Rat Study Elucidates Long-Ago Human Migration

Join Our Community of Science Lovers!

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

These days, rats are rarely a welcome sight but some 3,000 years ago, the ancestors of modern-day Polynesians brought the creatures along as a source of food as they migrated from other regions. By analyzing genetic changes in ancient and modern rats, scientists have tracked the paths of this human diaspora.

Elizabeth Matisoo-Smith and Judith H. Robins of the University of Auckland in New Zealand studied mitochondrial DNA (mtDNA) sequences from both ancient and extant Pacific rat populations throughout the Pacific and Southeast Asia. Rats may seem like an unlikely source of information about ancient human movement, but because Rattus exulans can¿t swim, scientists know they reached new islands solely because people transported them on ancient outrigger canoes. The researchers identified three genetically distinct populations of rats as well as clear geographic patterns in the mtDNA recovered from various locales, including Papua New Guinea, Thailand and Polynesia. (In total the team analyzed 131 samples, which included rat remains found in archaeological digs that were more plentiful and available for study than were human remains.)

According to a report published online this week by the Proceedings of the National Academy of Sciences, the findings rule out two simplistic models of how the ancient Lapita people dispersed into the islands of Oceania. Instead, the scientists suggest a more complex view of Lapita movement from Southeast Asia to Polynesia, with significant interaction with other cultures along the way. The authors conclude that "integrating these results with those from other fields such as archaeology, comparative linguistics and molecular biology of human populations will be the only way we can fully understand the complex prehistory of this region."

Subscribe to Support Independent Journalism

Great science journalism requires human expertise, time, effort and creativity. And it costs money. That’s why I and the journalists here at Scientific American hope you’ll join our community.

When you subscribe, you are supporting staff and freelance journalists who are passionate about telling science stories that are true, important and compelling. Our editors and reporters are often experts in their fields, which means they understand the nuances of big discoveries and can untangle the breakthroughs from the hype. With a subscription, you are also supporting rigorous fact-checking to ensure the words we publish are precise and accurate. And you’re supporting original illustrations, graphics and photos that bring you closer to an advanced laboratory, an ice sheet in Antarctica or a space mission in orbit. You’re helping us craft other types of high-quality journalism as well: Our newsletters are carefully written, edited and curated by staffers you have or will come to know and love. Our Science Quickly podcast is based on original reporting, collaboration with editors and scientists and exacting production.

Subscriptions keep this engine running so we can continue to deliver thoughtful, rigorous and independent science journalism to you. In an era of viral misinformation, this work is crucial. If you value what we do, I hope you’ll consider joining us as a subscriber

Thank you,

Jeanna Bryner, Editor in Chief, Scientific American