July 13, 2012 | 14
Once upon a time, the initial migration of humans into the New World looked like a very tidy story: the so-called Clovis people, it appeared, were the first to enter the Americas, arriving from Siberia by land bridge and spreading across the continental U.S. in pursuit of large game animals, leaving behind their telltale fluted stone tools and other remains. But in recent years, discoveries of remains that appear to pre-date the Clovis culture have upended that Clovis First scenario. Now new findings from the Paisley Caves in Oregon join the growing body of evidence that the human colonization of the Americas was more complex than researchers once thought, showing that a separate technological tradition co-existed with the Clovis one and may well have preceded it.
Previous work at the Paisley Caves had turned up preserved human feces (coprolites) containing DNA and some stone projectile points made in what archaeologists term the Western Stemmed Tradition, which differs from Clovis primarily in the way in which the point is affixed to a dart shaft. Initial dating results indicated that the remains rivaled Clovis in age, but questions about their antiquity lingered. In the new study, published in the July 13 Science, Dennis Jenkins of the University of Oregon and his colleagues report on high-precision radiocarbon dating of more than 100 new samples from Paisley Caves that establish the chronology of the site and put the oldest stone points at more than 13,000 years old, making them at least as old as the oldest known Clovis artifacts elsewhere.
The Clovis First theory predicts that the Western Stemmed technology evolved from the Clovis one, yet no Clovis tools or tools that look like they could have given rise to Clovis have turned up in Paisley Caves. Thus although Western Stemmed might share a common ancestral technology with Clovis, it does not come out of the Clovis lineage itself, Jenkins asserted in a press teleconference. In the Science paper he and his colleagues conclude: “The Paisley Caves evidence supports the hypothesis that the [Western Stemmed Technology] was an indigenous development in the far western United States, whereas Clovis may have developed independently in the Plains and Southeast.” The findings buttress claims for a non Clovis-derived tool-making tradition at the site of Monte Verde in Chile, Jenkins added, noting “this really seems to suggest there are multiple technology trajectories at the same time here at the end of the Pleistocene in the Western Hemisphere.”
The investigators also recovered more coprolites containing mitochondrial DNA (which is maternally inherited, as opposed to nuclear DNA, which is inherited from both parents) from the site, taking precautions to ensure the samples were not contaminated with foreign DNA. Sequencing confirmed earlier work indicating that the Paisley Cave folks carried the so-called haplogroup A mitochondrial lineage that is common among Native Americans today and is thought to have originated in Asia. Team member Eske Willerslev of the University of Copenhagen said in the press teleconference that the Paisley Cave people were Asian in origin and possibly related to or ancestral to modern day Native Americans. To nail the relationship down further , he said, the researchers will need to retrieve nuclear DNA from the coprolites.
The oldest coprolite at the site was radiocarbon dated to 14,500 years ago, making it the oldest directly dated human remain in the western hemisphere and older than the oldest point from the site by more than a thousand years. Whether the person who left behind that turd made tools in the Western Stemmed fashion is unknown, but study co-author Loren Davis of Oregon State University said in a statement that the DNA from that coprolite resembles the DNA from a coprolite that is the same age as the oldest points. “They were from the same genetic group,” he said.
According to Davis, more evidence that the Western Stemmed people were as early or earlier than the Clovis people may come from the site of Coopers Ferry in western Idaho, which contains points that have been preliminarily dated to 13,200 years ago—an age that he and his colleagues are working to confirm. As for the Paisley Caves, although more archaeological material remains to be unearthed there, Jenkins has terminated the excavations in order to preserve the contents for future archaeologists armed with improved study tools and methodologies. Analyses of materials already recovered from the site will continue, however.
In 2011, archaeologists working at the Debra L. Friedkin site in Texas reported on their discovery of thousands of stone tools dating to between 13,200 and 15,500 years ago that were also distinct from Clovis points. That assemblage was found under a level containing Clovis tools, however, and researchers involved in the discovery suggested that the Clovis style of projectile manufacture may have derived from that earlier tradition. No such technological precursor is known for Western Stemmed projectiles.