A prevailing theory on how the first humans traveled to America may be completely inaccurate, a new study suggests.
We've been taught in schools that the first Americans migrated to the continent through an ice-free corridor that stretched from Alaska to Montana. Now, an analysis led by Canadian, Danish and American paleogeneticists may refute this idea and prompt the formation of a new theory.
Refuting An Old Theory
For years, anthropologists have proposed that ancient humans from Siberia moved to North America through the Bering land bridge.
These first Americans were believed to have dispersed into the United States and Mexico via an ice-free corridor, which opened up between the melting ice sheets in what is now British Columbia and Alberta.
However, the findings of the new study reveal that this longstanding theory would have been impossible.
An analysis led by scientists from the University of Copenhagen suggests that the ice-free passageway became habitable approximately 12,600 years ago.
That's almost a thousand years after the emergence of the Clovis culture — known for their distinctive stone tools and were once considered as the first Americans — and even longer after the formation of other pre-Clovis cultures.
In fact, the food and vegetation growing in the corridor would have been insufficient to support the ancient travelers, until long after people were living south of the ice sheets.
"Our results reveal that [the ice-free corridor] simply opened up too late for that to have been possible," says Mikkel Pedersen, the study's lead author and a PhD student at the University of Copenhagen.
Indeed, the ice-free corridor would have been formed 14,000 years ago as North America was emerging from the last Ice Age.
Glaciers that covered central Canada melted to form the corridor, before the appearance of the Clovis people, researchers say.
David Meltzer, the study's co-author and an expert from Southern Methodist University, says the coincidence appeared too powerful to ignore. He says ancient humans living in Alaska for centuries probably saw the new land open up and came down the corridor into North America.
Plant And Animal DNA Analysis
Cracks in the prominent ice-free corridor theory began to manifest in the 1990s when scientists made a case that humans resided at Monte Verde, Chile more than 14,000 years ago.
The discovery of other pre-Clovis culture sites in North America further weakened the theory that the Clovis people were the first Americans.
Still, the idea that the ancestors traversed through the corridor persisted, although there was little consensus on when the passageway opened and became habitable.
That is why Pedersen, paleogeneticist Eske Willerslev and their colleagues assessed DNA samples in cores taken from underneath two lakes in Canada, in what used to be the last stretch of the corridor.
Researchers found that the first plant life, which comprised of sedges and thin grasses, dates back 12,600 years.
The passageway then became lusher as buttercups, sagebrush, roses and poplar and willow trees grew. This attracted bison first, then mammoths, voles, elk and the bald eagle. About 11,500 years ago, the passageway began to resemble the forests of today.
The study suggests that the dates of emergence rule out the use of the corridor by earlier Americans and the Clovis people. Instead, both groups probably migrated by coastal route, researchers say.
Archeologist Loren Davis says that because the ice-free corridor theory has been shaken, scientists can begin to look at other theories, such as a coastal migration route.
However, finding sites along the coastal routes will not be easy because most are probably buried underwater.
Still, Davis and his team began studying areas of the Pacific Ocean that might have been the pit stops for the ancient travelers. To search for signs of habitation, researchers will collect marine sediments such as ancient human DNA or stone artifacts in the area in 2017.
Details of the new study are featured in the journal Nature.