Scientists have long wondered how early people sailed to the island — as well as how they built the island’s impressive Moai.
Genetic tests have shown that the modern Rapanui people have a mix of Polynesian, South American and European ancestry. Some scientists have used the modern DNA results to suggest that Polynesians from the west and native South Americans from the east lived and intermingled on the island before Europeans first arrived in 1722. And in the famous Kon-Tiki expedition, a Norwegian explorer named Thor Heyerdahl showed on a balsa wood raft how South Americans could have voyaged to the Polynesian islands during pre-Columbian times.
But that does not mean it was probable, according to Lars Fehren-Schmitz, a biological anthropologist from the University of California, Santa Cruz, and lead author of the study.
Using rib bones from five Easter Island individuals from 1445 to 1945 that had been excavated in the 1980s and stored in the Kon-Tiki museum in Norway, Dr. Fehren-Schmitz and his colleagues attempted to sequence the genome of the island’s earliest inhabitants. The team extracted enough useful genetic information from the remains to analyze and draw conclusions that could be representative of the larger ancient population.
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“I was pretty surprised when we didn’t find any Native American signals in our pre-contact samples,” Dr. Fehren-Schmitz said. “Honestly, at first I thought I did something wrong with the statistics. Then it was an ‘a-ha moment.’”
Scientists who were not involved in the study pointed out some of its limitations.
“This is a valuable work as it presents the first ancient whole genome data from Rapa Nui,” Víctor Moreno-Mayar, a geneticist at the Natural History Museum of Denmark, said in an email. But he cautioned that with only a handful of samples, the team did not have enough data to generalize about the genetics of the entire ancient population.
He was lead author on a paper in 2014 about the genetical testing of a sample of 27 modern Rapanui that found they inherited about 8 percent of their DNA from Native Americans. The paper also suggested that natives of South America may have come or were brought to Easter Island around 1340 A.D.
Dr. Erik Thorsby, an immunologist at the University of Oslo in Norway and his co-author, agreed.
“A few Native Americans may have reached Rapa Nui early, and their ancestral genes may be easily missed when ancient DNA from only five individuals are investigated,” he said.
Dr. Fehren-Schmitz acknowledged that the sample size was limited, but he said his investigation has shown that the history of the populations on Rapa Nui is more complicated than previously thought.
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“What we can say is, at the time where those individuals lived that we tested, Native American ancestry was not distributed through the population of Rapa Nui,” he said. “Either that exchange didn’t happen or it only happened with specific parts of the population on the island. Both things would be very interesting.”
His colleague, Cat Jarman, a doctoral student and archaeologist from the University of Bristol in England and a co-author on the study, said that European enslavement of the islanders may account for Native American ancestry in the modern DNA of the Rapanui.
In the 1860s, Europeans took as much as half of the population of Easter Island to Peru as slaves. After a public outcry, the slavers were forced to return some of these people to Easter Island, though they came back with diseases and at one point the population fell to as few as 111 people, according to Mrs. Jarman.
“When we look at this modern DNA, it’s not necessarily representative of the population that was there 800 years ago because so much has happened,” Mrs. Jarman said. “So many people have moved because of slavery and it’s had a huge genetic impact that we need to take into account when we look at the modern population.”
Anna-Sapfo Malaspinas, a population geneticist at the University of Lausanne in Switzerland and was an author on the 2014 paper with Dr. Thorsby and Dr. Moreno-Mayar, said the latest study suggested possibilities for future research.
“At the time we published our paper, we felt that the way to go forward was to indeed analyze ancient DNA to give more insight into the timing of the mixture,” Dr. Malaspinas said. “It’s a mystery we need to work more on. There’s a lot still to uncover.”