NEW YORK – The people who settled the Mariana Islands may have come from the Philippines, a new analysis of ancient DNA suggests.
Humans first settled the Mariana Islands — a stretch of 15 islands that includes Guam — about 3,500 years ago, but it has been unclear who these settlers were and where they came from. Some evidence has suggested the Philippines, New Guinea, Indonesia, or the Bismarck Archipelago as the source of the settlers.
By analyzing ancient DNA isolated from two skeletons uncovered on Guam, an international team of researchers began to tease out where the early settlers may have been from. As they reported on Monday in the Proceedings of the National Academy of Sciences, the researchers uncovered evidence that those ancient Mariana Islanders had ancestry associated with the Philippines but were also closely related to Lapita populations that lived on Vanuatu and Tonga.
"These findings strengthen the picture that has emerged from linguistic and archaeological studies, pointing to an Island Southeast Asia origin for the first settlers of the Marianas," co-author Mike Carson, an archaeologist at the Micronesian Area Research Center at the University of Guam, said in a statement.
Radiocarbon dating of the two skeletons, uncovered at the Ritidian Site in northern Guam, indicated that the individuals lived about 2,180 years ago. While the researchers noted that that is about 1,000 years after Guam was initially settled, it precedes a time period of known cultural change by about 1,000 years and could still provide insight into the peopling of the Mariana Islands.
As there was not enough endogenous DNA for shotgun sequencing,the researchers focused on mitochondrial genome and SNP panel analyses.
The mitochondrial genomes of both samples belonged to haplogroup E2a, which is still the most common haplogroup among the modern Chamarro population of Guam and is also found to a lesser extent among populations in the Philippines and Indonesia. This not only suggests links between these ancient individuals and the Philippines and Indonesia, rather than to Indonesia or the Bismarck Archipelago, but also a degree of genetic continuity in the region, even with later cultural shifts and European colonial events, the researchers noted.
By analyzing these samples in conjunction with modern ones, the researchers additionally found that the Guam duo was most similar to modern samples from the Philippines and Taiwan and appeared to have no Papuan-related ancestry, which is found throughout New Guinea, Indonesia, and the Bismarck Archipelago.
The team further noted a close affinity between their ancient Guam individuals and early Lapita individuals who lived in Island Melanesia and western Polynesia beginning about 3,300 years ago. In particular, they found shared genetic drift among the Guam individuals and Lapita skeletons from Vanuatu and Tonga.
"This suggests that the Marianas and Polynesia may have been colonized from the same source population, and raises the possibility that the Marianas played a role in the eventual settlement of Polynesia," first author Irina Pugach, a researcher at the Max Planck Institute for Evolutionary Anthropology, said in a statement.
The researchers cautioned, though, that their analysis is based on samples from only two skeletons from individuals who lived 1,400 years after Guam was first settled and may not capture the full complexity of how the area was colonized, which would require further investigation.