There's treasure to be found in mining excrement. At least, it's treasure to scientists studying the diets, habits and health of people who lived centuries ago.
In a new study, Danish researchers dug up old latrines and sequenced the DNA they found in the ancient poop. The results paint a picture of diets and parasites spanning times and places that range from an ancient fort Qala'at al-Bahrain, near the capital Bahrain in 500 B.C.E. to the river-ringed city of Zwolle in the Netherlands in 1850. The researchers published their results in the journal PLOS One.
The team collected samples of old latrines and soil deposits at eight different archeological sites. They screened the samples for the eggs of parasites, which can last for centuries, and analyzed the DNA in each sample to determine species. They also gleaned the DNA of plants and animals from the samples to determine what people ate.
In some ways, the team found that life centuries ago was unhygienic as might be imagined. Most people probably dealt with intestinal parasites at least once in their life, veterinary scientist and paper co-author Martin Søe, with the University of Copenhagen, tells Angus Chen at NPR. "I think it's fair to say it was very, very common," he says. "In places with low hygienic standards, you still have a lot of whipworm and round worm."
Søe explains that the types of parasites they found could also give insight into the animals people consumed. Parasites that live in fish and pigs but that can also infect humans were a common find, indicating that undercooked or raw pork and fish was a diet staple.
The analysis also identified a handful of parasites that only infect humans such as the giant roundworm (Ascaris lumbricoides) and the whipworm (Trichuris trichiura).
By sequencing the mitochondrial DNA of the parasite eggs, the researchers found that Northern European whipworms from 1000 C.E. to 1700 C.E. were more closely related to worms found in present-day Uganda than to those in present-day China. Findings like this offer "hints about ancient patterns of travel and trade," writes Charles Choi for a blog post at Discover magazine.
Researchers also found parasites that don’t infect human but are more commonly found in sheep, horses, dogs, pigs and rats. This suggests the critters all likely lived near the latrines, leading people to dispose of the animal waste in the ancient toilets, Søe tells Choi.
The menagerie of ancient DNA helps paint a picture of life at some of the sites. For example, samples from Gammel Strand—a site in Copenhagen’s old harbor—include DNA from herring and cod, horses, cats and rats. The harbor was "[l]ikely a very dirty place by our standards, with a lot of activity from humans and animals," Søe says.
The findings also reveal information about ancient diets. DNA in Danish samples shows that the people probably ate fin whales, roe deer and hares, writes Sarah Sloat for Inverse. The study also delves into the analysis of plant DNA, which included cherries, pears, cabbages, buckwheat and other edible plants. The ancient Danes' waste had an abundance of DNA from hops, showing the people's fondness for beer, whereas the samples from the Netherlands showed people there had a preference for wine.
This isn't the first time that scientists have looked to unappetizing leavings to learn more about the past. Researchers have traced the path of explorers Meriwether Lewis and William Clark by looking for traces of mercury in the soil. The metallic element was in pills the men took to treat constipation and its presence indicates where the expedition dug latrines and camped. And parasites in a castle latrine in Cyprus attest to the poor health endured by crusaders. But the DNA analysis of the new study offers a uniquely detailed picture of the past.
Together, the new findings offer intriguing hints about ancient life. Following up on some of these leads could lead future researchers to tell us more about ancient people's health and the migrations of our ancestors. As Maanasa Raghavan, a zoologist at Cambridge University who wasn't part of the new study, tells NPR: "Having these datasets will help us look further at how these pathogens evolved over time or how people moved around."