As orthodox science accepts as proven fact that the Americas were peopled by a very limited group of people in a rapid expansion that spanned the continent from Alaska to Tierra del Fuego in a few milennia, they are now building "proof" to support this notion.
The proof is known as the "Beringian standstill hypothesis". It involves a Twentyfirst century lost continent, which is not Atlantis (the mythical land that sunk in the Atlantic Ocean) but "Beringia", a rehash of the legendary continent of "Lemuria" or "Mu", which were invented as dry land stepping stones before plate tectonics correctly explained how trees and animals managed to cross vast oceans and people distant lands.
In a nutshell, a recent paper ("Out of Beringia?" ) elaborates on a theory originally suggested by Eric Hultén in 1937 : that the Bering Strait land bridge was a refugia for tundra vegetation during the Ice Ages. The paper's authors, Hoffecker, Elias and O'Rourke contend that apart from tundra plants, Beringia was also "a glacial refugium and postglacial center of dispersal for the people who first settled the Americas" .
They believe that the ancestors of Amerindians split from their Asian relatives 25 kya, lived in Beringia for about 10,000 years and moved into America when the glaciers began melting and apart flooding Beringia, opened up the routes into the heart of America.
The 10 kya standstill arises because the distinct American Native mtDNA requires an isolation of several thousand years in isolation. The paper believes that it was possible because the tundra also supported some stunted trees (birch, adler, willow) which could have been used to ignite and burn megafaunal bones and give off plenty of heat. The land bridge also supported an edible fauna of mammoths, elk, moose and bison.
The New Lemuria
The new Lemuria (or Beringian Standstill hypothesis) arises to be able to explain how the "American founding fathers", ancestral to all Native Americans, managed to mutate their Asian mtDNA into novel haplotypes, develop new alleles that were distinct from the original Asian stock and then disperse across America without any of these genetic traces remaining back in Asia.
The fact is that there are mtDNA haplogroups found exclusively in America but not in Asia (A2, B2, C1b, C1c, C1d, D1 and D4h3). This pan-american uniqueness also extends to Y chromosome haplogroup Q1a3a-M3 and to some privatee alleles (i.e. autosomal 9-repeat at the microsatellite locus D9S 1120).
If they are not found in Asia, then, the obvious and most parsimonious answer is that they originated in America, and dispersed across the continent, but no, orthodoxy does not accept this, and had to invent a "Moses-like" band of migrants wandering in the wilderness. But instead of 40 years, these people spent 10,000 years in their Beringian "Sinai" before reaching the "Promised Land" of America.
The justification for the "Standstill" is the following:
- Large ice sheets blocked access into America until about 15,000 years ago.
- An earlier date (i.e. older than 15 kya) for the peopling of America is not acceptable for orthodox science.
- Modern humans are believed to have reached Eastern Asia 25,000 years ago, but did not move into America then (due to 1 and 2. above)
- mtDNA had to diversify into American haplogroups, which takes time (10 ky is sufficient).
- But diversification had to happen in isolation (to avoid any of it remaining in Asia).
- The only place this could happen: in between Asia and America: Beringia.
So we imagine a vast land with cold but bearable climate, cut off from Asia and America by ice fields that could not be crossed by men. And a group of humans isolated there for 10 ky, until the Alaskan gateways opened (I wonder why the Siberian one reamained closed... The mechanism is not explained. But it is necessary to avoid any of those distinct genetic markers from going back into Asia). Of course, since the oldest Paleoindian sites acceptable for orthodoxy are about 15 kya, (some are in South America), so this means that the peopling of the continent had to take place super fast. This means that these people who sat around Beringia for 10,000 years suddenly rushed across the New World and settled it immediately.
The map below summarizes it (source: wikipedia).
This is a bit too far fetched for my liking.
The Second Wave
Then, after this initial wave of Paleoindians, a second wave marched across Beringia from Eastern Siberia: the ancestors of those bearing hablogroups A2a, A2b, D2a, D3 and X2a, which are found in the north of North America, which by the way have similarities with Eastern Asian groups and share common languages.
However, there is a problem with the language question see my post on American Languages), which another recent paper has also attributed to a "Beringian isolation" (it is in vogue now), but different from the one in the paper mentioned above.
This paper uses phylogenetic methods to support the theory that the American Na Dene and the SiberianYeniseian languages connection is very probably due to a "radiation out of Beringia with back-migration into central Asia than a migration from central or western Asia to North America". 
So here we have another group in Beringia that moves both back into Asia and ahead, into North America. Which is almost simultaneous with the one mentioned above! So why didn't the genes follow the languages back into Asia? Also, it argues for an older initial population of America (15-40 kya) which predates the one mentioned above. Please allow me to quote the paper extensively (bold is mine):
"DNA evidence supports at least three migrations with the earliest 15–40,000 BP referred to generically as the Paleoindian and associated with the greatest distribution of language and cultural groups across North, Meso, and South America; the second 12–14,000 BP is the Na-Dene distributed in North America from Alaska to the Pacific Northwest and from Canada to the U.S. Southwest; and the third ca. 9000 BP is Eskimo-Aleut with circumpolar distribution.
Linguists have classified Eskimo-Aleut and Na-Dene as separate language stocks, and the rest of the languages of the Americas as belonging to numerous stocks, but have otherwise been mostly silent on questions that connect Asian and the American populations because, with the exception of Eskimo-Aleut, the dates of these earlier connections lie beyond the traditionally accepted limit for comparative reconstruction.
Linguistic claims of more distant relationships have relied instead on the more controversial method of mass (or multilateral) comparison of lexical items subjectively judged as similar. Using such methods a Dene-Yeniseian (DY) connection linking Asia to North America has been suggested for nearly 100 years, but only recently has a stronger case been made using methods of linguistic reconstruction, which has been peer reviewed with cautious optimism urging alternative methods for its evaluation. The hypothesis of a DY language family prompted claims of proof for the origin of Native Americans in central or western Asia, the relationship fitting into a popular narrative for the peopling of the Americas.
Our results support an argument that, if the Dene-Yeniseian connection is true, it more likely reflects radiation out of Beringia with both eastward migrations into North America and westward migration into Asia rather than a unidirectional migration from Asia to North America." 
The language flow (and the people speaking them) is bidirectional, 12-14kya and only corresponds to North American Na-Dene natives, while the other paper covers a unidirectional flow (into America), across the whole continent, 15 kya.
The theories are in conflict and should be compatibilized.
Let's take a look at the scene where these events took place:
The Beringian land bridge is currently submerged and only appeared when the glaciers accumulated enough water (as ice) to drop sea levels. This happened during the Ice Ages of the Pleistocene, and also earlier.
We know that it existed for about 10 ky between (roughly) 32 and 18 kya. It was narrow in its central part (current Bering Strait region) it was however wide at its oriental and occidental portions. It covered an area larger than the state of Texas .
The extreme dryness of the area did not allow snow to accumulate and build up glacers so it remained ice free, glaciation surrounded it, in the mountains in alaska and Siberia but not in the lowlands of Yukon, Alaska, Eastern Siberia and, of course, Beringia. These remained free of ice during the Pleistocene.
The period during which this "standstill" took place, the Last Glacial Maximum (LGM), was "relatively dry and cold with cooler summers" .
Perhaps the refugium applies to the Na-Dene speakers, late arrivals to the continent. But the Paleoindians definitively reached America over 30 kya. Future findings and older sites will confirm this hunch.
Land Bridges formed across Bering Strait many times during the past 1,500,000 years and were contemporary to hominds who could have marched across them: H. erectus, Neanderthals and even archaic Modern Humans from Asia.
I am surprised at the persistence of notions such as "a late peopling of America" and patches to try to justify the holes in the theory instead of building a new one that explains all facts.
 Mark A. Sicoli and Gary Holton, (2014). Linguistic Phylogenies Support Back-Migration from Beringia to Asia. March 12, 2014DOI: 10.1371/journal.pone.0091722
 S A Elias and J Brigham-Grette, (2013). Late Pleistocene Glacial Events in Beringia From: Encyclopedia of Quaternary Science, 2, (2013) 191-201. doi:10.1016/B978-0-444-53643-3.00116-3. pp +191
 John F. Hoffecker, Scott A. Elias and Dennis H. O'Rourke, (2014). Out of Beringia?. Science, vol. 343, no. 6174, pp. 979-980; doi: 10.1126/science.1250768
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