Bison fossils shed light on human migration in the Ice Age

JUNE 7, 2016

by John Hopton

Radiocarbon dating and DNA analysis of bison fossils has revealed that an ice-free corridor along the Rocky Mountains was fully open by around 13,000 years ago, during the late Pleistocene.

Geological studies in the 1970s led to the corridor being posited as a route for the colonization of the Americas by humans moving south from Alaska. But the new study, published in Proceedings of the National Academy of Sciences, suggests that the pathway was not the one taken during the initial migration.

It was, however, a likely route for later dispersal of people and animals.

"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 first author Peter Heintzman, a postdoctoral researcher at UC Santa Cruz who led the DNA analysis. (We like to think the bison were sharing ideas, too).

The most up-to-date thinking on the subject is that the Cordilleran and Laurentide ice sheets coalesced at the height of the last ice age, around 21,000 years ago, and closed the corridor much earlier than any evidence of humans south of the ice sheets. A Pacific coastal route is the more likely candidate for the first movement southwards, around 15,000 years ago.

In fact, according to Study coauthor Beth Shapiro, professor of ecology and evolutionary biology at UC Santa Cruz, archaeological evidence suggests that the predominant human migration within the Rocky Mountains corridor was from south to north.

"When the corridor opened, people were already living south of there. And because those people were bison hunters, we can assume they would have followed the bison as they moved north into the corridor," Shapiro said.

Southern bison to start moving northward as early as 13,400 years ago, as the south began to open first, before the corridor fully opened and the two populations overlapped by 13,000 years ago after northern bison had also started to move southward.

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