The study of the bones of 15 indigenous people debunks the myth that the Rapanui population caused its own decline by overexploiting the island’s resources.
Few stories raise as many questions as that of the vanished civilization of Easter Island, known indigenously as Rapa Nui. The most popular scenario is that a group of Polynesian navigators landed on the island in the early 12th century.e century to establish a thriving society there. Very quickly, the small community expanded, erecting the famous giant statues, the moai, exploiting the land and cutting down trees, thus prospering for several centuries. Until the inevitable happened: the resources were exhausted and could no longer support the rapid growth of the Rapanui population, which, according to some estimates, reached up to 15,000 inhabitants at its peak. Famine, war, disease and even cannibalism took away a large part of the inhabitants, victims of “ecological suicide” or ecocide. Shortly after, on April 5, 1722, Easter Day, the Europeans discovered the few survivors and renamed the island.
But this story, developed in the 19th century, is being challenged by scientists. Recent analyses of the DNA of bones of 15 indigenous individuals, preserved at the National Museum of Natural History and the Musée de l’Homme in Paris, provide new pieces to the puzzle. The results were published in the journal Nature.
A partly American genetic origin
While it has long been accepted that the roots of the inhabitants of Rapa Nui were exclusively Polynesian, several studies suggest on the contrary that the origins of this people reflect a more complex mix, a mixture of a dual Polynesian and South American ancestry. It is in particular the presence of several varieties of sweet potatoes found as far as the Pacific islands that put scientists on this track. Since the sweet potato is not indigenous to the Pacific islands, it has been established that its introduction was made from the American continent approximately one or two centuries before the arrival of Europeans on Rapa Nui. In other words, this suggests that contact inevitably took place between South American and Polynesian peoples in the pre-colonial period. The subject of trans-Pacific contact before the arrival of Europeans has sparked much debate for over a century, particularly around the work of Norwegian explorer Thor Heyerdahl, explains Aymeric Hermann, an archaeologist at the UMR Temps of the CNRS in Nanterre, who did not participate in the study. The latter defended throughout his life the idea that Polynesia could have been populated by people from South America, which was later refuted by evidence according to which the ancestors of all the island populations of the Pacific came from Southeast Asia and the islands of Papua and New Guinea. »
However, genetic analyses of individuals currently living in Polynesia show that they are carriers of this double crossbreeding, explains a study published in 2020. But they would in fact be Polynesian explorers who went as far as the South American coasts, returned and also settled on Easter Island. This new study confirms this on ancient DNA extracted from the bones of 15 indigenous inhabitants of Rapa Nui. “, underlines Aymeric Hermann. According to these analyses, the bones in question in fact bear a majority Polynesian signature, and 6% to 11.4% of their genetic material can be attributed to South American ancestors.
Ecocide theory denied
The enigma of the apparent disappearance of the Rapanui remains. The hypothesis of precolonial ecological suicide has been called into question several times, notably by archaeological dating according to which the construction of moai continued well after the arrival of Europeans. An argument that is now reinforced by these genetic analyses. First of all, radiocarbon dating of the bones suggests that the individuals studied lived between 1600 and 1900, up to 200 years after European contact in 1722. Using mathematical models, the scientists then traced the evolution of demographic dynamics, that is to say the moments of growth and decline that may have shaped the history of the island’s population. To do this, our work is based on the theory of coalescence, a mathematical model according to which the genome of each individual is made up of segments of genomes inherited from their ancestors, the length and number of which can indirectly give us an indication of the size of a given population over time. »explains Évelyne Heyer, professor of genetic anthropology at the Natural History Museum in Paris, co-author of this study.
« If there had been a population collapse at the time of a supposed ecocide, the authors would have observed a more accentuated profile (in number and length) of these genome segments, indicating that most of the genetic ancestors of the Rapanui would belong to a very small population. “, explains Lluis Quintana-Murci, a population geneticist at the Collège de France and the Pasteur Institute, who was not involved in the study. But analyses robustly suggest the opposite. “The population size was indeed small, and therefore genetically very little diverse, at the beginning of the settlement of the island in the 13e century. But it would then have gradually and regularly increased until around the middle of the 19the century, well after contact with Europeans. These results are an estimate, recalls Anna-Sapfo Malaspinas, a population genetics researcher in the Department of Computational Biology at the University of Lausanne in Switzerland, who led the study. But they could corroborate those of others recent archaeological works assuming that the population of Rapa Nui probably never housed much more than the approximately 3 000 people encountered by European colonizers in 1722. »
Little by little, the confrontation of historical accounts, archaeological evidence and now genetic analyses, thus converges towards the same idea: the demographic decline of Rapa Nui would not be linked to an ecocide. Far from blindly exploiting their environment, the Rapanui have managed to survive and prosper over several centuries in a harsh environment by implementing innovative agricultural techniques such as “stone mulching” to remedy the poor soils of the island and have even managed to maintain religious practices around sacred trees by organizing the cultivation of the endemic palm (Jubea sp.) in an exceptional ceremonial site of Ava Ranga Uka, recently discovered in the center of the island. », souligne Aymeric Hermann.
The demographic decline would have been initiated later by contact with Westerners, notably through the introduction of diseases, and by forced labor organized in the 1860s, when a large part of the island’s inhabitants were deported to South America by raids by Peruvian slave traders. The ethnologist Alfred Métraux mentions a population of only a hundred individuals at the end of the 19th century, some of whom followed French missionaries to the Gambier Islands in French Polynesia, and there are still descendants of this diaspora in Tahiti today. “, adds Aymeric Hermann.
