DNA from fossilized human feces found in an Oregon cave is 14,300 years old, at least 1,200 years older than previous evidence for humans in North America, researchers said Thursday.
The find provides the strongest evidence in an archaeological controversy about whether people of the Clovis culture, which manufactured distinctive stone tools and weapons, were the first to populate the Americas. The new evidence, reported online in the journal Science, indicates they were not.
The fossilized DNA “represents, to the best of my knowledge, the oldest human DNA obtained from the Americas,” said geneticist Eske Willerslev of Denmark’s University of Copenhagen, a co-author of the paper.
“If you are looking for the first people in North America, you are going to have to step back more than 1,000 years beyond Clovis to find them,” added archaeologist Dennis L. Jenkins of the University of Oregon, the lead author of the report.
The find is “a smoking gun” for the pre-Clovis colonization of the Americas, said anthropologist Ripan Malhi of the University of Illinois at Urbana-Champaign, who was not involved in the research.
In addition to changing ideas about when humans arrived here, the new research will also change ideas about how.
Archaeologists theorize that humans from Siberia and eastern Asia migrated to North America across the Bering land bridge when a global warming episode melted the glaciers that had blocked their progress and stranded them for thousands of years in the area known as Beringia.
If humans were on this continent 14,300 years ago -- at least 1,000 years before that melting episode -- they had to have come before the glacier blocked the route or by a different pathway, Willerslev said.
He argues that a strip of land along the western coast of North America was exposed during the Ice Age, allowing migration along the coast rather than by the favored inland route. Archaeological artifacts from that trek are now submerged under the Pacific Ocean, he said.
The feces fossils, technically called coprolites, were discovered by Jenkins in the summers of 2002 and 2003 in the Paisley Caves in the Summer Lake basin, about 220 miles southeast of Eugene. The eight caves are wave-cut shelters on the shoreline of Lake Chewaucan, whose levels rose and fell with changes in precipitation in the region.
In addition to the coprolites, Jenkins also found manufactured threads of sinew and plant fibers, hides, basketry, cordage, rope, wooden pegs, animal bones and a couple of projectile point fragments -- but not enough to link the cave’s inhabitants to the Clovis people or any others.
The small number of artifacts in the cave suggests that whoever occupied it did so only for a short period, rather than using it as a long-term residence, Jenkins said.
Organic material from the coprolites was radiocarbon dated, and the oldest ones were found to be 14,300 years old.
Willerslev’s lab analyzed mitochondrial DNA from the coprolites and concluded that it was similar to DNA from both Native Americans and the populations of Siberia and East Asia.
Fearing contamination of the samples, Willerslev also analyzed samples from all 55 people who visited the cave during the excavations, as well as from all 12 members of his laboratory and showed that none of them had similar DNA.
The coprolites also contained DNA similar to that of the red fox, coyote or wolf. Jenkins said the added DNA could have come from human ingestion of the animals or from the animals urinating on the feces.
Critics, such as anthropologist Gary Haynes of the University of Nevada, Reno, argued that the coprolites could be animal feces and that the human DNA was deposited when humans urinated on them much later.
But Jenkins said that the coprolites also contained human proteins in concentrations too high to have come from urine, as well as human hair.
“Whether the coprolites are human or canine is irrelevant, since for a canine to swallow human hair people had to be present in that environment,” he told Science. “Anyway you cut the poop, people and dogs would have had to be at the site within days of each other 14,000 years ago.”