Neanderthal and Denisovan DNA samples extracted from sediments

A new technique developed by an international team allowed to trace the remains of groups of hominids in sediments even in caves or in strata which have no skeletal remains. the researchers analysed 85 samples of sediments from the Pleistocene, between 550000 and 14000 years ago, from eight Eurasian caves, including El Sidrón (Spain) and Denisova Cave (Russia).

Scientists sampling sediments in Denisova Cave (by IAET SB RAS & Sergei Zelensky)

The scientists tested sediments from nine known archaeological sites in Belgium, Croatia, France, Russia and Spain. The sediments dated from between 14000-550000 years ago, with the oldest intact DNA found in sediments dating from 240000 years ago. One of the samples discovered is 50000-year-old DNA from the urine of a Neanderthal, found in a cave in Belgium.

Sediment profile in Trou Al’Wesse cave in Belgium (by Monika V. Knul)

The method is based on the analysis of fragments of mitochondrial DNA, which are most abundant in the majority of eukaryotic cells. According to the research, the soil unquestionably holds this information, given that it preserves the remains of organisms that have decomposed, defecated or bled into it. The origin of the recovered DNA seems to come from depositions made in situ or from the decomposition of the bodies in the caves themselves. The DNA was distinguished from modern DNA that could contaminate it during excavation or during laboratory tests, to make sure the samples really were from the dates indicated by the sediments they were found in. The presence of DNA from extinct animals in the same layers also indicated that the human DNA was from our ancestors and not modern people.

Taking soil samples (by El Sidrón research team)

At the Denisova Cave, known for numerous finds attributed to the Denisovans, an extinct species of human discovered in 2010, investigators have been able to detect which layer of soil corresponds to which hominid – as the cave was occupied by Denisovans, Neanderthals and Homo Sapiens. Moreover, the Denisovans appear in the bottommost stratum, that is, in the oldest of the deposits. Their DNA in this sediment, without being associated with any skeletal remains, is the oldest proof of their existence right now, according to the researchers. meanwhile at El Sidrón cave, situated in Piloña, Spain, test have provided the finest Neanderthal assemblage on the Iberian Peninsula. The cave is known for around 2,500 skeletal remains from at least 13 individuals of both sexes and of varying ages. A sample from a cave in Belgium is said to yield 50000-year-old DNA from the urine of a Neanderthal. According to the archaeologists, although the oldest DNA found was 240,000 years old, this is not likely to be the limit for this method.

(after International Business Times, EurekAlert!, Live Science, El Sidrón research team, Monika V. Knul, IAET SB RAS & Sergei Zelensky)

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