They say one man’s garbage is another man’s treasure — but in this case, scientists took it one step further: from parasite DNA found in ancient latrine feces, archaeologists have learned what people used to eat centuries ago, and what kind of animals they kept around the house (voluntarily or involuntarily).

Ancient latrines which were sampled in the study. Image credits: Søe et al (2018).

Historically, humans ingested a lot of parasitic worms. These worms infested the human intestine, where they lay eggs and got excreted in feces. These parasites could spread from human to human or from animal to human, thus perpetuating the infestation.

Recent advancements in DNA sequencing technology have opened up new directions for study, allowing researchers to examine the DNA in parasite eggs — even in century-old material.

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In a new study, Martin Søe of the University of Copenhagen, Denmark, along with colleagues began by filtering and concentrating the parasite eggs in their samples, which spanned from 500 B.C. (for samples from Bahrain) to 1700 A.D. (for samples from the Netherlands), to ensure that they would have enough genetic material to work with.

They found that most of the DNA came from parasites known to spread from human to human, but some also came from raw or undercooked fish and pork. The DNA also revealed several animal species which lived alongside the humans (sheep, horse, dog, pig, and, of course, rats).

“Ancient DNA from latrines was used to identify the remains of a broad range of human and animal parasites as well as animals and plants,” says Martin Søe. “This allows novel and unique insights into parasitism, diet and subsistence patterns of past populations.”

Researchers also complemented the parasitic DNA findings with animal and plant DNA analysis, painting a thorough picture of what people ate. For instance, they learned that some of the Danish samples (ranging from 1018 to 1400 A.D.) contained DNA from fin whales, roe deer, and hares. Most people in northern Europe also ate a lot of plants, including an abundance of cabbages and buckwheat.

While this is not the first study to follow this approach, and although this study builds on previous research, it also moves away from existing studies via its novel sequencing approach, which allowed researchers to completely reconstruct several ancient parasites’ mitochondrial genomes. This mitochondrial DNA also reveals evolutionary relationships and trends, so researchers can also gain insights into how parasites spread and infected their hosts.

Journal Reference: Søe MJ, Nejsum P, Seersholm FV, Fredensborg BL, Habraken R, Haase K, et al. (2018) Ancient DNA from latrines in Northern Europe and the Middle East (500 BC-1700 AD) reveals past parasites and diet. PLoS ONE 13(4): e0195481.