Studies genetically link early Americans to Siberians, but renew debates about how and where they traveled
How did humans first arrive in North America? Traditional science says they came from present-day Siberia, walking across what is now the Bering Strait but was then the Bering Land Bridge, then working their way south. That southern route, it was believed, took the travelers through an ice-free corridor in today’s Alaska and northern Canada.
But: scientists see a problem with that theory: Environmental DNA (eDNA) analysis now shows that the ice-free corridor was not actually ice free until 12,600 years ago—and the first humans were already far to the south by 15,000 years ago.
The age of the ice-free corridor was established in 2016 by noted Danish researcher Eske Willerslev—The New York Times once declared that Willerslev is “rewriting history with DNA”—and published by Nature.
The earlier estimate of the ice-free corridor opening squared fairly nicely with evidence of the Clovis people living in North America—which was roughly 13,000 years ago. But then researchers found evidence of even earlier settlements.
The new estimate from Willserslev was made by looking at pollen, plant, and animal fossils from two lakes thought to have been at the narrowest gap in the corridor and likely the last part to open. Scientists also gathered eDNA in the soil left behind by plants, roots, animal waste, and more. The analysis showed that there was little evidence of life for about 700 years after the ice retreated, then about 12,600 years ago steppe plants appeared, followed by animals like the woolly mammoth, bison, and jackrabbit, then trees like aspen and poplar. The presence of game animals is key, since at 900 miles long, early travelers would need something to eat along the way, Science noted.
So, if they didn’t take the inland route, how did humans move south?
Willerslev posits that both the pre-Clovis and Clovis people used a coastal route along what is now seaside Alaska and British Columbia, though there’s little evidence to prove it so far. Another says they came by boat, and one researcher found evidence of settlement as old as any other in the Americas, including an ancient fishhook, on an island off the west coast of Mexico, Isla de Cedros. Still another finds evidence that humans were in Chile more than 14,000 years ago and one more has humans along the Peruvian coast 15,000 years ago.
While the question of what route early Americans took is being debated, new evidence shows those travelers did indeed come from Siberia. A recent study in Cell suggests that people from Siberia, northeast Asia, and north Eurasia met and mingled in what is now the Lake Baikal region of Siberia and contributed ancestry to the earliest known people in the Americas.
In the Cell study, researchers used targeted and metagenomic sequencing to profile SNPs and pathogen patterns from 19 ancient Siberians and found genetic ties with Native Americans outside the Arctic.
“Our study demonstrates the most deeply divergent connection between Upper Paleolithic Siberians and the First Americans and reveals human and pathogen mobility across Eurasia during the Bronze Age,” the authors wrote.
So, if early Americans were actually Siberians, and they did not follow the ice-free corridor inland across Canada, how did they make it to Chile so quickly?
“Whereas archaeologists once thought that the earliest arrivals wandered into the continent through a gap in the ice age glaciers covering Canada, most researchers today think the first inhabitants came by sea,” reports Science. “In this view, maritime explorers voyaged by boat out of Beringia—the ancient land now partially submerged under the waters of the Bering Strait—about 16,000 years ago and quickly moved down the Pacific coast, reaching Chile by at least 14,500 years ago.”