Feb. 13, 2008 -- The first New World entrants, who likely came from Asia, endured a 20,000-year "layover" on a strip of land called Beringia that once connected Alaska to Siberia, according to a new research model.
The model combines genetics with climate, archaeological and geological information to paint a vivid picture of how the Americas were first populated by approximately 1,000 to 5,000 people, instead of just 100, as was previously believed.
The findings, published this week in the journal PLoS ONE, also explain why Native Americans are genetically similar to east central Asians, but show noticeable differences too.
"Twenty thousand years is sufficient time to create the genetic polymorphisms that distinguish Native Americans, although I don't think Native Americans are a different race," co-author Connie Mulligan told Discovery News.
"The genetic variation that distinguishes all Native Americans from other, non-Native American groups would have evolved during...the Beringian occupation," added Mulligan, who is a professor of anthropology at the University of Florida and serves as assistant director of the university's Genetics Institute.
She and her colleagues believe two massive glaciers prevented the Beringians from entering the New World over the multi-millennial period. They seemed to be eager to leave, however, and for good reason.
"Although Beringia was not covered in glaciers, it still would have been a cold, harsh climate, such that life would have been possible, but not luxurious," Mulligan said. "I would compare it to modern-day Siberia or Mongolia in the winters."
When the glaciers diminished, the melting was probably rapid, "a difference that could be seen over a person's lifetime," she said.
Archaeological evidence, in fact, recognizes that people started to leave Beringia for the New World around 40,000 years ago, but rapid expansion into North America didn't occur until about 15,000 years ago, when the ice had literally broken.
Mulligan and her colleagues took such archaeological data and plugged it into a model that included DNA sequences from modern Native American, other American, and Asian populations.
Henry C. Harpending, a distinguished professor and endowed chairman of anthropology at the University of Utah, said the new model represents "innovative anthropology and (an) edge-of-the-seat population study."
"The idea that people were stuck in Beringia for a long time is obvious in retrospect, but it has never been promulgated," he added. "But people were in that neighborhood before the last glacial maximum and didn't get into North America until after it. It's very plausible that a bunch of them were stuck there for thousands of years."
Mulligan hopes future research on the first major human migration into the Americas will answer other pressing questions concerning early New World colonization.
"Some of the most interesting questions to do with human movements concern, 'Why?'" she said. "Why did people leave Asia, settle in Beringia and move to the New World? I think (research like ours) offers our best chance of answering some of those elusive 'Why' questions."
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