Digging deep: DNA molecules in ancient dirt offer a treasure trove of clues to our past

Archaeological deposits typically consist of a mix of artefacts and the remains of plants and animals — including the occasional human fossil — all held in a matrix of dirt. But these days, we dig for a lot more besides fossils and artefacts.

Now we can find clues to the deep past in the very dirt that we excavate. Alongside plant and animal remains, the sediments in an archaeological deposit might also contain ancient DNA molecules that can be extracted and used to identify the species that once lived there.

This was the case at Denisova Cave in southern Siberia, where “sediment DNA” revealed the evolutionary comings and goings of two now-extinct groups of humans who once lived there: the Neanderthals and a mysterious group dubbed the Denisovans...