An international team of scientists led by Dr Dennis O’Rourke from the University of Utah has discovered how Native Americans may have survived the last Ice Age after splitting from their Asian relatives 25,000 years ago.
New study reveals that after the ancestors of Native Americans left Asia, they spent 10,000 years in shrubby lowlands on a broad land bridge that once linked Siberia and Alaska. Painting by G. Mülzel.
They have analyzed fossils which confirmed the theory that the ancestors of Native Americans lived on the Bering land bridge – the now-submerged plain that lies between northeast Asia and Alaska once exposed by a significantly lower sea level – in the neighborhood of 10,000 years, from roughly 25,000 years ago until they began moving into the Americas about 15,000 years ago once glacial ice sheets melted and opened migration routes.
The so-called Beringia Standstill theory was first proposed in 1997 by two Latin American geneticists and refined in 2007 by Estonian scientists that sampled mitrochondrial DNA from more than 600 Native Americans. The researchers found that mutations in the DNA indicated a group of their direct ancestors from Siberia was likely isolated for at least several thousand years in the region of the Bering land bridge.
The theory gained little traction outside of the genetics community after it was proposed and has been seen by some scientists outside of the field as far-fetched.
But the new results, published in the journal Science, add credence to this theory by further linking the genetics to the paleoecological evidence.
“A number of supporting pieces have fallen in place during the last decade, including new evidence that central Beringia supported a shrub tundra region with some trees during the last glacial maximum and was characterized by surprisingly mild temperatures, given the high latitude,” said lead author Dr John Hoffecker from the University of Colorado at Boulder.
The last glacial maximum peaked roughly 21,000 years ago and was marked by the growth of vast ice sheets in North America and Europe.
“Large herd animals like bison or mammoths likely lived on the highland steppe tundra because they graze. Many smaller animals, birds, elk and moose (which browse shrubs instead of grazing on grass) would have been in the shrub tundra,” Dr O’Rourke said.
While a debate rages on about when early humans first migrated into the New World, many archaeologists now believe it was sometime around 15,000 years ago after retreating glaciers opened access to coastal and interior routes into North America.
The relatively mild summer climate in Beringia at the time was caused by North Pacific circulation patterns that brought moist and relatively warm air to the region during the last glacial maximum. Geologists believe the Beringia gateway between Siberia and Alaska was more than 600 miles wide at the time.
The scientists are now theorizing that a population of hundreds or thousands of people parked itself in central Beringia for 5,000 years or more.
One key to the extended occupation may have been the presence of wood in some places to use as a fuel to supplement bone, which burns hot and fast. Experiments have shown that at least some wood is necessary to make bone practical as a fuel.
“Research using fossil pollen, plant and insect material from sediment cores from the now submerged landscape show that the Bering land bridge tundra environment contained enough woody plants and trees like birch, willow and alder to provide a supplement to bone,” said co-author Prof Scott Elias of Royal Holloway, University of London.
“We believe that these ancestors survived on the shrub tundra of the Bering land bridge because this was the only region of the Arctic where any woody plants were growing. They needed the wood for fuel to make camp fires in this bitterly cold region of the world. They would have used dwarf shrub wood to get a small fire going, then placed large mammal bones on top of the fire, to ignite the fats inside the bones. Once burning, large leg bones of Ice-Age mammals would have burned for hours, keeping people alive through Arctic winter nights,” Prof Elias explained.
The study also included the analysis of certain beetle species that live in very specific temperature zones, allowing them to be used as tiny thermometers. The insects indicated that temperatures there were relatively mild during last glacial maximum that ran from about 27,000 years to 20,000 years ago, only slightly cooler than temperatures in the region today.
“This work fills in a 10,000-year missing link in the story of the peopling of the New World,” Prof Elias said.
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John F. Hoffecker et al. 2014. Out of Beringia? Science, vol. 343, no. 6174, pp. 979-980; doi: 10.1126/science.1250768
