Ancient peoples only loosely related to modern Asians crossed the Arctic land bridge to settle America about 15,000 years ago, according to a study offering new evidence that the Western Hemisphere hosted 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 today's 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
C. Loring Brace, who led the team of researchers from the United
States, China and Mongolia who wrote the new report. We try to put
together more dimensions.
For decades, anthropologists held that the Americas were populated by a single migration from Asia about 11,200 years ago -- the supposed age of the earliest of the elegantly crafted, grooved arrowheads first found in the 1930s in Clovis, N.M.
By the end of the 1990s, however, the weight of evidence had pushed back the date of the first arrivals several thousand years. A site at Cactus Hill, near Richmond, 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 as far as 30,000 years.
But as the migration timetable slipped, additional questions and
controversies have arisen. The 1996 discovery in Kennewick, Wash., 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 migrations -- including a possible influx
from Europe.
The new study attempted to answer this question by comparing 21 skull and facial characteristics from more than 10,000 ancient and modern populations in the Western Hemisphere and the Old World.
The findings provide strong evidence supporting earlier work suggesting that ancient Americans, like Kennewick Man, were descended from the Jomon, who walked from Japan to the Asian mainland and eventually to the Western Hemisphere on land bridges as the Earth began to warm up about 15,000 years ago at the end of the last Ice Age.
Brace described these early immigrants as hunters and gatherers
following herds of mastodon first into North America, and eventually
spreading throughout the hemisphere. Because the North -- in both
Siberia and Canada -- was still extremely cold, only a limited number
of people could make the trek and survive.
So immigration slowed, Brace said, for about 10 millennia. Then, about
5,000 years ago, agriculture developed on mainland Asia, enabling
people to grow, store and carry food in more inhospitable
areas. Movement resumed, but the newcomers were genetically Asians --
distinct racially
from the first wave, Brace added.
The second wave spread across what is now Canada and came southward, cohabiting with the earlier settlers and eventually creating the hybrid population found by the Spaniards in the 15th century.
While many researchers agree on the likelihood of two migrations, both their timing and origin are matters of dispute. Brace's team suggests that both movements occurred after the last Ice Age began to moderate between 14,000 and 15,000 years ago.
But University of Pennsylvania molecular anthropologist Theodore Schurr said genetic data in American populations suggest that humans may have been in the Western Hemisphere much earlier -- 25,000 to 30,000 years ago.
This would mean that the first wave came before the glacial
maximum,
between 14,000 and 20,000 years ago, when the Ice Age was
at its fiercest and human movement was practically impossible,
Schurr said. Were there people here before the last glacial
maximum?
he asked. The suggestion is, 'Yes.'
To date, archaeological evidence for settlements earlier than 20,000 years ago is almost nonexistent, but Schurr suggested that researchers may have been reluctant to explore layers older than Clovis because of Clovis's predominance in the scientific community.
Still, neither Brace nor Schurr was prepared to endorse the view propounded by the National Museum of Natural History's Dennis Stanford: that at least some immigrants may have come from Ice Age Europe.
The environment in Europe was so harsh that land mammals were very
rare,
Stanford said, so they went to the beach.
If these
ancient people had boats, it was natural that they should go to sea to
look for food, and edging further north and west, they would
eventually reach the fish-rich Grand Banks. From there they move
right down the east coast
of North America, he said.
Stanford bases his theory on the presence of Clovis-like artifacts on the Iberian Peninsula around 20,000 years ago, and that there are more Clovis points in the eastern United States than in the West.
Also, he notes that genetic evidence links eastern Native American populations with ancient Europeans, but not with Asians.
He suggests the migrants moved on Ice Age land bridges from Iberia to
Wales and eventually to Ireland, then set sail to hunt the seals and
fish on the rim of the polar ice pack. They edged further and further
west, and when they reached North America they probably didn't even
know they were there.
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