Raw Fish and Tapeworms: Ancient Latrines Reveal the Diets of Our Ancestors

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Ancient latrines are pictured. These are a great place to look for old parasitic eggs. Søe et al (2018)

It's Denmark, 1020 AD and you're putting your feet up after a long day of pillaging with your Viking friends. What's on the table for dinner, you ask? Beer, buckwheat and undercooked fish—all sprinkled with a heady seasoning of parasites.

Scientists have performed DNA analysis on ancient stool samples from Northern Europe and the Middle East to get a glimpse of what our ancestors were eating. Research about the diets of people from Denmark, the Netherlands, Lithuania, Jordan and Bahrain was published Wednesday in the journal PLOS ONE.

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Researchers examined archaeological stool samples from medieval Europe and later, as well as much earlier samples from the Middle East. The earliest sample was produced in Bahrain sometime from 500-400 BC. Although it's uncertain exactly which sample is—shall we say—freshest, one stool from the Netherlands could date as late as 1850 AD.

In times of low personal hygiene, parasites were everywhere. Whipworms, roundworms, tapeworms—you name it, people had it. Uncomfortable as this might have been for our ancestors, the parasitic eggs ejected from their guts provide a goldmine of DNA for scientists today. Ancient stools can reveal "novel and unique insights into parasitism, diet and subsistence patterns of past populations," Martin Søe, one of the study authors and a researcher with the University of Copenhagen, said in a statement.

The researchers collected and filtered parasitic eggs from the collection of stools before sequencing the genetic material they found. They used a genomic database to match match up the DNA from their samples with known species. The tiny eggs revealed the diets of their human hosts, hundreds of years after they were dumped in a latrine.

Although the bulk of the DNA found in the samples came from parasites transmitted between humans, a substantial portion came from the parasites you'd find in raw or undercooked fish and pork.

"We see that [Northern Europeans] ate a lot of fish because they were eating fish tapeworms," Søe told NPR. Danish excrement from the 17th century contained the kinds of parasites you would only come across in the stool of someone who had eaten undercooked pork. Danish stool from Viking times held the DNA of parasites that thrive in pork, fish and even fin whales.

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In addition, the team found evidence of fruit and vegetable consumption—cabbage, peas and strawberries, for example—in Northern European samples. Traces of grapes in the Dutch samples and of a sprinkling of hops in the Danish and Lithuanian stools suggest some of these Europeans also drank wine and beer.

As well as revealing the diets of the past, the ancient excrement gave Søe and his team some insight into the living conditions at the time. The team found DNA from parasites that only infect some animals—cats, horses and rats, for example—in their human stool samples. "Whipworms excreted from mouse feces were mixed up in the samples, too," Søe told NPR. Animals, too, were riddled with parasites, and their feces may have been dumped in the same place as humans'.

Further research into ancient parasites' DNA, the researchers hope, will reveal more about the ways they spread between their hosts.