New World Settlers Took 20,000-Year Pit Stop

February 14, 2008

Human settlement of the New World occurred in three separate stages and involved a 20,000-year layover on the land bridge that once connected Asia to the Americas, scientists say.

The trip was also a much larger affair than previously thought, involving about 4,500 individuals instead of the hundred or fewer previously estimated to have made the journey.

"Our model makes for a more interesting, complex scenario than the idea that humans diverged from Asians and expanded into the New World in a single event," said study co-author Connie Mulligan.

(Related news: "Did First Americans Arrive By Land and Sea?" [November 6, 2003].)

The study, conducted by researchers at the University of Florida, appeared in a recent edition of the journal PLoS ONE.

Beringia Land Bridge

The researchers compared differences in the DNA sequences of modern Native American and Asian populations.

"By looking at the kinds and frequencies of these mutations in modern populations, we can get an idea of when the mutations arose and how many people were around to carry them," said study co-author Michael Miyamoto.

According to the new theory, humans heading east after leaving Asia about 40,000 years ago were blocked by two huge glaciers that met at present-day Alaska.

With no way forward, the humans settled on the land bridge, called Beringia, that connected Asia and North America.

There they remained for 20,000 years. Beringia was cold and harsh, comparable to winters in modern-day Siberia. Small populations of mammoth, bison, caribou, and other animals provided sustenance for the migrants.

Over time descendants developed a unique culture—one that was different from the original migrants' way of life in Asia but which contained seeds of the new cultures that would eventually appear throughout the Americas.

Then about 15,000 years ago the world warmed and a path through the glaciers opened up. After generations of perhaps imagining what lands might lie beyond the impassable walls of ice, the people living in Beringia moved east into North America.

(See a map of human migration routes about 15,000 years ago.)

Testable Theory

One of the virtues of the new theory is that it is testable, said David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas, who was not involved with the research.

Rising seas submerged much of Beringia about 10,000 years ago.

But if humans once lived in the region, archaeological evidence should exist, Meltzer said.

"The [new study's] model implies a long term and significant archaeological presence that, to date, has yet to be found," he said.

"[But] that does not mean it won't be."

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