What uniparental genetic markers tell us about the prehistoric human colonization of the Americas
OBJECTIVESFrom the perspective of uniparental markers, the view of the human prehistoric settlement of America is that it resulted from a single main migration after the Last Glacial Maximum, following a long or short period of genetic isolation in Beringia. Ancient DNA and whole genome analyses have confirmed this view. My objective here is to demonstrate that humans entered America before the LGM and that the documented post-LGM expansions began in South instead North America. METHODSIn this work, I have reanalyzed all publicly available mitochondrial DNA and Y-chromosome haplogroups in the American population using simple phylogenetic and phylogeographic methodologies. RESULTSThe arrival of the American settlers occurred more than 30,000 years ago, preceding the LGM. As genomic studies have uncovered, at least two Asian populations contributed to the ancestry of the immigrant population. Low population density and climatic deterioration led to a long period of demographic eclipse, during which small bands of hunter-gatherers made long journeys in search of favorable niches. After the LGM, the climate improved, and demographic expansions occurred in multiple independent centers. The founding and expansion ages of the uniparental haplogroups indicate that these centers were in South America, particularly the Colombian isthmus, the Andean region, the Southern Cone, and the Amazon. Subsequent dispersals occurred in North America, one involving mitochondrial haplogroups A2, C1, and D1, but not B2, and another, of lesser magnitude, represented by the expansion of haplogroups C4c and X2a. DISCUSSIONThis work offers a previously unexplored model for the colonization of the Americas. RESEARCH HIGHLIGHTSSince the past century, the predominant molecular genetic theory explaining the prehistoric human colonization of the Americas has been that Asian hunter-gatherers entered North America across a Beringia land bridge during or after the LGM. Complementary hypotheses have resolved the evident problem of crossing the existing ice sheets at that epoch, such as the LGM Beringian standstill or the existence of a Pacific maritime coastal route during that period. In contradiction, here, the reanalysis of uniparental genes shows that people were already in America before the LGM and that the post-LGM expansions detected with all kinds of molecular markers occurred first in the southern areas of the continent instead of North America.