New Genetic Insights into the Settlement History of the Americas

Or, did the ancestors of today’s Native Americans come from other parts of Asia or Polynesia, arriving multiple times at several places on the two continents, by sea as well as by land, in successive migrations that began as early as 30,000 years ago? Such questions have fascinated anthropologists and archaeologists for decades.

An international team of geneticists and anthropologists, from U.S., British, Canadian, Swiss, and Central and South American universities, have produced new genetic evidence that is likely to hearten proponents of the land bridge theory. This study, published PLoS Genetics, is one of the most comprehensive analyses to date among efforts to use genetic data to shed light on the settlement history of the Americas.

The researchers examined genetic variation at 678 key locations or markers in the DNA of present-day members of 29 Native American populations across North, Central and South America. They also analyzed data from two Siberian groups. The analysis shows that genetic diversity, as well as genetic similarity to the Siberian groups, decreases the farther a native population is from the Bering Strait – adding to existing archaeological and genetic evidence that the ancestors of Native North and South Americans came by the northwest route.

The analysis also shows that a unique genetic variant is widespread in Native Americans across the American continents – suggesting that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources. This variant has not been found in genetic studies of people elsewhere in the world except in eastern Siberia.

The researchers say the variant likely occurred shortly prior to migration to the Americas, or immediately afterwards. “We have reasonably clear genetic evidence that the most likely candidate for the source of Native American populations is somewhere in east Asia,” says Noah A. Rosenberg, Ph.D., assistant professor of human genetics and assistant research professor of bioinformatics at the Center for Computational Medicine and Biology at the University of Michigan Medical School and assistant research professor at the University of Michigan Life Sciences Institute.

“If there were a large number of migrations, and most of the source groups didn’t have the variant, then we would not see the widespread presence of the mutation in the Americas,” he says.

The pattern that the research uncovered – that as the founding populations moved south from the Bering Strait, genetic diversity declined – is what one would expect when migration is relatively recent, says Mattias Jakobsson, co-first author of the paper. There has not yet been time for mutations that typically occur over longer periods to diversify the gene pool.

In addition, the study’s findings hint at supporting evidence for scholars who believe early inhabitants followed the coasts to spread south into South America, rather than moving in waves across the interior. “Assuming a migration route along the coast provides a slightly better fit with the pattern we see in genetic diversity,” Rosenberg says.

Funding for the research came from the National Institutes of Health, the Canadian Institutes of Health Research, Fondecyt Proyecto, the Swiss National Foundation and the University of Michigan.