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Ancient Genome Studies Provide Insights on Early Migrations Into Americas, Iceland

NEW YORK (GenomeWeb) – Two independent research teams have analyzed ancient human genomes to gather new insights on historical human migrations into the Americas and Iceland.

For one of these studies, published online today in Science, investigators in the UK, Estonia, the US, and elsewhere looked at the relationships between northern and southern Native American branches using the whole-genome sequences of 91 ancient Indigenous individuals, whose remains were found in California's Channel Islands or in southwestern Ontario, Canada.

The ancient samples, which are a couple hundred to several thousand years old, were analyzed alongside modern mitochondrial genome samples from 45 Native American individuals who were sequenced previously.

"Working in partnership with Indigenous communities, we can now learn more about the intricacies of ancestral histories in the Americas through advances in paleogenomic technologies," co-senior author Ripan Malhi, an anthropology researcher at the University of Illinois, Urbana-Champaign, said in a statement. "We are starting to see that previous models of ancient populations were unrealistically simple."

Somewhat unexpectedly, the team saw signs for northern Indigenous ancestry in southern populations, pointing to interactions between northern and southern Indigenous branches after their initial split roughly 15,000 to 18,000 years ago. In Central and South America, for example, ancient Indigenous individuals had 42 percent to 71 percent northern branch ancestry, reflecting admixture events estimated to have taken place some 13,000 years ago.

"We now find that all native populations in North, Central, and South America also draw genetic ancestry from a northern branch most closely related to Indigenous peoples of eastern Canada," co-senior author Toomas Kivisild, an archeology researcher affiliated with the University of Cambridge and the University of Tartu, noted in the statement. "This cannot be explained by activity in the last few thousand years. It is something altogether more ancient."

From their analysis, the researchers also suggested the Clovis culture — a stone tool-using group found in New Mexico roughly 13,000 years ago — descended from the southern branch, contrary to the notion that this population was ancestral to all Native Americans.

"In populations living today across both continents we see much higher genetic proportions of the southern, Clovis-related branch," first author Christina Scheib added, noting that this population may have expanded faster recently owing to an advantageous technology or cultural practice.

In another ancient genomics study published in Science today, researchers from Decode Genetics, the University of Iceland, and elsewhere used ancient and modern genome sequences to retrace the consequences of migrations into Iceland from Norway and the British Isles, which took place around 1,100 years ago.

"Our study of DNA from the teeth of Viking-age Icelanders provides the first in-depth investigation of how a new population is formed through admixture," co-senior author Agnar Helgason, an anthropology researcher affiliated with Decode and the University of Iceland, said in a statement.

Based on the whole-genome sequences of 27 individuals — believed to be part of the first generation of settlers in Iceland — and available sequences for more than 2,100 modern-day Europeans, the team found that early Icelanders tended to be far more closely related to Norse, Gaelic, and other source populations than to individuals living in Iceland today.

The researchers attributed this pronounced population genetic shift to a combination of admixture and substantial genetic drift in the years since the region was first settled, leading to unequal founder population contributions to Iceland's current gene pool. Iceland's population did not creep past 50,000 individuals until the 1850s, the team noted, when it surged toward present day levels. The country currently has a population of more than 334,000.

"Repeated famines and epidemics led to a substantial loss of sequence diversity from the Icelandic gene pool, causing it to drift away from its source populations in Scandinavia and the British-Irish Isles," co-senior author Kári Stefánsson, CEO of Decode and a researcher in the University of Iceland's faculty of medicine, said in a statement. "This is a fascinating example of how a population is shaped by its environment, in this case the harsh and marginal conditions of medieval Iceland."