Posted on 10/25/2007 2:48:27 PM PDT by decimon
CHAMPAIGN, Ill. — 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.” Click photo to enlarge Photo by L. Brian Stauffer Ripan Mahli, a geneticist in the department of anthropology, believes there was much more genetic diversity among the migrating people from Asia to the Americas 30,000 years ago than previously thought.
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.
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Gods |
Thanks decimon and indcons. |
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I heard a theory, long ago, probably on TV, so probably garbage, but it did seem to make sense to my uneducated self.
It went something like...
Boats. The earliest migrants to the Americas came across the water in the same kind of boats that are still made in the arctic cultures.
These were migratory peoples by custom. They originally settled along the coast all the way down the line. They were kept close to the coasts by both habit and by the megafauna. I believe one of the principle critters held responsible was the “God Bear”. A big huge monster of a bear that skeletal remains indicate could move very quickly and might have even been an endurance runner type.
It was only after something crunched the mega fauna that humans began to move away from the coasts.
I do wonder what would snuff the mega monsters but not the humans.
It strikes me as curious that people would “pause” so far north during a glacial max and not move south toward warmer climes. Maybe it was the food. The Alaskan fisheries are among the most productive in the world. The megafauna was probably good too.
I gagged on the guy's naivete before a third of the book.
It is also a minor peeve of mine that Archeologists have traditionally greatly discounted the possibility that humans could have followed the coast (not the interrior) around the Pacific. This area would likey have been very cold and very dry, thus not supporting much in they way of life (unless you ascribe to the theory of polar shift).
“...several of the island groups in the atlantic were once much more extensive, (but) it was not the mid-Atlantic ridge.”
After posting the above, I thought you might find the following of interest:
“Proposing what is essentially...the ‘forebulge effect’ ...downward pressure on the continental landmasses of Northern Europe and North America during the Ice Age could, through isostatic compensation, have forced the mid-Atlantic Ridge upwards, perhaps far enough upwards to have elevated its highest peaks and plateaux above water for as long as 40,000 years before the ice-sheets went into meltdown.” (Underworld, by Graham Hancock, p.513)
The Azores Island group is part of a submerged plateau associated with the mid-Atlantic Ridge, and that plateau would most certainly have been above see level 15,000 years ago, and could even have still been above sea level as recently as 9,600 years ago.
Mind you, I’m not a cheerleader of either Graham Hancock or Jared Diamond, but both men are relentless researchers and have provided interesting facts for me to ponder.
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