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Rat DNA reveals human migration history

Scientists believe that the seafaring Lapita culture, which appeared in the Western Pacific about 3,500 years ago, is ancestral to Polynesian and many other Pacific cultures. As the Lapita colonists spread throughout Oceania they introduced several species of plants and animals, including the Pacific rat, Rattus exulans, which was often transported as food in the colonizing canoes. Since these rats do not swim, humans were solely responsible for their dispersal throughout the Pacific. 

To trace the pattern of human migration within Oceania, Elizabeth Matisoo-Smith and colleagues compared mitochondrial DNA (mtDNA) sequences of ancient and modern rat populations throughout the Pacific and Island Southeast Asia. Mitochondrial DNA is a type of DNA passed down only through the female line, and present in energy-producing cellular organelles called mitochondria. 

By creating evolutionary trees of rat mtDNA, the researchers identified three geographically distinct populations. These results are inconsistent with what are known as "Fast Train" models of Lapita migration, which emphasize rapid dispersal from Southeast Asia to Polynesia, with little or no contact with indigenous people along the way. 

Rather, the results suggest a slower and more complex migration scenario involving significant interactions among populations. The authors note that integrating these results with data from archaeology, comparative linguistics, and molecular biology of human populations will further illuminate the complex prehistory of this region.

The research, from the University of Auckland, is published in the June 7 early online edition of the Proceedings of the National Academy of Sciences, a research journal.