Fossilized excrement found in an Oregon cave has given scientists the hardest evidence to date that humans roamed the New World at least 1,000 years earlier than previously believed.
The prehistoric poop, deposited in a cave some 14,300 years ago, contains DNA from the forebears of modern-day Native Americans, according to the research.
The discovery reported today by the journal Science added fresh weight to emerging theories that Stone Age people from Asia somehow bypassed ice sheets sealing off North America before 11,000 BC. Nearly all scholars agree that humans were present by then, but until recently few archaeologists accepted that an earlier arrival was even possible because of the formidable ice barriers.
The new dating comes from 14 pieces of fossilized excrement, called coprolites, found within the Paisley Caves CQ complex by University of Oregon archaeologist Dennis L. Jenkins, and painstakingly analyzed by genetic anthropologists in Denmark.
"This is the earliest direct evidence of a human presence in the Americas," said Eske Willerslev, director of the University of Copenhagen's Center for Ancient Genetics, which extracted human mitochondrial DNA from six of the feces.
"There were humans doing their business in a cave in Oregon long before many scientists believed there were any humans at all in North America," Willerslev said in an interview.
According to the research, the coprolites contained DNA "signatures" that could only belong to native Americans. Excrement contains no genetic material, but typically contains particles of tissue from the intestines, and these fragments yield DNA.
"People shed gut tissue just like they shed skin flakes," said M. Thomas P. Gilbert, lead author of the study.
The research triggered immediate controversy, with some archaeologists arguing that the Danish team had failed to entirely rule out the possibility that the coprolites were tainted by DNA from later humans.