Re: Beringian Standstill and Spread of Native American Founders

On Oct 26, 5:44 am, Doug Weller <dwel...@xxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
" the initial founders of the Americas emerged from a single source
ancestral population that evolved in isolation, likely in Beringia....the
isolation in Beringia might have lasted up to 15,000 years. Following this
isolation, the initial founders of the Americas began rapidly populating
the New World from North to South America."http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1952074

Beringian Standstill and Spread of Native American Founders

PLoS ONE. 2007; 2(9): e829.
Erika Tamm,1 Toomas Kivisild,1,2 Maere Reidla,1 Mait Metspalu,1 David
Glenn Smith,3 Connie J. Mulligan,4 Claudio M. Bravi,5 Olga Rickards,6
Cristina Martinez-Labarga,6 Elsa K. Khusnutdinova,7 Sardana A.
Fedorova,1,8 Maria V. Golubenko,1,9 Vadim A. Stepanov,9 Marina A.
Gubina,1,10 Sergey I. Zhadanov,1,10,11 Ludmila P. Ossipova,10 Larisa
Damba,1,10 Mikhail I. Voevoda,10 Jose E. Dipierri,12 Richard Villems,1 and
Ripan S. Malhi13*
--
Doug Weller --
A Director and Moderator of The Hall of Ma'athttp://www.hallofmaat.com
Doug's Archaeology Site:http://www.ramtops.co.uk
Amun - co-owner/co-moderatorhttp://groups.yahoo.com/group/Amun/

Another view of the article from Science Daily with a nice color
map.

New Ideas About Human Migration From Asia To Americas

Map showing migration of humans from Asia to the Americas. (Credit:
Image courtesy Ripan Mahlir)

ScienceDaily (Oct. 25, 2007) - Questions about human migration from
Asia to the Americas have perplexed anthropologists for decades, but
as scenarios about the peopling of the New World come and go, the big
questions have remained. Do the ancestors of Native Americans derive
from only a small number of "founders" who trekked to the Americas via
the Bering land bridge? How did their migration to the New World
proceed? What, if anything, did the climate have to do with their
migration? And what took them so long?

A team of 21 researchers, led by Ripan Malhi, a geneticist in the
department of anthropology at the University of Illinois, has a new
set of ideas. One is a striking hypothesis that seems to map the
peopling process during the pioneering phase and well beyond, and at
the same time show that there was much more genetic diversity in the
founder population than was previously thought.

"Our phylogeographic analysis of a new mitochondrial genome dataset
allows us to draw several conclusions," the authors wrote.

"First, before spreading across the Americas, the ancestral population
paused in Beringia long enough for specific mutations to accumulate
that separate the New World founder lineages from their Asian sister-
clades." (A clade is a group of mitochondrial DNAs (mtDNAs ) that
share a recent common ancestor, Malhi said. Sister-clades would
include two groups of mtDNAs that each share a recent common ancestor
and the common ancestor for each clade is closely related.)

Or, to express this first conclusion another way, the ancestors of
Native Americans who first left Siberia for greener pastures perhaps
as much as 30,000 years ago, came to a standstill on Beringia - a
landmass that existed during the last glacial maximum that extended
from Northeastern Siberia to Western Alaska, including the Bering land
bridge - and they were isolated there long enough - as much as 15,000
years - to maturate and differentiate themselves genetically from
their Asian sisters.

"Second, founding haplotypes or lineages are uniformly distributed
across North and South America instead of exhibiting a nested
structure from north to south. Thus, after the Beringian standstill,
the initial North to South migration was likely a swift pioneering
process, not a gradual diffusion."

The DNA data also suggest a lot more to-ing and fro-ing than has been
suspected of populations during the past 30,000 years in Northeast
Asia and North America. The analysis of the dataset shows that after
the initial peopling of Beringia, there were a series of back
migrations to Northeast Asia as well as forward migrations to the
Americas from Beringia, thus "more recent bi-directional gene flow
between Siberia and the North American Arctic."

To investigate the pioneering phase in the Americas, Malhi and his
team, a group of geneticists from around the world, pooled their
genomic datasets and then analyzed 623 complete mitochondrial DNAs
(mtDNAs) from the Americas and Asia, including 20 new complete mtDNAs
from the Americas and seven from Asia. The sequence data was used to
direct high-resolution genotyping from 20 American and 26 Asian
populations. Mitochondrial DNA, that is, DNA found in organelles,
rather than in the cell nucleus, is considered to be of separate
evolutionary origin, and is inherited from only one parent - the
female.

The team identified three new sub-clades that incorporate nearly all
of Native American haplogroup C mtDNAs - all of them widely
distributed in the New World, but absent in Asia; and they defined two
additional founder groups, "which differ by several mutations from the
Asian-derived ancestral clades."

What puzzled them originally was the disconnect between recent
archaeological datings. New evidence places Homo sapiens at the Yana
Rhinoceros Horn Site in Siberia - as likely a departure point for the
migrants as any in the region - as early as 30,000 years before the
present, but the earliest archaeological site at the southern end of
South America is dated to only 15,000 years ago.

"These archaeological dates suggested two likely scenarios," the
authors wrote: Either the ancestors of Native Americans peopled
Beringia before the Last Glacial Maximum, but remained locally
isolated - likely because of ecological barriers - until entering the
Americas 15,000 years before the present (the Beringian incubation
model, BIM); or the ancestors of Native Americans did not reach
Beringia until just before 15,000 years before the present, and then
moved continuously on into the Americas, being recently derived from a
larger parent Asian population (direct colonization model, DCM).

Thus, for this study the team set out to test the two hypotheses: one,
that Native Americans' ancestors moved directly from Northeast Asia to
the Americas; the other, that Native American ancestors were isolated
from other Northeast Asian populations for a significant period of
time before moving rapidly into the Americas all the way down to
Tierra del Fuego.

"Our data supports the second hypothesis: The ancestors of Native
Americans peopled Beringia before the Last Glacial Maximum, but
remained locally isolated until entering the Americas at 15,000 years
before the present."

The team's findings appear in a recent issue of the Public Library of
Science in an article titled, "Beringian Standstill and Spread of
Native American Founders."

Adapted from materials provided by University of Illinois.


http://www.archaeologynews.org/story.asp?ID=237190&Title=New%20Ideas%20About%20Human%20Migration%20From%20Asia%20To%20Americas

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