Combing through samples of ancient faeces probably isn’t visiting be many people’s idea of a roaring blast. However, for archaeologists keen on learning more about the health and diet of past populations—as well as how certain parasites evolved, the evolutionary history of the microbiome—such samples will be a veritable goldmine of knowledge.
Yet it will be difficult to work out whether faecal samples are human or were produced by other animals, particularly dogs. Now a global team of scientists has devised a replacement method of doing so combines host DNA and gut microbiome analysis with open-source machine-learning software, in step with a replacement paper within the journal PeerJ.
The challenge of determining whether paleofeces and coprolites are of human or animal origin dates back to the 1970s. Usually, only those samples found with human skeletons or mummies can be designated as being of human origin with any certainty. Exceptions can be made for samples found in ancient latrines since they’re highly likely to be human; samples found in trash deposits, however, are more ambiguous.
Subsequent work to document the morphology of mammal faeces has made it easier to separate human from animal samples since there are enough differences to form such distinctions. The exception is dog poo, which bears a strikingly close resemblance to human faeces in both size and shape, is usually found at the identical archaeological sites, and includes a similar composition. and albeit, some ancient societies routinely ate dog meat, while dogs are known to nibble on human faeces. So DNA from both will be present within the same archaeological sample.
There are some helpful clues. for example, ancient dog poo samples “typically contain masses of short, nibbled dog hairs and odd inclusions, like fragments of clothing and cord,” the authors of the PeerJ paper wrote. The presence of specific parasites may also indicate whether a sample is human or canine, like eggs from pinworms (Enterobius vermicularis), which are typically only present in human faeces. Scanning microscopy (SEM) may also be useful for identifying plant remains (such as pollen grains) in ancient samples. Rehydrating the samples may also help make excellence since human faeces will turn the rehydration solution dark brown or black; animal samples typically remain clear or turn yellow.