Ice age bison DNA sheds light on human migration
A new study shows when an important route through the Rocky Mountains was opened from north to south. Bill Condie reports.
A 13,000-year-old bison fossil has shown the most likely migration route of some of the first native Americans.
DNA from the bison remains has narrowed down the time period when an ice-free corridor opened up along the Rocky Mountains during the late Pleistocene.
That corridor was a vital route for migrations between what is now Alaska and Yukon in the far north and the rest of the North American continent.
Researchers had previously suspected this was the way migrating humans and animals must have travelled, but were unclear about how and when it was used.
But now, a new study published in Proceedings of the National Academy of Sciences, shows the route was fully open by about 13,000 years ago.
While this route was closed when the very first humans moved south of the ice sheets into North America around 15,000 years ago (they probably took a Pacific coastal route), it is thought it later became a well-travelled thoroughfare in both directions.
“The opening of the corridor provided new opportunities for migration and the exchange of ideas between people living north and south of the ice sheets,” said Peter Heintzman, of UC Santa Cruz, who led the DNA analysis.
His coauthor Beth Shapiro, also from UC Santa Cruz, has previously shown that bison populations north and south of the ice sheets were genetically distinct by the time the corridor opened.
So, armed with that knowledge, the researchers have been able track the movement of northern bison southward, and southern bison northward.
“The radiocarbon dates told us how old the fossils were, but the key thing was the genetic analysis, because that told us when bison from the northern and southern populations were able to meet within the corridor,” Heintzman said.
The southern part of the corridor opened first, allowing southern bison to start moving northward as early as 13,400 years ago, with the two populations overlapping in the corridor by 13,000 years ago.
Archaeological evidence from hunting sites of the prehistoric Clovis culture suggests that human migration within the corridor was mostly from south to north.
The distinctive fluted pointed spearheads of the Clovis culture were widespread south of the corridor around 13,000 years ago, but a Clovis site in Alaska has been dated to no earlier than 12,400 years ago.
“When the corridor opened, people were already living south of there,” says Shapiro. “And because those people were bison hunters, we can assume they would have followed the bison as they moved north into the corridor.”
The DNA analysis used in this study focused on mitochondrial DNA, which is easier to recover from fossils than the DNA in chromosomes, because each cell has thousands of copies of the relatively short mitochondrial DNA sequence.