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Currently the archaeological, geographic, and ethnographic evidence indicates that the ancestors of today’s American Indians migrated into the Americas from north Asia some 15,000-13,000 years ago. This evidence has long been the basis for standard theories concerning the peopling of the Americas. However, with the development of new technologies comes new evidence; evidence that at times challenges long held theories. Such a restructuring of our knowledge is currently taking place, changing how we understand the early history of people in the Americas. With the advent of molecular genetic equipment and methods, theories concerning the early peopling of the Americas are slowly beginning to push back the date of first entry.
Two types of data are the basis for the molecular genetic evidence, which argues that the initial migration into the Americas originated somewhere in south-central Siberia between 35,000–20,000 years before present. These dates are much earlier than previous estimates based on radiocarbon analysis of archaeological material. Using the frequency of genetic markers found in either mitochondrial DNA (mtDNA) or Y chromosome DNA, the new understanding of the peopling of the Americas argues that the first migrants followed what has come to be called the Northwest Coast route. These early north Asian migrants moved along the Northwest coast of North America until they were south of the Pleistocene glacial ice sheets that covered much of Canada, at which point they expanded into all continental regions. These people are hypothesized to have brought mtDNA haplogroups A-D and Y chromosome haplogroup P-M45a and Q-242/Q-M3 haplotypes. A second, slightly later migration is hypothesized to have entered the Americas somewhat later, bringing mtDNA haplogroup X and Y chromosome haplogroups P-M45b, C-M130, and R1a1-M17, possibly using an interior route. A third and final migration is hypothesized to have taken place after the last glacial maximum in northern North America.
Based on this genetic evidence, it has also been possible to geographically position the area in north Asia where these early migrants most likely came from. For example, the major Y haplotype present in most American Indians has been traced back to recent ancestors common with Siberians, namely, the Kets and Altaians from the Yenissey River Basin and Altai Mountains, respectively. Going further back, the next common ancestor in the genetic lineage gave rise also to Caucasoid Y chromosomes, probably from the central Eurasian region. The mtDNA evidence argues for a similar conclusion, although it places the homeland of the north Asian first Americans somewhere between contemporary Mongolia and Siberia, most likely around present-day Tibet and Ulan Bator. This is based on evidence indicating that all mtDNA lineages can be found in Siberia except lineage B, which is found in the Ulan Bator region of north Asia.
No molecular genetic evidence has been found to support theories that argue Pleistocene Europeans, ocean going Polynesians, sea-faring Persians, or other cultural groups migrated to the Americas. In fact, the molecular genetic evidence is fairly conclusive: today’s American Indian, Alaskan Native, and First Nation people’s ancestors originally migrated to the Americas from north Asia. The exact times when these migrations took place are still under dispute, but the molecular genetic evidence strongly argues for a greater time depth of human occupation in the Americas.