Ancestors of America\'s original people lived on long-gone land bridge

Ancestors of North America's indigenous peoples paused en route from Asia, spending 10,000 years on the Bering Land Bridge, now under the sea, researchers say. Genetic and environmental evidence indicates as those ancient people migrated from Asia they spent time living in shrubby lowlands on a broad land bridge known as Berengia, which once linked Siberia and Alaska but became submerged when sea levels rose, University of Utah anthropologist Dennis O'Rourke says. O'Rourke and his colleagues John Hoffecker of the University of Colorado at Boulder and Scott Elias, a paleoecologist at the University of London, writing in the journal Science, said cumulative evidence indicates the ancestors lived on the Bering land bridge from roughly 25,000 years ago until they began moving into the Americas about 15,000 years ago once glacial ice sheets melted and migration routes opened. "Nobody disputes that the ancestors of Native American peoples came from Asia over the coast and interior of the land bridge" during an ice age called the "last glacial maximum," which lasted from 28,000 to at least 18,000 years ago, O'Rourke said. But the absence of archaeological sites and the inhospitable nature of open, treeless landscape known as tundra steppe mean "archaeologists have not given much credence to the idea there was a population that lived on the Bering land bridge for thousands of years," he said. However, he said, sediment cores from the Bering Sea and Alaskan bogs contain pollen, plant and insect fossils, suggesting the Bering land bridge was dotted with refuges where there were brushy shrubs and even trees such as spruce, birch, willow and alder. "We're putting it together with the archaeology and genetics that speak to American origins and saying, look, there was an environment with trees and shrubs that was very different than the open, grassy steppe," O'Rourke said. "It was an area where people could have had resources, lived and persisted through the last glacial maximum in Beringia." In addition, the possibility that humans inhabited the Bering land bridge in isolation for about 10,000 years "helps explain how a Native American genome [genetic blueprint] became separate from its Asian ancestor," he said.