RARE DNA VARIANT MAY DISPROVE PALEOLITHIC MIGRATION TO AMERICA ACROSS THE ATLANTIC
http://ohio-archaeology.blogspot.com/2011/12/rare-dna-variant-may-disprove.html
...C4c has clear roots in Asia and is found in Great Lakes and Great Plains Native American populations. These are the same areas in which the X2a haplogroup has been identified suggesting that “these two lineages possibly arrived together from Beringia with the same Paleo-Indian group(s) that entered North America from Beringia through the ice-free corridor between the Laurentide and Cordilleran ice sheets” at around 18-15,000 years ago.