Friday, July 27, 2012
Spearheads and DNA Point to a Second Founding Society in North America
Stone spearheads and human DNA found in Oregon caves, anthropologists say, have produced firmer evidence that these are the oldest directly dated remains of people in North America. They also show that at least two cultures with distinct technologies — not a single one, as had been supposed — shared the continent more than 13,000 years ago.
In other words, the Clovis people, long known for their graceful, fluted projectile points, were not alone in the New World. The occupants of Paisley Caves, on the east side of the Cascade Range, near the town of Paisley, left narrow-stemmed spear points shaped by different flaking techniques. These hunting implements are classified as the Western Stemmed Tradition, previously thought to be younger than the Clovis technology.
The new research, based on the recent discovery of the artifacts and more refined radiocarbon dating tests, established that the cave dwellers who made the Western Stemmed points overlapped or possibly preceded the Clovis artisans elsewhere, the scientists reported in a paper published online Thursday by the journal Science.
“These two distinct technologies were parallel developments, not the product of a unilinear technological evolution,” the research team, led by Dennis L. Jenkins of the University of Oregon, concluded in the report. “The colonization of the Americas involved multiple technologically divergent, and possibly genetically divergent, founding groups.”
Indeed, new genetic evidence described in the current issue of the journal Nature shows that the Americas appeared to be first populated by three waves of migrants from Siberia: one large migration about 15,000 years ago, followed by two lesser migrations. Such a pattern had been hypothesized 25 years ago on the basis of Native American language groups spoken today, but had not been widely accepted by linguistics scholars.
Dr. Jenkins and colleagues did not discuss in the paper or at a news conference how the divergent technologies might be related to initial migration patterns. They noted only that the human DNA from the cave, extracted from coprolites, or dried feces, pointed to Siberian-East Asian origins of the people.
The findings lend support to an emerging hypothesis that the Clovis technology, named for the town in New Mexico where the first specimens were discovered, actually arose in what is now the Southeastern United States and moved west to the Plains and the Southwest. The Western Stemmed technology began, perhaps earlier, in the West. Most artifacts of that kind have been found on the West Coast and in Idaho, Nevada, Utah and Wyoming.
“We seem to have two different traditions coexisting in the United States that did not blend for a period of hundreds of years,” Dr. Jenkins said.
Although other pre-Clovis sites have been claimed, only the 14,600-year-old Monte Verde campsite in Chile and now Paisley Caves have so far cleared most hurdles of critical review. When the first dating of human DNA from the caves was reported in 2008, some archaeologists worried that the coprolites could have been seriously contaminated, possibly by the leaching of later DNA from humans by water and rodent urine downward through the caves’ many layers of sediment.
So Dr. Jenkins returned to the caves in 2009 and each year since. Digging five to six feet into silt, the archaeologists uncovered the Western Stemmed projectile points and not a single Clovis point. They extracted DNA from more coprolites. Since DNA cannot be directly dated with radiocarbon technology, researchers instead dated fibers from the coprolites, residue of the food the cave dwellers had eaten. Any contaminating carbon was washed out of the coprolites with distilled water.
One of the samples, found with one of the Western Stemmed points, was dated to 13,000 to 13,200 years ago. The researchers said they conducted DNA analysis on 65 coprolites and obtained 190 radiocarbon dates from material at several of the caves.
Michael R. Waters, director of the Center for the Study of the First Americans at Texas A & M University, who was not involved in the new research, said the Paisley Caves findings “really provide solid evidence that the two technologies are contemporaneous.” Dr. Waters specializes in investigating Clovis sites.
Eske Willerslev of the Center for GeoGenetics at the University of Copenhagen said that independent tests at two other laboratories confirmed his findings that the DNA was human and that some of the specimens were possibly of a pre-Clovis age.
In a teleconference with reporters, Dr. Willerslev said it was no easy matter getting DNA out of ancient coprolites. So far, the researchers have extracted only mitochondrial DNA, which is inherited from the mother, but this “definitely suggests,” he said, that these people were from Asia and could be related to today’s Native Americans.
“We are trying to retrieve nuclear DNA from the site,” he added, which should provide more precise information about who are the “closest contemporary people” associated with the cave dwellers.