Who came first – the Paleo- or Native American?

In yet another infamous Science vs Nature race, two studies published this Tuesday toss more cans of worms at the ongoing debate about the founding of the Americas – with disparate findings. Uh oh.

Representatives of six native American tribes bury the remains of Anzick-I. Image courtesy:http://hereandnow.wbur.org/2014/07/22/clovis-boy-reburied

Skoglund et al. Nature (2015) Genetic evidence for two founding populations of the Americas

In further evidence for what’s come to be known as the Paleoamerican model, Skoglund et al. (2015) analyzed genomic ancestries of 63 individuals in 21 Native American populations with little evidence of European or African ancestries at 600,000 SNP’s by computing f4 statistics, and reject the null hypothesis that Native Americans descend from one single homogenous population after divergence from other discernible distinct populations across the world. Native Americans also cluster with Amazonian, Mesoamerican, Australasian, and other Pacific island populations. Further analyses also indicate the possibilities of (a) Amazonians descending from an ancestor of Anadamanese and other Australasian populations, perhaps more plausibly, (b) ancestral admixture of Amazonians and ancestors of Native Americans, termed the population “Y”. While questions remain about how the “Y” populations migrated into South America, this study warrants genomic analyses of more ancient remains to fill up the blanks.

Raghavan et al. Science (2015) Genomic evidence for the Pleistocene and recent population history of Native Americans

Raghavan et al. (2015) analyze whole genome sequences of 31 present day individuals from the Americas, Siberia, and Oceania (with a similar sampling strategy as Skoglund et al. (2015)), 23 ancient genomes from the Americas, and SNP genotypes from 79 individuals from the Americas and Siberia. Admixture analyses indicate structuring of all Native Americans into one cluster (at K=4), indicating common ancestry of all Native Americans. At K=15, however, some Native American individuals are indicative of shared ancestry with Anzick-1 (from the Clovis site), with others clustering with Siberians, further ascertained by admixture graph analyses. Estimation of time of divergence between Native Americans, Siberians, and Han Chinese indicated a unanimous splitting time of around ~23,000 ybp for both Native American groups. Analyses of SNP chip data however reveals a similar story as reported by Skoglund et al. (2015), indicative of an ancestral admixture event which resulted in Oceanic ancestry in some Native American populations, however purportedly more recent – particularly after the peopling of the Americas. Studying the ancient genomes also revealed no evidence of admixture of Oceanic populations into ancient American peoples, further indicating no support for the Paleoamerican model.

References

Skoglund et al. “Genetic evidence for two founding populations of the Americas.” Nature (2015) DOI: http://dx.doi.org/10.1038/nature14895

Raghavan et al. “Genomic evidence for the Pleistocene and recent population history of Native Americans.” Science (2015) DOI: http://dx.doi.org/10.1126/science.aab3884

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About Arun Sethuraman

I am a computational biologist, and I build statistical models and tools for population genetics. I am particularly interested in studying the dynamics of structured populations, genetic admixture, and ancestral demography.
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