested by other recent studies. We suggest that this bottleneck erased the signals of ancient demographic history from recent Native American mtDNA pool, and conclude that the proposed early expansion and occupation of Beringia is an artifact caused by the misincorporation of non-Native American haplotypes.
Highlights
The Americas were the last continents to be settled by modern humans, most probably from northeast Asia through Beringia, the landmass that connected Asia and the Americas during periods of low sea-level [1]
To better test whether the anomalous early expansion seen in Kitchen et al [20] Bayesian Skyline Plot (BSP) results could be explained by the non-Native American mitochondrial DNA (mtDNA) genomes, we created a set of 10 alignments with nine genomes each randomly selected from the mtDNA genomes from the macrohaplogroups M and N [24]
These results clearly show that the signal for a population expansion that they detected [20] in Native Americans mtDNAs much before Last Glacial maximum (LGM) is an artifact caused by the incorporation of non-Native American haplotypes into the analysis
Summary
The Americas were the last continents to be settled by modern humans, most probably from northeast Asia through Beringia, the landmass that connected Asia and the Americas during periods of low sea-level [1]. Archeological data suggest that the continent was colonized in the late Pleistocene after the Last Glacial maximum (LGM). The scarceness of late Pleistocene human remains in northeast Asia make it difficult to evaluate the details of the population processes in Beringia that led to the peopling of the New World. As an alternative to the study of archeological data, molecular data have been extensively used to infer when and how modern humans colonized the world reviewed in [2,3]. In Native Americans, early studies of mtDNA variation found that these populations have five distinct major mtDNA haplogroups (A, B, C, D and X) [6,7], all of Asian origin
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