lunes, 1 de noviembre de 2010

I'm a beringian

A journey to another land
The wind cutting our faces

Hardened by the cold
The road taking us nowhere

Ice crystals adorning our hair
As the mammoths roam the plain

And a full moon rides up the sky
Guiding us towards a place

Beyond the ice floats
Drifting in the water

Un viaje a otras tierras

El viento quemando nuestras caras

Que el frio ha curtido

Y el camino nos lleva al infinito

Mientras que el hielo nos cuelga del pelo

Los mastodontes buscan sus pastos

Cuando la luna aparece en el cielo

Detrás de las montañas mágicas

My family spent 20.000 years in the freezing land between Siberia and Alaska, called Beringia, 16.000 years ago. I can't help thinking about their lives in the ice age, while staying in tents like tepees and looking after their reindeer.

Through mitochondrial DNA research and lots of other scientific things , researches have found an interesting fact.

“Nearly all of today’s Native Americans in North, Central and South America can trace part of their ancestry to six women whose descendants immigrated around 20,000 years ago” - New York (AP)

Through research, these six women could not have been from Asia but most probably had lived in Biringia, the now submerged land. There's also evidence to think they may have lived for 20.0000 years in Beringia, but finding more on that is difficult since Biringia is submerged and Alaska and Siberia are hard climates for investigation.

For now, research talks about “six women” but with further discoveries this number may vary. And the question as to where and how many people lived in Beringia is still to be answered.

“New findings reveal the settling of the New World did not come in a single burst, as is suggested by most theories, but was, in a way, a play with three acts, each separated by thousands of generations.”

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Native Mtdna

Thousands Of Humans Inhabited New World's Doorstep For 20,000 Years

ScienceDaily (Feb. 13, 2008) — The human journey from Asia to the New World was interrupted by a 20,000 -year layover in Beringia, a once-habitable region that today lies submerged under the icy waters of the Bering Strait. Furthermore, the New World was colonized by approximately 1,000 to 5,000 people - a substantially higher number than the 100 or fewer individuals of previous estimates.

See Also:

Fossils & Ruins

Reference

The developments, to be reported by University of Florida Genetics Institute scientists in PloS One, help shape understanding of how the Americas came to be populated - not through a single expansion event that is put forth in most theories, but in three distinct stages separated by thousands of generations.

"Our model makes for a more interesting, complex scenario than the idea that humans diverged from Asians and expanded into the New World in a single event," said Connie Mulligan, Ph.D., an associate professor of anthropology at the College of Liberal Arts and Sciences and assistant director of the UF Genetics Institute. "If you think about it, these people didn't know they were going to a new world. They were moving out of Asia and finally reached a landmass that was exposed because of lower sea levels during the last glacial maximum, but two major glaciers blocked their progress into the New World. So they basically stayed put for about 20,000 years. It wasn't paradise, but they survived. When the North American ice sheets started to melt and a passage into the New World opened, we think they left Beringia to go to a better place."

UF scientists analyzed DNA sequences from Native American, New World and Asian populations with the understanding that modern DNA is forged by an accumulation of events in the distant past, and merged their findings with data from existing archaeological, geological and paleoecological studies.

The result is a unified, interdisciplinary theory of the "peopling" of the New World, which shows a gradual migration and expansion of people from Asia through Siberia and into Beringia starting about 40,000 years ago; a long waiting period in Beringia where the population size remained relatively stable; and finally a rapid expansion into North America through Alaska or Canada about 15,000 years ago.

"This was the raw material, the original genetic source for all of the Americas," said Michael Miyamoto, Ph.D., a professor and associate chairman of zoology in UF's College of Liberal Arts and Sciences. "You can think of the people as a distinct group blocked by glaciers to the east. They had already been west, and had no reason to go back. They had entered this waiting stage and for 20,000 years, generations were passing and genetic differences were accumulating. By looking at the kinds and frequencies of these mutations in modern populations, we can get an idea of when the mutations arose and how many people were around to carry them."

Working with mitochondrial DNA - passed exclusively from mothers to their children - and nuclear DNA, which contains genes from both parents, UF scientists essentially added genetic information to what had been known about the archaeology, changes in climate and sea level, and geology of Beringia.

The result is a detailed scenario for the timing and scale of the initial migration to the Americas, more comparable to an exhaustive video picture rather than a single snapshot in time.

"Their technique of reading population history by using coalescence rates to analyze genetic data is very impressive - innovative anthropology and edge-of-the-seat population study," said Henry C. Harpending, Ph.D., a distinguished professor and endowed chairman of anthropology at the University of Utah and a member of the National Academy of Sciences who was not involved with the research. "The idea that people were stuck in Beringia for a long time is obvious in retrospect, but it has never been promulgated. But people were in that neighborhood before the last glacial maximum and didn't get into North America until after it. It's very plausible that a bunch of them were stuck there for thousands of years."

As for Beringia, sea levels rose about 10,000 to 11,000 years ago, submerging the land and creating the Bering Strait, which now separates North America from Siberia with more than 50 miles of open, frigid water.

"Our theory predicts much of the archeological evidence is underwater," said Andrew Kitchen, a Ph.D. candidate in the anthropology department at UF who participated in the research. "That may explain why scientists hadn't really considered a long-term occupation of Beringia."

UF researchers believe that their synthesis of a large number of different approaches into a unified theory will create a platform for scientists to further analyze genomic and non-genetic data as they become available.

Citation: Kitchen A, Miyamoto MM, Mulligan CJ (2008) A Three-Stage Colonization Model for the Peopling of the Americas. PLoS One 3(2): e1596. doi:10.1371/journal.pone.0001596

Maps depicting each phase of our three-step colonization model for the peopling of the Americas. (Credit: Kitchen A, Miyamoto MM, Mulligan CJ (2008) A Three-Stage Colonization Model for the Peopling of the Americas. PLoS ONE 3(2): e1596. doi:10.1371/journal.pone.0001596)

20.000 years

First Americans Endured 20,000-Year Layover

Jennifer Viegas, Discovery News

Reminiscent of History

Feb. 13, 2008 -- The first New World entrants, who likely came from Asia, endured a 20,000-year "layover" on a strip of land called Beringia that once connected Alaska to Siberia, according to a new research model.

The model combines genetics with climate, archaeological and geological information to paint a vivid picture of how the Americas were first populated by approximately 1,000 to 5,000 people, instead of just 100, as was previously believed.

The findings, published this week in the journal PLoS ONE, also explain why Native Americans are genetically similar to east central Asians, but show noticeable differences too.

"Twenty thousand years is sufficient time to create the genetic polymorphisms that distinguish Native Americans, although I don't think Native Americans are a different race," co-author Connie Mulligan told Discovery News.

"The genetic variation that distinguishes all Native Americans from other, non-Native American groups would have evolved during...the Beringian occupation," added Mulligan, who is a professor of anthropology at the University of Florida and serves as assistant director of the university's Genetics Institute.

She and her colleagues believe two massive glaciers prevented the Beringians from entering the New World over the multi-millennial period. They seemed to be eager to leave, however, and for good reason.

"Although Beringia was not covered in glaciers, it still would have been a cold, harsh climate, such that life would have been possible, but not luxurious," Mulligan said. "I would compare it to modern-day Siberia or Mongolia in the winters."

When the glaciers diminished, the melting was probably rapid, "a difference that could be seen over a person's lifetime," she said.

Beringian 2

Peopling of the Americas: mtDNA tells us of the Beringian Standstill

with 6 comments

A new study of over 600 mtDNAs from 20 American and 26 Asian populations is shedding some unique insight on how the Americas were peopled. As you may have been taught, it was thought that the Americas were founded by a not so diverse founding population or two. Before this paper, only about 70 left their genetic print in modern descendants, a very small but effective founder population.

But, there are new results, which were published almost two months ago, that show that there was much more genetic diversity in the founder population than was previously thought. I didn’t catch it until I saw both Razib and Science Daily report on it a couple days ago.

The paper, “Beringian Standstill and Spread of Native American Founders,” was published in the freely accessible PLoS One. Beringia is a fancy way of naming the Bering Land Straight that once connected the north east Asia continent to north west America continent.

One of the more interesting lines of evidence they found from their sequence comparison and their revised phylogenetic map is that the ancestral population literally chilled out in Beringia for a long time. The authors estimate about 15,000 years. That’s long enough so that specific mutations accumulated which separated the New World founder lineages from the Asian sister-clades.

The other more interesting thing that was uncovered was that the founding haplotypes are uniformly distributed across North and South America. They do not show a nested structure from north to south. That means that after what the authors are terming the Beringian standstill and what I’m calling the Beringian chillout, the initial North to South migration was very swift. It was not a gradual diffusion.

And as Razib pointed out in his post, during the last 30,000 years, there was a lot more bouncing back and forth from Northeast Asia and North America. The analysis shows that there was a series of back migrations to Northeast Asia as well as forward migrations to the Americas from Beringia, “more recent bi-directional gene flow between Siberia and the North American Arctic.”

Overall, this study tells us a lot on how people were moving about in the northern hemisphere. But what about oceanic travel, and the recent chicken population genetic similarities? They seem to have made some cultural if not genetic contribution to populations here.

Related sidenote, I like how this study one ups an older PLoS paper, which I reffered to above (the 70 people one). If you want, check out that paper, “On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas.”

Early Americans in Beringia

Early Americans May Have Been 'Stuck' for 20,000 Years

Andrew Kitchen, Michael Miyamoto, Connie Mulligan, PLoS ONE

The proposed first two stages of colonization of the Americas. 'Kya' indicates 'thousands of years ago.'

The epic journey by which the Americas were first settled has been a great mystery for centuries.

Did it happen by land or by sea? Did it happen one dozen or so millennia ago, or three dozen?

The answer might be "yes."

• Click here to visit FOXNews.com's Archaeology Center.

New findings reveal the settling of the New World did not come in a single burst, as is suggested by most theories, but was, in a way, a play with three acts, each separated by thousands of generations.

The first stage of this voyage involved a gradual migration of people from Asia through Siberia starting about 40,000 years ago into Beringia, a once-habitable grassland populated with steppe bison, mammoths, horses, lions, musk oxen, sheep, wooly rhinoceros and caribou that nowadays lies submerged under the icy waters of the Bering Strait.

The second phase of the journey was basically a layover in Beringia.

"Two major glaciers blocked their progress into the New World. So they basically stayed put for about 20,000 years," said researcher Connie Mulligan, a molecular anthropologist at the University of Florida in Gainesville.

The population there apparently did not grow or shrink much during this era, which suggests Beringia "wasn't paradise, but they survived."

In the final act, "when the North American ice sheets started to melt and a passage into the New World opened, we think they left Beringia to go to a better place," Mulligan explained.

That resulted in a rapid expansion into the New World about 15,000 years ago.

Research done by Mulligan and her colleagues suggests the New World was settled by approximately 1,000 to 5,000 people — a substantially higher number than the 100 or fewer individuals of some prior estimates.

How did the researchers come up with their findings? Well, DNA allows scientists to deduce the history of populations.

For instance, mutations that all New World populations have in common with each other and no one else means they share a common ancestry, suggesting there was just one wave of migration into the Americas, as opposed to several unrelated waves.

However, the molecular evidence was confusing as to when this wave of migration took place.

DNA accumulates mutations over time, serving like a clock, but some DNA suggested people came to the New World about 13,000 years ago, while other sequences hinted at 30,000 or more years ago.

Mulligan and her colleagues' new analysis of DNA from Native American and Asian populations seem to help resolve conflicts in past research by suggesting a long waiting period on the doorstep to the New World.

As for Beringia, sea levels rose about 10,000 to 11,000 years ago as the peak of the ice age waned, submerging the land and creating the Bering Strait, which now separates the New World from Siberia with at least 60 miles of open, frigid water.

The expansion into the New World may have occurred by land after the ice sheets covering what is now Canada began to retreat 14,000 to 17,000 years ago, the scientists noted.

However, they added that glaciers on the northwest Pacific coast of North American also might have receded by about 17,000 years ago, thus presenting a viable coastal route by sea to the continent.

"It doesn't have to be an either-or thing. They could have used both routes," Mulligan said.

Innovative work

Anthropologist and population geneticist Henry Harpending at the University of Utah, who did not participate in the research, said he found the work innovative.

"The idea that people were stuck in Beringia for a long time is obvious in retrospect, but it has never been promulgated," said Harpending, who found it very plausible that people were stuck in Beringia "for thousands of years."

Although this new theory could resolve some of the conflicting results scientists have come up with over the years, "I don't pretend this inclusive approach will make us any friends, just more critics," Mulligan told LiveScience.

For instance, one criticism Mulligan anticipates is the fact that "20,000 years in Beringia is a long time. Some people will say, 'Get real — where's the evidence?' We would say that there's no one that does Arctic underwater archaeology."

Researcher Andrew Kitchen added, "Our theory predicts much of the archaeological evidence is underwater. That may explain why scientists hadn’t really considered a long-term occupation of Beringia."

Mulligan noted one might also contend that any evidence of such a 20,000-year stay in Beringia might have left evidence in Siberia or Alaska.

"But we envision a small population there that probably left a relatively light footprint on the landscape," she explained. "And the areas we're talking about — Siberia, Alaska — there's no way to argue that researchers have covered those areas thoroughly, with their incredibly harsh climates."

Native Mtdna ,

The Peopling Of The Americas: Genetic Ancestry Influences Health, Anthropologist Says

ScienceDaily (Aug. 16, 2009) — At one time or another most of us wonder where we came from, where our parents or grandparents and their parents came from. Did our ancestors come from Europe or Asia? As curious as we are about our ancestors, for practical purposes, we need to think about the ancestry of our genes, according to Cecil Lewis, assistant professor of anthropology at the University of Oklahoma. Lewis says our genetic ancestry influences the genetic traits that predispose us to risk or resistance to disease.

See Also:

Health & Medicine

Fossils & Ruins

Reference

Lewis studies genetic variation in populations to learn about the peopling of the Americas, but his studies also have an impact on genetic-related disease research. Some 15,000-18,000 years ago, people came from Asia through the Bering Strait and began to fill the American continents. The Americas were the last continents to be populated, so Lewis wants to understand how this process happened. His recent study focuses on South America and asks what part of the subcontinent has the most genetic diversity.

A complete understanding of this research depends on a very important population genetic process called the “founder effect.” The geographic region with the most genetic diversity is characteristic of the initial or “parent” population. For example, a group of people leave a parent population and become founders of a new daughter population in an uninhabited geographic region. They typically take with them only a small set of the parent population’s genetic diversity. This is called a founder effect.

The world pattern of founder effects in human populations begins in Africa. The genetic diversity in the Middle East is largely a subset of the genetic diversity in Africa. Similarly, the genetic diversity in Europe and Asia is largely a subset of the genetic diversity in Africa and the Middle East. The genetic diversity of the Americas is largely a subset of that in Asia. As a result, DNA tells a story about human origins, which began in Africa and spread throughout the world

Lewis is interested in the founder effects within the Americas with a particular focus on South America. At the outset, Lewis expected western South America to have a more diverse population than eastern South America because most anthropologists believe South America to have been peopled from west to east. Unexpectedly, the genetic data from the Lewis study was not consistent with this idea.

In this new study, Lewis looked at more than 600 independent genetic markers called short-tandem repeats. These markers were dispersed throughout the human genome. They were initially published by Lewis and his colleagues in large scale collaboration; the dataset is the largest survey of Native American genetic diversity today. Surprisingly, genetic analysis of these data estimated more genetic diversity in eastern than western South America. This was not the first time Lewis observed this pattern.

Lewis first observed this pattern in 2007 with his post-doctoral advisor using a more limited genetic dataset. The fact that the new genome-wide dataset provided a similar result was surprising; this result questions the most widely accepted scenario for the peopling of South America. While the focus of this study was South America, a similar and interesting pattern of genetic diversity emerged in North America. The pattern suggests another major founder effect in North America, but after the initial founder effect from Asia.

A founder effect provides an opportunity for dramatic changes in the frequencies of genetic traits. Genetic alleles or traits may be rare in a parent population, but because of the founder effect they can become common or even lost in the daughter population. These traits include those that may predispose for a risk or resistance to disease.

“We cannot assume that all Native American populations will have similar trait frequencies nor will they have similar expectations for genetic risk or resistance to disease. Rather, the history of founder effects in the Americas, and around the world, contributes to the understanding of how well one local population might reflect a broader community,” says Lewis.

A paper by Lewis on this subject is currently available on “Early View” in the scientific journal American Journal of Physical Anthropology.

Ice free corridor

The Ice-Free Corridor Revisited
Lionel E. Jackson Jr. and Michael C. Wilson

Editor's note: This feature is a history of studies of early Americans and serves as a primer for the following feature.

This map shows the extent of the Laurentide Ice Sheet (LIS) at about 11,000 years before present, generalized from Deglaciation of North America and overlaid on the North America shaded relief map (courtesy of the U.S. Geological Survey EROS Data Center). Inset shows the western limit of the LIS and the location of the Foothills Erratics Train, which lies along a zone of coalescence between LIS and glaciers from the Cordilleran Ice Sheet. Earliest known archaeology sites are C - Charlie Lake; V - Vermilion Lakes; S - Sibbald Creek; W - Wally's Beach; N - Niska. Image courtesy of Lionel E. Jackson Jr.

In 1927, a visit by eminent paleontologists to an excavation in the wall of an arroyo near Folsom, N.M., confirmed that humans had coexisted with extinct Pleistocene animals at about the time of the Wisconsin Glaciation in North America (now known to have occurred between about 25,000 and 10,000 years before present). The excavation of a butchering site revealed finely crafted thin, leaf-shaped stone projectile points imbedded in the bones of large bison. These distinctive projectile points, dubbed "Folsom points," were fluted on each side to facilitate securing them to projectile shafts.

Paleontologists uncovered an even older site with indisputable evidence of human hunting of mammoths in 1932 near Clovis, N.M. However, this location revealed a different type of projectile point, longer than the Folsom point and with a partial flute on each side. The researchers named the points and the people who created them "Clovis." The question immediately arose as to how these hunters had reached the mid-latitudes of North America at a time when the northern half of the continent was apparently buried beneath the Laurentide and Cordilleran ice sheets.

In 1933, W.A. Johnston of the Geological Survey of Canada (GSC) proposed an answer. He and colleagues had investigated the Pleistocene geology of the Rocky Mountain foothills of Alberta between Calgary and the Montana border. They believed that there had been several overlapping advances of the Laurentide ice sheets and glaciers from the Rocky Mountains. What remained unclear to Johnston at the time, however, was whether the glaciers actually had coalesced or whether the mixed provenance tills along the Rocky Mountain Foothills represented out-of-phase advances of glaciers from the Rocky Mountains and the Laurentide Ice Sheet. He favored a more restricted Wisconsin Glaciation limit of the Laurentide Ice Sheet and, on this basis, proposed that people could have reached the lands south of the ice via a passage between glaciers advancing into the plains from the Rocky Mountains and continental glaciers.

In 1935, Ernst Antevs coined the term "ice-free corridor" to describe this passage. Johnston's suggestion was a bold one, as it was based on very modest geological evidence. Such a corridor would have stretched 2,500 kilometers from the limits of glaciation along the Arctic coast in northern Yukon to northern Montana. Only the most general of geological surveys had been done for this area by 1933 and basic topographic mapping of much of it was not completed for another 20 years. Systematic surficial geology mapping for most of the region was not completed until the 1990s.

Despite numerous archaeological surveys, it has taken almost 60 years for a rigorous test of the hypothesis that the ice-free corridor was the path by which the first Americans reached the mid-latitudes. To do so, researchers have developed several analytical techniques, including radiocarbon and cosmogenic exposure dating, to resolve geological and archaeological controversies. Through the investigation of pre-Clovis archaeological sites and the reconstruction of North America's glacial past, scientists are now suggesting that the ice-free corridor may not have been a feasible route for the early Americans.

Glacial reconstruction

The northern ice-free corridor encompasses the Mackenzie Mountains, the northern continuation of the Rocky Mountains and the adjacent valley of the Mackenzie River. It is essentially a roadless area accessible only by helicopter or airplane. Regional mapping of this area by GSC geologists Alejandra Duk-Rodkin and Owen Hughes in the 1980s and 1990s determined that the limit of the Laurentide Ice Sheet from the last glacial maximum represented the alltime limit of glacial ice cover. Furthermore, they cited evidence that suggested that the maximum push of the ice sheet into the front (Canyon) ranges of the Mackenzie Mountains occurred as early as 30,000 years before present as determined by radiocarbon dating (YBP).

However, a revisiting of the chronology of the maximum advance of the Laurentide Ice Sheet in this region by Arthur Dyke of GSC and university colleagues in 2002 concluded that the maximum advance was more likely in the range of about 21,000 YBP, which is compatible with the last glacial maximum. Duk-Rodkin also mapped re-advance positions of the Laurentide Ice Sheet. She concluded that the actual opening of a corridor to the south could not have occurred until about 13,000 YBP and extensive glacial lakes occupied much of the area until around 12,000 YBP, affirmed in subsequent studies by Dyke and colleagues.

Settling the glacial history of the southern part of the ice-free corridor proved to be a thornier problem, with two competing interpretations of stratified glacial tills along the Rocky Mountain foothills and adjacent interior plains. One camp viewed these tills as representing deposits of several separate glaciations, spanning perhaps hundreds of thousands of years. The other camp viewed them as the result of glacial advances and retreats during a single glaciation, complicated stratigraphically through ice-thrusting of sediments. A significant aspect of the controversy was determining if and when glaciers from the Rocky Mountains merged with the Laurentide Ice Sheet. The key to solving the debate lay in the discovery of the origin of the Foothills Erratics Train, a remarkable feature consisting of thousands of quartzite boulders ranging up to car-sized and even house-sized blocks.

In the 1950s and 1960s, GSC geologist Archie Stalker and others traced the boulders over 600 kilometers from northern Montana northwestward to the Mt. Edith Cavell area in Jasper National Park. They found that the erratics train was as narrow as a kilometer in some areas and was found in a belt of mixed Rocky Mountain and Laurentide Ice Sheet till. The only viable explanation for the narrow belt and its southward deflection parallel to the Rocky Mountain foothills was that the erratics were transported along a zone of coalescence between valley glaciers that advanced from the Rocky Mountains and the southwestern margin of the Laurentide Ice Sheet. But when? The work of two groups would help settle the dating.

Jim Burns of the Provincial Museum of Alberta and Robert Young, then at the University of Calgary, obtained radiocarbon dates from bones found in gravels beneath the single Laurentide till that exists in the Edmonton area. This underlying preglacial gravel lacks any clasts derived from the Canadian Shield, the source of the Laurentide Ice Sheet. Twenty-nine sub-till radiocarbon ages fell between 21,000 and 43,000 YBP. These ages plus others from locations northwest and south of Edmonton indicated that the last Laurentide Ice Sheet was the only continental ice sheet ever to inundate the Edmonton area and, by inference, reach the eastern margin of the Cordillera to the west.

This example of one of the Foothills erratics lies near Glenwoodville, Alberta. Its upper surface yielded a cosmogenic chlorine-36 exposure age of about 17,000 years indicating that it was emplaced during the last glacial maximum. Image courtesy of Lionel E. Jackson Jr.

The second research group, comprising first author Jackson in collaboration with Fred Phillips at New Mexico Tech and GSC colleagues, set out to directly date the emplacement of the Foothills Erratics Train and other erratics, marking the alltime Laurentide Ice Sheet limit along the Canada-United States border, using cosmogenic chlorine-36 exposure dating. Phillips had previously applied this technique to moraines in the Mackenzie Mountains with Duk-Rodkin. Twelve exposure ages on the Foothills Erratics Train showed them to have been emplaced between 11,000 and 18,000 YBP, which falls within the Wisconsin Glaciation. Furthermore, 16 ages determined on erratics along the limit of glaciation by the Laurentide Ice Sheet yielded compatible ages, in the range of 12,000 to 22,000 YBP. These ages not only corroborated the dated stratigraphy from the Edmonton area, but also, taken with the results from the Mackenzie Mountains, showed that the last Laurentide Ice Sheet surpassed all previous ones in extent in western Canada.

Artifacts and animals

The implications for the ice-free corridor hypothesis from this body of work were clear: There had been no ice-free passage south along the eastern margin of the Cordillera from about 21,000 YBP (perhaps earlier) to as late as 12,000 YBP. This left little or no time for Clovis people (circa 11,200 YBP) to reach the mid-continent; the route would be untenable if people were in the Americas prior to 12,000 YBP.

For archaeologists, the glacial findings were disquieting; the idea that the ice-free corridor had been the route for peopling of the mid-continent was well-entrenched and appeared to have no credible alternatives. However, existing archaeological evidence from the corridor region is consistent with the new geological chronology. Few archaeological or paleontological sites in the corridor area are older than 10,000 YBP, and only paleontological sites have yet given dates over 11,000 YBP. The earliest archaeological sites include the Vermilion Lakes site, near Banff, Alberta; the Sibbald Creek site in the Alberta Foothills; Charlie Lake Cave in northeastern British Columbia; and Niska in southern Saskatchewan.

At Charlie Lake, people were using fluted projectile points more than 10,500 YBP, but these were points that fit neither the Clovis nor the Folsom category; they are smaller, more triangular, and have multiple flutes at the base, a distinctive enough pattern that they are now called Charlie Lake points.

One of the most striking relationships from a geographical standpoint is that the distribution of fluted projectile points on the Canadian plains, as mapped by second author Wilson, fits very well into the southern half of a corridor between the Cordilleran and Laurentide ice sheet margins for about 11,000 YBP as depicted in the Deglaciation of North America by Dyke and GSC colleagues. This ice margin was reconstructed independently based on nonarchaeological data. The oldest fluted-point sites are still those in the southern Great Plains and American Southwest, so this distribution seems more consistent with a northward movement of fluted point-using peoples from the mid-continent than with a southward movement through the ice-free corridor. Archaeologists have found a few fluted points in Alaska, but none in dated contexts, giving little evidence to suggest that they are comparably old. Cultural assemblages in Alaska that are of antiquity comparable to Clovis are technologically different from those of the mid-continent.

Corroborative evidence for a northward movement of fauna into the opening corridor comes from the late Wisconsinan vertebrate faunas (circa 11,500 to 10,000 YBP) found in the Canadian plains. These include numerous finds, such as those from gravel pits in the Cochrane-to-Calgary and Peace River areas, described by C.S. Churcher of the Royal Ontario Museum and Wilson, and from loess at the extensive Wally's Beach site on St. Mary Reservoir in southern Alberta, described by Brian Kooyman, Len Hills and co-workers at the University of Calgary. The faunal assemblage includes mammoths, camels, bison, helmeted musk-oxen and horses that again strongly resemble southern species. Bison resembling Alaskan species did not appear on the southern Alberta plains until about 10,500 YBP, if indeed even those were truly of Alaskan origin.

It appears that as the glaciers receded, southern-derived fauna moved northward to colonize the newly available territory, which probably resembled open tundra to steppe for the first millennium or so of exposure. In fact, the ice-free corridor also saw the transient presence of numerous, sometimes extensive glacially dammed lakes, given that the regional gradient dropped eastward and meltwaters pooled against the retreating Laurentide ice front, spilling southeastward along the margin in the southern corridor and northward in the northern corridor. Ephemeral ice dams were prone to failure, resulting in frequent outburst floods along the ice margin.

Despite decades of aggressive efforts by archaeologists from the universities of Alberta, Calgary and Lethbridge, together with the "First Albertans" program of the Archaeological Survey of Alberta (now within the Provincial Museum of Alberta), no credible pre-Clovis finds have yet been found in datable contexts within the corridor area. A potentially exciting find of human remains, the "Taber Child," was made by Stalker of in what appeared to be Pleistocene deposits, but was reinterpreted to be Holocene upon further excavations and radiocarbon dating by Wilson and R.G. Forbis.

Archaeologists may ascribe part of the paucity of early archaeological material to widespread landscape instability and preservation factors; however, the rarity even of radiocarbon-dated vertebrate remains older than 11,500 YBP stands in striking contrast to their abundance in immediately younger deposits. This evidence is consistent with a view that the corridor was closed during the last glacial maximum and unavailable as a dispersal route until Clovis times, if not later.

The weight of evidence therefore seems to point to the fact that the ice-free corridor was a transient feature at best, of late Pleistocene age. The Cordilleran and Laurentide ice sheets coalesced, closing off any "corridor" through most of the Wisconsin Glaciation. The opening of the corridor was biotic as well as physical: For each species of plant or animal, there was an "opening" in terms of opportunity and dispersal ability. Physical opening did not initiate a sudden stampede southward. Given the evident antiquity of South American Paleo-Indian sites, which predate the oldest Clovis site by a thousand years, the role of the ice-free corridor seems moot. Thus it would appear that evidence for the earliest human migrations to the mid-continent should be sought elsewhere, and the west coast is becoming more and more credible as an alternative.

Dating differences

Radiocarbon dating is the most frequently used method of dating in the Quaternary. Carbon has two stable isotopes, carbon-12 (12C) and carbon-13 (13C) — of which 12C is 500 hundred times more abundant — and one unstable radioactive isotope, carbon-14 (14C), which forms in the upper atmosphere, where its concentration relative to 12C is minute. Half of a quantity of 14C formed at any given time will decay to nitrogen-14 every 5,730 years. Radiocarbon (14C) enters the tissues of all living things, including bones and shells, while they are alive and consuming carbon from the atmosphere or oceans. Once the organism is dead, the radiocarbon clock begins to tick. Because of its geologically short half-life, the method is only applicable to approximately the past 50,000 years.

Radiocarbon dating measures the concentration of 14C in a specimen. Using that concentration relative to the concentration of 14C present in the atmosphere in the year 1950 ("year zero" for 14C dating) permits the calculation of an age based upon the 5,730-year half life. The method also assumes that the 14C:12C ratio in the biosphere and hydrosphere is in equilibrium with the atmosphere, and that the organism has not incorporated additional 14C since its death.

However, by 14C dating of tree rings, each of which represent a calendar year (one revolution of Earth around the Sun), researchers have determined that radiocarbon-dated years differ from calendar years. This discrepancy is due to the fact that 14C concentrations vary over time because of fluxes in Earth's magnetic field (and, more recently, nuclear weapons testing in the atmosphere). Much research has been devoted to correction of radiocarbon years to calendar years because the relation is not a straight-line function. Further, it is difficult to recalibrate radiocarbon dates older than approximately 15,000 years.

Some examples of conversions include:

14,000 radiocarbon years = 16,300 calendar years before present
12,000 radiocarbon years = 13,550 calendar years before present
11,500 radiocarbon years = 13,050 calendar years before present
11,000 radiocarbon years = 12,550 calendar years before present

To avoid misunderstanding and conversion error, scientists usually publish radiocarbon ages and define the method used in citing ages throughout their publication: for example, 11,500 radiocarbon years before present (YBP or RYBP). For a detailed explanation of radiocarbon dating, cosmogenic exposure dating and other methods used for in Quaternary research, see Jay Stratton Noller, Janet M. Sowers, William R. Lettis (Editors), 2000, "Quaternary Geochronology: Methods and Applications." AGU Reference Shelf Series, Vol. 4, American Geophysical Union, Washington.

Renée Hetherington and Lionel Jackson

Jackson is a Quaternary geologist with the Geological Survey of Canada in Vancouver, British Columbia, and an adjunct professor of earth science at Simon Fraser University. He has mapped the surficial geology of extensive areas of the Alberta Foothills and Yukon Territory. He has a longstanding interest in how and when the first people came to the Americas.

Wilson is an instructor in both the department of geology (of which he is past chair) and the department of anthropology at Douglas College, New Westminster, British Columbia. His primary research interests are vertebrate paleontology, Quaternary stratigraphy, geoarchaeology and human-landscape interactions. He is also adjunct professor of archaeology at Simon Fraser University.

Beringia

A Beginner's Guide to the

Homeland of the Peoples of the Americas

Glaciers & Sea Levels

In glacial ages more of the earth's water was locked in polar and mountain ice caps, lowering sea levels. The lower sea levels exposed additional land area along the coasts of the present continents. This coastal land, now below the surface of the ocean, were home to populations of plants and animals, and in the normal course of their lives they came to be distributed over wide areas, some of which, when the waters rose again, were bodies of land that are separated by water today.

The Bering Strait is today a relatively shallow body of water between Russia and Alaska. It partially dried up in some of these periods, producing a vast stretch of land that united northeast Asia with the Americas. The region was home to a wide range of cold-adapted animals and, at some periods, human beings.

This body of land is referred to as Beringia. (Link: http://www.beringia.com.) At times of lowest seas, it was about a thousand miles from north to south (roughly the distance between San Diego and Seattle or between Ottawa and Winnipeg).

Because this land lay across the modern divide between Eurasia and the Americas, it is also called the "Bering Straits Land Bridge." Some of the plants and animals living there (including people) are said to have "migrated to the Americas from Siberia" by this "route," even though they themselves probably had no sense that they were doing anything more than minding their own business and foraging on the landscape where they lived.

Scientists are now striving to understand the paleoenvironments of Beringia. Such research should eventually help us to figure out what animals and plants were found there during the various times when it was above sea level, and what environmental factors might have been conducive to long-term "transcontinental" movement of plants and animals (and microbes and viruses, for that matter). Much attention has been paid to the possibilities of steppe or tundra environments in this region. (Click for more about steppe environments or tundra environments.)

Crossing Beringia

Most early human populations of the Americas are descended from the peoples who lived in Beringia and, over the course of generations, "crossed" Beringia, so that when the waters eventually rose again, their descendants were dwelling on the American side. Part of our reconstruction of the peopling of the New World therefore depends in part upon knowing the periods when Beringia was above water and available for settlement.

(Increasing evidence suggests that some small North American populations, perhaps earlier ones, may have entered the Americas from elsewhere, since some early human remains in this continent do not seem to bear the expected close physical resemblence to subsequent pre-Columbian populations. Unfortunately relevant evidence has been systematically suppressed as many of the critical specimens found in the United States have been reburied by their modern "descendants," preventing further study. This is possible because a loophole in American law provides for modern descendants to have authority over their ancestors' remains, but does not recognize the possibility of ancient populations that are not ancestral to any modern groups. The specimen receiving most press attention recently is called Kenwick Man.)

Inland Route

The same cold weather that lowered the sea levels as much as 120 meters below their present level also produced glaciers over much of northern North America. During some periods when Beringia itself was available, however, a wide unglaciated "corridor" extended southwestward on the east side of the Canadian Rockies, even though the area along the coast of Alaska and Canada was covered with ice. The ice-free inland corridor followed the Mackenzie River basin in Northwest Territories and is therefore called the "Mackenzie Corridor." It could perhaps have provided a possible inland route for human migration, although there is no evidence that it was in fact used.

Coastal Route

At other periods glaciers covered the Mackenzie Corridor, but not the western coast of the North American continent, which provided a potential coastal route for possible migration, either on foot, or in part using simple water craft and living on coastal sea resources. Once again, there is no evidence that such a route was in fact used. In the case of the coastal route, we might expect that any scant remains of prehistoric coastal settlements would today be under water, since the modern higher seas would have covered the old coasts, so it is hard to imagine that we will ever have solid evidence for this path of migration.

One attempt to study the coastal terrain of this area as it was about 10,000 BC used a bathymetric map to locate areas for submarine sample collection which could be Carbon-14 dated. This provided evidence of coastal forests that had covered the area by that time, even though a couple of thousand years earlier it would have been frozen. One stone tool was even recovered dating from about 8,000 BC from a level 53 meters below the present sea level. These finds suggest continuing human populations in these coastal areas, and increase the probability of a model that would see the coast as also having been an early "migration route" into the Americas.

Dates

The following dates summarize the availability of unobstructed routes for human migration southward from Beringia during the ice age. During the "warm" periods of melted glaciers and high sea water, when Beringia itself was submerged, naturally both the coastal and inland routes were ice-free. Although the chart suggests a binary "open" and "shut" distinction, this is too simplistic: "open" does not always mean equally inviting, as the variation in sea levels and coastal woodland ecology clearly shows.

From the paleoclimatological information given here, it looks as though the coastal route hypothesis is stronger than the inland route hypothesis, and as though the "smart money" would be on the period 22,000-15,000 BC as the most probable time for this initial migration, with 38,000-34,000 as a provocative early-end hypothesis.

Dates BC	Beringia "Land Bridge"	Coastal Route	Mackenzie Corridor
38,000-34,000	accessible (open)	open	closed
34,000-30,000	submerged (closed)	open	open
30,000-22,000	accessible (open)	closed	open
22,000-15,000	accessible (open)	open	closed
15,000 BC - today	submerged (closed)	open	open

We have seen that archaeological evidence of such a migration has not been found in the Mackenzie Corridor, and that if it is in the Coastal Corridor it is under the sea. But paleoclimatological and archaeological data are not the only way to approach this issue. By the turn of the XXIst century, the most likely reconstruction, based on linguistic and genetic evidence, suggested that we should think of three separate "waves" of migration of pre-Columbian ancestors of modern North American populations:

Dates BC	Linguistic & Genetic Evidence
30,000	ancestors of Amerind speakers (now distributed over nearly all of the Americas)
9,000 - 12,000	ancestors of Na-Diné speakers (distributed over the northern half of North America)
4,800 - 5,400	ancestors of Eskimo-Aleut ("Eskaleut") speakers (distributed in the northernmost part of North America)

(This listing does not include immigrants who, so far as we know, were not ancestral to anyone alive in North America today, possibly including Kennewick Man and similar specimens.)

If we combine the paleoclimatological dates with the linguistic-genetic dates we notice that the inland route was "open" about 4,000 years earlier than the time when the linguistic and genetic "clocks" said these events would have happened. One view was that this might be the result of some kind of error in fixing dates for the linguistic and genetic evidence, or it could simply mean that a newly opened route wasn't immediately populated.

By 2010, DNA research was indeed pointing to somewhat earlier dates, with separate "Eskaleut" and Na-Diné migrations both occurring about 18,000 years ago, when both the land bridge and the sea route were negotiable:

Dates BC	Linguistic & Genetic Evidence
30,000	ancestors of Amerind speakers (now distributed over nearly all of the Americas)
16,000	ancestors of Na-Diné speakers (distributed over the northern half of North America)
16,000	ancestors of Eskimo-Aleut ("Eskaleut") speakers (distributed in the northernmost part of North America)

With these changes in our understanding of genetic evidence, the linguistic and genetic dates still fit will with the history of coastal route accessibility, but fit better with the history of land-bridge availability.

This suggests that the balance of evidence (for the time being) points to the now submerged coast in combination with a nomadic foraging way of life on the land bridge as the most probable migration route for these populations.

Beringia

Beringia: humans were here

Beringia is thought by a handful of renegade scientists to be a prehistoric homeland for aboriginal people who later spread across the Americas and the key to one of archeology's greatest Holy Grails - figuring out how humans first got to this continent.

By The Gazette (Montreal) May 17, 2008 Comments (5)

Story

Beringia is thought by a handful of renegade scientists to be a prehistoric homeland for aboriginal people who later spread across the Americas and the key to one of archeology's greatest Holy Grails - figuring out how humans first got to this continent.

This July, Jacques Cinq-Mars, a renowned archeologist living in Longueuil, is heading to Beringia - a vast territory that once spanned the Yukon, Alaska and Siberia - in hopes of resolving a controversy he unleashed nearly 20 years ago when he chanced upon a curious-looking cave in the Yukon's Keele Mountain Range, perched on a ridge high above the Bluefish River.

Here, at a site known as the Bluefish Caves, Cinq-Mars's team discovered something that would turn archeology on its ear and has fuelled debate ever since - a chipped mammoth bone that appeared to have been fashioned into a small harpoon point. Radiocarbon dating showed the bone to be 28,000 years old.

The find stunned archeologists who had long presumed the first people to enter the Americas did so 13,000 years ago via a land bridge from Siberia after the end of the last Ice Age.

Until that point, routes from Alaska down into the Americas were blocked off by glaciers up to four kilometres thick, which would have cut off any possibility of migration for thousands of years.

But scientists have unearthed a growing number of ancient human sites across the continent that date back much more than 13,000 years. How did those people get here? No one knows for sure.

Cinq-Mars, a retired former curator at the Canadian Museum of Civilization, believes the answers lie in the lost land of Beringia.

Named after 18th-century Danish explorer Vitus Bering, this territory emerged from under the sea when advancing glaciers locked up seawater and caused ocean levels to fall 120 metres. The 1,000-kilometre-wide land bridge that joined the two continents was so arid it remained a glacier-free oasis of grassland steppes that teemed with life at the height of the Ice Age.

People here lived alongside giant and outlandish animals - beavers the size of today's bears, fearsome carnivorous bears that would have dwarfed today's grizzlies, sloths as big as oxen, mastodons, lions and woolly rhinos and camels.

Cinq-Mars, who has been exploring Beringia since his student days in 1966, believes the region was not only a way-point for people migrating into the Americas, but also a homeland for aboriginal people for millennia as they sought refuge during the Ice Age.

If he is right, his finds at the Bluefish Caves and even older mammoth bone flakes found by another Canadian team at nearby Beringian sites mean people were already trundling around in the Americas long before the Ice Age. (Radiocarbon dating puts the age of the mammoth bone flakes found by the Archeological Survey of Canada team at 40,000 years old.) Nearly 20 years after the initial mammoth bone find was publicized in the early 1990s, however, much of the archeological establishment remains skeptical about Cinq-Mars's discoveries in Beringia. His finds clash with a long-held view known as the "Clovis First" theory, which is based on 13,000-year-old spear points found near Clovis, New Mexico, in the 1930s.

The Clovis theory, which dominated archeological thinking until recent years, holds that people first spilled into the Americas across the Siberian land bridge only after retreating glaciers opened passages through Canada to the south.

Archeologists who question Clovis First have been branded as renegades, said Raymond Le Blanc, an archeologist at the University of Alberta. "It's almost like admitting you saw a UFO," he said.

Le Blanc was a grad student on Cinq-Mars's team at the Bluefish Caves in the mid-1970s, when the exploration there started. (It took another 15 years to analyze the material uncovered and publish the results.) Far from being a ticket to fame and fortune, bucking the Clovis First doctrine has meant "you become part of the fringe. It's not great for your career. It becomes a little more difficult to get (research) money," he said.

Indeed, since the potentially stunning finds in Beringia, Cinq-Mars said he has struggled to cobble together research funds to continue the exploration and analyze what's been found.

"My biggest problem is getting access to funding. This is a scientific gold mine we've been sitting on for years, but many people just didn't give a hoot. There has been and still is very strong resistance. Clovis First has been the credo of archeology for decades," he said.

The waters have been muddied by scientific acrimony about the Bluefish Cave mammoth bone evidence. Some of Cinq-Mars's detractors say the bone could have been chipped at a later point long after the mammoth died or through natural processes like erosion or falling rocks.

"I'm very, very skeptical about cave data," said Bob Gall, a veteran archeologist with the U.S. National Park Service in Fairbanks, Alaska.

"They're occupied by animals and people, and material rolls down slopes. You have rock falls and material that's really difficult to sort out." Even if the mammoth bone was indeed modified by a person, Gall said it's still not clear when that would have happened. "From the time that elephant died, up until the present, it could have been modified by man," he said.

Subsequent research showed the bone was indeed likely to have been chipped by humans shortly after the mammoth died, but the questions have lingered, with many scientists saying more confirming data is needed.

That, in turn, has led to an archeological Catch-22: Little funding is available to pursue the Beringia research. "There are more things from that site we could date, but there has been a lack of money," Le Blanc said.

Complicating the search for confirming evidence is the fact that the best human sites to explore in the region are now probably at the bottom of the Bering Strait, said Ruth Gotthardt, an archeologist with the Yukon government. "The evidence is not co-operating," she said.

But now, the region is seeing renewed scientific interest as evidence emerges to suggest Cinq-Mars may have been on the right track after all.

Since the mid-1970s, more than two dozen other possible sites predating Clovis have been unearthed across North and South America. Perhaps the most famous is a 14,500-year-old settlement at Monte Verde, Chile, including a human footprint, tools and living quarters for 20 to 30 people.

Initially dismissed by archeologists, the Monte Verde site has become widely accepted as legitimate in recent years.

In 2004, the Clovis theory suffered another indirect blow when scientists in Siberia - in what used to be the western edge of Beringia - found a 30,000-year-old human site with tools fashioned from mammoth and rhino tusks.

The discovery showed humans had adapted to the extreme cold of the Far North thousands of years earlier than previously thought. It has also rejuvenated interest in Beringia, Le Blanc said. "If people got to the Arctic, I don't see why they couldn't have penetrated farther east." Meanwhile, Cinq-Mars has been amassing evidence from European researchers that shows chipped mammoth bones were used there as spear points more than 200,000 years ago - more evidence that the bone chips in Beringia were a widespread ancient technology.

And in July, Cinq-Mars plans to return to the region that ignited the controversy 30 years ago with hopes of finding more clues. He has received funds from the Yukon's Gwitchin First Nation in order to explore several sites, including the Bluefish Caves.

"There are layers there that have yet to be looked at which are likely to be older (than the original Bluefish find)," he said.

Cinq-Mars also has another mission for this trip - helping the Gwitchin village of Old Crow create a cultural centre to showcase the region's rich history.

In August, Le Blanc will also be poking around at another site called Gwizi Cave, about 60 kilometres to the north of Cinq-Mars's expedition. Le Blanc believes it, too, could yield more ancient remains.

Finding undisputed evidence of a pre-Ice Age human presence there, both men said, would force scientists to rewrite the history of the Americas.

"Beringia is the only site that explains the pre-Clovis finds," Le Blanc said. "The area has profound importance."

- - -

Following a trail of archeological clues over the millennia

40,000 to 28,000 years ago:

Age of chipped mammoth bones found at the Yukon's Bluefish Caves and nearby sites in the 1970s and '80s by archeologist Jacques Cinq-Mars and his team.

30,000 years ago:

Siberian mammoth hunters were found to have penetrated far into the Arctic by this period.

23,000 years ago:

The Ice Age entombs the northern hemisphere in glaciers, cutting off routes from Siberia to the south.

15,000 to 17,000

years ago:

Archeologists say people were living at Cactus Hill, Virginia, where stone tools and charcoal from a fire pit have been dated to this period.

14,500 years ago:

Humans were living in Monte Verde in southern Chile, where human tools, a dwelling structure and a person's footprint have been dated to this period.

14,000 years ago:

Archeologists believe this is when receding glaciers probably first opened an ice-free corridor through Canada between Alaska and the rest of the Americas. The conundrum: How did people get to Cactus Hill and Monte Verde before this?

13,000 years ago:

People were living near Clovis, New Mexico, where tools from this era were found in the 1930s. This find gave rise to the widely held Clovis First theory that people spread through the Americas only after the Ice Age.

11,000 years ago:

As the Ice Age ends, melting glaciers raise sea levels 120 metres, submerging the land bridge between Alaska and Siberia.

Beringia

Humans in the Americas Earlier than Previously Thought

DNA Studies Reveal Asians Arrived in North America 20,000-30,000 Years Ago

by Dr. Barry Starr, Stanford UniversityApril 11, 2008

Previous studies had suggested that humans first crossed over from Siberia to Alaska around 13,000 years ago. Two new DNA studies reveal that humans probably came to North America more like 20,000-30,000 years ago.

Some time after these Asian settlers arrived, glaciers or some other barrier kept them from returning back to Asia. And from moving south into North America.

Then, around 19,000 years ago, the Earth started to warm up. This warm up created the Bering Strait which kept these people from going back to Asia. But it allowed them to spread quickly through North and South America. In fact, it only took them a few thousand years to reach the southern part of South America.

Scientists in two separate studies figured this out by reading the entire mitochondrial DNA (mtDNA) sequence of hundreds of Native Americans and Asians. A different group confirmed that humans were in Oregon 14,000 years ago by looking at the mtDNA of some really old poop.

The Three Studies

Old Poop and Mitochondrial DNA

Humans may have crossed over from
Asia earlier than previously thought.

Scientists can learn a lot from poop. They can tell how many pandas are in the wild. They can tell which group of chimps the virus that causes AIDS came from. And they can tell when people were in North America.

Scientists do all of these things by looking at the DNA in this fecal matter. A group of scientists discovered some coprolites (a fancy word for old poop) in a cave in Oregon that they thought might be human.

They thought it was human because the coprolites looked like human poop. In the words of the authors, the 14 coprolites were "…morphologically human based on size, shape, constituents, and color." What piqued these researchers' interest was that they found the poo in a very old part of the cave. From a region of the cave that should have predated humans in America.

When they did carbon dating on these coprolites, they determined that they were around 14,000 years old. This contradicted older theories about the settling of the New World and so they set out to prove that the poo was human.

They did this by looking at the mitochondrial DNA (mtDNA) in the coprolites. There are thousands of copies of this DNA per cell so it is ideal for studies of older samples where lots of the DNA might be degraded.

The researchers did find human DNA in the coprolites. But this didn't prove that the poop was human.

A big problem with studying old specimens like this comes from contamination with modern human DNA. What if they were really looking at some of the researchers' own DNA that had somehow ended up on the coprolites? Or what if human DNA from a more recent sample had leached into this sample?

These can be tricky questions to answer. Luckily, it is relatively easy to tell different people's mtDNA apart.

Proving the Poo is Old Poo

DNA recombines in sperm and
eggs. This makes most DNA
hard to trace.

MtDNA is very different from the rest of our DNA. First off, it is found in the mitochondria and not the nucleus. Second, it passes directly from mother to child. Dad's mtDNA is destroyed as soon as the egg is fertilized.

These properties make mtDNA ideal for ancestry and, in cases like this, identification purposes. Why? Because this DNA does not recombine.

Remember, that with the exception of the Y chromosome, we have two copies of each of our chromosomes. One copy comes from mom and the other from dad.

Just before a sperm or egg is made, each pair of chromosomes swaps some DNA. This is a wonderful process for creating ever more unique individuals. But it means that after a few generations, DNA gets pretty jumbled up and becomes hard to trace.

Because mtDNA has no partner and dad's mtDNA is destroyed, it doesn't undergo recombination. This DNA passes virtually unchanged directly from mother to child. Which means scientists can trace back this DNA for thousands of years along a line from mom to grandma to great grandma, etc.

When the researchers looked at the DNA in the poop, they found that it was Native American mtDNA. They checked the mtDNA of anyone involved in the research or who might have come into contact with the samples and showed that none of them had Native American mtDNA. So the DNA did not come from the researchers.

The next step was to show that the DNA didn't come from other samples in the cave. One of the ways they decided to rule this out was to look for wood rat DNA in the samples.

Wood rat remains litter the cave where they found these coprolites. So if any DNA were going to leach into their samples and contaminate them, it would be wood rat DNA. They found no wood rat DNA in the samples.

They did many other experiments to show that the DNA didn't leach from somewhere else too and all the results were negative. So most likely the poop was human and around 14,000 years old. This means humans were almost certainly in North America longer than had been previously thought.

Divining American History through DNA

Scientists can learn a lot
about history by studying
people's DNA.

Now that researchers had confirmed that humans were as far south as Oregon by 14,000 years ago, the next question is how did they get there? Two research groups came up with a theory based on studying the mtDNA of hundreds of Asians and Native Americans.

Of course, people had done these kinds of studies before. These earlier studies had shown that there were five main groups of Native American mtDNA—A, B, C, D, and X.

Scientists believed that A-D came from Asia as it matched up very well with mtDNA from Siberia. The X group was a mystery though. The latest theory was that these people's ancestors might have come from Europe based on the fact that there were a few X groups
there too.

What is different about these two groups' new research is that they looked at more of each person's mtDNA. The older work looked at just a snippet or two of the mtDNA. The new research looked at all 16,569 DNA bases.

When they did this they were able to see patterns that were hidden before. For example, the X group looked much more similar to the A-D groups than had been previously thought. Most likely the X group was part of the original group that came over from Asia.

The researchers also studied the differences between all of these people. Because mtDNA doesn't recombine, these differences came from the occasional DNA change that crops up in any DNA over time*.

By looking at these changes, scientists could figure out that the founding group was probably larger than scientists originally thought. Older data suggested that as few as 80 people came over from Asia. The new data suggested that the number was probably closer to 1000.

The data also suggested that this group stayed small and did not mix with other groups for thousands of years. Then, around 18,000 or 19,000 years ago, the group suddenly expanded greatly in size.

It is from this kind of data that the researchers came up with their theory about how the Americas were populated. Their theory is that Asians settled in what is now North America 20,000-30,000 years ago.

This group continued to interact with the original Asian populations for many years but then stopped for some reason. The numbers line up with a new ice age which is where the idea that they became trapped by glaciers came from.

The group was then stuck there for thousands of years and never grew much beyond 1000 people. Then when the thaw opened up access to North and South America along the Pacific coastline, the population quickly spread.

It is important to remember that this is just a theory to explain the DNA data the researchers saw. And that more extensive studies may change the storyline. But one thing is for sure; humans were in North America much earlier than was previously thought.

* These mutations can be caused by something in the environment that damages the DNA. Or the cells can do it to themselves when they make a mistake copying their DNA.

Beringia

American Beginnings: The Prehistory and Palaeoecology of Beringia

Antiquity, March, 1997 by Herbert D.G. Maschner

The peopling of Beringia is perhaps one of the most contentious and competitive areas of research in American archaeology. Few sites and data, poor reporting of finds and a complete lack of theory have left the field open to speculation, misrepresentation and inaccuracy. American beginnings attempts to 'present as much concrete evidence as could be marshaled on the matter of the first settlement of the New World' (West p. 537) in hopes of solving some of the problems faced by this area of study.

American beginnings includes much of the data available on the Late Pleistocene and early Holocene archaeology of Beringia. The book begins with an introductory essay by one of the fathers of Beringian studies, David M. Hopkins (Hopkins 1967; Hopkins et al. 1982), who presents his thoughts on the history of scientific dialogue that has attempted to understand the geology, palaeoecology and archaeology of Beringia. This is followed by a Preamble by Frederick Hadleigh West (the volume editor) where he describes in greater detail the history of research on Beringia, especially the archaeological evidence. The body of the book is divided into three parts, each part into thematic chapters and each chapter into short data articles by specific investigators.

Part 1: Paleoenvironmental Research is introduced by West's long-term collaborator Paul Colinvaux. Chapter i includes four papers on the geological record of Beringia and chapter 2 has eight articles on the biotic records of Beringia. These are important chapters. They set the scene, or the context, for investigating the initial human occupation of the region.

Part 2: Archaeological Evidence is introduced by John Hoffecker. Part 2 is subdivided into two sections: Western Beringia and Eastern Beringia. Western Beringia includes three geographically based chapters with 19 articles on either individual sites or groups of sites. Eastern Beringia has six regional chapters with 36 site descriptions. All of the archaeological articles are fairly uniform in their presentation of the data with a section on site history, geography, stratigraphy, fauna (where present), and lithics, with good graphics and artefact drawings. Many of the sites have never, before now, been published in any detail.

Part 3: Conclusions has only one chapter with two articles, one on Native American linguistics by Joseph Greenberg and a summary overview of the archaeological evidence by West. These are perhaps the critical articles in the book, especially the concluding overview. It is here that West provides the only synthetic statement in the entire book, attempting to draw together a comprehensive understanding of the nature of the Beringian archaeological record. This is also where he presents a view that many of the individual authors would probably not agree with. In fact, many of the conclusions and inferences described by West in his concluding chapter are directly contradicted by the data presented in the individual articles, making one wonder if he actually read them. Since the Conclusion is the only synthesis and context for the individual contributions, I will begin with the conclusion and present West's view of Beringia. I will limit most of my comments to the archaeological data, having excavated at several of the sites in this volume and translated most of the Siberian literature. The palaeoecology will not be discussed in detail. I am not a specialist in Beringian palaeoecology, merely a consumer of the good work that has been done there.

West's world

In the Introduction, David M. Hopkins defines Beringia as the area between the Kolyma River in northeastern Siberia and the Mackenzie River in northwestern Canada (p. xvii). This region is defined on the basis of geology, palaeoecology, climate, vegetation, geography, and a number of other natural characteristics along the same lines as Hulten's early use of vegetation (1937). In the Preamble, West extends Beringia to include all of the Lena and Aldan River regions (p. 1). Why? West has a rather specific agenda. He wants to see all of Beringian prehistory as an eastern extension of the Eurasian Upper Palaeolithic, which, in his view, requires that the archaeological data from the Lena Basin be included. This includes all of the various archaeological complexes and traditions such as Dyuktai and Ushki in western Beringia and Denali, Nenana, and Anangula in eastern Beringia. West follows three lines of reasoning to make this Upper Palaeolithic connection.

First, the greater majority of archaeological assemblages from Beringia are dominated by core and blade technologies. In the case of the earliest core and blade sites, these blades can be considered microblades that were intended to be inset in bone, antler or ivory projectiles. They are not usually modified into other tool forms. West sees this as the eastern extension of the Upper Palaeolithic. He is not concerned that the core and blade technologies of western Eurasia are dominated by larger blades or that tools are often made on blades, but only finds relevance in the fact that it was a blade technology. When considering sites that do not have microblades (Hoffecker et al. 1993; Goebel et al. 1991), West considers these assemblages to be sites without microblades, not non-microblade complexes. Although he is willing to recognize variability in the Beringian archaeological record, he does not consider it significant. He goes on to argue that the Clovis Tradition must be derived directly from the Beringian Tradition (West's term for all Beringian assemblages) based on time and geography. He states that many Clovis tools have Beringian similarities and thus, the Clovis Tradition is also a product of the Upper Palaeolithic tool kit, although somewhat removed in space and time. While the Alaskan assemblages are indeed quite similar or the same as some of the east Asian assemblages, there is still much debate as to whether these microblade-based tool kits are derived from Europe or from independent events that occurred in China, Mongolia or Japan.

I'm a beringian

Beringia

The Bering land bridge was a land bridge roughly 1,000 miles (1,600 km) north to south at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. It was not glaciated because snowfall was extremely light due to the southwesterly winds from the Pacific Ocean having lost their moisture over the fully glaciated Alaska Range. The grassland steppe including the land bridge and stretching for several hundred miles either side of it has been called Beringia . It is believed that a small human population of at most a few thousand survived the last ice age in Beringia, isolated from its ancestor populations in Asia for at least 5,000 years, before expanding to populate the Americas sometime after 16,500 years ago, as the American glaciers blocking the way southward melted.

Geography

The Bering Strait, the Chukchi Sea to the north and the Bering Sea to the south, are all shallow seas ( map, right ). During cycles of global cooling, such as the most recent ice age, enough sea water became concentrated in the ice caps of the Arctic and Antarctic that the subsequent drop in eustatic sea levels exposed shallow sea floors. Other land bridges around the world have been created and re-flooded in the same way: approximately 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania; the British Isles were an extension of continental Europe via the English Channel; and the dry basin of the South China Sea linked Sumatra, Java and Borneo to the Asian mainland.

The rise and fall of global sea levels has exposed and submerged the land bridge in several periods of the Pleistocene. The bridging land mass called "Beringia" is believed to have existed both in the glaciation that occurred before 35,000 BC and during the more recent period 22,000-7,000 years ago. By c. 4000 BC the coastlines had assumed approximately their present configurations.

Beringia constantly transformed its ecology as the changing climate affected the environment, determining which plants and animals were able to survive. The land mass could be a barrier as well as a bridge: during colder periods, glaciers advanced and precipitation levels dropped. During warmer intervals clouds, rain and snow altered soils and drainage patterns. Fossil remains show that spruce, birch and poplars once grew beyond their northernmost modern range today, indicating there were periods when the climate was warmer and wetter. Mastodons, which depended on shrubs for food, were uncommon in the open dry tundra landscape characteristic of Beringia during the colder periods; in this tundra, mammoths flourished instead.

Human habitation

The Bering land bridge is significant for several reasons, not least because it is believed to have enabled human migration to the Americas from Asia about 25,000 years ago. A study by Hey (2005) have indicated that of the people migrating across this land bridge during that time period, only 70 left their genetic print in modern descendants, a minute effective founder population—easily misread as though implying that only 70 people crossed to North America. Seagoing coastal settlers may also have crossed much earlier, but scientific opinion remains divided on this point, and the coastal sites that would offer further information now lie submerged in up to a hundred metres of water offshore. Land animals were able to migrate through Beringia as well, bringing mammals that evolved in Asia to North America, mammals such as proboscideans and lions, which evolved into now-extinct endemic North American species, and allowing equids and camelids that evolved in North America (and later became extinct there) to migrate to Asia.

A new study published November 26, 2007 (see PLoS Genetics), which was led by University of Michigan and University College London researchers, seems to suggest that the Bering land bridge migration occurred during one specific time period which was 12,000 years ago, that every human who migrated across the land bridge all came from Eastern Siberia during that time period, and that every native American is directly descended from that same group of Eastern Siberian migrants. The claim suggests that a "unique genetic variant widespread in natives across both continents — suggesting that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources".

Previous connections

Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils have been found between Asia and North America. For instance the dinosaur Saurolophus was found in both Mongolia and western North America. Relatives of Troodon, Triceratops, and even Tyrannosaurus rex all came from Asia.

While there is considerable evidence for faunal interchange of dinosaurs in the Campanian and Maastrichtian phases of the Late Cretaceous, mammals, however, seem not to have dispersed so easily, perhaps because of their relatively small size; at any rate, there is no direct evidence supporting mammalian faunal exchange in the Cretaceous. Fossils in China demonstrate a migration of Asian mammals into North America around 55 million years ago. By 20 million years ago, evidence in North America shows a further interchange of mammalian species. Some, like the ancient saber-toothed cats, have a recurring geographical range: Europe, Africa, Asia, and North America. The only way they could reach the New World is through the Bering land bridge. Had this bridge not existed at that time, the fauna of the world would be very different.

Molecular phylogenetics is now being used to trace the history of faunal exchange and diversification, through the genetic history of parasites and pathogens of North American ungulates. An international Beringian Coevolution Project is collaborating to provide material to assess the pattern and timing of faunal exchange and the potential impact of past climatic events on differentiation.

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Peopling of the Americas: Three Step Model for Colonizing the Americas

14 Thursday Feb 2008

Posted by Kambiz Kamrani in Blog, Physical Anthropology

≈ 22 Comments

Tags

coalescence theory, mtDNA, native americans, peopling of the americas, Physical Anthropology, population genetics

To supplement last September’s conclusion that the peopling of the Americas was initiated by a pretty diverse group of people who camped out in Beringia for a long time, long enough to differentiate from their Asian sister-clades, comes this study published in this week’s PLoS One, “A Three-Stage Colonization Model for the Peopling of the Americas.”

The new study offers up perhaps the largest published alignments of Native American mtDNA, spanning all Native American haplogroups. Over 77 full mitochondrial coding genomes were constructed from 812 concatenated mtDNA hypervariable region (HVR) I and II sequences. They took these mitochondrial genomes, aligned them up, and applied the same algorithims, Bayesian skyline plotting, used in a recent paper to estimate prehistoric population sizes. Bayesian skyline plots are a unique approach to the coalescent modeling, that assume a single migration event, and thus test the generally agreed consensus that there was a single migration of people in the Americas.

The dominant model on the peopling of Americas started with the the ice sheets advancing and sea levels falling about 17,000 years ago. It is during this time that people are thought to first migrate across the Eurasian landmass and into the Americas. It was thought that a very small number of people, maybe even as small as 70 or so, who crossed over. Perhaps they were nomadic hunters, following game herds from Siberia across what is today the Bering Strait into Alaska, and then gradually spreading southward. Based upon the distribution of Amerind languages and language families, a movement of tribes along the Rocky Mountain foothills and eastward across the Great Plains to the Atlantic seaboard is assumed to have occurred some 10,000 years ago.

What this new study found doesn’t indicate that the peopling of the Americas happened in one fell swoop. Rather, it supplements the paper I mentioned above, “Beringian Standstill and Spread of Native American Founders,” and offers up an interesting time frame, a three stage colonization event that is effectively illustrated by the authors. I’ve cut out the figure the authors provided, it’s to your left. The first stage began about 40,000 years ago with a gradual ancestral population expansion of people from an East Central Asian gene pool into Beringia. The second stage of ‘proto-American Indians’ was marked by almost no population growth for about 20,000 years, which confirms the previous Beringian standstill conclusion. The last stage started about 16,000 years ago with a massive rush of people, about 5,000 strong, fleeing out of Beringia and into the “ice free, inland corridor between the eastern Laurentide and western Cordilleran Ice Sheets and/or along the Pacific coast.” This challenges the n=70 founding population estimation.

The authors offer up no discussion about a possibility of bidirectional gene flow, which was shown in the September 2007 Beringian Standstill study that I keep referring too. I’m thinking its cause the skyline plots test for single migration events and not backflows.

Either way, it is a very enlightening study especially because other models, such as the Clovis archaeological model, which says the peopling of the Americas happened in 11,000 years, estimate really rapid colonization events. That’s awfully fast. Pushing back first rush of people to 16,000 years ago can help us better explain how the Clovis culture radiated so fast.

Amerindian DNA

Amerindian mitochondrial DNAs have rare Asian mutations at high frequencies, suggesting th

TG Schurr, SW Ballinger, YY Gan, JA Hodge, DA Merriwether, DN Lawrence, WC Knowler, KM Weiss, DC Wallace

The mitochondrial DNA (mtDNA) sequence variation of the South American Ticuna, the Central American Maya, and the North American Pima was analyzed by restriction-endonuclease digestion and oligonucleotide hybridization. The analysis revealed that Amerindian populations have high frequencies of mtDNAs containing the rare Asian RFLP HincII morph 6, a rare HaeIII site gain, and a unique AluI site gain. In addition, the Asian-specific deletion between the cytochrome c oxidase subunit II (COII) and tRNA(Lys) genes was also prevalent in both the Pima and the Maya. These data suggest that Amerindian mtDNAs derived from at least four primary maternal lineages, that new tribal-specific variants accumulated as these mtDNAs became distributed throughout the Americas, and that some genetic variation may have been lost when the progenitors of the Ticuna separated from the North and Central American populations.

[Pubmed Record - new window] | [Full Text - new window]

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frequencies, mtDNAs, Amerindian mtDNAs, Pima, prevalent, tribal-specific, lost, progenitors, North, trnalys genes, Ticuna separated, oxidase subunit, Amerindian populations, restriction-endonuclease digestion, North American Pima, HaeIII, AluI, mitochondrial dna mtdna, cytochrome, Asian-specific deletion, COII,

Dating of the human-ape splitting by a molecular clock of mitochondrial DNA.
J Mol Evol Jan 23, 1986
... data. The molecular clock of mitochondrial DNA (mtDNA) was calibrated by setting the date of divergence between primates ... human-ape splitting. Another likelier possibility is that mtDNA was transferred through hybridization between a proto-human and a proto ...

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