Ancient DNA tracks migrations around the Americas

Previous GEITP pages have noted that ancestral Amerindians had diverged from Siberian and East Asian populations around 25,000 ± 1100 years ago, followed by a split (divergence of ancestral Amerindians from Ancient Beringians) between 22,000 and 18,000 years ag). Subsequently, Amerindians diverged (between ~17,500 and 14,600 years ago) into two branches Northern Native Americans and Southern Native Americans. All contemporary and ancient Amerindian individuals, for whom genome-wide data have been generated, prior to the present study [attached], are derived from either the North American or South American branch.

However, there is disagreement over claims of earlier migrations into the Americas possibly related to Australasians or by bearers of a distinctive cranial form (“Paleoamericans”). Whether there were additional splits within the Americas, how many migratory movements north and south took place, and the speed of human dispersal at different times and regions are still being debated. Overall, the degree of population isolation, admixture, or continuity in different geographic regions of the Americas, after initial settlement, is poorly understood.

Authors in the 1st publication [see attached] sequenced 15 ancient human genomes — spanning from Alaska to Patagonia; six were ≥10,000 years old. All were most closely related to Native Americans, including an Ancient Beringian individual, and two morphologically distinct “Paleoamericans.” Authors found evidence of rapid dispersal and early diversification (including previously unknown groups), as people moved south. This resulted in multiple, independent, geographically uneven, migrations — including one that provides clues of a Late Pleistocene (18,000 to 11,700 years ago) Australasian genetic signal, and a later Mesoamerican-related (1500 B.C. to 300 A.D.) expansion. These results portray the complex and dynamic population histories from North to South America..!!

In the 2nd study [attached], authors report genome-wide ancient DNA from 49 individuals forming four parallel time transects in Belize, Brazil, the Central Andes, and the Southern Coneeach dating to at least ~9,000 years ago. The common ancestral population radiated rapidly from just one of the two early branches that contributed to Native Amerindians today. Authors document two previously unappreciated streams of gene flow between North and South America: one affected the Central Andes by ~4,200 years ago, whereas the other explains an affinity between the oldest North American genome (from what is now New Mexico) associated with the Clovis culture and the oldest Central and South Americans from Chile, Brazil, and Belize. However, this was not the primary source for later South Americans, because the other ancient individuals are the result of lineages without specific affinity to the Clovis-associated genome. These data suggest a population replacement that began at least 9,000 years ago and was followed by substantial (complicated) population continuity in multiple regions.    🙁


Cell   15 Nov 2o18; 175, 1185–1197

Science   Moreno-Mayar et al, (2018)

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