Combing through samples of ancient feces probably isn't going to be many people's idea of a roaring good time. 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 can be a veritable goldmine of information.
Yet it can be difficult to determine whether fecal samples are human or were produced by other animals, particularly dogs. Now an international team of scientists has devised a new method of doing so that combines host DNA and gut microbiome analysis with open source machine-learning software, according to a new paper in 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 could be designated as being of human origin with any certainty. Exceptions could be made for samples found in ancient latrines, since they are highly likely to be human; samples found in trash deposits, however, are more ambiguous.
Subsequent work to document the morphology of mammal feces has made it easier to separate human from animal samples, since there are enough differences to make such distinctions. The exception is dog poo, which bears a strikingly close resemblance to human feces in both size and shape, is frequently found at the same archaeological sites, and has a similar composition. And frankly, some ancient societies routinely ate dog meat, while dogs are known to nibble on human feces. So DNA from both can be present in the same archaeological sample.
There are some helpful clues. For instance, ancient dog poo samples "typically contain masses of short, nibbled dog hairs and odd inclusions, such as fragments of clothing and rope," the authors of the PeerJ paper wrote. The presence of specific parasites can also indicate whether a sample is human or canine, such as eggs from pinworms (Enterobius vermicularis), which are typically only present in human feces. Scanning electron microscopy (SEM) can also be useful for identifying plant remains (such as pollen grains) in ancient samples. Rehydrating the samples can also help make the distinction, since human feces will turn the rehydration solution dark brown or black; animal samples typically remain clear or turn yellow.
Dog or human?
This new coprolite identification method, dubbed coproID, combines host DRead More – Source