Study of modern DNA shakes up ideas of when and where contact happened

8 Jul 2020

    By Lizzie Wade 

    By about 1200 C.E., Polynesians were masters of oceanic exploration, roaming 7000 kilometers across the Pacific Ocean in outrigger canoes. Guided by subtle changes of wind and waves, the paths of migrating birds, bursts of light from bioluminescent plankton, and the position of the stars, they reached and settled islands from New Zealand to Rapa Nui, or Easter Island, the closest Polynesian island to South America.

So it's natural to wonder: Did these world-class explorers make it the last 3800 kilometers to South America? A genomic study of more than 800 modern Polynesians and Native Americans suggests they did.

The work strengthens earlier evidence that somewhere—perhaps on the northern coast of South America—the two groups met and mixed well before the era of European colonialism. And it shakes up the most popular model of where Native American genes first took root in Polynesia, shifting the focus from Rapa Nui to islands farther west.
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"This is an excellent, exciting study," says Lars Fehren-Schmitz, an anthropological geneticist at the University of California (UC), Santa Cruz. Expanding genomic research to islands beyond Rapa Nui "was what was missing from the whole picture."

Earlier hints of contact between the two regions included the sweet potato, which was domesticated in the Andes but grown and eaten all over Polynesia for hundreds of years before Europeans arrived. And a 2014 study of 27 modern people from Rapa Nui found they had Native American ancestry dating back to between 1300 C.E. and 1500 C.E.—at least 200 years before the first Europeans landed there in 1722 C.E. But a 2017 ancient DNA study, led by Fehren-Schmitz, found no sign of Native American ancestry in five people who lived on Rapa Nui before and after European contact.

Population geneticist Andrés Moreno-Estrada and anthropologist Karla Sandoval, both at Mexico's National Laboratory of Genomics for Biodiversity, traveled to Rapa Nui in 2014 and invited the community to participate in a study. They analyzed genome-wide data from 166 people from the island. Then they combined those data with genomic analyses of 188 Polynesian people from 16 other islands, whose genetic samples had been collected in the 1980s.

"It's an amazing data set," says Anna-Sapfo Malaspinas, a population geneticist at the University of Lausanne who led the 2014 work that found evidence for contact.

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Moreno-Estrada, Sandoval, and their team found that people on many islands had both Polynesian and European ancestry, reflecting their colonial histories. But they were also able to detect a small amount of Native American ancestry in people from the eastern Polynesian islands of Palliser, the Marquesas, Mangareva, and Rapa Nui. The Native American sequences were short and nearly identical—seemingly a legacy of one long-ago meeting with a Native American group, rather than sustained contact over generations, Moreno-Estrada says.

Comparing those sequences with genomes from people from 15 Indigenous groups from the Pacific coast of Latin America, researchers found most similarity to the Zenu, an Indigenous group from Colombia, the team reports today in Nature.

Analyses of the length of the Native American sequences show this ancestry appeared first on Fatu Hiva in the South Marquesas roughly 28 generations ago, which would date it to about 1150 C.E. That's about when the island was settled by Polynesians, raising the possibility the contact happened even earlier. The genetic legacy of that mixing was then carried by Polynesian voyagers as they settled other islands, including Rapa Nui.

Where exactly the first encounter took place, the team can't say. Modern Latin American fishermen lost at sea have been known to drift all the way to Polynesian islands. "It could have been one raft lost in the Pacific," Moreno-Estrada says.

But it's more likely that Polynesians traveled to the northern coast of South America, says Keolu Fox, a genome scientist at UC San Diego. Polynesian voyagers frequently traveled between islands and could have journeyed to South America and back, perhaps multiple times, Fox says. "In the process, these Polynesians bring back the sweet potato, and they also bring back a small fragment of Native American DNA" from relationships on the mainland. "The ocean is not a barrier" for Polynesians, he says.

Fehren-Schmitz and other researchers agree contact is likely, but stress that only ancient DNA can provide direct evidence of an encounter. But DNA degrades quickly in the tropics—and Polynesian communities that remember being disrespected by Western scientists in the past may be reluctant to grant permission for genetic studies of their ancestors, says Fox, who is Kānaka Maoli (Native Hawaiian). To move forward, he says, researchers need to deeply engage on an ongoing basis with descendant communities on many islands.

For now, "This study shows us a new path to follow," says Francisco Torres Hochstetter, an archaeologist at the Father Sebastian Englert Anthropological Museum in Hanga Roa on Rapa Nui. "It opens our minds."