D. Burley et al., PLoS ONE 7, 11 (2012)

Epic pre-Columbian voyage suggested by genes

Polynesians from Easter Island and natives of South America met and mingled long before Europeans voyaged the Pacific, according to a new genetic study of living Easter Islanders. In this week’s issue of Current Biology, researchers argue that the genes point to contact between Native Americans and Easter Islanders before 1500 C.E., 3 centuries after Polynesians settled the island also known as Rapa Nui, famous for its massive stone statues. Although circumstantial evidence had hinted at such contact, this is the first direct human genetic evidence for it.

In the genomes of 27 living Rapa Nui islanders, the team found dashes of European and Native American genetic patterns. The European genetic material made up 16% of the genomes; it was relatively intact and was unevenly spread among the Rapa Nui population, suggesting that genetic recombination, which breaks up segments of DNA, has not been at work for long. Europeans may have introduced their genes in the 19th century, when they settled on the island.

Native American DNA accounted for about 8% of the genomes. Islanders enslaved by Europeans in the 19th century and sent to work in South America could have carried some Native American genes back home, but this genetic legacy appeared much older. The segments were more broken and widely scattered, suggesting a much earlier encounter—between 1300 C.E. and 1500 C.E.

But did Polynesians land on South American beaches, or did Native Americans sail 3500 kilometers into the Pacific to reach Rapa Nui? “Our studies strongly suggest that Native Americans most probably arrived [on Rapa Nui] shortly after the Polynesians,” says team member Erik Thorsby, an immunologist at the University of Oslo. He thinks that could support the controversial theory, posited by Norwegian adventurer Thor Heyerdahl more than a half-century ago, that Native Americans had the skills to move west across the Pacific.

But many scientists say that Pacific currents and Polynesian mastery of the waves make it more likely that the Polynesians were the voyagers. They may have sailed to South America, swapped goods for sweet potatoes and other novelties—and returned to their island with South American women.

Sweet potato was domesticated in the Andean highlands, and researchers recently determined that the crop spread west across Polynesia before Europeans arrived. Another hint of trans-Pacific exchange comes from chicken bones—unknown in the Americas before 1500 C.E.—excavated on a Chilean beach, which some believe predate Christopher Columbus.

Skeptics say that genetic evidence from modern human populations is not enough to prove ancient contact. The genetic clock is often uncertain, says anthropologist Carl Lipo of California State University, Long Beach. “We need ancient DNA from skeletal evidence—not modern evidence—to resolve this question.”

*Clarification, 27 October, 11:50 a.m.: Erik Thorsby is described as supporting the hypothesis that Native Americans voyaged on their own to Easter Island. Thorsby, like most scientists, believes it much more likely that Polynesians brought Native Americans to the island.