The first people to arrive in America traveled as at least two separate groups to arrive in their new home at about the same time, according to new genetic evidence published online in Current Biology.

After the Last Glacial Maximum some 15,000 to 17,000 years ago, one group entered North America from Beringia following the ice-free Pacific coastline, while another traversed an open land corridor between two ice sheets to arrive directly into the region east of the Rocky Mountains. Those first Americans later gave rise to almost all modern Native American groups of North, Central, and South America, with the important exceptions of the Na-Dene and the Eskimos-Aleuts of northern North America, the researchers said.

Recently, molecular genetics, together with archaeology and linguistics, has begun to provide some insights. In the new study, Ugo Perego and Alessandro Achilli of Torroni's team analyzed mitochondrial DNA from two rare haplogroups, meaning mitochondrial types that share a common maternal ancestor. Mitochondria are cellular components with their own DNA that allow scientists to trace ancestry and migration because they are passed on directly from mother to child over generations.

Their results show that the haplogroup called D4h3 spread from Beringia into the Americas along the Pacific coastal route, rapidly reaching Tierra del Fuego. The other haplogroup, X2a, spread at about the same time through the ice-free corridor between the Laurentide and Cordilleran Ice Sheets and remained restricted to North America.

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