The population of Rapa Nui, also known as Easter Island, interbred with Native Americans before Europeans arrived, despite 3,700 kilometers (2,300 miles) between them, ancient DNA suggests. The islanders, once the poster child for a people who brought about environmental collapse through overharvesting of resources, also appear to be innocent of this charge, according to the same research.

Rapa Nui is so incredibly remote that even finding it is considered one of humanity’s most remarkable achievements before the acquisition of technology like compasses and large vessels. The civilization built there by the native people was made famous by the enormous carved monoliths they constructed, but it has fascinated anthropologists for other reasons.

One of these is the possibility that the inhabitants sailed on and reached South America. On the one hand, it’s a lot harder to miss a continent than a small island, but on the other, this would have required a voyage almost twice as long as the one from the Polynesian islands from which the Rapanui came.

Genetic testing of the modern population of Rapa Nui has shown a diversity of ancestry, but that is distorted by the Europeans who first visited in 1722 and subsequently kidnapped most of the population for slaves. Now, however, DNA has been found from 15 people who lived on the island, in some cases as far back as 1670, and whose remains are stored in the Musée de l’Homme in Paris.

The possibility of interchange between Polynesia and the Americas via Rapa Nui has been very controversial, but the presence of foods like sweet potato, which originated in South America, is hard to explain any other way. It also seems the first South American chickens were Polynesian breeds.

The new study shows that about 10 percent of the ancestry of the pre-European contact Rapanui was Indigenous American. That means some of the population not only sailed all the way to South America, but found their way back to their tiny dot in the vast Pacific, bringing people they’d visited with them. Not surprisingly, the Native American genetic inheritance of the population most closely matches peoples from coastal Chile and Peru.

No Ecocide

A more famous controversy about Rapa Nui relates to the idea that deforestation of the island caused a collapse in food production, leading to famine and war. The idea was popularized by Jared Diamond in his book Collapse, but he didn’t come up with it. Many scientists had proposed it before Diamond based on estimates of a peak population of 15,000 and European reports of 1,500-3,000 when Europeans visited.

Others, however, have questioned the narrative. "While it is well established that the environment of Rapa Nui was affected by anthropogenic activity, such as deforestation, we did not know if or how these changes led to a population collapse," said study author Anna-Sapfo Malaspinas, of the University of Lausanne in a statement. Diamond’s book has been presented as an example of the way a well-written account of one side of a live scientific debate can grab the public imagination and become accepted wisdom among those without specialist expertise.

The DNA indicates something very different. Population crashes lead to inbreeding. However, Bárbara Sousa da Mota said: "Our genetic analysis shows a stably growing population from the 13th century through to European contact in the 18th century. This stability is critical because it directly contradicts the idea of a dramatic pre-contact population collapse.” 

The finding is consistent with a recent study undermining the claim a large population was needed to build so many monoliths. 

How the population managed to feed themselves after denuding the island of most of its trees is not clear; perhaps the crops some adventurers had brought back from South America helped.

However, one part of the collapse theory does seem to have been vindicated by the new research. The genetics suggest interbreeding occurred between 1250 and 1430. That means voyages took place not long after Polynesians reached the island, and that they beat Columbus to the Americas. However, the reason the contact stopped is probably because after felling most of the palm trees, the Rapanui couldn’t make boats capable of such long journeys.

The scientific debate about ecological collapse has also become highly politicized. The claimed collapse has been used as a warning about the fate that could befall the whole planet if we fell the forests, but others see it differently.

"Personally, I believe the idea of the ecocide is put together as part of a colonial narrative. That is this idea that these supposedly primitive people could not manage their culture or resources, and that almost destroyed them. But the genetic evidence shows the opposite,” said study author Dr Victor Moreno-Mayar of the University of Copenhagen.

In keeping with a more respectful approach to Rapanui culture, the authors of this research met with the surviving community to seek permission to test the museum specimens and define the questions to be studied. Proof the specimens are closely related to modern inhabitants of the island will be used to mount a case to bring the remains home.

The study is published in Nature.