Archaeological treasures of a special kind: manure fossils can provide exciting insights into human history. So far, however, there has been a problem in researching the petrified shops: it was often unclear whether the findings were actually human remains or dog droppings. But now researchers have developed a new analysis method that enables clear assignment. Traces of the typical gut microbial communities provide the clue.
What did people eat once, did they suffer from parasites and how was their intestinal flora composed? Investigations of so-called coprolites can provide insights into these questions. Archaeologists find these fossilized remains of excrement in many places where people once lived. But to what extent can you be sure that they were responsible for the legacies? The distinction between human and dog excrement has so far been particularly difficult, according to the researchers led by Maxime Borry from the Max Planck Institute for the History of Mankind in Jena (MPI-SHH).
Human or dog droppings?
As they explain, the faeces of the two creatures are very similar in size and shape and also have a comparable composition. In addition, humans and their animal companions often lived together at many sites. The detection of remains of the producer DNA in the feces can only provide limited information. The reason: dogs have been eaten in some cultures and the animals in turn tend to eat human feces sometimes. Both of these aspects can lead to traces of dog and human DNA in the shops of both species, Borry and her colleagues explain.
In order to be able to reliably determine the origin of paleo faeces, they have now developed the “coproID” (coprolite identification) method. The system is based on the detection of traces of the characteristic bacterial communities that live in the intestines of humans and dogs. As the scientists explain, these microbes also left their genetic signature in the petrified faecal samples – it is so-called fossil DNA. Specifically, the researchers used machine learning to develop software that, in addition to the host DNA, can also recognize the sequences of the intestinal bacteria in the genetic profiles of the petrified excrement.
Traces of the intestinal flora allow the assignment
The scientists demonstrated the performance of their concept through tests: coproID was able to reliably determine the origin of archaeological faeces by analyzing sequencing data. It was shown that the combination of the detection of host DNA and the genetic traces of the typical intestinal microbes of humans and dogs enables an exact differentiation of their faeces, the scientists sum up. “An unexpected result of our study was that many archaeological finds have a large proportion of dog droppings,” says co-author Christina Warinner from the MPI-SHH.
In addition to the study of eating habits, diseases and parasites, the method now also has another potential: The changes in the structure and function of the human intestinal flora over time can be better investigated, the researchers say. They hope that this will provide insights into food intolerance and other aspects of human health. “Identifying human coprolites should be the first step in analyzing old human microbiomes,” says Borry. In addition, she and her colleagues hope that coproID could also be used in other areas – for example in forensics, ecology or general research into the intestinal flora.
Source: Max Planck Institute for Human History, professional article: PeerJ, doi: 10.7717 / peerj.9001