The Americas weren't initially populated in one sweeping migration across the land bridge from Siberia, but in three distinct waves, according to a new DNA study. By comparing genetic markers on 52 modern day Native American populations and 17 Siberian ones, they've concluded that while the Americas were mostly populated in an initial wave 15,000 years ago, two smaller subsequent migrations brought the Eskimos, Aleutians, and the Na-Dene speaking peoples, the Wall Street Journal reports.
The three-migration theory was first put forth by linguist Joseph Greenberg in 1987, and has been hotly debated ever since, the New York Times explains. The DNA study is the most comprehensive yet on the topic. "This is monumental work," says one anthropologist, praising "the enormity of the database and the global approach." The study largely vindicates Greenberg, but whereas Greenberg imagined three completely distinct groups, the study shows that later waves intermingled with the first; Eskimos, for instance, inherit about half their genes from first-wavers.