http://esciencenews.com/articles/2009/01/08/first.americans.arrived.2.separ
ate.migrations.according.new.genetic.evidence

First Americans arrived as 2 separate migrations, according to new genetic
evidence

Published: Thursday, January 8, 2009 - 13:14 in Paleontology & Archaeology

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 on January 8th in Current Biology, a Cell
Press publication. 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. (Beringia is the landmass that connected northeast Siberia to
Alaska during the last ice age.) 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.

"Recent data based on archeological evidence and environmental records
suggest that humans entered the Americas from Beringia as early as 15,000
years ago, and the dispersal occurred along the deglaciated Pacific
coastline," said Antonio Torroni of Università di Pavia, Italy. "Our study
now reveals a novel alternative scenario: Two almost concomitant paths of
migration, both from Beringia about 15,000 to 17,000 years ago, led to the
dispersal of Paleo-Indians—the first Americans."

Such a dual origin for Paleo-Indians has major implications for all
disciplines involved in Native American studies, he said. For instance, it
implies that there is no compelling reason to presume that a single
language family was carried along with the first migrants.

When Columbus reached the Americas in 1492, Native American occupation
stretched from the Bering Strait to Tierra del Fuego, Torroni explained.
Those native populations encompassed extraordinary linguistic and cultural
diversity, which has fueled extensive debate among experts over their
interrelationships and origins.

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.

"A dual origin for the first Americans is a striking novelty from the
genetic point of view and makes plausible a scenario positing that within a
rather short period of time, there may have been several entries into the
Americas from a dynamically changing Beringian source," the researchers
concluded.