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Settlement of Micronesia Emerges from Ancient DNA Analysis

NEW YORK – The western Pacific Ocean islands that make up modern-day Micronesia appear to have been peopled through at least five main migration waves from islands in Southeast Asia, new genetic research suggests. In addition, early settlements in this region showed matrilocal, female-centered social structures and appeared to have more migratory male individuals.

The findings complement prior archeological and linguistic findings that pointed to human settlement in remote parts of Oceania within the last 3,500 years or so and uncovered distinct cultural artifacts and language patterns over time in different parts of the Micronesian region.

As they reported in Science on Thursday, researchers from Harvard University, the University of Vienna, and other international centers used an enrichment sequencing strategy to target some 1.2 million SNPs in 164 ancient human samples from five archeological sites in Micronesia.

When they analyzed these sequences — as well as new genotyping profiles for 112 individuals from similar locations in present-day Micronesia and published sequence data on ancient and modern representatives in the region — the team was able to retrace migrations across periods named for the Unai, Lapita, and Latte groups that appeared to dominate over time in different regions, based on burial complexes and other artifacts left behind.

Among other findings, the investigators saw that the Micronesia populations tended to show distinct and highly differentiated mitochondrial DNA sequences, consistent with settlement by matrilocal groups, meaning communities where women typically did not move away to have a family.

"Female-inherited mitochondrial DNA was highly differentiated across early Remote Oceanian communities but homogeneous within," co-senior and co-corresponding authors David Reich and Ron Pinhasi and their colleagues explained, "implying matrilocal practices whereby women almost never raised their children in communities different from the ones in which they grew up."

Reich is a geneticist and human evolutionary biology researcher affiliated with Harvard and the Broad Institute, while Pinhasi belongs to evolutionary anthropology and human evolution and archeological sciences departments at the University of Vienna.

The team's ancestry and modeling analyses pointed to three migrations stemming from East Asian groups related to present-day populations in the Philippines and Taiwan, as well as migrations to Micronesia from Polynesia and from Papua New Guinea. The latter migration seemed to involve male migrants coming from a Papuan group that is distinct from Papuans contributing ancestry to sites in the southwestern Pacific.

Papuan ancestry appeared to be widespread in populations from Remote Oceania, the investigators reported, but did not turn up in populations from a crescent-shaped island chain in the northwestern Pacific Ocean, known as the Mariana Archipelago, where East Asian ancestry predominated in pre-colonial periods.

"Since colonial times, Pacific peoples have been divided into 'Melanesians,' 'Polynesians,' and 'Micronesians,' driven by theories of shared origins," the authors noted. "However, our results show that people in Micronesia have a diversity of ancestral origins even within the same geographic region, implying that the term 'Micronesian' should be used as a geographic label without implying a specific biological profile."