Rat DNA points to Pacific migrations

Archaeologists regard members of the ancient, seafaring Lapita culture as the ancestors of Polynesians, who now live on a large group of western Pacific islands collectively known as Oceania. Where the Lapita originally came from and the way in which they occupied a string of islands that spans more than 2,000 miles remains a topic of hot debate.

PACIFIC PIONEER. Wood carving depicts an ancestral Polynesian colonist of Oceania accompanied by Pacific rats, which are now offering genetic clues to the human settlement of the region. T. Mackrell

A new genetic analysis of Pacific rats, which canoe-traveling Lapita colonists brought with them for food and introduced to Oceania, adds weight to an earlier theory that Lapita mariners based in Southeast Asia moved across the region in a series of migrations, from 6,000 to 3,000 years ago.

Elizabeth Matisoo-Smith and Judith H. Robins, both of the University of Auckland in New Zealand, obtained mitochondrial DNA from more than 100 Pacific rats. These genetic samples had been extracted either from bones found at Lapita archaeological sites or from the remains of recently deceased animals throughout Oceania.

A mutation-rich stretch of the rats’ mitochondrial DNA exhibits three geographically distinct nucleotide-sequence patterns, the investigators report in the June 15 Proceedings of the National Academy of Sciences. One pattern appears only on islands just off the Asian coast, reflecting interaction among people who probably didn’t migrate elsewhere, Matisoo-Smith and Robins propose. A second pattern extends from the same islands into Oceania’s western half, apparently mirroring human migration along that path. A third pattern appears on one western island, Halmahera, and on several of Oceania’s easternmost islands, possibly marking a separate Lapita dispersal.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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