Once, twice, thrice into the Americas

摘要

Who were the first Americans? The most comprehensive analysis of DNA from Native American populations to date supports the controversial theory that the Americas were populated in three initial waves rather than just one. The first settlers are thought to have set foot in North America some 15,000 years ago, crossing a land bridge between Siberia and Alaska that existed at the time. Linguists originally suggested that Native Americans could be divided into three groups based on their languages, and argued that these may represent three waves of migration. Although differences in dental morphology between people belonging to the language groups supported the idea, not all linguists agreed about lumping so many diverse languages together.