One, Two, Three

It had been thought that North and South America were populated in one large migratory wave from Siberia, but a new study published in Nature shows that there were probably three waves of migrants who became the Native Americans of North and South America, says The New York Times' Nicholas Wade. Researchers at Harvard Medical School studied the whole genomes of Native Americans in South America and Canada, and found that people who became the ancestors of today's Eskimos and Aleutians, and people speaking Na-Dene, whose descendants settled in North America, each had their own small migrations from Siberia after the more central migration that mostly populated the continents 15,000 years ago, Wade says. "The new DNA study is based on gene chips that sample the entire genome and presents a fuller picture than earlier studies, which were based on small regions of the genome like the Y chromosome or mitochondrial DNA," he adds. "Several of the mitochondrial DNA studies had pointed to a single migration." Admixture may be to blame for the results of earlier efforts to trace ancestry and migration, he adds, as research participants thought to be wholly Native American may have had European or other ancestry as well.