Examining the contents of ancient toilets may not be every scientists dream job but for researchers into pre-industrial societies it may hold important evidence for our health today.

Piers Mitchell of Cambridge University specialises in the gut contents of past people through analysis of unusual substrates. By looking at the contents of archaeological latrines and desiccated faeces under the microscope, he and his team have learned volumes about the intestinal parasites that plagued our ancestors.

Piers Mitchell explained:

“Microscopic analysis can show the eggs of parasitic worms that lived in the intestines, but many microbes in the gut are simply too small to see.”

The researchers looked at latrines in Jerusalem and Riga dating from the 14th and 15thC. They identified a wide range of bacteria, archaea, protozoa, parasitic worms, fungi and other organisms, including many taxa known to inhabit the intestines of modern humans.

Researcher Susanna Sabin, a doctoral alumna of the MPI-SHH who co-led the study, compared the latrine DNA to those from other sources, including microbiomes from industrial and foraging populations, as well as waste water and soil.

She said:

“We found that the microbiome at Jerusalem and Riga had some common characteristics – they did show similarity to modern hunter gatherer microbiomes and modern industrial microbiomes, but were different enough that they formed their own unique group. We don’t know of a modern source that harbours the microbial content we see here.”

The use of latrines, where the faeces of many people are mixed together, allowed the researchers unprecedented insight into the microbiomes of entire communities.

Piers Mitchell said:

“These latrines gave us much more representative information about the wider pre-industrial population of these regions than an individual faecal sample would have.

“Combining evidence from light microscopy and ancient DNA analysis allows us to identify the amazing variety of organisms present in the intestines of our ancestors who lived centuries ago.”

And how does this help us today? A growing body of evidence has linked changes in our microbiome to many of the diseases of the modern industrialised world, such as inflammatory bowel disease, allergies, and obesity.

Piers Mitchell explains

“If we are to determine what constitutes a healthy microbiome for modern people, we should start looking at the microbiomes of our ancestors who lived before antibiotic use, fast food, and the other trappings of industrialisation.”

The current study helps to characterize the change in gut microbiomes and highlights the value of ancient latrines as sources of bio-molecular information.

Kirsten Bos, a specialist in ancient bacterial DNA from the Max Planck Institute for the Science of Human History and co-leader the study, commented:

“It seems latrines are indeed valuable sources for both microscopic and molecular information.”

The research was published in the journal Philosophical Transactions of the Royal Society B