Kon Tiki — revisited: South American genes found in Polynesia

These GEITP pages often cover topics of evolution, including the Great Human Diaspora (i.e. the multiple Homo sapiens migrations out of Africa, between 25,000 and more than 100,000 years ago; these migrations resulted in the five major geographically-isolated subgroups — Africans, East Asians, Oceanians, Europeans and Amerindians). A longstanding controversy about Oceanian history concerns the possibility of prehistoric admixture (i.e. hanky-panky) between Polynesian and Amerindian populations. The early peopling of Polynesia attracted worldwide interest in 1947, when the Norwegian explorer Thor Heyerdahl set sail on the Kon-Tiki expedition to test his migration theory; the crew left Peru on a wooden raft and — after 101 days and a voyage of more than 7,000 kilometers — they reached Polynesian shores, thus proving the possibility of early travel from South America westward to these Pacific islands. Heyerdahl challenged the scientific community’s view that evidence pointed instead to populating Polynesia by people traveling east from Asia; his idea that Polynesia was initially populated by South Americans was generally criticized by scholars. However, the sweet potato (a South American plant) has a long history of cultivation in eastern Polynesia.

Previous scientists — investigating this question through genetics — had focused on Easter Island (Rapa Nui). As the Polynesian island closest to the Americas, and the one having the most elaborate megalithic culture (giant heads made of stone), Rapa Nui has been considered a likely locus for contact. High-resolution analyses of human leukocyte antigen (HLA) alleles had revealed an Amerindian component in modern individuals with self-identified Rapanui ancestry. However, in the only two whole-genome sequencing (WGS) studies of Rapanui variation — only one of eight modern individuals, and one of five skeletal remains — was Amerindian DNA found. Thus, these studies reached opposing conclusions about pre-European contact between Polynesian individuals on Rapa Nui and Amerindian individuals.

To date, no WGS studies have considered the possibility of pre-European Amerindian contact on other Polynesian islands. Authors [see attached article & editorial] first analyzed 807 individuals from 17 island populations, and 15 Pacific coast Amerindian groups, searching for signs of admixture. Authors then performed high-density WGS analyses of a smaller data set (166 Rapanui and 188 additional individuals from islands spanning the eastern Pacific). They found conclusive evidence for prehistoric contact of Polynesian individuals with Amerindian individuals (~1200 AD) simultaneously with individuals in remote Oceania. This study therefore strongly suggests that a single contact event occurred in eastern Polynesia — before the settlement of Rapa Nui — between Polynesian individuals and an Amerindian group most closely related to the indigenous inhabitants of present-day Colombia. In other words, Thor Heyerdahl’s theory was correct…!! 😊


Nature 23 Jul 2020; 583: 572-577 & Editorial pp 524-525

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