Americas Settled Twice, New Study Finds

A new round has been fired in the long-running controversy about who first settled the Americas.

An international team of researchers compared the shape of more than 1100 skulls from South America, Asia and Australo-Melanesia dating from 11,500 years ago to the present. They found that they could account for the marked differences between the skulls of early and more recent Americans only if there were two founding waves of migration from Asia separated by several thousand years.

Luzia, facial reconstruction by Dr. Richard Neave of 10,500 year old skull from Lagoa Santa, Brazil, published with permission from LEEH-IB-USP

Their conclusions disagree with recent genetic studies, most of which conclude that just one wave of migration from eastern Asia can explain the genetic diversity of American indigenous groups.

Katerina Harvati, a paleoanthropologist at Eberhard-Karls University in Tübingen, Germany and one of the lead authors of the new study says that their results make the one-entry model improbable and refute the widely accepted argument that the differences between early and more recent indigenous Americans can be explained by genetic drift or other evolutionarily neutral processes.

“The two-migration model is the only one whose predictions matched the observed differences,” Harvarti says.

Morphing Skulls through Time and Space

Harvati, along with Mark Hubbe, at the Catholic University of the North, in Chile, Walter Neves, at the University of Sao Paulo, Brazil, used previously published measurements of 1178 skulls, including 69 from South America that were older than 7000 years—the largest sample ever studied--as the basis for their analysis.

Researchers have pointed out since the 1990s that the skulls of the earliest Americans, or Paleoamericans, differ markedly from those from more recent times and those of current indigenous groups, or Amerindians.

“Paleoamerican crania do not look particularly similar to recent Native American groups [but] similar to African and Australian populations,” says Harvati. “Whereas recent Americans resemble Asians more closely.”

Harvati and her colleagues found that for Amerindians to have descended directly from Paleoamericans would have demanded a very unlikely rate of change of skull shape “For the [one migration] scenario to have been true there would have had to have been some unique circumstances and strong selection pressure different from selection to climate,” says Harvati.

The one-entry model also predicts substantial correlations between how close two sets of skulls are geographically and how similar they are in shape. In contrast, if nearby populations descended from different founders, that correlation breaks down.

That’s just what the researchers found. Two founding waves reproduced the observed correlations significantly better than just one.

Controversial but Important

Ted Schurr, a molecular anthropologist at the University of Pennsylvania, finds the study worth paying attention to. Although his own genetic studies have suggested that a single expansion from Northeast Asia can explain the genetic variation among Native Americans, he does not rule out the group’s conclusions. . “I am willing to accept that there were pulses of migration into the Americas from Northeast Asia at different times, such that a pattern which Hubbe et al. identify might emerge,” he says.

Dennis O’Rourke, an anthropologist at the University of Utah, in Salt Lake City, Utah, agrees. “More recently, a number of genetic analyses have demonstrated that two, and perhaps more, migrations are more likely given the current understanding of genetic diversity in the Americas,” he says. “Contrasting the results from morphometric and molecular studies is one way to sharpen our perspective and refine hypothesis for future tests.”

It’s those further tests that Harvati and her colleagues hope to spur. “Currently there seems to be a gap in our understanding of the peopling of the Americas,” says Harvati. “I hope that our work will prompt others to revisit these questions with renewed interest and will help resolve that gap in our knowledge.”

Journal reference: Mark Hubbe, Walter A. Neves & Katerina Harvati, “Testing Evolutionary and Dispersion Scenarios for the Settlement of the New World,” PLoS ONE, 14 June 2010.

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For a more detailed description of this research, click on my Suite101 article here.