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Post by Admin on Sept 11, 2024 23:57:43 GMT
Easter Island, also known as Rapa Nui, is one of the most isolated inhabited places in the world. It has captured the imagination of many owing to its archaeological record, which includes megalithic statues. Two prominent contentions have arisen from the extensive study of the island. First, its history has been presented as a warning tale of resource overexploitation that would have culminated in a major population collapse — the ‘ecocide’ theory. Second, the possibility of trans-Pacific voyages to the Americas pre-dating European contact is still debated. To address these questions, a team of scientists from the Globe Institute and elsewhere sequenced and analyzed the genomes of 15 Rapanui individuals who lived between 1670 and 1950.  Located in the Pacific, on the easternmost tip of the Polynesian Triangle, it lies 3,700 km west of South America and more than 1,900 km east of the closest inhabited island. Despite the remoteness of Rapa Nui, archaeological and genetic evidence shows that Polynesian peoples from the west had already reached the island about 1250 CE. The following five centuries saw the Rapanui, the inhabitants of Rapa Nui, develop a culture characterized by iconic megalithic statues (moai) and monumental stone platforms (ahu). Owing to the isolation of Rapa Nui, Europeans reached the island only in 1722 CE. Over the years, European visitors had a devastating impact on the Rapanui as they killed local inhabitants and introduced deadly pathogens that the islanders had not been exposed to before. Subsequently, a smallpox outbreak decimated the Rapanui population and it fell to an estimated 110 individuals. “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 Dr. Anna-Sapfo Malaspinas, a researcher at the University of Lausanne and the SIB Swiss Institute of Bioinformatics. www.nature.com/articles/s41586-024-07881-4 |
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Post by Admin on Sept 13, 2024 2:28:33 GMT
Ancient Rapanui genomes reveal resilience and pre-European contact with the Americas
Rapa Nui (also known as Easter Island) is one of the most isolated inhabited places in the world. It has captured the imagination of many owing to its archaeological record, which includes iconic megalithic statues called moai1. Two prominent contentions have arisen from the extensive study of Rapa Nui. First, the history of the Rapanui has been presented as a warning tale of resource overexploitation that would have culminated in a major population collapse—the ‘ecocide’ theory2,3,4. Second, the possibility of trans-Pacific voyages to the Americas pre-dating European contact is still debated5,6,7. Here, to address these questions, we reconstructed the genomic history of the Rapanui on the basis of 15 ancient Rapanui individuals that we radiocarbon dated (1670–1950 CE) and whole-genome sequenced (0.4–25.6×). We find that these individuals are Polynesian in origin and most closely related to present-day Rapanui, a finding that will contribute to repatriation efforts.
Through effective population size reconstructions and extensive population genetics simulations, we reject a scenario involving a severe population bottleneck during the 1600s, as proposed by the ecocide theory. Furthermore, the ancient and present-day Rapanui carry similar proportions of Native American admixture (about 10%). Using a Bayesian approach integrating genetic and radiocarbon dates, we estimate that this admixture event occurred about 1250–1430 CE.
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Post by Admin on Sept 14, 2024 23:40:01 GMT
Rapanui history has been presented as a warning tale for humanity’s overexploitation of resources. According to the theory of ecological suicide (‘ecocide’), before European contact, the Rapanui would have deforested the island and decimated the local fauna to maintain a flourishing culture and a growing population of about 15,000 individuals2,3,14. Consequently, resource scarcity would have led to the so-called Huri Moai cultural phase—a period of famine and war that would have escalated to the point of cannibalism and ultimately culminated in a population and cultural collapse in the 1600s, abruptly ending statue carving2,3,15. European visitors to the island in the 1700s estimated that the Rapanui population size varied between 1,500 and 3,000 individuals, which corresponds to between 10% and 20% of the population surviving the population collapse proposed by the ecocide theory16. Although it is well established that the environment in Rapa Nui was affected by anthropogenic activity (for example, deforestation), it remains unclear whether or how these changes would have led to a population collapse1. Several lines of bioanthropological, archaeological and historical evidence have been used to challenge the ecocide scenario4,16,17,18. Yet the collapse hypothesis has remained very popular2.
The depletion of wood for canoe building and renovation eventually led to the isolation of the island owing to the abandonment of long-distance seafaring—a hallmark of Polynesian cultures. However, several pieces of evidence suggest that Rapa Nui did not constitute the easternmost point of long sea voyages and that Polynesian peoples eventually reached the Americas before Columbus19,20,21,22,23 (but see refs. 24,25). Genetic studies on present-day individuals have supported such contact. Present-day Rapanui were found to harbour Native American and European admixture in their genomes5. Notably, in that work, Native American admixture (dated 1280–1495 CE) was estimated to pre-date European admixture (dated 1850–1895 CE).
More recently, Native American admixture was detected not only in present-day individuals from Rapa Nui, but also from Rapa Iti, Tahiti, Palliser, Nuku Hiva (North Marquesas), Fatu Hiva (South Marquesas) and Mangareva7. In that study, the Native American gene flow in the different islanders was dated between 1150 (South Marquesas) and 1380 CE (Rapa Nui), in line with the date estimated in ref. 5. However, the only two ancient DNA studies of ancient Rapanui so far did not find evidence for Native American admixture6,26. The first study focused on mitochondrial DNA from 12 individuals, whereas the second analysed low-depth (0.0004–0.0041×) whole-genome data from 5 individuals dating before and after European contact. In the latter, downstream population genetic analyses confirmed that the five ancient individuals were Polynesian. However, even though the analysed human remains were post-dating the inferred Native American admixture time, no Native American ancestry was reported in these ancient genomes, casting doubt on the findings based on data from present-day populations.
To infer the genomic history of ancient Rapanui, we have generated whole-genome sequencing data from 15 ancient individuals who were, according to museum records, found in Rapa Nui (Methods section ‘Ethics and inclusion’). We analyse these genomes and other publicly available data to: infer the genomic ancestry of these individuals; determine whether the Rapanui experienced a population collapse in the 1600s; and investigate whether Polynesians and Native Americans admixed before European contact.
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Post by Admin on Sept 17, 2024 18:42:23 GMT
Community engagement
Throughout the course of the study, we met with representatives of the Rapanui community on the island, the Comisión de Desarrollo Rapa Nui and the Comisión Asesora de Monumentos Nacionales, where we presented our research goals and ongoing results. Both commissions voted in favour of us continuing with the research. The results of our study were communicated to the community several times, including before first submission (Methods section ‘Ethics and inclusion’). We presented the research project in public talks, a short video and radio interviews on the island giving us the opportunity to enquire about the questions that are most relevant to the Rapanui community. These discussions have informed the research topics we investigated in this work
Ancient genomes and radiocarbon dates
Following strict museum guidelines, we sampled petrous bone and teeth material from 15 individuals—labelled as Rapanui—from the Muséum national d’Histoire naturelle, France, Pinart (1877) and Métraux (1935) collections using a minimally invasive method27 (Supplementary Information section 1). This included the retrieval of loose teeth whenever possible (4 individuals) and 60–120 mg of petrous bone powder in other cases (11 individuals). We obtained direct radiocarbon dates from 11 individuals at the Oxford Radiocarbon Accelerator Unit and Bristol Radiocarbon Accelerator Mass Spectrometer. Results are reported in radiocarbon years before present, corrected for isotopic fractionation using the 13C/12C ratio. The results were calibrated to take into account marine reservoir effects derived from the consumption of marine proteins, and broadly range between 1670 and 1950 CE28,29,30(Supplementary Information section 2). Although most of this range postdates European contact in 1722, these skeletal remains must pre-date the date in which they were collected according to the museum archives (that is, 1877 (11 individuals) and 1934–1935 CE (4 individuals)). Thus, it is unlikely that these individuals were born after the 1860s Peruvian slave raids and subsequent epidemics that decimated the island population to an estimated 110 individuals1,13. We sequenced the whole genomes from the 15 ancient individuals to an average depth of coverage between 0.4 and 25.6× (Supplementary Information sections 2 and 3 and Supplementary Table 1). For all libraries, we estimated <5% contamination (Supplementary Information section 3 and Supplementary Table 1). To leverage the whole-genome dataset, we produced imputed diploid genotypes with GLIMPSE31. We validated the imputed data with benchmarking and downsampling experiments, and by repeating allele sharing and local ancestry inference analyses with subsets of the reference panels (Supplementary Information sections 4 and 5). In what follows, we rely on these imputed genotypes for population genomics analyses and confirm our results using standard pseudohaploid calls when adequate. In addition to the ancient Rapanui genome data, we used present-day Rapanui single nucleotide polymorphism (SNP) array data and ancient genome data from two individuals of previously demonstrated Polynesian genetic ancestry, but uncertain origin location, from the Museu Nacional, Brazil32. We refer to the latter as Ancient Polynesians (Supplementary Information section 4.2).
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