Native Americans descended from a single ancestral group, DNA study confirms (5/1/2009)
|A distinct DNA signature was found among all but one of the populations shown as points 32 to 53 on this map. The Fox tribe, point 48, was the exception. But DNA samples of only 2 Fox people were tested -- too few to provide a valid result. The DNA signature was absent in all Asian groups sampled, points 1-32. - Kari Britt Schroeder/UC Davis|
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."
Note: This story has been adapted from a news release issued by the University of California - Davis
5/1/2009 1:03:06 PM MST
"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." ... so then, if a migration via the Bering Straights land bridge during the last ice age wasn't the source of modern day Native American populations, if you look back far enough, where do Native American populations originate from?
5/1/2009 3:27:16 PM MST
That's not quite what the article says. It says the Native American founders separated from Eurasians thousands of years ago, stayed together or in small enough numbers for the allele to mutate and become established in the founding population, and then the population dispersed throughout the Western hemisphere. Where the isolation occurred -- on the land bridge, in Siberia, or in North America itself -- can't be specified.
If other migrations occurred later, they were in numbers small enough and contacted the founders quickly enough to "drown in the local gene pool."
5/1/2009 5:59:11 PM MST
Men have mitochondrial DNA too!
5/11/2009 1:10:40 PM MST
We don't need mitochondrial DNA we have teh power of themz Y-CHROMOSOMES
5/14/2009 10:03:58 AM MST
"Men have mitochondrial DNA too!"
Well more precisely "men have their mom's mitochondrial DNA"
7/1/2009 2:48:47 PM MST
So we're all sissies!
10/27/2009 3:29:15 PM MST
"Where the isolation occurred -- on the land bridge, in Siberia, or in North America itself -- can't be specified."
I wonder if the fact that the only population with the 9-repeat allele outside of the Americas (and Greenland) is located on the Asian (western) side of the Bering Strait tends to indicate that the isolation occurred on the eastern side of the Bering Strait in the new world. Further, that this supports those arguing for a preclovis migration.
If an isolation of a sustainable population occurred many thousands of years ago in a scarcely populated section of the western Bering straight, how come those people only migrated east (into the new world) and not also west? Seems odd. One would think the center of the civilization that gave rise to the mutation was located in the new world given it's dispersion over time.
10/27/2009 6:04:39 PM MST
After fusion of the sperm and egg, the zygote only contains mitochondria from the mother.
10/28/2009 12:59:13 AM MST
thats because to the west was siberia joe.
10/28/2009 8:48:37 AM MST
Perhaps the NA in America were survivors of a continent that no longer exists. I have often wondered if perhaps we were descendants of the continent of Atlantis, presuming it was somewhere off the shores of America to the East and that the inhabitants fled in all directions, including America both North and South. This is compatible with legends as well.
10/28/2009 4:03:28 PM MST
I may be reading this wrong, but if lack of similar surrounding dna rules out selective breeding, wouldn't that also confirm random mutation (and vise-versa)? also I understand polynesians are related to tlinglit people from canada, but the 9-repeat allele says they aren't, how come?
10/29/2009 11:11:02 AM MST
Why not test in Europe or Africa for the allele? Isn't it possible the ancestors were isolated in the Americas and spread over to the western Bering from there.
Or it's possible Eurasians came to America and some went back across the Bering much later to find the population there, in the same way the Inuit found their way to Greenland.
12/13/2009 3:39:17 AM MST
Eurasian ONLY refers to the continental location NOT the DNA. ALL Native American are purely Mongoloid of origin.
4/6/2010 1:04:24 PM MST
I've always thought from my tribes' (and others) legends along with the legend of Atlantis that perhaps the Red Man migrated here from Atlantis prior to its destruction. Particularly if it was in the Atlantic rather than the Mediterranean and they dispersed to South Central & North America. I thought perhaps some of them also migrated to Spain & and Africa. If it were closer to Florida than to the middle of the Atlantic this would make sense. Perhpas the Mongoloid race itself migrated originally from Atlantis, or perhaps there were more than three races and those from Atlantis were a fourth race approximately the same size as the Mongoloids or a combination of them.
10/18/2010 2:27:24 AM MST
Its a big Discovery dude.!
12/4/2010 7:50:17 AM MST
I am writing thesis about Native Americans (I am from EU actually)... I find this very interesting!
12/7/2010 11:16:01 AM MST
Hey it is great, I did it when I was a student too... good luck Nikola!
10/13/2011 9:26:20 AM MST
Simply due to the fact that the oldest human ancestral lineage that has been found to date lies in Africa, I can't understand why we so blindly accept that it was at one singular spot where the transition to homonid occurred. People simply accept these statements as truth. Considering there is so much of South America that is still being discovered (and so many aspects of "lost" civilizations we can only speculate on), it would be nice to see some open-mindedness to alternative theory. Not that I necessarily support Atlantis theories or anything of that nature, but blindly accepting land bridge theories when a fraction of the planet has been researched seems pretty presumptuous to me. Maybe I've read too much Vine Deloria, but we thought the world was flat at one time, too.
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