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Polynesians settled Easter Island and built its famous moai sculptures. Grafissimo

Did early Easter Islanders sail to South America before Europeans?

Nearly 2000 kilometers from its nearest neighbor in the Pacific Ocean, Rapa Nui, also known as Easter Island, seems an unlikely crossroads for the world’s cultures. But in recent years, some scientists have argued that the island’s first inhabitants—Polynesians who settled there by 1200 C.E.—may have sailed all the way to South America and back, making contact with Native Americans long before Europeans. Now, DNA from people who lived on Rapa Nui before European contact suggests that may not be the case, throwing a wrench into one of the biggest remaining mysteries about human migration.

The result shocked Lars Fehren-Schmitz, a biological anthropologist at the University of California, Santa Cruz, who led the study. When he sequenced genomes from the rib bones of five individuals who lived on Rapa Nui before and after European contact, he expected to find a population with mixed Polynesian and Native American ancestry. Polynesian voyages to and from South America, though thousands of kilometers, “just seem to be plausible,” he says, and archaeological evidence shows that the sweet potato, domesticated 8000 years ago in Peru, had spread to Polynesian islands as early as 1000 C.E. But the DNA of the individuals, who lived between the 13th and 19th centuries, showed no signs of Native American ancestry, Fehren-Schmitz and his colleagues write today in Current Biology.

This contradicts a 2014 study, also published in Current Biology, that analyzed the genomes of 27 modern Rapanui who, like most people who live on the island today, have Polynesian, European, and Native American ancestry. About 8% of their DNA was inherited from Native American ancestors, appearing in their genomes in short bursts rather than long stretches. Because the contribution of each group’s DNA becomes more fragmented over time, that’s a strong signal of a long-ago meeting between different populations. Based on the length of the Native American DNA sequences, the researchers concluded that the Rapanui’s Polynesian and Native American ancestors must have met at least 19 generations ago, between 1280 C.E. and 1495 C.E.—long before Europeans arrived on the island in 1722 C.E.

There are a few ways to explain the discrepancy, researchers say. The most likely, says Anna-Sapfo Malaspinas, a population geneticist at the University of Lausanne in Switzerland who led the 2014 research, is that when the pre-Columbian individuals Fehren-Schmitz analyzed were alive, contact with Native Americans was recent and their genetic signature hadn’t yet spread to the whole population of Rapa Nui. “One would like to see more individuals … before you really say there was no contact,” agrees Hannes Schroeder, an ancient DNA researcher at the University of Copenhagen who wasn’t involved in either paper.

But Fehren-Schmitz proposes another possibility. Some of the colonial slave traders who targeted Rapa Nui were from Peru, where European and Native American genes had mixed since the 16th century. When they arrived on the island in the 18th and 19th centuries, they already carried short bursts of Native American DNA, and they could have passed those on to the still purely Polynesian Rapanui. That might have made it look like contact between Polynesians and Native Americans happened long before it actually did, he says.

Malaspinas says her team tested a scenario like this, and it didn’t fully explain their results. But she says it’s possible her model couldn’t precisely capture the myriad ways colonialism and the slave trade affected the Rapanui’s genomes. On the often surprising gaps between scientific models and what actually happened in the past, she and Fehren-Schmitz agree: “When it comes to human behavior and human history, there’s so much more complexity to it,” he says.