Ancient peoples only loosely related to modern Asians crossed the Arctic land bridge to settle America some 15,000 years ago, according to a study offering new evidence that the Western Hemisphere played host to a more genetically diverse population at a much earlier time than previously thought.
The early immigrants most closely resembled the prehistoric Jomon people of Japan and their closest modern descendants, the Ainu, from the Japanese island of Hokkaido, the study said. Both the Jomon and Ainu have skull and facial characteristics more genetically similar to those of Europeans than to mainland Asians.
The immigrants settled throughout the Hemisphere, and were in place when a second migration, from mainland Asia, came across the Bering Strait beginning 5,000 years ago and swept southward as far as modern-day Arizona and New Mexico, the study said. The second migration is the genetic origin of today's Eskimos, Aleuts and the Navajo of the U.S. Southwest.
The study in the July 30 edition of the Proceedings of the National Academy of Sciences adds new evidence to help settle one of anthropology's most contentious debates: Who were the first Americans? And when did they come?
"When this has been done before, it's been done from one point of view," said University of Michigan physical anthropologist Loring Brace, who led the team of researchers from the United States, China and Mongolia that wrote the new report. "We try to put together more dimensions."
For decades, anthropologists' dogma held that the Americas were populated by a single migration from Asia around 11,200 years agothe supposed age of the earliest of the elegantly crafted, grooved arrowheads first found in the 1930s at Clovis, New Mexico.
By the end of the 1990s, however, the weight of evidence had pushed the date of the first arrivals back several thousand years. A site at Cactus Hill, near Richmond, Virginia, may be 17,000 years old. In Chile, scientists excavating a 12,500-year-old settlement at Monte Verde have found evidence of a human presence that may extend back as far as 30,000 years.
But as the migration timetable slipped, additional questions and controversies have arisen. The 1996 discovery in Kennewick of the nearly complete skeleton of a 9,300-year-old man with "apparently Caucasoid" features stimulated interest in the possibility of two or more migrationsincluding a possible influx from Europe.
The new study attempted to answer this question by comparing 21 different skull and facial characteristics from more than 10,000 ancient and modern populations in both the Western Hemisphere and the old world.
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