There's new evidence that the first inhabitants of North America might have arrived by both land and sea. Researchers analyzed the genetic material of modern indigenous people from North and South America to trace two rare lines back to the continents' first inhabitants. The study, published in Current Biology, provides the first genetic evidence that the ancestors of many living Native Americans took two distinct routes from Beringia (a region that included the now-submerged Bering land bridge as well as portions of Siberia and Alaska) some 15,000 to 17,000 years ago.

The new findings fly in the face of the prevailing genetic theory that just one wave of migration traveled down the ice-free Pacific coast from Beringia. 

"They all arrived at the same time — it's the arrival route that's different," says lead study author Ugo Perego, a postdoctoral genetics student at the University of Pavia, Italy. Perego and his team studied genetic information from the Sorenson Molecular Genealogy Foundation in Salt Lake City, which has a large collection of genetic and genealogical data.

The new picture painted by this study shows one seafaring path to the Pacific coast and another route overland via an ice-free passageway just east of the Rocky Mountains (between the Laurentide and Cordilleran ice sheets) to the Great Lakes area. The Pacific course would have led to the rapid population of the western coasts of both continents down to Tierra del Fuego, and the land-bound travelers would have remained in the Great Plains and eastern regions of North America.

"It's interesting," says Connie Mulligan, an anthropology associate professor at the University of Florida in Gainesville. "It's the first genetic evidence that both a land and sea route may have been used." But Mulligan says more research is needed to confirm the findings, which may be explained by  a population bottleneck in Beringia, during which great deal of differentiation could have occurred.

Researchers widely believe that the American migration began in Asia before crossing into Beringia — much of which is now under the waters of the Bering Sea. But there is disagreement among geneticists, archeologists and linguists about the timing, frequency and location of the movement of people from Beringia into North America. Some posit that indigenous languages were too diverse to have stemmed from a single group of people. 

"Our genetic study reveals a scenario in which more than one language family could have arrived in the Americas with the earliest Paleo-Indians," study co-author Antonio Torroni, a professor of genetics at the University of Pavia, said in a statement. The two paths might also explain some of the large technological differences between regions in the pre-Columbian Americas.

In March 2008, the same team of researchers completed a massive genetic tree of indigenous American DNA, which revealed that about 95 percent of Native Americans today could trace their genetic heritage back to six individuals who lived 15,000 to 17,000 years ago. This fact, however, actually made tracing the migration routes more difficult. "Super common lineages were so common that they created a lot of background noise," says Perego. So Perego and his team used the genetic material from descendants of the other 5 percent to home in how the first inhabitants got here.

Perego hopes to soon use the more common lineages now to explore lines of expansion.

Image © iStockphoto/Oytun Karadayi