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Topic Name: Migration from Asia to the Americas have perplexed Anthropologists
Category: Genetic Engineering
Research persons: Ripan Singh Malhi
Location: University of Illinois, United States
Details
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.
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.”
“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.”
Before coming to Illinois 14 months ago, Malhi taught at the University
of California at Davis and was a co-founder of Trace Genetics, now part of
DNAPrint Genomics Inc. At Illinois Malhi directs the Molecular Anthropology
Laboratory, which conducts research in the areas of molecular anthropology,
ancient DNA analysis, phylogenetics, evolutionary genomics, forensic science and
population genetics.
In figure, Map showing migration of humans from Asia to the Americas.
Note for Human migration
Human migration denotes any movement by humans from one locality to another, often over long distances or in large groups. Humans are known to have migrated extensively throughout history and prehistory.
Migration and population isolation is one of the four evolutionary forces (along with natural selection, genetic drift, and mutation). The study of the distribution of and change in allele (gene variations) frequencies under such influences is the discipline of Population genetics.
The movement of populations in modern times has continued under the form of both voluntary migration within one's region, country, or beyond, and involuntary migration (which includes slave trade, Trafficking in human beings and ethnic cleansing). The people who migrate are called migrants, or, more specifically, emigrants, immigrants or settlers, depending on historical setting, circumstance and perspective.
Note for Haplogroup C (mtDNA)
In human mitochondrial genetics, Haplogroup C is a human mitochondrial DNA (mtDNA)
haplogroup.
Haplogroup C is believed to have arisen in Asia some 60,000 years before present. It is a descendant of the haplogroup M.
Haplogroup C is found in Northeast Asia (including Siberia) and is also one of five haplogroups found in the indigenous peoples of the
Americas, the others being A, B, D, and X.
In his popular book The Seven Daughters of Eve, Bryan Sykes named the originator of this mtDNA haplogroup
Chochmingwu.
About Researcher:
Ripan Singh Malhi
Assistant Professor
Department of Anthropology
Animal Biology
Institute for Genomic Biology
University of Illinois Urbana-Champaign
185 Davenport Hall
607 Matthews Ave.
Urbana, IL 61801
(217) 265-0721
malhi@uiuc.edu
EDUCATION
2001 University of California, Davis, Ph.D. Anthropology
1994 University of California, Davis, B.S., Anthropology and Biology
GRANTS AND AWARDS
2004 National Science Foundation Grant: Genetic Diversity in the American Southwest and Mesoamerica.
2000 Wenner-Gren Dissertation Fieldwork Grant: Investigating prehistoric population movements in North America using ancient and modern mtDNA.
2000 National Science Foundation Dissertation Improvement Grant: Investigating prehistoric population movements in North America using ancient and modern mtDNA.
2000 Sigma Alpha Mu: Samuel A. Miller Award.
2000 UC Davis Block Grant
1997 Sigma Alpha Mu: Samuel A. Miller Award.
PUBLICATIONS
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