Washington, March 14 : A new study has sparked debate over the colonization of the Americas, suggesting that the bulk of the region wasn't settled until as late as 15,000 years ago.
According to a report in National Geographic News, archaeologists at Texas A and M University carried out the study.
Researchers analyzed both archaeological and genetic evidence from several dozen sites throughout the Americas and eastern Asia to come up with their new theory.
The study shows that the first Americans came from a single Siberian population and ventured across the Bering land bridge connecting Asia and North America about 22,000 years ago.
It suggests that the group got stuck in Alaska because of glacial ice, however, so humans probably didn't migrate down into the rest of the Americas until after 16,500 years ago, when an ice-free corridor in Canada opened up.
According to lead author Ted Goebel, an archaeologist at Texas A and M University in College Station, scientists have long agreed that the first Americans came from northeast Asia.
But the new study - which analyzed genetic and archaeological evidence from 43 sites, including a dozen sites in Asia-better pins down the makeup of the first Americans.
Genetic evidence, for instance, points to a founding population of less than 5,000 individuals.
Some geneticists had also previously suggested that the migration across the land bridge could have occurred as early as 30,000 years ago.
"Now, there seems to be consensus among those studying mitochondrial DNA and chromosome records of modern native Americans that it happened pretty late, after the last glacial maximum, maybe as late as 15,000 calendar years ago," said Goebel.
Archaeological evidence shows that there were people occupying the Asian side of the Bering land bridge area as early as 30,000 years ago.
"That tells us that once early modern humans spread out of Africa around 50,000 years ago and colonized temperate Eurasia, it wasn't very long before they had developed the technology and the skills needed to be able to make a go of it in the Arctic," said Goebel.
According to the study, modern humans spread across the land bridge about 22,000 years ago, but got stuck for up to 5,000 years, blocked by thick ice sheets across Canada.
It was only when the ice had melted sufficiently that humans began to spread south, either along the coast or though an interior corridor in western Canada, it added.
"That might have been the bottleneck that kept people from draining south from Alaska into temperate North America," said Goebel. "This suggests that the first Americans may have spread through the New World along a coastal route," he added.