Ancient DNA analysis obtained from two human skeletons found on Guam dating to around 2,200 years ago suggests that the ancestry of the Mariana Island settlers is linked to the Philippines.
The analysis also suggests a shared genetic drift among the two Guam skeletons to the skeletons of Lapita populations from Vanuatu and Tonga.
The new research was conducted by researchers from the Max Planck Institute for Evolutionary Anthropology, Australian National University and the University of Guam to find out where people came from to get to the Marianas, and how the ancestors of the present Mariana Islanders, the Chamorro, might be related to Polynesians.
The question as to the origin of the first colonizers of the Marianas showed various lines of evidence pointing to the Philippines, Indonesia, New Guinea, or the Bismarck Archipelago.
The researchers analyzed the ancient DNA isolated from the two skeletons found at the Ritidian Beach Cave site in northern Guam. Their analyses uncovered evidence that that the skeletons from Guam appeared most similar to modern samples from the Philippines and Taiwan, and that no Papuan-related ancestry was found.
The two skeletons, a male and a female found at the Ritidian site clearly predated the latte period. The skeletons were found outside a ritual cave site, buried side by side inside distinctive pits. The skeletons offered a rare view of ancient burial practice in the Marianas region similar to the burial practices observed in the Philippines and Indonesia.
The researchers extracted specimen and bone powder from each to conduct their study. Based on the research, the radiocarbon dating of the two skeletons indicated that the individuals lived about 2,180 years ago. Guam was initially settled about 1,000 years after.
"Analyses of complete mitochondrial DNA genome sequences and genome-wide SNP data strongly support ancestry from the Philippines, in agreement with some interpretations of the linguistic and archaeological evidence, but in contradiction to results based on computer simulations of sea voyaging," the research showed.
“We found that the ancestry of these ancient skeletons is linked to the Philippines,” Dr. Irina Pugach, a researcher in the Department of Evolutionary Genetics at the Max Planck Institute for Evolutionary Anthropology said. She added that the analysis suggested that the early Mariana Islanders may have been involved in the colonization of Polynesia.
“We know more about the settlement of Polynesia than we do about the settlement of the Mariana Islands,” said Dr. Pugach.
The research article stated that humans reached the Mariana Islands in the western Pacific by 3,500 years ago, contemporaneous with or even earlier than the initial peopling of Polynesia. They crossed more than 2,000 km (1,243 miles) of open ocean to get there, while voyages of similar length did not occur anywhere else until more than 2,000 years later.
“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,” said co-author Dr. Mike Carson, an archaeologist in the Micronesian Area Research Center at the University of Guam.
“The peopling of Guam and the settlement of such remote archipelagos in Oceania needs further investigation,” said senior author Dr. Mark Stoneking, a researcher in the Department of Evolutionary Genetics at the Max Planck Institute for Evolutionary Anthropology.
The researchers however said that their analysis is based on samples taken only from the two skeletons that date from around 1,400 years after the first human settlement in Guam and "may not capture the full complexity of how the area was colonized, which would require further investigation."