Sampling of an undisturbed block of impregnated silt. The credit is given to the MPI f. Evolutionary anthropology.
Most archaeologists think that the by-products of excavations are unimportant. In the last few years it has been shown that ancient biomolecules can be found in the soil. The Max Planck Institute for Evolutionary Anthropology has a study on the use of ancient human and faunal DNA to investigate the geographical and temporal distribution of ancient humans and other organisms at sites where their skeletal remains are rare or absent.
Max Planck researchers collaborated with an international group of archaeologists who apply geological techniques to reconstruct the formation of the site to study the origin of the DNA. They soaked the blocks of undisturbed blocks in synthetic plastic-like material. The hardened blocks were taken to the laboratory to be sliced in sections for analysis.
The researchers successfully obtained the genetic material from a collection of blocks that were prepared as long as 40 years ago from sites in Africa, Asia, Europe and North America. Despite being stored in plastic for decades, these blocks are an excellent source of ancient DNA, including that originated from hominins. The study opens up a new era of ancient DNA studies that will revisit samples stored in labs, allowing for analysis of sites that have been back-filled, which is especially important given travel restriction and site inaccessibility in a Pandemic world.
A section of undisturbed block from Denisova Cave. Credit: Mike Morley.
Micro remains in the matrix.
The scientists found that small organic particles yielded more DNA than random samples from the Denisova Cave, a site located in the Altai Mountains in South Central Siberia where ancient DNA from Neanderthals, Denisovans and modern humans has been retrieved. Vera Aldeias says that the high success rate of ancient mammal DNA retrieval from Denisova Cave is due to the abundance of micro remains in the sediment matrix rather than free extracellular DNA from feces, bodily fluids or decomposing cellular tissue. "This study is a big step closer to understanding precisely where and under what conditions ancient DNA is preserved," says Morley.
The approach described in the study allows highly localized micro-scale sampling of the soil for analysis of ancient DNA, and shows that it is not uniformly distributed in the soil. Susan Mentzer is a researcher at the Senckenberg Centre for Human Evolution and Palaeoenvironment in Germany.
The lead author of the study was able to recover substantial amounts of Neanderthal DNA from a small amount of sediment. He was able to identify the sex of the individuals who left their genes behind, and he was able to show that they were related to a Neanderthal population. He says that the Neanderthal DNA in the small samples was more concentrated than in loose material. It will be possible in the future to analyze the DNA of many different ancient human individuals from just a small cube of solidified sediment. It is amusing to think that the cave was used as a toilet tens of thousands of years ago.
The research was published in a journal.
Microstratigraphic preservation of ancient faunal and hominin DNA in Pleistocene cave sediments, is a paper in the National Academy of Sciences.
The National Academy of Sciences has a journal.
There is a story about how DNA is preserved in archaeological artifacts for thousands of years.
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