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. Several of the mitochondrial DNA studies had pointed to a single migration.

A team led by David Reich of Harvard Medical School and Dr. Andres Ruiz-Linares of University College London reported that there was a main migration that populated the entire Americas. They cannot date the migration from their genomic data but accept the estimate by others that the migration occurred around 15,000 years ago. This was in the window of time that occurred after the melting of great glaciers that blocked passage from Siberia to Alaska, and before the rising waters at the end of the last ice age submerged Beringia, the land bridge between them.

They also find evidence for two further waves of migration, one among Na-Dene speakers and the other among Eskimo-Aleut, again as Dr. Greenberg predicted. But whereas Dr. Greenberg’s proposal suggested that three discrete groups of people were packed into the Americas, the new genome study finds that the second and third waves mixed in with the first. Eskimos inherit about half of their DNA from the people of the first migration and half from a second migration. The Chipewyans of Canada, who speak a Na-Dene language, have 90 percent of their genes from the first migration and some 10 percent from a third.

It is not clear why the Chipewyans and others speak a Na-Dene language if most of their DNA is from Amerind speakers. Dr. Ruiz-Linares said a minority language could often dominate others in the case of conquest; an example of this is the ubiquity of Spanish in Latin America.