American Indian HLA Genes on Easter Island
Phil. Trans. R. Soc. B 19 March 2012 vol. 367 no. 1590 812-819 doi: 10.1098/rstb.2011.0319
The Polynesian Gene Pool: An Early Contribution by Amerindians to Easter Island
Abstract. It is now generally accepted that Polynesia was first settled by peoples from southeast Asia. An alternative that eastern parts of Polynesia were first inhabited by Amerindians has found little support. There are, however, many indications of a ‘prehistoric’ (i.e. before Polynesia was discovered by Europeans) contact between Polynesia and the Americas, but genetic evidence of a prehistoric Amerindian contribution to the Polynesian gene pool has been lacking. We recently carried out genomic HLA (human leucocyte antigen) typing as well as typing for mitochondrial DNA (mtDNA) and Y chromosome markers of blood samples collected in 1971 and 2008 from reputedly non-admixed Easter Islanders. All individuals carried HLA alleles and mtDNA types previously found in Polynesia, and most of the males carried Y chromosome markers of Polynesian origin (a few had European Y chromosome markers), further supporting an initial Polynesian population on Easter Island. The HLA investigations revealed, however, that some individuals also carried HLA alleles which have previously almost only been found in Amerindians. We could trace the introduction of these Amerindian alleles to before the Peruvian slave trades, i.e. before the 1860s, and provide suggestive evidence that they were introduced already in prehistoric time. Our results demonstrate an early Amerindian contribution to the Polynesian gene pool on Easter Island, and illustrate the usefulness of typing for immunogenetic markers such as HLA to complement mtDNA and Y chromosome analyses in anthropological investigations.
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Erik Thorsby’s study appears to be the first clear documentation of a genetic contribution of Amerindians to Polynesians that happened prior to the Peruvian slave trade in the 19th century. He detected two Amerindian-specific HLA alleles (A*02:12 and B*39:05) among unadmixed Easter Islanders. These alleles complement the otherwise-typical Polynesian pool of Easter Islanders. It’s unlikely that these alleles were more wide-spread in Polynesia in the past (as Thor Heyerdahl would want to have it). Thorsby offers a better explanation: in accordance with the findings of chicken remains with Polynesian mtDNA in El Arenal, southern Chile and the suggestive evidence of pre-Columbian Polynesian ancestry in Mocha Island, Chile, he writes, “…There is strong evidence that Polynesians had been in South America early, i.e. in pre-Columbian time. After having arrived in South America, some of them may have returned to Polynesia, including Easter Island, not only taking the sweet potato and bottle gourd, etc., but also some native Americans with them.”