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Discovery casts doubt on Bering land bridge theory
By Allison M. Heinrichs
LOS ANGELES TIMES
Posted on Wed, Jul. 30, 2003

An archaeological site in Siberia, long thought to be the original jumping-off point for crossing the Bering land bridge into North America, is actually much younger than previously believed, shaking the theory that the first Americans migrated overland during the final cold snap of the last great ice age.

Using radiocarbon dating, scientists found that the Ushki site, the remains of a community of hunters clustered around Ushki Lake in northeastern Russia, appears to be only about 13,000 years old, 4,000 years younger than originally thought.

The new date places the Ushki settlement in the same time period as the Clovis site, an ancient community found in New Mexico, making it highly unlikely that people could have traversed the thousands of miles from Siberia in such a short period.

"This was the last site out there in Siberia that could have been an ancestor for the Clovis," said Michael Waters, co-author of the research that appeared last week in the journal Science. "We have to think bigger now and start thinking outside the box."

History books have long touted the idea that the first Americans, perhaps hunting a herd of mammoths, crossed into North America across the Bering land bridge, a strip of land believed to have linked Russia to the United States between 10,000 to 18,000 years ago.

The land is thought to have been exposed during a period of glaciation when arctic ices locked away much of the oceans' waters, making sea levels nearly 400 feet lower than today.

"The new age assessments may indicate that archeologists continue to search in the wrong direction for an answer to Clovis origins," said Anthony Boldurian, a University of Pittsburgh anthropologist who subscribes to the relatively new idea that the first Americans may have used boats to skip across Atlantic ice floes from Europe, entering North America perhaps as early as 20,000 years ago.

Other archeologists, such as Michael Collins from the Texas Archeological Research Laboratory at the University of Texas at Austin, believe that early humans from the Japanese archipelago followed whales and other marine food sources across the Pacific Ocean to North America's west coast.

"If you open up the possibility of water routes, even in the glacial maximum, they could skirt around the edge of the icepack in the North Pacific and come down the West Coast," he said.

With the re-dating of the Ushki site, the oldest verified site near the Bering land bridge is now the 14,000-year-old Broken Mammoth settlement in central Alaska.

The Clovis site in New Mexico has yielded the earliest unequivocal archaeological evidence that people were settled in North America 13,600 years ago. Archaeologists point to a variety of other locations, including the Monte Verde site in southern Chile and the Cactus Hill site in Virginia, both about 12,500 years old, as evidence that the land-bridge theory is faulty.

University of Kansas anthropological geneticist Michael Crawford said early humans probably could not have crossed the land bridge and traveled to New Mexico in 400 years. Reaching South America by foot within 1,000 years was even less likely.

He believes that people may have entered North America across the Bering land bridge at an earlier point through multiple migrations.

"Certainly the molecular genetics shows that it wasn't just a single migration," he said. Genetic research shows that "humans have been in America for at least 20,000 years."

But some archaeologists argue that due to the nomadic characteristics of America's first settlers, the seemingly difficult feat of traversing both North and South America in 1,000 years is not impossible.

"We are talking about tiny numbers of people, highly mobile, who would have traversed thousands of square miles as part of their hunting round within surprisingly few generations," said Brian Fagan, an emeritus professor of anthropology at UC Santa Barbara.

The Ushki, Clovis, and other sites were given ages using radiocarbon dating. All organisms contain regular and radioactive carbon. Radioactive carbon decays in a known amount of time.

Since dead plants and animals do not continue to take in radioactive carbon, the age of an organic sample, such as wood or bone, can be determined by comparing the amounts of each type of carbon remaining in the sample.

Radiocarbon dating may confirm that many other early American sites are actually pre-Clovis settlements. This possibility, combined with the fact that earlier Siberian sites have not been found, has left archaeologists and anthropologists "scratching their heads," Waters said.

"It's one of those things where we don't have all the answers right now and that's what makes it so exciting," he said. "I think we're in the threshold in the next 20 years of basically rewriting North American history."

Did First Americans Arrive By Land and Sea?

Hillary Mayell
for National Geographic News
November 6, 2003

A growing number of experts are radically rethinking how the Americas were first populated. Scientists say an emerging picture suggests that the earliest people to reach the New World may have arrived by both land and coastal routes.

For the last several decades, prevailing theory held that a small group of big game hunters in Siberia followed the Pleistocene megafauna—mammoth, mastodon, and extinct bison—across a land bridge that formed during the last Ice Age. Known as Beringia, it connected Asia to Alaska and northwestern Canada. As the glaciers began to retreat, an ice-free corridor opened up around 12,000 years ago, allowing people to make their way south to populate North and South America.

However, recent archaeological finds and geophysical studies have dramatically challenged this picture, advancing the possibility that people traveled both by boat and by foot.

"A variety of different lines of evidence have led to a wholesale reconsideration of the possibility of a coastal route," said Jon M. Erlandson, an anthropologist at the University of Oregon in Eugene.

Vance T. Holliday, an anthropologist and geoscientist at the University of Arizona in Tucson, said: "Recent findings have made it clearer that regional climate and geography played a much larger part in early migration patterns than previously thought, and increases the likelihood that people arrived using a coastal route."

Holliday organized the scientific panel that presented its findings at the annual conference of the Geological Society of America which concluded yesterday in Seattle, Washington.

"The change in emphasis from interior corridor to coastal route has been truly astonishing and only occurred in the last year or so," said Charlotte Beck, an anthropologist at Hamilton College in Clinton, New York. "This is really new for everybody."

Clovis First

The earliest reliably dated evidence of human habitation in North America are 11,500-year-old fluted projectile points found in Clovis, New Mexico. The distinctive points, which could be attached to a wooden spear to make a formidable weapon, became identified with small groups of people spreading slowly across North America who came to be known as the "Clovis" culture.

One of the first pieces of evidence to call the interior route—the so-called "Clovis first" theory—into question was confirmation in 1997 of human habitation at a site known as Monte Verde in southern Chile. Artifacts left there by early peoples predate the earliest known Clovis artifacts by 1,000 years.

The find raised the question of how people could have reached South America without leaving a trace of their presence in North America. (Erlandson notes that "new evidence suggests that the ice-free corridor from Beringia does not appear to have been open early enough for it to have contributed to the 12,000 to 12,500 year old settlement of Monte Verde.")

Now, new, more precise geophysical data from geologists suggests there was a great deal of variation in regional climate and habitat across time in Beringia.

"The Bering corridor may have been open for much longer than previously thought," said Andrea K. Freeman, an archaeologist at the University of Calgary in Alberta, Canada. "It's possible the western end of Beringia was open as much as 30,000 years ago, while the regions bordering the Gulf of Alaska remained glaciated."

More telling has been a reappraisal of the southern coastline of Beringia.

For decades it was simply assumed that the coast of Beringia was an inhospitable place to live, said Erlandson. New evidence suggests that instead of a straight-line coast, the southern coastline of Beringia was comprised of hundreds of islands, shallow bays, and inlets. Such coastal topography would have facilitated coastal living and migration.

"This type of relatively complex coastline is much more conducive to human habitation," said Erlandson. "It provides more protected habitat. And it's much more productive, providing a wealth of resources for early settlers."

Similar shorelines around the Pacific Rim today frequently support large underwater kelp forests. Kelp forests provide habitat for sea mammals, shellfish, fish, and sea birds, providing a ready source of food. The forests also tend to break up waves heaving on shore, making for safer boating.

"The other thing that has occurred is a reappraisal of the maritime skills of early peoples," said Erlandson. "In the last several years, there has been a pretty dramatic shift about the role of the sea in human history."

Once humans moved out of Africa and into Asia and Europe, three waves of migration occurred: People traveled to Australia, Japan and the islands in western Melanesia, and to the Americas.

"We know that at least two of [these waves] occurred by boat," said Erlandson, noting that humans arrived in Australia by boat at least 50,000 years ago. "There's no reason to think the Americas couldn't have been colonized in the same way," he said.

Arguing for a Sea Route

Until now, one of the primary arguments against a coastal migration route has been the lack of archaeological evidence. "There are no sites," said Beck. "Of course, rising sea levels mean that most, if not all, of the sites would be underwater now."

Erlandson, who has written extensively on the importance of coastal habitats and the seafaring abilities of early humans, urges caution.

"We haven't proven it happened yet," he said. "There was no archaeological evidence supporting the interior route theory. It was really a leap of faith." He's also careful to add that "there's embarrassingly little data" to support arguments for a coastal route. "But that's what makes it interesting."

"The only thing that's certain is it has to be more complicated than just one group migrating across Beringia," said Beck. "It's more likely that there were numerous migrations at different times, by different routes."

My prediction is that, well within our lifetimes, the Bearing Strait land bridge theory is going to put out to pasture, if by that is meant the sole or even the primary route of human migration to this continent for which virtually all the native inhabitants owe their genetic endowments.

In other words, the genetic history of the Americas is much more complex and multifaceted than the traditional theories would have it. My prediction is that, well within our lifetimes, the Bearing Strait land bridge theory is going to put out to pasture, if by that is meant the sole or even the primary route of human migration to this continent for which virtually all the native inhabitants owe their genetic endowments.

Its going to get a great deal more interesting before all is said and done (and the critics will be talking, no doubt, right up to the very end).

"The new age assessments may indicate that archaeologists continue to search in the wrong direction for an answer to Clovis origins," said Anthony Boldurian, a University of Pittsburgh anthropologist who subscribes to the relatively new idea that the first Americans may have used boats to skip across Atlantic ice floes from Europe, entering North America perhaps as early as 20,000 years ago.

Other archaeologists, such as Michael Collins from the Texas Archaeological Research Laboratory at the University of Texas at Austin, believe that early humans from the Japanese archipelago followed whales and other marine food sources across the Pacific Ocean to North America's west coast.

Once humans moved out of Africa and into Asia and Europe, three waves of migration occurred: People traveled to Australia, Japan and the islands in western Melanesia, and to the Americas.

"We know that at least two of [these waves] occurred by boat," said Erlandson, noting that humans arrived in Australia by boat at least 50,000 years ago. "There's no reason to think the Americas couldn't have been colonized in the same way," he said.

A US genetic study bolsters claims that Native Americans are descended from one migrant group that crossed a lost land link from modern Siberia to Alaska -- not waves of arrivals from Asia, as rival theories say.

The new study by the University of Michigan, published Monday, examined genes of indigenous people from North to South America and from two Siberian groups, the university said in a report introducing the research.

Analysis found one unique genetic variant widespread across both the northern and southern American continents -- suggesting that all Native Americans were descended from a single group, not various ones as the rival theory holds.

This variant "has not been found in genetic studies of people elsewhere in the world except eastern Siberia," the report said.

"If there were a large number of migrations, and most of the source groups didn't have the variant, then we would not see the widespread presence of the mutation in the Americas," Noah Rosenberg, a geneticist who worked on the study, was quoted as saying.

Anthropologists and archeologists have long argued over whether Native Americans are descended from migrants who crossed by land to the northwest 12,000 years ago, or waves of arrivals by sea and land from elsewhere in Asia and Polynesia beginning up to 30,000 years ago.

The land link has long since disappeared, giving way to the Bering Strait -- a narrow sliver of sea separating the far northwestern US state from far eastern Russia.

The study also found that genetic diversity increased the further away people were from the Bering Strait -- as would be expected if the migration were "relatively recent," the report said, citing the authors of the study.

It is published in the specialist journal PLoS Genetics.