Topic ID #38523 - posted 7/20/2017 4:28 PM

A genomic view of the peopling of the Americas



Charlie Hatchett

A genomic view of the peopling of the Americas

Pontus Skoglund and David Reich


Very interesting article. Thanks Gisele.



...Under the hypothesis that Native American ancestry

stems from a single founder population that separated

earlier from Eurasian populations, differences in allele

frequencies between Native American groups should

have developed independently from Eurasian allele frequencies.

This simple null hypothesis makes it possible

to explicitly test hypotheses about the number of American

founder populations...”



...Reich et al. [23""] applied this idea to the first comprehensive

genome-wide data from Native American populations (52 populations,

but none from the continental United States), and concluded that at

least three ancestral populations were required to explain

the similarities between Native Americans and East Asians...”


...Central and South America fit a

model of a single founder population...”



...Athabaskan-speaking Chipewyan revealed that

they could not solely have their ancestry from the same

founding population as other Northern-, Meso- and South

American populations...”


And a heavy concentration of mtDNA hg X2...Western Eurasian.



...genome from the remains of a child

(‘Anzick-1’) buried with Clovis artifacts in

western Montana and directly dated to

12,600 before present (BP) [25""]. This child

was consistent with deriving all of his ancestry

from the same founding population as Central

and South Americans...”


Clovis is a technology not a culture.



...This suggests that the present-day structuring of the

main ancestry in Native Americans into northern and

southern lineages [23""] dates back to more than

12,600 years ago [25""]. This event divided the ancestry

of present-day Native Americans into two main streams,

one of which includes the ancestors of present-day

Northern Native Americans analyzed (‘NNA’: including

Cree, Ojibwa, and Algonquin), and the other of which

includes the Anzick individual and present-day Central

American groups and South American groups (‘SA’:

including Mixe, Quechua, and Yaghan)...”



...Diverse population lineages that genetic evidence suggest were present in

Northeast Asia and contributed to the ancestry of present-day Native Americans. These comprise people with ancestry related to present-day Andamanese and Australo-Melanesians (red), people related to present-day East Asians such as Han Chinese (pink), and people related to the 24,000 year old Mal’ta child buried near Lake Baikal (dark blue)...”

Southeast Asia, East Asia and Western Eurasia...today, the Andamanese related

ancestry can be detected as an excess affinity to present-day Amazonians...”



...More recent genome sequencing [28] of the 9000 year old

Kennewick individual did not provide resolution about this issue.

While the genome analysis convincingly showed that the Kennewick

individual had the great majority of its ancestry from the same deep

source as other present-day Native Americans, his affinity to the SA

and NNA lineages remains ambiguous...”


mtDNA X2a



...However, the analysis of the genome of a 24,000 year-old individual

from the Mal’ta site near Lake Baikal in Central Siberia

revealed that this model is untenable. The Mal’ta individual

shared genetic affinities to both European (West

Eurasian) and Native American populations [35""]...”



...However, the data was consistent with a

model in which Native Americans are admixed between

lineages related to Mal’ta on the one hand (between ¼

and ½ of Native American ancestry) and East Asians on

the other hand (Figure 1). Thus, Native Americans and

East Asians do not in fact descend from a common

ancestral population that separated earlier from a lineage

leading to Mal’ta and to West Eurasians [35""]...”



...The major admixture related to the Mal’ta lineage in the ancestry of

all Native Americans is inconsistent with the assumption

of a simple population split between Native Americans

and East Asians that has been the basis for the most

attempts to date to infer the population split times, and

which have suggested dates of around 23,000 years ago

[33,34"]. The substantial contribution of the Mal’ta lineage

to Native Americans may have the effect of upwardly

biasing estimates of the time of divergence of Native

Americans and East Asians...”



...Recently, we carried out a stringent test of the null

hypothesis of a single founding population of Central

and South Americans using genome-wide data from diverse

Native Americans [36""]. We detected a statistically

clear signal linking Native Americans in the Amazonian

region of Brazil to present-day Australo-Melanesians and

Andaman Islanders (‘Australasians’). Specifically, we

found that Australasians share significantly more genetic

variants with some Amazonian populations — including

ones speaking Tupi languages — than they do with other

Native Americans. We called this putative ancient Native

American lineage ‘Population Y’ after Ypykue´ra, which

means ‘ancestor’ in the Tupi language family...”



...We found that the patterns of genomic

variation of present-day Amazonians could be explained

by as little as 2% admixture from an Australasian-related

population, that would thus have penetrated deep inside

the Americas without mixing with the main ancestral

lineage of present-day Native Americans...”









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