More than 800 years ago, Polynesians sailed thousands of miles across the Pacific Ocean to one of the most remote islands on earth, Rapa Nui.

A study of ancient genomes from descendants of these seafarers is now answering key questions about the history of the island. It refutes the idea of ​​a population collapse hundreds of years ago and confirms contact with indigenous Americans before colonial times.

The theory that the early indigenous inhabitants of Rapa Nui — also known as Easter Island — devastated their ecosystem and caused the population to collapse before the arrival of Europeans in the early 18th century was supported by the bookCollapsepopularized by geographer Jared Diamond in 2006. But subsequent scientists have questioned this theory.

The current analysis, published on September 11th inNature 1, “represents the final nail in the coffin of this collapse narrative,” says Kathrin Nägele, an archaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “It corrects the image of indigenous people.”

The study was conducted with the support and input of authorities and members of the indigenous community in Rapa Nui. The authors say their data could help repatriate the remains collected in the study, which were collected in the 19th and 20th centuries and are now kept in a Paris museum.

Answers from DNA

After the Polynesians conquered Rapa Nuiad1200 settled, they developed a thriving culture that is famous for its hundreds of colossal stone figures, the moais.

When Europeans first reached the island in 1722, they estimated the population at 1,500 to 3,000 people and found a landscape cleared of the palm trees that once covered the forest. By the end of the 19th century, the indigenous population, known as Rapanui, had dwindled to 110 people, caused by a smallpox outbreak and the kidnapping of a third of the inhabitants by Peruvian slave traders.

The theory of 'ecocide', which suggests that a pre-contact population of 15,000 or more plundered the island's once-pristine resources, has been challenged by researchers critical of human influence on deforestation and its impact on food production, as well as inflated population numbers.

Anna-Sapfo Malaspinas, a population geneticist at the University of Lausanne, Switzerland, and Víctor Moreno-Mayar, an evolutionary geneticist at the University of Copenhagen, were confident that ancient Rapanui DNA could help resolve the ecocide theory as well as another lingering question: When did ancient islanders interbreed with Native Americans?

Her team's 2014 study of contemporary Rapanui genomes identified that these people had some Native American ancestry that appeared to have been acquired before the arrival of Europeans 2, suggesting travel to America. However, a 2017 study found no evidence of Native American ancestry in the genomes of three individuals who lived on Rapa Nui before 1722 3.

To find answers, researchers turned to human remains at the National Museum of Natural History in France, collected in the 19th and early 20th centuries. Genome sequences of teeth or inner ear bones from 15 individuals and comparisons with other ancient and modern populations suggested they were Rapanui, and radiocarbon dating indicated they lived between 1670 and 1950.

No population collapse

Both ancient and modern genomes contain information about how the size of a population has changed over time. When the population is small, stretches of DNA shared between individuals — that come from a common ancestor — tend to be longer and more numerous, compared to stretches of DNA from times of higher numbers.

In the ancient Rapanui genomes, there were signs of a population bottleneck at the time the island was settled, which is to be expected when a founding group arrives. Thereafter, the island's population appeared to grow steadily until the 19th century.

Translating these developments into actual population numbers is not easy, but further modeling suggested that the genetic data is inconsistent with a decline from 15,000 to 3,000 people before the 18th century. “There was no major collapse,” says Malaspinas. “We’re pretty confident that didn’t happen.”

All ancient Rapanui carried Indian-American ancestry in their genomes, which the researchers attributed to admixture dating to the 14th century. The sections of indigenous American heritage most closely resembled DNA from ancient and modern inhabitants of the central Andean highlands in South America. However, the lack of ancient and modern human genomes from the Americas makes it impossible to accurately determine the people the ancient Rapanui encountered, Moreno-Mayar adds. Still, the finding that Rapanui encountered Native Americans hundreds of years before Europeans arrived is “an outstanding result,” Nägele says. “We can track where this happened and who traveled.”

Community participation

Keolu Fox, a genomic scientist at the University of California, San Diego, says the finding that Rapanui reached the Americas will not surprise the Polynesian people. “We’re confirming something we already knew,” he says. “Do you think that a community that discovered things like Hawaii or Tahiti would have missed an entire continent?”

The researchers received a similar reaction when they presented their initial results in Rapa Nui. Malaspinas remembers being told that “of course we went to America.” She, Moreno-Mayar and other colleagues made several trips to the island to consult with officials and residents throughout the study.

Malaspinas and her colleagues received approval for the study from committees that monitor land use and cultural heritage on the island. The researchers sought her permission after collecting the remains in Paris — something Malaspinas now regrets. “I would do things differently if I started the project today,” she says, adding that her team was prepared to put the work on hold if the committees said no.

Community involvement in Rapa Nui shaped the questions the project addressed, says Malaspinas, such as attempting to clarify the relationship between ancient and modern Rapanui. There has also been strong interest in repatriating the remains, which researchers hope will eventually happen.

Nägele, who works in Polynesia, thinks the researchers have done a good job connecting with the people of Rapa Nui. But she adds that scientists should play a stronger role in pressuring foreign institutions to return indigenous remains to their place of origin.