DNA analysis of Polynesians and Native South Americans has revealed ancient genetic signature that has resolved the debate between the interaction of these two populations and origins of Polynesians. The results were published in Nature journal on May 22, 2020.
About 800 years ago, Indigenous South Americans traveled 7,000 kilometers of open sea to reach eastern Polynesia. According to researchers, these South Americans mated with Polynesian inhabitants during the initial discovery period of discovery and settlement on remote islands.
Alexander Ioannidis (computational biologist) and Andrés Moreno-Estrada (population geneticist) said that “this ancestry spread as far east as Easter Island, (also known as Rapa Nui). This discovery offers first genetic glimpse of a prehistoric event that left no conclusive evidence, except for the one recorded in the DNA of those who had contact 800 years ago in one of the most remote places on Earth.”
The idea of inhabitation of Polynesia has always lead to a scientific debate. Norwegian explorer Thor Heyerdahl went on his Kon-Tiki expedition in 1947 to test his migration theory. The crew left Peru on a wooden raft, and after 101 days traveled 7,000 km, and reached Polynesian shores. The expedition demonstrated the possibility of early travel from South America to these Pacific islands. While the rest of the scientific community at the time assumed that Asians had journeyed east about 3,500 years ago to western Polynesian region and populated the area.
DNA evidence on the interaction between the two populations
Ioannidis and the rest of the team analyzed the DNA of people from Rapa Nui while studying DNA of people from 17 populations of Pacfic islands and 15 Native American populations from Pacific coast of South America. A total of 807 people were selected for DNA analysis to discover the evidence of ancestors from different populations who interbreed together (admixture analysis).
Admixture analysis is a computational method in which a person’s probable genetic ancestry and its geographical origins are studied through the gene flow. The researchers correlated dominant Polynesian DNA markers with those of people from other regions as well, including; Melanesia, Africa, America, and Europe.
During research analysis, the team postulated the timing of admixture events using a technique known as “tract-length distribution analysis” as per this technique, length of DNA segments are assessed for genomic segments inherited from different ancestral populations. Smaller DNA segments are assumed to show older instances of mating across populations and longer segments due to the breakdown of shared segments in later generations. The authors of the study propose that the discovery of genetic signatures in Native South Americans population were probably the result of a single ancient contact.
Their model suggests that the mixed population then spread from central eastern Polynesia around AD 1200 to other Polynesian islands during an early eastern Polynesian expansion, and finally reached Rapa Nui. These spectacular results have major implications for future discussions concerning early migrations and interactions in Polynesia. Rapa Nui itself is not suggested to be the initial point of contact between Polynesians and South Americans, but the admixture identified there is thought to have arisen elsewhere in Polynesia in a population that eventually reached Rapa Nui.
By using these genetic methods the scientists discovered an initial admixture event between Polynesians and Native South Americans that dated back to 1150 to 1230 AD. The research team also raised another possible contact scenario: for example, Polynesian populations made traveled to South America and then returned to Polynesia along with South American people, or that people returned to Polynesia who carried Native South American genetic heritage.
The researchers suggest that further inquiry into the genetic studies are required to address such an alternative hypotheses. Further research into DNA studies of other living populations not included in the author’s research sample, as well as DNA extracted from ancient bones will give insights into the remaining questions.
Genetic analysis of early sweet-potato plants preserved in herbarium collections from the eighteenth century show that these plants found in Polynesia originated from the northern coasts of South America. Some genetic variations in these specimens reveal the possibility of several introduction events in Polynesia. Additional research and analysis on this topic can shed light on the possibility of more than just one early contact from South America.
Native South Americans were early inhabitants of Polynesia
Paul Wallin | July 8, 2020 | Nature News & Views