Genetic analysis reveals diversity of America's first waves of
humans
22 January 2009
America’s earliest ice age people included diverse genetic groups
traveling widely separated migratory paths during the same time
period, according to an international team of scientists
Genetic researchers from the Sorenson Molecular Genealogy
Foundation (SMGF) in Salt Lake City working with scientists
from the University of Pavia in Italy have published a study
shedding new light on the puzzling question of why Native
Americans exhibited such extraordinary linguistic and
cultural diversity when the first Europeans arrived in 1492.
Published in Current Biology, the finding by an international
team of researchers challenges the traditional idea that the first
groups of humans to colonize the Americas came from a single population
source, which would imply one language family, technology and culture,
when they crossed an Ice Age land bridge connected to Asia 15-17,000
years ago.
By analyzing for the first time at the highest level of molecular
resolution two rare lineages of the maternally inherited mitochondrial
DNA (mtDNA) from modern Native Americans, geneticists identified
separate migratory paths that marked the initial stages of human
colonization.
Traveling concurrently, one genetic group of Paleo-Indians followed
the Pacific coastline route and arrived at the southern tip of South
America, while the second group followed an ice-free corridor east of
the Rocky Mountains and settled in the Great Plains and Great Lakes
regions.
The evidence that separate groups of people with distinctive genetic
roots entered the Americas independently at the same time strongly
implies linguistic and cultural differences between them.
“The origin of the first Americans is very controversial to
archaeologists and even more so to linguists,” said study corresponding
author Professor Antonio Torroni, heading the University of Pavia group.
“Our genetic study reveals a scenario in which more than one language
family could have arrived in the Americas with the earliest Paleo-Indians.”
Torroni is a world-renowned population geneticist in the field of
mtDNA research and the first to identify the major genetic groups to
which 95 percent of Native Americans belong.
In March 2008, the same research team published a study that was the
first to compile all known Native American mtDNA sequences into a single
genetic tree with branches dated. Results showed almost all modern
Native Americans descended from six ancestral founding mothers. They
used the built-in molecular clock of DNA to establish the time the first
humans moved into the Western Hemisphere, finding a narrow window
between 15-17,000 years ago.
For both studies researchers combed the Sorenson database — the
world’s largest collection of correlated genetic genealogy information
containing DNA collected in more than 170 countries — for mtDNA
belonging to Native American lineages. Then, using techniques developed
at the University of Pavia, the samples were analyzed using a complete-mtDNA
genome approach for the first time.
“Six major genetic lineages account for 95% of Native American mtDNA
and are distributed everywhere in the Americas,” said first author Ugo
Perego, director of operations at SMGF. “So we chose to analyze two rare
genetic groups and eliminate that ‘statistical background noise.’ In
this way, we found patterns that correspond to two separate migration
routes.”
Today’s study analyzed two rare genetic groups. D4h3 spread into the
Americas along the Pacific coast and, at the same time, X2a migrated
inland through an ice-free corridor between the Cordilleran and the
Laurentide glaciers. The D4h3 group is rare today in North America,
while X2a is found exclusively in the US and Canada, mainly in the Great
Lakes and Great Plains regions. The six most common Native American
mtDNA lineages are A2, B2, C1b, C1c, C1d and D1.
“This study does not end the debate,” said co-author Dr. Alessandro
Achilli, researcher at the University of Pavia and assistant professor
at the University of Perugia, “but the implications of our findings are
significant. The distinct industries and technologies observed in North
American archeological sites might be related to separate genetic groups
using different migratory routes rather than being the result of in
situ differentiation. Future research will dissect common
pan-American lineages into sub-branches, and we do expect distribution
of some of these subgroups will parallel that of D4h3 and X2a.”
The study, “Distinctive Paleo-Indian Migration Routes from Beringia
Marked by Two Rare MtDNA Haplogroups,” is published in Current
Biology online and in the print version of Jan. 13, 2009.
Bookmark this page