[Aztlan] Populating the Americas

[Bruce Rogers]

Listeros,

As an "added value feature" about the peopling of the Americas, here 
is a link to one of the latest genetic findings about that history.
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Northwest Passage: genetics show Americas populated via Alaska

Brian Vastag, Science News on-line, Week of Dec. 1, 2007; Vol. 172, 
No. 22  , p. 339

A single population of prehistoric Siberians crossed the Bering 
Strait into Alaska and subsequently fanned out to populate North and 
South America, according to a new genetic analysis of present-day 
indigenous Americans.

The study also hints that early Americans reached Central and South 
America by migrating down the Pacific coast by land or sea and only 
later spread into the interior of South America.

"We have good evidence that a single migration [from Siberia] 
contributed a large fraction of the ancestry of the Americas," says 
population geneticist Noah Rosenberg of the University of Michigan in 
Ann Arbor, who led the large international study team.

The finding draws on the largest database of Native American genetics 
ever compiled. The data include DNA from nearly 500 people belonging 
to 29 groups scattered across Canada, Mexico, Central America, and 
South America. The researchers also studied samples from 14 Tundra 
Nentsi individuals living in eastern Siberia.

"They should be commended for bringing together an enormous database, 
something no one has done before," says Tom Dillehay, an 
archaeologist at Vanderbilt University in Nashville.

The team examined 678 genetic markers in the human genome and found 
that one of the markers ties every Native American group to the 
Tundra Nentsi. The marker, moreover, is found nowhere else in the 
world. "It's extremely difficult to explain this kind of pattern 
unless all of the Native American populations ... have a large degree 
of shared ancestry," says Rosenberg.

In addition, the Canadian groups share more genes with the Siberians 
than do the groups in Central and South America, Rosenberg and his 
team report online in the November PLoS Genetics.

Tracing further migration through the Americas, the team then 
correlated genetic variations among different tribes with each 
group's location as measured along inland or coastal routes. The 
genetic data suggest that most migration to Central and South America 
followed the coast.

"That's the easy way south," says Vance Holliday, an archaeologist at 
the University of Arizona in Tucson. He cautions, however, that the 
groups that populated the South American interior would have had to 
surmount the formidable Andes Mountains.

Despite the migration findings, Holliday and Dillehay both say that 
southward migration along interior routes should still be considered. 
Dillehay notes that the current study excludes Native Americans from 
the United States and eastern Brazil. "It's a sampling bias," he 
says, that might have erroneously favored the Pacific coast migration 
model.

Rosenberg says that a second paper will soon address the genetics of 
tribes in the United States and whether there was more than one major 
Siberian migration.

While the study points to an eastern Siberian origin for most of the 
genes that spread across the Americas, it can't rule out small 
genetic contributions from other groups, says Kari Britt Schroeder of 
the University of California, Davis. In 2001, scientists unearthed 
8,000- to 11,000-year-old skulls in Brazil that strikingly resemble 
today's Australian aborigines (SN: 4/7/01, p. 212). The find fueled 
speculation that several waves of immigrants from different parts of 
Asia reached the Americas.

"Even if Native Americans share a lot of ancestry from a single 
origin, there still could be contributions from other groups," says 
Schroeder.

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cheers,
Bruce Rogers, Earth scientist on a good day