The research suggests that the people directly ancestral to Native Americans actually split away from their Siberian cousins as early as 23,000 years ago. This population migrated only as far as Beringia at first, because glaciers blocked the way farther eastward into the Americas. Genetic analysis shows that this Beringian period lasted no longer than 8,000 years before the population pushed into North and, eventually, South America.
That was not the only migration event, however.
“We’re still not entirely sure” how many migrations there were, says Pontus Skoglund, a geneticist at Harvard University. He thinks there were as many as five separate waves and believes there may have been distinct ethnic groups within the population living in Beringia at the time the Americas were first settled, which could confuse the picture. The lead author of a separate 2015 study in Nature, Skoglund looked at the genomes of ancient and modern Native Americans. His team’s research found that a specific Australasian genetic signature — one found in people who lived in Australia, Indonesia and the Andaman Islands, off the coast of Burma — survives today in some of South America’s indigenous people. Skoglund believes this genetic signature is evidence of another, smaller migration that was separate, but possibly concurrent, with the main wave from Beringia.
These studies showing greater genetic diversity in ancient populations suggest it may not be so far-fetched to think that Siberians could have come into contact with people carrying Australasian genes.
On its surface, the presence of Australasian genes might seem to indicate that people had sailed from that area across the Pacific Ocean to the Americas, but that genetic signature does not show up in people in the Pacific islands, which likely would have been along the route. Unlike Skoglund, Willerslev believes that this signature was brought by a group of people who migrated via Beringia, or possibly boated along the coast from Siberia to South America, around 13,000 years ago — a couple of thousand years after the initial, larger migration.
The debate comes down to how each team interprets the genetic data. For now, the ancient Siberian genome also analyzed in the Science study supports the idea of a highly genetically diverse population living in Siberia prior to migration into the Americas. The 24,000-year-old Siberian individual who was sequenced had ancestry in common with people in Europe, which shows that these Paleolithic hunter-gatherers were moving over a larger territory than had been assumed. In October, a separate study of the maternally inherited mitochondrial DNA of the remains of two Alaskan children, dated to 11,500 years ago, revealed that one child had a rare genetic signature found on the southern edge of Siberia. These studies showing greater genetic diversity in ancient populations suggest it may not be so far-fetched to think that Siberians could have come into contact with people carrying Australasian genes, and then taken those signatures to the Americas over subsequent generations.