Manataka American Indian Council

 

 

FEATURE

 

 

Land Bridge Migration Theory Finally Debunked

By Takatoka

 

For as far back as our stories and collective memories go back in time, indigenous people have always believed that we began our journey on Turtle Island tens of thousands of years ago -- long before most anthropologists theorize.  A majority of scientists assume that migration began in Asia by a small human population who survived the last glacial movement in Beringia, the "Land Bridge" between today's Alaska and China.  According to the theory, the small group was isolated from its ancestor populations in Asia as the glaciers melted for at least 5,000 years, before expanding to populate the North American continent sometime after 16,500 years ago.

 

We are happy to report the latest scientific DNA studies show a much different picture, one that proves American Indians did not originate from Asian Mongolians, but are a separate and distinct race who evolved tens of thousands of years ago from islands or a single island in the Pacific Ocean. 

 

 

We invite you to read two reports attached to this article that offer strong evidence that will hopefully, once and forever, debunk the Land Bridge theory:

 


 

Native Americans Descended From A Single Ancestral Group, DNA Study Confirms

 

ScienceDaily (Apr. 29, 2009) — For two decades, researchers have been using a growing volume of genetic data to debate whether ancestors of Native Americans emigrated to the New World in one wave or successive waves, or from one ancestral Asian population or a number of different populations.

 

Now, after painstakingly comparing DNA samples from people in dozens of modern-day Native American and Eurasian groups, an international team of scientists thinks it can put the matter to rest: virtually without exception, the new evidence supports the single ancestral population theory.

 

“Our work provides strong evidence that, in general, Native Americans are more closely related to each other than to any other existing Asian populations, except those that live at the very edge of the Bering Strait,” said Kari Britt Schroeder, a lecturer at the University of California, Davis, and the first author on the paper describing the study.

 

“While earlier studies have already supported this conclusion, what’s different about our work is that it provides the first solid data that simply cannot be reconciled with multiple ancestral populations,” said Schroeder, who was a Ph.D. student in anthropology at the university when she did the research.

The study is published in the May issue of the journal Molecular Biology and Evolution.

 

The team’s work follows up on earlier studies by several of its members who found a unique variant (an allele) of a genetic marker in the DNA of modern-day Native American people. Dubbed the “9-repeat allele,” the variant (which does not have a biological function), occurred in all of the 41 populations that they sampled from Alaska to the southern tip of Chile, as well as in Inuit from Greenland and the Chukchi and Koryak people native to the Asian (western) side of the Bering Strait. Yet this allele was absent in all 54 of the Eurasian, African and Oceanian groups the team sampled.

 

Overall, among the 908 people who were in the 44 groups in which the allele was found, more than one out of three had the variant.

 

In these earlier studies, the researchers concluded that the most straightforward explanation for the distribution of the 9-repeat allele was that all modern Native Americans, Greenlanders and western Beringians descend from a common founding population. Furthermore, the fact that the allele was absent in other Asian populations most likely meant that America’s ancestral founders had been isolated from the rest of Asia for thousands of years before they moved into the New World: that is, for a period of time that was long enough to allow the allele to originate in, and spread throughout, the isolated population.

As strong as this evidence was, however, it was not foolproof. There were two other plausible explanations for the widespread distribution of the allele in the Americas.

 

If the 9-repeat allele had arisen as a mutation multiple times, its presence throughout the Americas would not indicate shared ancestry. Alternatively, if there had been two or more different ancestral founding groups and only one of them had carried the 9-repeat allele, certain circumstances could have prompted it to cross into the other groups and become widespread. Say that there was a second allele — one situated very close to the 9-repeat allele on the DNA strand — that conferred a strong advantage to humans who carried it. Natural selection would carry this allele into new populations and because of the mechanics of inheritance, long stretches of DNA surrounding it, including the functionless 9-repeat allele, would be carried along with the beneficial allele.

To rule out these possibilities, the research team, which was headed by Noah Rosenberg at the University of Michigan, scrutinized DNA samples of people from 31 modern-day Asian populations, 19 Native American, one Greenlandic and two western Beringian populations.

 

They found that in each sample that contained the 9-repeat allele, short stretches of DNA on either side of it were characterized by a distinct pattern of base pairs, a pattern they seldom observed in people without the allele. “If natural selection had promoted the spread of a neighboring advantageous allele, we would expect to see longer stretches of DNA than this with a similarly distinct pattern,” Schroeder said. “And we would also have expected to see the pattern in a high frequency even among people who do not carry the 9-repeat allele. So we can now consider the positive selection possibility unlikely.”

 

The results also ruled out the multiple mutations hypothesis. If that had been the case, there would have been myriad DNA patterns surrounding the allele rather than the identical characteristic signature the team discovered.

 

“There are a number of really strong papers based on mitochondrial DNA — which is passed from mother to daughter — and Y-chromosome DNA — which is passed from father to son — that have also supported a single ancestral population,” Schroeder said. “But this is the first definitive evidence we have that comes from DNA that is carried by both sexes.”

 

Other authors of the study are David G. Smith, a professor of anthropology at UC Davis; Mattias Jacobsson, University of Michigan and Uppsala University in Sweden; Michael H. Crawford, University of Kansas; Theodore Schurr, University of Pennsylvania; Simina Boca, Johns Hopkins University; Donald F. Conrad and Jonathan Pritchard, University of Chicago; Raul Tito and Ripan Malhi, University of Illinois, Urbana-Champaign; Ludmilla Osipova, Russian Academy of Sciences, Novosibirsk; Larissa Tarskaia, Russian Academy of Sciences, Moscow; Sergey Zhadanov, University of Pennsylvania and Russian Academy of Sciences, Novosibirsk; and Jeffrey D. Wall, UC San Francisco.

 

The work was supported by NIH grants to Rosenberg and Smith and an NSF Graduate Research Fellowship to Schroeder.

 

Journal reference:

Schroeder et al. Haplotypic Background of a Private Allele at High Frequency in the Americas. Molecular Biology and Evolution, 2009; 26 (5): 995 DOI: 10.1093/molbev/msp024    Adapted from materials provided by University of California, Davis.

 

Reference

http://www.sciencedaily.com:80/releases/2009/04/090428223836.htm

 


 

Strands of Time

Variations in Fragments Hint Some American Natives May Hail From Polynesia
by Jerry E. Bishop, staff reporter
 

St. Louis -- Douglas C. Wallace can see the future in a tiny strand of DNA. ... But he also can peer deep into the past. He has looked back more than 100,000 years to the first humans in Africa. And recently, as a gathering here of science reporters, he painted a picture of prehistoric migrations emerging from DNA that is exciting anthropologists.

 

The scene depicts groups of prehistoric, intrepid mariners moving, not out of Siberia as anthropologists have long assumed, but out of Southeast Asia across the Pacific into the Americas 6,000 to 12,000 years ago. If this picture is accurate, it makes many American Indians distant cousins of the Polynesians.

 

Dr. Wallace's crystal ball is a unique fragment of DNA hidden in every human cell. This clairvoyant DNA is distinct and separate from the long strings of DNA that house almost all human genes in the cell nucleus. It resides, instead, in an outlying compartment called a mitochondrion. Hence its name: mitochondrial DNA, or simply mtDNA.

 

The mtDNA contains a mere 37 genes compared with the 50,000 to 100,000 genes in nuclear DNA. And these few mtDNA genes are devoted largely to the mitochondria's principal job of producing chemical energy for the thousands of second-by-second chemical reactions in a cell.

Yet, astonished medical researchers are finding that defects in this snippet of DNA can cause human disease. And, to the surprise of anthropologists, mtDNA is turning into a kind of biological Rosetta stone for decoding human origins.


Loud Ties, Deep Theories

Few scientists studying mtDNA are probing deeper--and risking more--than Doug Wallace, a professor of genetics and molecular medicine at Emory University in Atlanta. Slight and bespectacled, the 47-year-old scientist is famous among his students for loud neckties and, until recently, his polyester suits. ("When I finally got a raise my wife took all my leisure jackets and threw them away," he says.)

 

Clearly, mtDNA has become Dr. Wallace's consuming, almost obsessive interest. ... Yet this detour into anthropology via mtDNA isn't without controversy.

Dr. Wallace, for example, subscribes to the much-publicized "Eve hypothesis," in which a reading of mtDNA indicates modern humans originated in Africa 100,000 to 200,000 years ago. Some anthropologists retort that mtDNA is an unreliable clock for timing human evolution, and that the fossil evidence shows modern humans evolved much earlier than mtDNA indicates.

 

But it is another strange property of mitochondria that unexpectedly thrust the young scientist into the study of human origins. Humans inherit two copies of the nuclear genes, one from each parent. But only the mother's mitochondrial genes are passed on to the child for reasons still not fully understood.

Thus, every person's mtDNA is descended in a direct line through female ancestors. There isn't any DNA from the father's side of the family mixed in to confuse the line of descent. This phenomenon of maternal inheritance had been seen in animals but it was a young Doug Wallace who showed it occurred in humans in a series of experiments in 1979 at Stanford University in Palo Alto, Calif.

 

Dr. Wallace ... saw in this maternal inheritance a way to tell how closely groups of people are related. As mtDNA is passed down from mother to daughter, innocuous alterations or mutations are bound to occur. Over a few thousand years, groups of people who live together and intermarry will accumulate distinctive patterns of these mutations.


Continental Divide

In 1981 Dr. Wallace headed a Stanford research team that found that ethnic groups could be identified and linked to their continent of origin by the mutation patterns in their mtDNA. Moreover, by determining how often these telltale mutations occurred, it was possible to calculate how long ago certain groups stopped intermarrying and separated, each going off to develop its own unique pattern of mtDNA mutations.

 

"Each continent had a different pattern" of mtDNA mutations, Dr. Wallace recalls of his research findings. Africans had mtDNA variations that distinguished them from Asians who, in turn, had variations that distinguished them from European-American Caucasians. "That's when I knew we had an anthropological story," he says. ...

 

Dr. Wallace began studying the mtDNA of Native Americans in the mid-1980s in hopes of resolving a long-raging debate over when prehistoric peoples entered the Americas. The presumption long has been that the ancestors of Native Americans came from Siberia. But anthropologists have argued for year over how many, and when, such migrations occurred.

 

The mtDNA analyses are showing that the ancestors of the Amerinds, who comprise most Native Americans, entered the Americans in a single migratory wave 20,000 to 40,000 years ago, Dr. Wallace and his Emory colleagues ... reported last year. This puts humans in the Americas long before a fluted stone-spear point--the oldest American tool ever found--was dropped by a prehistoric dweller near Clovis, N.M., 11,000 years ago.

The researchers also found that ancestors of the Navajo, Apache and other members of a Native American group, known collectively as the Na-Dene, are latecomers; they entered the continent in a second migration a mere 5,000 to 10,000 years ago, the research indicates.


Polynesian Links?

To their surprise, however, the researchers found that native Siberians lack one peculiar mutation that appeared in the Amerinds 6,000 to 10,000 years ago. This raises the question of where, if not from Siberia, this mtDNA originated.

 

It turns out, Dr. Wallace says, that this particular mutation pattern is also found in aboriginal populations in Southeast Asia and in the islands of Melanesia and Polynesia. This hints at what may have been "one of the most astounding migrations in human experience," he says. A group of ancient peoples moved out of China into Malaysia where they became sailors and populated the islands of the South Pacific.

 

Then some 6,000 to 12,000 years ago these ancient mariners made it to the Americas. "I don't know how they came," Dr. Wallace says. "They either came across the Pacific to Central and South America or they went up the east coast of Asia and across the northern Pacific to Alaska and Canada," he says. He already is examining mtDNA samples from natives of the Kamchatka Peninsula north of Japan to see if there is any mtDNA trace of these ancient sailors.

 

 


 

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