Lumps of desiccated feces, dug from a cave in Oregon and stored in plastic bags on a shelf in a science lab, now have some scientists convinced that humans have been in North America for 1,000 years longer than previously thought.
The find turned out to be the oldest directly-dated evidence of human habitation in North America - a 14,300-year- old piece of the puzzle of when we arrived in the New World.
Researchers say the clumps, known as coprolites, were left by Native Americans who were in the region at least 1,000 years before prehistoric tribes known as Clovis people began using their famous spear points to hunt game and carve tools.
Evidence of prehistoric hearths, stone tools and carved bones that are nearly as old have been uncovered in caves and clearings throughout the Americas, including intensively studied sites in Virginia, Pennsylvania and South America.
But the discovery in Oregon's Paisley caves was the first in which scientists were able to pinpoint a date using human DNA. The results were reported yesterday in the online edition of the journal Science.
"We've actually dated human cells to this time period," said Dennis L. Jenkins, an archaeologist at the University of Oregon's Museum of Natural and Cultural History and a member of the international team that published the findings.
Many scientists have thought humans first migrated to North America from Asia by crossing an ice-free corridor in western Canada about 13,500 years ago. They spread out quickly, designing spears and pointed tools they used to hunt to extinction the woolly mammoths, mastodons and other large mammals they found.
But the latest discovery is likely to rekindle debate over how humans first arrived in the Americas. The age of the coprolites indicates that humans were here hundreds of years before the Clovis culture and before the ice-free corridor was formed, experts say.
"The peopling of the Americas is still a big question among scientists," said Fatimah Jackson, a professor of biological anthropology at the University of Maryland. "How did humans first get here, and what were the characteristics of those first people, and how did they survive?"
Scientists found human and canine DNA at the site. To skeptics, that means the human DNA detected by the researchers could have come from people whose remains became mixed in with the feces of earlier animals.
"These guys are making the strongest case anyone ever has that humans were here that early, and I'm 99 percent convinced," said Ted Goebel, a professor of anthropology at Texas A&M; University. "But it could be they have 14,000-year-old wolf coprolites."
But the researchers say the evidence is clear, and that it shows North America was colonized by explorers who probably traveled along the Pacific coast.
"I think it is likely they took a route along the coast, and came either by boat or by walking," said Eske Willerslev, an evolutionary biologist at the University of Copenhagen and the study's lead author.
The coprolites were discovered on federally protected lands in south-central Oregon, a site of sporadic archaeological excavations since the 1930s, Jenkins said. The cave probably was used as some kind of temporary shelter, and the coprolites were near the entrance in "kind of an alcove off to one side," he said.
"They've come across a human bathroom," Jackson said.
The samples were about 6 or 7 feet down in dry soils. There are probably other sites with pre-Clovis human remains in North America, but the Oregon cave provided a particularly good setting for preservation, the researchers say. "You have hot and dry conditions and stable temperatures because it's in a cave, which makes for good conditions," Willerslev said.
The researchers used two independent labs equipped with accelerator mass spectrometers to date the coprolites. The labs, in Florida and England, used different methods, but came out with the same dates. Mitochondrial DNA analysis links the coprolites to two genetic subgroups of Native Americans that can be traced to East Asia and Siberia.
"They were real careful about contamination issues and handling the DNA, which is typical in this kind of work," said Robert Wall, a Towson University archaeologist not involved in the project.
What was disappointing: the absence of stone tools and other artifacts, Wall said.
The only artifacts nearby were a sharpened object that may have been used as a tool and a polished rock that may have been used to smash bones or remove hair from a horse hide, Jenkins said.
Future efforts will focus on analysis of the samples to determine exactly what the natives ate, Willerslev said.
Jenkins and teams of students uncovered the coprolites in 2002 and 2003, but they remained on a shelf in his lab until the spring of 2004.
When early testing showed the samples contained Native American DNA, Jenkins tracked down the 55 students involved in the excavation work years earlier and arrange for them to send him four personal hair samples to ensure their DNA hadn't contaminated the test results. It was painstaking work, but had to be done, he said.