Traces of prehistoric human DNA have been found in caves without bones in an advance that could shed new light on human history and evolution.

While many prehistoric sites in Europe and Asia contain tools and other human-made artefacts, skeletal remains of ancient humans are scarce.

Because of this, the DNA found between cracks of rock could help us better understand how early humans such as Neanderthals and Denisovans evolved

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Traces of early human DNA from up to 550,000 years ago have been found in between layers of rock. Pictured is a scientist preparing a sediment sample for DNA extraction

DNA DISCOVERY The researchers excavated seven archaeological sites in Belgium, Croatia, France, Russia and Spain. Overall, they collected sediment samples covering a time span from 14,000 to over 550,000 years ago. The researchers recovered and analysed fragments of mitochondrial DNA, the genetic material from the mitochondria - the 'energy factories' of the cell. They identified them as belonging to twelve different mammalian families that include extinct species such as the woolly mammoth, the woolly rhinoceros, the cave bear and the cave hyena. The researchers then looked specifically for ancient hominin DNA in the samples. Eight sediment samples contained Neanderthal mitochondrial DNA from either one or multiple individuals, while one sample contained Denisovan DNA. Advertisement

'This work represents an enormous scientific breakthrough,' said Antonio Rosas, scientist at Spain's Natural Science Museum in Madrid.

'We can now tell which species of hominid occupied a cave and on which particular stratigraphic level, even when no bone or skeletal remains are present.'

To uncover human traces, scientists relied on analysing fragments of mitochondrial DNA.

'The technique could increase the sample size of the Neanderthal and Denisovan mitochondrial genomes, which until now were limited by the number of preserved remains,' explained Spanish National Research Council scientist Carles Lalueza-Fox.

'And it will probably be possible to even recover substantial parts of nuclear genomes.'

The researchers excavated seven archaeological sites in Belgium, Croatia, France, Russia and Spain.

From sediment samples, they 'fished out' tiny DNA fragments that had once belonged to a variety of mammals - including our extinct human relatives.

Researchers found DNA from Neanderthals in cave sediments of four archaeological sites, where no hominin skeletal remains have ever been discovered.

They also found Denisovan DNA in sediments from Denisova Cave in Russia.

'We know that several components of sediments can bind DNA', said Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology.

'We therefore decided to investigate whether hominin DNA may survive in sediments at archaeological sites known to have been occupied by ancient hominins.'

A researcher showing the location of a sediment sample collected at the site of Caune de l'Arago, France, from a layer where a 560,000-year-old human tooth was discovered in 2015

The Galería del Osario ('tunnel of bones') at the archaeological site of El Sidrón, Spain. Neanderthal DNA was retrieved from sediment collected from a layer of rock

Overall, they collected sediment samples covering a time span from 14,000 to over 550,000 years ago.

The researchers recovered and analysed fragments of mitochondrial DNA, the genetic material from the mitochondria - the 'energy factories' of the cell.

They identified them as belonging to twelve different mammalian families that include extinct species such as the woolly mammoth, the woolly rhinoceros, the cave bear and the cave hyena.

Traces of Neanderthal and Denisovan DNA were found in ancient caves without skeletal remains throughout Europe

Profile of the Chagyrskaya Cave, Russia, from which sediment samples were collected for genetic analyses

WHO WERE THE NEANDERTHALS? An artist's impression of a Neanderthal man, our closest human relatives that lived in Europe and Asia from around 200,000 years ago to 30,000 years ago Neanderthals are our closest human relatives that lived in Europe and Asia from around 200,000 years ago to 30,000 years ago in the Pleistocene Epoch. Our primitive cousins looked similar to us, but they were shorter, more heavily built and had wide noses and prominent brow ridges. Their skeletons were discovered in the Victorian times, and it was once believed that Neanderthals were less intelligent than modern humans and more aggressive. But recent discoveries have proved that they used tools, held elaborate burial ceremonies and could even use fire. There is also genetic evidence that Neanderthals and the ancestors of modern humans frequently interbred and large swathes of our genome are still made up of Neanderthal DNA. There is some debate about whether Neanderthals were truly a distinct species or a subspecies of Homo sapiens. Professor Zilhao believes that his discovery reinforces the idea that Neanderthals were not a distinct species. Advertisement

The researchers then looked specifically for ancient hominin DNA in the samples.

'From the preliminary results, we suspected that in most of our samples, DNA from other mammals was too abundant to detect small traces of human DNA', said Viviane Slon, PhD student at the Max Planck Institute.

'We then switched strategies and started targeting specifically DNA fragments of human origin.'

Nine samples from four archaeological sites contained enough ancient hominin DNA for further analyses.

The researchers excavated seven archaeological sites in Belgium, Croatia, France, Russia and Spain. Pictured is the entrance to the archaeological site of Vindija Cave, Croatia

Eight sediment samples contained Neanderthal mitochondrial DNA from either one or multiple individuals, while one sample contained Denisovan DNA.

'By retrieving hominin DNA from sediments, we can detect the presence of hominin groups at sites and in areas where this cannot be achieved with other methods', said Svante Pääbo, director of the Evolutionary Genetics department at the Max Planck Institute for Evolutionary Anthropology.

'This shows that DNA analyses of sediments are a very useful archaeological procedure, which may become routine in the future'.