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A model farm template is imagined as the central methodology. A broad range of timely science news and other topics of interest are commented on.
Thursday, July 19, 2012
Three Key Migrations Identified
There are plenty of problems with all this of course but we have at
least identified three major streams and a necessary back stream in
terms of conjectures posted in this blog.
Conjecture: Ice Age peoples became skilled in the use of skin boats
at least twenty thousand years ago. This is confirmed by carbon
dating and upper arm muscle marking in skeletons. This permitted
colonization of both the Pacific Coastal Plain and the Atlantic
Coastal Plains on both sides and from there to move south.
Populations then moved southward and ultimately filled in the
interior of both continents taking several thousands of years.
Conjecture: approximately 5000 years ago, the last remnants of the
ice sheet disappeared allowing easy travel from the Alaskan portion
of Beringia of both the Na-dene and the Eskimo. They then did so
and began the process of inter mixing also with established
population. The archeology so far does not support even the 5000
years so I may be too conservative.
Conjecture: Approximately 13,000 years ago populations in North
America were destroyed by what I call the Pleistocene Nonconformity.
This event had limited survivability East of the Rockies in North
America. This opened the door for a repopulation movement out of
South America. Thus confirmation is rather welcome.
Conjecture: Further populations of Bronze Age Mediterranean and
European peoples were established in the Americas and thrived until
the Bronze Age collapse of 1159 BC. Thereupon these populations were
generally absorbed by larger indigenous populations over the next
2500 years although contact remained into Roman times.
populations descend from three key migrations
by Staff Writers
London, UK (SPX)
Jul 13, 2012
the most comprehensive survey of genetic diversity in Native
Americans so far, the team took data from 52 Native American and 17
Siberian groups, studying more than 300,000 specific DNA sequence
variations called Single Nucleotide Polymorphisms to examine patterns
of genetic similarities and differences between the population
have found that Native American populations - from Canada to the
southern tip of Chile - arose from at least three migrations, with
the majority descended entirely from a single group of First American
migrants that crossed over through Beringia, a land bridge between
Asia and America that existed during the ice ages, more than 15,000
By studying variations
in Native American DNA sequences, the international team found that
while most of the Native American populations arose from the first
migration, two subsequent migrations also made important genetic
contributions. The paper was published in the journal Nature this
"For years it has
been contentious whether the settlement of the Americas occurred by
means of a single or multiple migrations from Siberia," said
Professor Andres Ruiz-Linares (UCL Genetics, Evolution and
Environment), who coordinated the study.
"But our research
settles this debate: Native Americans do not stem from a single
migration. Our study also begins to cast light on patterns of human
dispersal within the Americas."
In the most
comprehensive survey of genetic diversity in Native Americans so far,
the team took data from 52 Native American and 17 Siberian groups,
studying more than 300,000 specific DNA sequence variations called
Single Nucleotide Polymorphisms to examine patterns of genetic
similarities and differences between the population groups.
The second and third
migrations have left an impact only in Arctic populations that speak
Eskimo-Aleut languages and in the Canadian Chipewyan who speak a
Na-Dene language. However, even these populations have inherited most
of their genome from the First American migration.
derive more than 50% of their DNA from First Americans, and the
Chipewyan around 90%. This reflects the fact that these two later
streams of Asian migration mixed with the First Americans they
encountered after they arrived in North America.
"There are at
least three deep lineages in Native American populations," said
co-author David Reich, Professor of genetics at Harvard Medical
lineage leading to First Americans is the most anciently diverged,
whereas the Asian lineages that contributed some of the DNA to
Eskimo-Aleut speakers and the Na-Dene-speaking Chipewyan from Canada
are more closely related to present-day East Asian populations."
The team also found
that once in the Americas, people expanded southward along a route
that hugged the coast with populations splitting off along the way.
After divergence, there was little gene flow among Native American
groups, especially in South America.
exceptions to this simple dispersal were also discovered. First,
Central American Chibchan-speakers have ancestry from both North and
South America, reflecting back-migration from South America and
mixture of two widely separated strands of Native ancestry.
Second, the Naukan
and coastal Chukchi from north-eastern Siberia carry 'First American'
DNA. Thus, Eskimo-Aleut speakers migrated back to Asia, bringing
Native American genes.
The team's analysis
was complicated by the influx into the hemisphere of European and
African immigrants since 1492 and the 500 years of genetic mixing
that followed. To address this, the authors developed methods that
allowed them to focus on the sections of peoples' genomes that were
of entirely Native American origin.
"The study of
Native American populations is technically very challenging because
of the widespread occurrence of European and African mixture in
Native American groups," said Professor Ruiz-Linares.
"We developed a
method to peel back this mixture to learn about the relationships
among Native Americans before Europeans and Africans arrived,"
Professor Reich said, "allowing us to study the history of many
more Native American populations than we could have done otherwise."
The assembly of DNA
samples from such a diverse range of populations was only possible
through a collaboration of an international team of 64 researchers
from the Americas (Argentina, Bolivia, Brazil, Canada, Chile,
Colombia, Costa Rica, Guatemala, Mexico, Peru, Russia and the USA),
Europe (England, France, Spain and Switzerland) and Russia.
American population history' is published in the journal Nature.