Angela
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Reich and Haak are in on this one.
"Ancient mitochondrial DNA provides high-resolution time scale of the peopling of the Americas
See:
http://advances.sciencemag.org/content/2/4/e1501385.full
"The exact timing, route, and process of the initial peopling of the Americas remains uncertain despite much research. Archaeological evidence indicates the presence of humans as far as southern Chile by 14.6 thousand years ago (ka), shortly after the Pleistocene ice sheets blocking access from eastern Beringia began to retreat. Genetic estimates of the timing and route of entry have been constrained by the lack of suitable calibration points and low genetic diversity of Native Americans. We sequenced 92 whole mitochondrial genomes from pre-Columbian South American skeletons dating from 8.6 to 0.5 ka, allowing a detailed, temporally calibrated reconstruction of the peopling of the Americas in a Bayesian coalescent analysis. The data suggest that a small population entered the Americas via a coastal route around 16.0 ka, following previous isolation in eastern Beringia for ~2.4 to 9 thousand years after separation from eastern Siberian populations. Following a rapid movement throughout the Americas, limited gene flow in South America resulted in a marked phylogeographic structure of populations, which persisted through time. All of the ancient mitochondrial lineages detected in this study were absent from modern data sets, suggesting a high extinction rate. To investigate this further, we applied a novel principal components multiple logistic regression test to Bayesian serial coalescent simulations. The analysis supported a scenario in which European colonization caused a substantial loss of pre-Columbian lineages."
So, the precipitous decline in overall population resulted in extinction of many mtDna lines, even though some survived.
I found this interesting about the various migration waves:
"Genetic studies of Native American populations are complicated by the demographic collapse and presumed major loss of genetic diversity following European colonization at the end of the 15th century (7). However, geographically widespread signals of low diversity and shared ancestry (8–13)—particularly striking in maternally inherited mitochondrial and paternally inherited Y-chromosome sequence data—suggest that small founding groups possibly initially entered the Americas in a single migration event that gave rise to most of the ancestry of Native Americans today (9, 12, 14). In contrast, the distribution of some of the rare founding mitochondrial haplogroups (D4h3a along the Pacific coast of North and South America, and X2a in northwestern North America) suggests that distinct migrations along the coastal route and the ice-free corridor occurred within less than 2000 years (15). Recent studies have identified a weak Australasian genomic signature in several Native American groups from the Amazon, compatible with two founding migrations (16), although the Australasian gene flow may have occurred after the initial peopling (17). Irrespective of the number of migration waves, the founding population appears to have rapidly grown and expanded southward (8, 14, 18), with low levels of gene flow between areas following initial dispersion (12, 14)."
"The estimated times to most recent common ancestor (TMRCA) for haplogroups A2, B2, C1, D1, and D4h3a were highly synchronous (Fig. 3 and fig. S8), confirming previous interpretations that all five haplogroups were part of one initial population."
Whether they're right about the timing I don't know.
I was very interested to see if they said anything else about mtDna X2a, which they maintain may have arrived in the last 2000 years, but I couldn't find anything. With whom and from what direction did it come?
"Ancient mitochondrial DNA provides high-resolution time scale of the peopling of the Americas
See:
http://advances.sciencemag.org/content/2/4/e1501385.full
"The exact timing, route, and process of the initial peopling of the Americas remains uncertain despite much research. Archaeological evidence indicates the presence of humans as far as southern Chile by 14.6 thousand years ago (ka), shortly after the Pleistocene ice sheets blocking access from eastern Beringia began to retreat. Genetic estimates of the timing and route of entry have been constrained by the lack of suitable calibration points and low genetic diversity of Native Americans. We sequenced 92 whole mitochondrial genomes from pre-Columbian South American skeletons dating from 8.6 to 0.5 ka, allowing a detailed, temporally calibrated reconstruction of the peopling of the Americas in a Bayesian coalescent analysis. The data suggest that a small population entered the Americas via a coastal route around 16.0 ka, following previous isolation in eastern Beringia for ~2.4 to 9 thousand years after separation from eastern Siberian populations. Following a rapid movement throughout the Americas, limited gene flow in South America resulted in a marked phylogeographic structure of populations, which persisted through time. All of the ancient mitochondrial lineages detected in this study were absent from modern data sets, suggesting a high extinction rate. To investigate this further, we applied a novel principal components multiple logistic regression test to Bayesian serial coalescent simulations. The analysis supported a scenario in which European colonization caused a substantial loss of pre-Columbian lineages."
So, the precipitous decline in overall population resulted in extinction of many mtDna lines, even though some survived.
I found this interesting about the various migration waves:
"Genetic studies of Native American populations are complicated by the demographic collapse and presumed major loss of genetic diversity following European colonization at the end of the 15th century (7). However, geographically widespread signals of low diversity and shared ancestry (8–13)—particularly striking in maternally inherited mitochondrial and paternally inherited Y-chromosome sequence data—suggest that small founding groups possibly initially entered the Americas in a single migration event that gave rise to most of the ancestry of Native Americans today (9, 12, 14). In contrast, the distribution of some of the rare founding mitochondrial haplogroups (D4h3a along the Pacific coast of North and South America, and X2a in northwestern North America) suggests that distinct migrations along the coastal route and the ice-free corridor occurred within less than 2000 years (15). Recent studies have identified a weak Australasian genomic signature in several Native American groups from the Amazon, compatible with two founding migrations (16), although the Australasian gene flow may have occurred after the initial peopling (17). Irrespective of the number of migration waves, the founding population appears to have rapidly grown and expanded southward (8, 14, 18), with low levels of gene flow between areas following initial dispersion (12, 14)."
"The estimated times to most recent common ancestor (TMRCA) for haplogroups A2, B2, C1, D1, and D4h3a were highly synchronous (Fig. 3 and fig. S8), confirming previous interpretations that all five haplogroups were part of one initial population."
Whether they're right about the timing I don't know.
I was very interested to see if they said anything else about mtDna X2a, which they maintain may have arrived in the last 2000 years, but I couldn't find anything. With whom and from what direction did it come?