Archeologists at the University of Oregon, Oregon State University and the University of Copenhagen used radiocarbon dating and DNA analysis to examine fossilized excrement, obsidian projectile points and the stratified sediment inside a series of caves located in the Summer Lake basin in south-central Oregon.
The caves are part of a unique archeological site that is part of the Great Basin watershed and thanks to its arid climate has been able to preserve some of the oldest human remains in the Western Hemisphere.
The researchers concluded that the human DNA they found in the Paisley Caves excrement was as old as 14,000 years, and the spear points dated from about 13,230 to 12,960 years ago and did not resemble the spearheads used by the Clovis people, who are believed to have settled in North America between 13,400 and 12,800 years ago.
The find suggests North America was colonized by multiple cultures, some of whom arrived possibly earlier than the Clovis.
"Our investigations constitute the final blow to the Clovis First theory," said Eske Willerslev of the University of Copenhagen's Centre for GeoGenetics, which did the DNA analysis, in a news release. "Culturally, biologically and chronologically, the theory is no longer viable.
"The dissimilar stone artifacts, as well as the DNA-profiling of the human excrement, show that humans were present before Clovis and that another culture in North America was at least as old as the Clovis culture itself."
Clovis First theory dominated since 1930s
The Clovis First theory of how North America was settled proposes that a group of Paleo-Indian people, dubbed Clovis after the New Mexico town where the first evidence of them was found, were the first humans to settle in North America. They are believed to have arrived from Asia via a land bridge over the Bering Strait at the end of the last Ice Age and then spread throughout the continent.
The theory has been dominant since a number of spear points thought to be the first evidence of humans' arrival in North America were discovered in 1932 near the village of Clovis.
The Clovis method of making spear points out of flakes of obsidian rock has been thought to be the "mother technology" for all later technologies that emerged in North America. The spearheads are fluted and have a unique notch at the base where a large flake of stone has been removed.
But the U.S. and Danish archeologists working at the Paisley Caves found evidence of so-called Western Stemmed spearheads at the site. These indicated a different technology from Clovis spears, one that produces spear points that are narrower and differ in the way they are attached to the base of the projectile.
"Stemming means that there is a long portion of the artifact that is not a part of the blade, and that goes down into the wood of the dart shaft, and then you lash it up and hope that it doesn't split when you cast it into the animal," said Dennis Jenkins of the University of Oregon, the lead author of a paper on the find, which was published Thursday in the journal Science.
"That technology or shape is found in Siberia and Asia, and it's there much earlier than we have dated it here in the United States.
"What we see here [in the U.S.] is Western points that are regional derivatives of that form."
The spear points Jenkins and his team found are the earliest examples of Western Stemmed points found in the U.S. to date, Jenkins said Thursday in an interview with CBCNews.ca.
"These two approaches to making projectile points were really quite different," said study co-author Loren Davis of Oregon State in a news release. "And the fact that Western Stemmed point-makers fully overlap, or even pre-date, Clovis point-makers likely means that Clovis peoples were not the sole founding population of the Americas."
Link to ancient animals missing
To date, there has been doubt that enough evidence exists that a separate group of hunter-gatherers lived in North America at the same time as or earlier than the Clovis.
"The point about Clovis First has been: if there is somebody else on the landscape, why haven't we found them?" said Jenkins. "For 70 years or more, we have been capable of finding Clovis points and associating them with mastodons and mammoths and other extinct animals, but we haven't been able to do the same thing with any other projectile points."
While the current find doesn't definitively demonstrate that the Western Stemmed spears were being used to hunt ancient animals, since they weren't found in direct proximity to animal bones, it dates the spears to a period that overlaps with such animals and suggests the presence of a people pre-dating Clovis and who had already been the subject of an earlier find made by Jenkins and Willerslev.
In 2008, the two managed to date a series of coprolites (fossilized excrement) found at the Paisley Caves to 14,340 years ago, and to show through DNA analysis that they came from people who originated in Asia and were likely predecessors of modern indigenous North Americans.
The new discovery provides further evidence of the presence of people in that pre-Clovis period, and although it does not provide DNA evidence that these people were genetically different from the Clovis, in Jenkins's view, it does support the idea that there were two separate migrations to North America — one that came by way of a Pacific coastal route and another that came from the north via an ice-free corridor in the middle of the continent.
"What it does is raise the spectre further that glaciers blocked the way through the middle portion of the northern part of the continent — in other words, Canada was under ice," Jenkins said.
"And even if the ice-free corridor was open, we are not certain that it was a pleasant or habitable environment to be, so there's a lot of questions about the feasibility of bringing somebody through the middle portion of the continent and into the northern plains of the United States through Canada.…
"Western Stemmed points are so common in the western United States and much less common in the eastern United States, and Clovis is just exactly the opposite ... so it really looks like there is this east-west dichotomy."
DNA not contaminated, researchers say
What makes the current results stronger than past data is that previous DNA-containing excrement found at the Paisley Caves was thought to be likely contaminated by DNA from later periods that seeped into the soil by way of water and urine from humans and animals.
The researchers behind the current study say there is no chance of that in this case.
They say they have conducted a detailed microscopic analysis of the soil structure and sediment that accumulate in the caves and ruled out any contamination.
The sediment contains layers and layers of dust, twigs, sand, soil, bones and other plant and animal matter, including chunks of fossilized excrement from different periods.
To establish how old the DNA is, the archeologists had to extract a fibre of hair, bone or fibrous plant material that survived the digestive process and apply radiocarbon dating methods to that — since the genetic material itself cannot be carbon dated.
When testing the carbon in the fossilized exrement at the Paisley Caves, Jenkins and his colleagues found that in most cases, it was older than the materials it was found in, indicating it came from the surrounding environment and not from later material that filtered down into the lower soil.
"We've completed more than 141 new radiocarbon measurements on materials ranging from coprolites to wood and plant artifacts, fossil plants and mummified animals, to unique, water-soluble chemical fractions from sediments and the coprolites themselves," said Thomas Stafford of the Centre for GeoGenetics in the news release.
"We have used carbon-14 dating to physically and temporally dissect the Paisley Caves strata at the millimetre level.
"At present, we see no evidence that geologically younger, water-borne molecules — DNA in particular — have moved downward and contaminated deeper, older coprolites."
Technology only hints at culture
Jenkins is cautious to point out that he and his colleagues were unable to link the Western Stemmed spears directly to specific genetic or cultural differences and that, ultimately, what spear points can tell us about a people is limited.
"What we have are really techno-cultures, if you will," he said. "We look at the projectile points, and we call that a culture, but in reality, it's not. It doesn't speak language; it doesn't have genetics. We don't know anything about its social organization — or very little.
"It's not really a culture; it's a technology or a tradition that you look at and then try to extrapolate from there what the culture might have been like."
It's likely that hunter-gatherers would have passed down one specific method of spear-making from father to son, Jenkins said, and while the two spearhead types definitely indicate different approaches to crafting tools, it's less clear whether these approaches were applied by distinct groups.
It's entirely possible the different types of spearheads represent an evolution of tools or a contemporaneous use of tools for different purposes, he said — although there were no Clovis points found at the site Jenkins's team examined.
"It could be the same people using different tools at the same time," he said. "You could have different groups that emphasize different subsistence patterns."Suggest a correction