Ancient DNA from Guam and the Peopling of the Pacific

Abstract

23 24 Humans reached the Mariana Islands in the western Pacific by ~3500 years ago, 25 contemporaneous with or even earlier than the initial peopling of Polynesia. They crossed 26 more than 2000 km of open ocean to get there, whereas voyages of similar length did not 27 occur anywhere else until more than 2000 years later. Yet, the settlement of Polynesia has 28 received far more attention than the settlement of the Marianas. There is uncertainty over 29 both the origin of the first colonizers of the Marianas (with different lines of evidence 30 suggesting variously the Philippines, Indonesia, New Guinea, or the Bismarck Archipelago) 31 as well as what, if any, relationship they might have had with the first colonizers of 32 Polynesia. To address these questions, we obtained ancient DNA data from two skeletons 33 from the Ritidian Beach Cave site in northern Guam, dating to ~2200 years ago. Analyses of 34 complete mtDNA genome sequences and genome-wide SNP data strongly support ancestry 35 from the Philippines, in agreement with some interpretations of the linguistic and 36 archaeological evidence, but in contradiction to results based on computer simulations of sea 37 voyaging. We also find a close link between the ancient Guam skeletons and early Lapita 38 individuals from Vanuatu and Tonga, suggesting that the Marianas and Polynesia were 39 colonized from the same source population, and raising the possibility that the Marianas 40 played a role in the eventual settlement of Polynesia. 41 42 43 Significance Statement 44 45 We know far more about the settlement of Polynesia than we do about the settlement of the 46 Mariana Islands in the western Pacific. There is debate over where people came from to get 47 to the Marianas, with various lines of evidence pointing to the Philippines, Indonesia, New 48 Guinea, or the Bismarck Archipelago, as well as uncertainty over how the ancestors of the 49 present Mariana Islanders, the Chamorro, might be related to Polynesians. We analyzed 50 ancient DNA from Guam, from two skeletons dating to ~2200 years ago, and found that their 51 ancestry is linked to the Philippines. Moreover, they are closely-related to ancient 52 Polynesians from Vanuatu and Tonga, suggesting that the early Mariana Islanders may have 53 been involved in the colonization of Polynesia. 54 55 2 bioRxiv preprint doi: https://doi.org/10.1101/2020.10.14.339135; this version posted October 14, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license. 56