Over 14,000 years ago, near a stone fire pit in the cool, dry depths of a cavern in the Pacific Northwest, a group of humans heard a call that nobody can deny: the call of nature.
This wasn’t unusual — everybody poops — but unlike the vast majority of deposited droppings, these were preserved in the arid climate of what are today called the Paisley Caves of Oregon. On Wednesday, a paper published in Science Advances confirmed that the droppings are among the oldest known evidence of human presence in North America, which could help settle an argument about when people first arrived in the Americas, as well as crucial clues to how they lived.
Starting in the 1930s, some archaeologists studying the peopling of the Americas believed that the Clovis culture — a group represented in the archaeological record by distinctive spearheads — were the first humans to arrive in the Americas, around 13,000 years ago. But newer evidence has challenged this idea.
“For the past decade, it’s been quite well accepted that pre-Clovis populations were present in America,” said Lisa-Marie Shillito, an archaeologist at the University of Newcastle in England and lead author on the study. “Paisley Cave is one of the key case studies for pre-Clovis populations, because it’s one of the only sites where we have archaeological material like stone tools in direct association with material that can be dated.”
The most famous signs of human occupation at Paisley Caves are preserved dung called coprolites. In 2007, an ongoing excavation of the caves led by Dennis Jenkins of the University of Oregon, a co-author of the new study, found a new set of coprolites at the lowest levels of the dig, and radiocarbon dated them to around 14,000 years old.
According to Vaughn Bryant Jr, a specialist in coprolites at Texas A&M who was not involved in the study, the first round of DNA analysis suggested that the coprolites had been deposited by humans. But some archaeologists argued that the specimens had been left by animals and were accidentally contaminated by later humans.
Contamination is always a possibility with DNA analysis, said Ian Bull, a chemist at the University of Bristol in England and a co-author on the paper. But in 2017, Dr. Shillito’s team analyzed the droppings using a technique that looked for organic compounds called lipids. Unlike DNA, the process of identifying lipids doesn’t amplify them: the fecal biomarkers are very difficult to accidentally contaminate. The presence of both human DNA and human fecal markers makes it all but certain that the dung belonged to 14,000-year-old squatters.
“This is a really good example of how you can get synergy between multiple lines of analysis,” Dr. Bull said. “You see some studies out there that’ll just hang everything on one type of analysis, and we absolutely don’t believe in that.”
But the Paisley Caves aren’t just America’s oldest-known outhouse. Coprolites can also offer a glimpse into how people lived.
“They’re really great not just for looking to see whether people are present, but as nice little packages of information about diet and health,” Dr. Shillito said.
The dung found at Paisley Cave suggests a varied diet, not just of large game like mammoths that early Americans are stereotyped as eating. It contains partially digested seed coatings, rodent bones and the outer casings of insects, as well as organic compounds from plants.
Dr. Shillito said that in coprolites, “what you largely find is that maybe they were hunting large animals sometimes, but on a day-to-day basis their diets were a lot more varied and diverse.”
The coprolites in Paisley Cave also aren’t concentrated in latrines or central rubbish pits, which became common in Europe and Asia around 12,000 years ago, as roving bands began living in more permanent settlements, and thus had to begin managing their waste.
Instead, Dr. Shillito said, the droppings in the cave generally seem to have been left where they lay. While that might seem strange to us, Dr. Shillito said, it makes sense for nomadic people who likely used the cave sporadically.
The team’s research is part of a larger project studying the entire assemblage of coprolites laid down in Paisley Caves over thousands of years, in hopes of mapping how diets changed alongside shifts in the climate and environment. Moreover, these fecal remains — along with others from Texas, New Mexico, and Utah — suggest how quickly the first Americans settled the continent.
As more pre-Clovis sites are found, Dr. Shillito said, so do opportunities for research. “We’ll get a more detailed idea of exactly how people were moving around across the continent, and what they were doing in the environment, rather than just thinking about when they got there.”