<P> As the chronology of deglaciation in the interior and coastal regions of North America became better understood, the coastal migration hypothesis was advanced by Knute Fladmark as an alternative to the ice - free corridor hypothesis . Debate on coastal versus interior migration for initial settlement has centered on evidence for chronology of initial settlement of Beringia, interior North America, the Pacific coast of the Americas, and timing of the opening of coastal versus interior migration routes indicated by geological evidence . Complicating the debate has been the absence of archaeological data from the coastal and interior migration routes from the periods when the initial migration is proposed to have occurred . A recent variation of the coastal migration hypothesis is the marine migration hypothesis, which proposes that migrants with boats settled in coastal refugia during deglaciation of the coast . The proposed use of boats adds a measure of flexibility to the chronology of coastal migration, as a continuous ice - free coast (16k - 15k cal years BP) would no longer be required . A coastal east Asian source population is integral to the marine migration hypothesis . </P> <P> In 2014, the autosomal DNA of a toddler from Montana, dated at 10.7 k C years (12.5 - 12.7 cal years) BP was sequenced . The DNA was taken from a skeleton referred to as Anzick - 1, found in close association with several Clovis artifacts . The analysis yielded identification of the mtDNA as belonging to Subhaplogroup D4h3a, a rare subclade of D4h3 occurring along the west coast of the Americas, as well as geneflow related to the Siberian Mal'ta population . The data indicate that Anzick - 1 is from a population directly ancestral to present South American and Central American Native American populations . Anzick - 1 is less closely related to present North American Native American populations . D4h3a has been identified as a clade associated with coastal migration . </P> <P> The problems associated with finding archaeological evidence for migration during a period of lowered sea level are well known . Sites related to the first migration are usually submerged, so the location of such sites is obscured . Certain types of evidence dependent on organic material, such as radiocarbon dating, may be destroyed by submergence . Wave action can destroy site structures and scatter artifacts along a prograding shoreline . Additionally, Pacific coastal conditions tend to be unstable due to steep unstable terrain, earthquakes, tsunamis, and volcanoes . Strategies for finding earliest migration sites include identifying potential sites on submerged paleoshorelines, seeking sites in areas uplifted either by tectonics or isostatic rebound, and looking for riverine sites in areas that may have attracted coastal migrants . Otherwise, coastal archaeology is dependent on secondary evidence related to lifestyles and technologies of maritime peoples from sites similar to those that would be associated with the original migration . </P> <P> Other coastal models, dealing specifically with the peopling of the Pacific Northwest and California coasts, have been advocated by archaeologists Knut Fladmark, Roy Carlson, James Dixon, Jon Erlandson, Ruth Gruhn, and Daryl Fedje . In a 2007 article in the Journal of Island and Coastal Archaeology, Erlandson and his colleagues proposed a corollary to the coastal migration theory--the "kelp highway hypothesis"--arguing that productive kelp forests supporting similar suites of plants and animals would have existed near the end of the Pleistocene around much of the Pacific Rim from Japan to Beringia, the Pacific Northwest, and California, as well as the Andean Coast of South America . Once the coastlines of Alaska and British Columbia had deglaciated about 16,000 years ago, these kelp forest (along with estuarine, mangrove, and coral reef) habitats would have provided an ecologically similar migration corridor, entirely at sea level, and essentially unobstructed . </P>

Of the following who stepped foot on the american continent first