Kirsten Bos at the Max Planck Institute for Human History was skeptical when Piers D. Mitchell of the University of Cambridge contacted her. Mitchell and his team examine archaeological latrines under the microscope to identify intestinal parasites that lived in our ancestors’ guts. He wanted to know if Bos could use DNA analysis to get even more insight into the gut health of people who used two medieval latrines, one in Riga, Latvia, and one in Israel. Though DNA that old can survive for archaeological sequencing, it’s usually taken from bones or dental plaque, not from muddy poop pits. It turns out that Bos and PhD student Susanna Sabin were able to find DNA to analyze (Philos. Trans. R. Soc., 2020, DOI: 10.1098/rstb.2019.0576). Much of the DNA that Sabin found and sequenced was environmental, human or from parasites like tapeworms, but some was clearly from bacteria that make their home in the human gut. And some of those bacteria, such as Treponema succinifacens, are often found in hunter-gatherers but not in industrialized populations. Bos says the work started as a proof of principle for the field. The plan now, she says, is to study additional latrines and fossilized feces, called coprolites, to understand more about gut microbiomes from the past.