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Ancient voyage carried Native Americans’ DNA to remote Pacific islands

Finding that some Polynesians have genetic ancestry from South America supports long-held theory that ancient populations met and produced offspring.

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Moais on Easter Island

Stone statues on Easter Island.Credit: Gregory Boissy/AFP/Getty

Traces of Native American ancestry have been found in the genomes of modern inhabitants of some Polynesian islands, suggesting that ancient islanders met and mixed with people from South America hundreds of years ago.

Polynesia was one of the last corners of the world that humans settled, as island-hopping groups from Asia and Oceania began to push farther east some 1,000 years ago. A study published in Nature on 8 July supports the long-standing, but unproven, theory that ancient Polynesians had contact with Native Americans1. Researchers had thought that this was most likely to have happened on Easter Island, also called Rapa Nui, because of its proximity to South America. But the latest data suggest that these encounters — or perhaps a single meeting — happened on islands thousands of kilometres farther away from the continent.

Abundant archaeological and genetic evidence indicates that Polynesian islands were first settled by humans travelling east from Asia, but there are some clues that these people made contact with South Americans. Sweet potatoes, which originate in the Andean highlands, grow across eastern Polynesia, and samples of Polynesian sweet potatoes from the eighteenth century share genetic markers with coastal South American varieties2. A 2014 genome study found that the ancestors of modern inhabitants of Rapa Nui had produced offspring with Native Americans3, but DNA from ancient-human remains from that island and another in French Polynesia found no such signs4,5.

Mixed ancestry

To broaden the search, a team led by population geneticist Andrés Moreno-Estrada, at the National Laboratory of Genomics for Biodiversity in Irapuato, Mexico, analysed DNA from 166 people currently living on Rapa Nui, as well 188 individuals from more than a dozen islands across the Pacific. They identified Native American ancestry not only in the Rapa Nui, but also in people from the remote eastern Polynesian islands of Palliser, Nuku Hiva in the Northern Marquesas, Fatu Hiva in the Southern Marquesas and Mangareva. Comparisons of this genetic material with that from Native American groups suggested that Zenu people, an Indigenous group in Colombia, carry DNA most like that found in Polynesians.

Moreno-Estrada’s team then attempted to determine when the two populations had produced offspring — to distinguish ‘pre-Columbian’ contact between the groups from the mixing that took place in the centuries after European colonization of South America and Polynesia. On the basis of the length of shared DNA segments — which shorten in successive generations — the researchers estimate that people in remote eastern Polynesia produced offspring with South Americans between ad 1150 and ad 1230, whereas those in Rapa Nui mixed closer to ad 1380. They also found evidence of mixing in the eighteenth and nineteenth centuries.

Some researchers have proposed that Polynesians voyaged to the coast of South America. But Moreno-Estrada thinks that contact occurred in Polynesia — and that it might have involved a single group of Native Americans. The team calculated similar dates for the appearance of Native American ancestry on different islands, and another analysis found that the South American DNA segments in the genomes of people from different Polynesian islands appear to have come from the same Native American people. Archaeological evidence suggests that there were maritime trade routes between Mexico and Ecuador around that time, Moreno-Estrada says. “Maybe a small raft of Native American sailors got adrift into the Pacific.”

Moreno-Estrada thinks that the Polynesians who settled Rapa Nui around ad 1200 already carried South American ancestry. But Paul Wallin, an archaeologist at Uppsala University in Sweden, wonders whether groups of Native Americans might have also travelled there from South America at a later date. Large stone monuments, similar to those in South America, were first constructed on Rapa Nui around ad 1300–1400, hundreds of years before they appeared on other Polynesian islands, he notes.

“The results are very convincing,” says Lars Fehren-Schmitz, an anthropological geneticist at the University of California, Santa Cruz. He thinks too much focus has been placed on Rapa Nui, and that it makes sense for contact to have occurred elsewhere in Polynesia.

“It is a very fascinating story,” says Cosimo Posth, a palaeogenomicist at the University of Tübingen, Germany. He and his colleagues are scouring the region for the remains of ancient islanders who carry a mix of the two ancestries — or better yet, those of South American people who might have made the long voyage. “Only ancient DNA from eastern Polynesia can settle this riddle,” he says.

doi: 10.1038/d41586-020-02055-4

References

  1. 1.

    Ioannidis, A. G. et al. Nature https://doi.org/10.1038/s41586-020-2487-2 (2020).

  2. 2.

    Roullier, C., Benoit, L., McKey, D. B. & Lebot, V. Proc. Natl Acad. Sci. USA 110, 2205–2210 (2013).

  3. 3.

    Moreno-Mayar, J. V. et al. Curr. Biol. 24, 2518–2525 (2014).

  4. 4.

    Fehren-Schmitz, L. et al. Curr. Biol. 27, 3209–3215 (2017).

  5. 5.

    Posth, C. et al. Nature Ecol. Evol. 2, 731–740 (2018).

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