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Early Colonization of the Americas

Although a large volume of literature relative to the colonization of the Americas has been generated over the past three decades,some aspects of these studies are still in the embryonic stage.People could have walked across the emergent lands of Beringa from NE Siberia to Alaska  from ca 40000-9000 BCE,when conditions were favourable.Except for a relatively narrow channel by the Siberian coastline,which provided a conduit to an inland sea,the Aleutian Islands were the approximate southern extent of Beringia during the Last Glacial Maximum [LGM] ca 23000-16000 BCE,cal.A number of research articles have suggested,that even during the LGM there was wild terrestrial game to supplement natural marine resources proximal to the shoreline.Various analyses [eg:beetles] imply that climatic conditions along the southern shores of Beringia were not overly harsh during some phases of the LGM.Elias [1997] contends that lowland portions of this region were covered in Mesic birch and grominoid during this era.Dry grominoidtundra vegetation grew on the uplands of the Seward Peninsula [Gretehaus,2001].Brown bears were reported to have recolonized Beringia ca 22450 +/-650a,cal’05,[P Mattews,2004].This lends credence to the premise that the southern lowlands of Beringia had sufficient natural resources to sustain nomadic foragers during at least some periods of the LGM,when the climate was highly variable.Fluctuations in the carrying capacity ofBeringia probably exerted some influence on migration patterns to the New World.

The Yana River flows northward about 880km through NE Siberia to the Laptec Sea.Hunter-gatherers used the Yana game river crossing site about 71 degrees N ca 30090+/-210a,cal’07.Their stone tool industry varied from the lithic artifacts of the later Duuktai cultural sites [V Pitulka ,2004].Mammal bones,which had been modified by humans,date to 29175-28260 BCE at the Old Crow River site and to 27460 +/-2200a,cal’05,at the Blue Caves in the same region of the Canadian Yukon [J Cinq Mars,2002].There is not sufficient data to ascertain,whether these early hunter-gatherers in northern Canada became extinct,returned to Beringia or treked to the southern USA before the Laurentide and Cordilleran  ice sheets merged during the LGM to block the inland conduit to the south.There are no indications that the clade 4 brown bear occupied Beringia post ca 33200 BCE,cal’05.The well preserved cranial fragments of a clade 4 brown bear were retrieved from Edmonton,Alberta,Canada.The AMS age of these fossils are estimated at 28890 BCE +/-1000a,cal’07 [P Matheus,2004],which is broadly coeval with the age of the butchered mammal bones at the Old Crow River site.Since bears could travel south along the inland route east of the Rocky Mountains prior to the LGM,it is not inconceivable that Palaeolithic humans could not have utilized the same passage south.Glacial advances and retreats have probably minimized traces of any attempts,that may have been made to colonize Canada and the northern USA prior to 24000 BCE.

The Cordilleran ice sheets covered most of British Columbia,Canada, during the last ice age.Portions of  the northern Yukon and Alaska,where the precipitation rates were low,were not glaciated. T Keifer [2005] and M Sarthien [2006] attempted to reconstruct the climatic patterns along the northern and eastern  Pacific Ocean seaboard post ca 17000 BCE.Collation of their research results that generally moderate weather conditions prevailed from ca 16200—15200,14800-14500,and 13200-12650 BCE along the southern coasts of Beringia and the western shoreline of British Columbia.People could have migrated to North America during any of these periods.There may have been an earlier window of opportunity during the LGM.Mandryk [2001] proposed that the north Pacific and Gulf of Alaska might have been ice free during the last glacial era.Initial deglaciationmay have commenced at some seaboard locales ca 1700-16000 BCE.D Mann reported large ice free areas on Kodiak Island and at least one on the Alaska Peninsula ca 1800-15000 BCE.There is palaeocogical evidence of treeless herb and dwarf shrub tundra on Washington State’s Olympic Peninsula from ca 16370-14020 BCE.Sedge grasses, herbs and dwarf shrubs were recorded in NE Haidi Gwaii from ca 17000-13500 BCE. A twig in ponded sediments on Graham Island dates to ca 16090 BCE +/-700a,cal’07.A partial bear femur on Moseby Island [ca 15940 BCE +/- 70a,cal'07] suggests that humans could have survived on some areas of Haidi Gwaii for short periods of time [D Fedjectal, 2005]. Today it is possible to drift on the Kuro Siwo current from Japan to Alaska or British Columbia.Numerous Japanese fishermen have survived the voyage [Hornell,1945],which could have been shorter,when sea level was lower.

Integration of the above data indicates that newcomers in water craft could have island hopped along the west coast of British Columbia from Beringia to warmer lands to the south utilizing the available marine resources during favourable climatic conditions post 16200 BCE,cal.The oldest known site proximal to the western seaboard is Monte Verde,Chili,which was occupied ca 13000 BCE,cal’07 [T Dillehay,1997].

There are at least 4 sites distal to the west coast with reasonable evidence of earlier occupation.These include Meadowcroft,Pa,ca 16000 BCE or earlier [Adovascio,1999]:Cactus Creek,Va,ca 17000 BCE [J McAvoy,2000]:Saltville Valley,Va,ca 14000BCE,[J Mcdonald,1999]:and Aubrey,Texas,ca 14750? BCE,cal’05 [Taylor,1996].The chronologies at these excavations have not gained the same acceptance as those for Monte Verde.The prevalence of pre-Clovis sites east of the Rocky Mountains can not be ignored.If the age determinations for the basal cultural horizons at Meadowcroft and Cactus Creek are reasonably accurate,the first American settlers could have arrived before the LGM and sought refuge from the cold temperatures in the southern USA. Alternately,there is a remote possibility.that colonists may have taken advantage of a warm phase during the LGM to venture south to California in boats,before trekking to the eastern USA [snow in the Rockies would have been a formidable barrier].The third and least likely option is that marine foragers travelled along the edge of the ice sheets from Europe to America.The huge ice age tides offshore from Labrador would have made such an undertaking very high risk.It is difficult to rationalize why people would make such a long,perilous journey to an unknown destination [on a clear day the mountains of Alaskacan be seen from NE Siberia].There are numerous unanswered questions about the early colonization of the Americas.

Over the past decade a wealth of genetic data has been published,which is relevant to the settlement of America.Initial mtDNA studies identified the 4 American founding haplogroups [Hgs] A2,B2,C1 and D1,with the later addition of clade X2a.Today there are 13 founding genetic lineages and more will probably be revealed in the future. Amerindians did not have immunity to European diseases[eg:smallpox,measles,etc] and in some regions it is estimated that 90% of native populations perished from these diseases.A number of these individuals could have harboured additional mtDNA founding lineages.

Minimal mtDNA Hg B2 and no X2a samples have been reported in NE Asia.Hg B  occurs in the Siberian Altai-Sayan uplands and on St Lawerence Island in the Bering Strait [G Horvat,2005].Hg B2 has at least the 4 sub-Hgs B2a-B2d.B2d is common over a significant portion of lower Central America The distribution of Hg B2 is compatible with a marine migration,that largely bypassed the west coast of Canada and proceeded south to Chili.Their descendants journeyed a considerable distance inland.

Hg A2 has the sub-Hgs A2a-A2k with numerous back mutations [A Achilli,2009].The Hg A2 cline generally diminishes southward from a dominant position in the NW. Although it is present in many South American regions,it has not been observed in PatigoniaThe exceptionally high occurrence of Hg A2 [92%] distinguishes El Salvador from other Central American populations.El Salvador has preserved a large portion  of its mtDNA intact and may have been settled soon after HgA2 was introduced to America [A Salos,2009].Complete mtDNA genomes were generated for 14 Canadian Inuits.Four belong to sub-Hg A2a and ten were classified as sub-Hg A2b,which is roughly similar to the frequencies that were reported for earlier Thule people [N Thomas,2008],who rapidly expanded relatively recently across Alaska and northern Canada.

Hgs A2 and B2 are derived from macro-Hg M.They have quite a few more American specific mutations than Hgs C1 and D1,which are derived from macro-Hg M.This might imply that the latter two were separated from their Asian counterparts later than Hgs A2 and B2 [G Horvat,2008].Hgs A2 and B2 were dated to ca 12400 BCE,cal’08,at Paisel cave 5,Oregan.After analyzing 623 complete mtDNA sequences from Asia and the Americas E Tamm postulated that the ancestors of the Palaeoindians could have established themselves in Beringia long enough for the American lineages to differentiate themselves from their sister Asian lineages.Tamm’s results could also apply to glacial refugia in the southern USA.Beringia may have been colonized as early as 30000 BCE.

Hg C1 is widely dispersed in the Americas.It has minimal presence in Canada and Central America and dominates eastern Patigonia.Hg D1 might have been a maritime [?] migration along the Pacific seaboard.It is common between Prince Rupert,British Columbia and southern Oregan.There are localized pockets in the southern USA and it is virtually absent in Central America.Frequencies are relatively high along the north and west coast of  South America,with strong representation along the west coast of Chili.Clade X2a is restricted to North America and tends to be concentrated around the Great Lakes region,with a diminishing cline to the west and SW.Several samples have been found in British Columbia.Founding lineages D3 and D2a are also restricted to North America.D3 is largely restricted to Eskimos and D2a has been detected among Nadene,Eskimos and Aleuts.This distribution pattern largely  parallels A2a..D3 and D2a have been identified in NE Asia,but have not been observed among southern Amerindians.This could infer that the Nadene,Eskimos and Aleuts emerged from genetic sources ,that are temporally and regionally distinct from the origins of the earliest American colonists.D2a is deemed to be older than A2a and might have evolved in the Amur River region.

Numerous cranial morphology studies infer that the early inhabitants of South America[eg:Luzia] had affinities with some indigenous Australians and Polynesians;that Amerindians in  South America often vary from those in North America;and that Palaeoindians in North America usually differ from recent or extant Amerindians,who commonly exhibit asome Mongoloid facial features.Current mtDNA estimates for the arrival of the first Americans generally range from ca 16000-13000 BCE,cal,with a few earlier predictions.The number of significant human influxes from Asia to America varies between publications.Collation of the above comments suggests 2-3 major people movements and numerous,sporadic smaller ones might be a realistic assessment.Traffic was probably not always one way,because genetic studies have  a few possible back migrations.N Fagundes [2008] stated “our results indicate,that strictly speaking,we may never be able to pin point a single precise date for the entry to America,because it occurred,when Asia and were connected and because it lasted thousands of years beginning with the isolation from the Asian ancestors and ending in a population size  and range expansion into the continent.”Estimates for the initial colonization of the Americas currently range from ca 30000-13000 BCE,with many authors opting for the 15000-13000BCE,cal, bracket.

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