February 14, 2008...11:55 am
Peopling of the Americas: Three Step Model for Colonizing the Americas
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.
- Kitchen, A., Miyamoto, M.M., Mulligan, C.J., Harpending, H. (2008). A Three-Stage Colonization Model for the Peopling of the Americas. PLoS ONE, 3(2), e1596. DOI: 10.1371/journal.pone.0001596
12 Comments
February 14, 2008 at 7:00 pm
The three step model makes sense. Years ago Greenberg and Rhulen controversially grouped most Native American languages into just one huge family. They grouped the remainder into two, Na-Dene and Inuit.
http://www.merrittruhlen.com/files/Greenberg-Ruhlen.pdf
February 16, 2008 at 1:22 pm
I so don’t believe this. Human beings would not want to live in Beringia during the LGM. The reason it wasn’t glaciated was it was sooo dry and cold. Yes there were intervals when climate was somewhat milder but for the most part it was an inhospitable frozen hell. Imagine the wind chill coming of the Pacific ocean, wind driven waves as high as fifty feet are common in the Bering Strait. The evidence the authors cite is unemcumbered by archaeological backup and really only suggests their thesis as a possibility. Much more likely would be occasional/episodic/seasonal occupation from a more sheltered source. Probably hunters taking big game and sailing home in boats. A very flat semi desert permafrost environment subject to minus 30-40 degree F temperatures and frequent hundred mile an hour gales is no place to pitch your tent and hunker down for the winter no matter how many mammoth you might kill. Secondly I would be greatly surprised if big game wintered there. Most would migrate to a more sheltered area either in Alaskan or Siberian valleys. Proof of their thesis would be found in such areas as people would be better able to survive in such locations. There will have to be finds of semi-permanent 25000 bp year old camps on both sides of the Bering Strait before I believe anyone lived in the middle. People are so much more mobile and adaptable than this theory gives them credit for. Personally I think its just as likely the Americas were settled by people following those wild displays of the Aurora Borealis in the warm period (comparatively that is) about 18000 years bp before Heinrich Event 1 and then sailing south.
February 16, 2008 at 9:41 pm
I would have to agree, this is an interesting theory but still a long way from conclusive. To bring in Greenberg’s theory I would argue is to not understand it. His theory rests on the assumption that the “three” original languages have their origins in Asia - not Beringia - and that they are also tied to dentition (Turner’s theory). These two theories would not seem to jive with this new evidence unless backmigration were allowed. I think we need to look back even further, especially since new South American evidence puts the date back to 40,000 ya.
February 17, 2008 at 1:11 pm
Charlie, I see a lot of conjecture in your comment. Furthermore, I think you’re horribly mistaken with your, “I don’t think people would like the cold that much that’s why this theory isn’t applicable.” There are many populations, such as the Inuit, that have always been living in the cold. These populations have adapted to living in cold climates and seem perfectly happy to have spent millenia in the cold.
Native American Geneticist, can you expand on the ‘new South American’ evidence puts the data back to 40,000 years ago? Correct me if I’m wrong, but are you saying people were in South America 40,000 years ago? Or that the Americas began being peopled 40,000 years ago?
Kambiz
February 17, 2008 at 7:26 pm
Kambiz
I am familiar with the Inuit and other cold adapted peoples and the fact is at the LGM (24,000 to 18,000) there just isn’t any evidence of people living that far north anywhere in the world. It might in fact be possible to eek out some sort of a living under those harsh conditions but the evidence indicates at least so far (at least as far as I know about) the only people to colonize the high Arctic were the Inuit some time after the peopling of North America.
My point is the LGM in Beringia is not comparable to any existing environments today for several reasons: extreme cold, c3 vegetation, low co2 levels (very low yield from plant foods per area), lack of sheltering topography, aridity (lack of snow and/or rivers/lakes), permafrost (digging is almost impossible), total lack of trees. These obstacles have to have been overcome to winter there.
A sea going people would have the advantages of seasonal hunting and fishing without the profound disadvantages of actually living there. The Inuit are a seagoing people par excellence as well as big game hunters highly adapted to the environment we have now. Drop the temperature of the areas where they live 20-40 C and they would migrate somewhere warmer as would the large animals they hunted, common sense really. The LGM is truly another country, our reconstructions incomplete. The above study isn’t bad or anything it does however assert a pulsed migration from a truly harsh landscape over a 20,000 year period without any evidence anyone ever lived there. It maybe true but without some backup it’s just a possibility. I love these studies on genetics and migration but there must be an interdisciplinary verification as many models may generate the same data. Occam’s razor just doesn’t apply very well to us crazy humans just think about professional wrestling and religion. I’m just saying.
Thanks for the chance to rant a bit.
February 17, 2008 at 8:32 pm
Kambiz
Sorry I forgot a point. The steppes before the invention of the wheel apparently greatly hindered the movement of people on foot. The people generally followed rivers or coastlines rather than crossing wide plains with scarce water. Seems to me this would also apply to Beringia.
Charlie
February 19, 2008 at 5:57 pm
[...] Siberian Origin of Na-Dene Languages Jump to Comments Following up on recent discussion of the peopling of the Americas, The University of Alaska at Fairbanks is hosting a conference about the possible link between [...]
February 22, 2008 at 5:56 am
The fact that some population does not grow for 20 k years does not imply that this population lived in Beringia ice hell. This is only conclusion of the authors. This population could live in America, as well and not grow for 20 k years, for some unknown reasons, and after last ice age expand. This is just another explanation … which can also give answer to some findings in south America older than 15 k years.
March 3, 2008 at 1:28 pm
I’m new here, but the peopling of the Americas is one of my favorite subjects.
We know that Australia was colonized as long as 40,000 YBP, so maritime technology was advanced enough by that time to permit the colonization of the Pacific Rim. During the Glacial Maximum the continental shelf was exposed for 20-40 miles, an environment that does not exist today, free from mountain ranges that might hinder travel. The only obstacles would have been rivers, conveniently full of salmon, which a seagoing people would have had no trouble crossing but which would have been a problem for pedestrians without a maritime history.
This wide plain would have been stocked with a variety of grazing animals, but more important, the shore would have been teeming with pinnipeds whose prime shore-based predators were bears, but which would have been defenseless from shoreline predators that cut off their escape to the sea by attacking from boats.
Mountains of meat, bird’s eggs and shellfish on virgin shorelines would have been plenty attractive to seagoing peoples, and they would have followed the rim of the Pacific right into the Americas. When the sea rose again any evidence of their passage would have been obliterated.
There is no reason for a maritime culture to venture inland until the familiar resources at the shoreline are either claimed or exhausted, and it seems unlikely that they would have ventured inland until long after the initial colonization.
I don’t offer any physical evidence for this other than the fact that there is no evidence indicating a land migration and plenty of reasons to suspect that crossing Beringia (as noted above) would have been tough sledding, and would have required a massive cultural shift to land-based hunting in extreme cold. But we know that maritime cultures capable of reaching the Americas existed 40,000 years ago in Southeast Asia. The human presence in the Americas seems to have exploded from nowhere about 13,000 YBP, and I submit it was growing quietly on the continental shelf until that time.
March 3, 2008 at 7:52 pm
Repack Rider. A problem with that theory is that Y-chromosome and mtDNA haplogroups of Australia and America are pretty much unrelated. Admittedly this difference could be a result of more recent selection or drift. On the other hand I agree there seems no reason why your theory is impossible. One explanation I have thought of over the years is that the coast is a narrow ecological zone. With increasing distance inbreeding would become an increasing problem. This could have limited population growth until a new group moved in, perhaps 15,000 years ago. The combined population was able to rapidly expand in numbers. This effect would also help explain the genetic differences between east and west in America. Anyone else any ideas?
March 3, 2008 at 8:45 pm
Terry,
Thanks for the response. I am not suggesting that the same groups that colonized Australia also colonized the Americas, merely that seagoing technology existed long before the migration into the Americas.
This technology could easily have spread through contact with other groups, one of which could have been the ancestors of those who colonized the Americas.
March 4, 2008 at 8:31 pm
True. Technology can obviously travel independent of genes.
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