Posted on 12 July 2012
An international team of researchers from 13 institutions, including the University of York, outline their findings in Science this week.
The researchers also provide new documentation, including "blind-test analysis" by independent laboratories, that confirms the human DNA pulled earlier from human coprolites (dried faeces) and reported in Science (May 9, 2008) dates to the same time period.
The new conclusions are based on 190 radiocarbon dates of artifacts, coprolites, bones and sagebrush twigs meticulously removed from well-stratified layers of silt in the ancient caves.
But lead researcher Dr Dennis Jenkins of the University of Oregon's Museum of Natural and Cultural History, says that diagnostic evidence of the Palaeo-Indian Clovis culture such as the broad, concave-based, fluted Clovis projectile points, is absent from the caves.
According to the researchers, the radiocarbon dating of the Western Stemmed projectiles to potentially pre-Clovis times provides new information in the decades-old debate that the two point-production technologies overlapped in time and may have developed separately. It suggests that Clovis may have arisen in the Southeastern United States and moved west, while the Western Stemmed tradition began, perhaps earlier, in the West and moved east.
One example, Dr Jenkins says, is the discovery of Clovis points below Western Stemmed points at Hell Gap, Wyoming. While this example suggests that Clovis was older in that location than Western Stemmed, the new Paisley Caves evidence indicates that Western Stemmed are at least the same age as Clovis (about 12,800-13,000 years old) in the northern Great Basin of Oregon – about 1,000 miles west of Hell Gap.
At least three other Western sites – Cooper's Ferry in Idaho and Nevada's Smith Creek Cave and Bonneville Estates Rockshelter – also contain only Western Stemmed points in deposits of this age.
Dr Jenkins said: "From our dating, it appears to be impossible to derive Western Stemmed points from a proto-Clovis tradition. It suggests that we may have here in the Western United States a tradition that is at least as old as Clovis, and quite possibly older. We seem to have two different traditions co-existing in the United States that did not blend for a period of hundreds of years."
The results of this study are exciting because they show that the hypothesis that the Clovis people were the first native Americans, which has been the prevailing idea for the last decades, is wrong
Professor Michi Hofreiter
DNA cannot be directly dated with radiocarbon technology. Instead, researchers extracted components of the diet eaten by the early inhabitants and washed potentially contaminating carbon out of the coprolites with distilled water. The digested fibres and carbon fraction were then radiocarbon-dated separately and the results compared.
Researchers at the University of York independently replicated some of the data at York’s Ancient DNA laboratory.
Professor Michi Hofreiter, of the Department of Biology at the University of York, said: “Through replicating data we were able to confirm the authenticity of what is the oldest direct evidence for humans in the Americas. The results of this study are exciting because they show that the hypothesis that the Clovis people were the first native Americans, which has been the prevailing idea for the last decades, is wrong. Now researchers need to come up with a new model for the settling of the Americas.”
The Paisley Caves are in the Summer Lake basin near Paisley, about 220 miles southeast of Eugene on the east side of the Cascade Range. The complex includes eight westward-facing caves, all wave-cut shelters, on the highest shoreline of pluvial Lake Chewaucan, which rose and fell in periods of greater precipitation during the Pleistocene, or last glacial period.
"Following the recession of lake waters, the caves began to accumulate different kinds of terrestrial sediments," said co-author Loren Davis, an archaeologist at Oregon State University in Corvallis.
"The caves contain a series of deposits that were created by the combination of wind, gravity, water-borne and biological processes. Archaeological evidence suggests that humans visited the cave many times, leaving behind material traces in the form of stone tools, lithic chipping debris, organic craft items, food wastes and even coprolites. These cultural materials were entombed largely as they were left behind as sediments continued to accumulate."