A review of ancient DNA evidence suggests that people most likely arrived in the Americas between 20,000 and 14,000 years ago, during the coldest stretch of the last ice age.
The study, led by Bethany Potter of the University of Kansas and published in Current Opinion in Genetics & Development, weighed three competing timelines for the arrival of modern humans.
One holds that people came before the Last Glacial Maximum (aka the ice age), more than 25,000 years ago. Another places their arrival during the glacial maximum itself, a harsh period between 20,000 and 14,000 years ago when immense ice sheets blocked much of the continent. A third rests on the long-held traditional consensus that humans arrived in the Americas only after the ice retreated, which was roughly 14,000 years ago.
Putting the models to the test
Potter and her colleagues tested each scenario against genetic samples, archaeological evidence, and environmental data.
And the genetic record proved decisive.
By about 15,000 years ago, the ancestors of Native Americans had already divided into distinct Northern and Southern lineages, a split that could only have happened if people were already living on the continent.
That rules out an arrival after the ice receded. Then there’s the fact that researchers have found no DNA evidence of comparable population splits older than 25,000 years, which weakens the case for a much earlier migration, that is, before the glacial maximum.
By overturning the traditional 14,000-year consensus and ruling out a pre-25,000-year arrival, the findings rewrite the migration narrative to the second scenario, firmly pinning the first arrivals to the 20,000 to 14,000-year window.
While the review does not dismiss the archaeological sites that appear to show human activity before 25,000 years ago, the authors offer two explanations for the discrepancy. Those early traces may have been left by isolated groups that died out or left few descendants. What is also likely is that DNA from those early populations exists but has not yet been recovered or identified in later groups.
Potter concludes that the field’s next steps should involve more than genetics. “It is critical that paleogenomics research be rooted in questions articulated by archaeologists and tribal historians, and that such research be attuned to the needs and priorities of descendant communities,” she notes in the paper.
Sources: ScienceDirect, Archaeology Magazine