Эрдэмтэд агуйн хананаас эртний хүний ДНХ-ийн ул мөрийг анх удаа илрүүллээ

At Escoural Cave in southern Portugal, a thin mineral crust had formed over a patch of ancient pigment. Geneticists in Leipzig, Germany, broke down a fragment of that crust. Buried inside was human DNA, carrying the chemical damage that marks genetic material as very old.

The study, published in Nature Communications, provides the first evidence that human DNA can survive on cave walls for thousands of years. Until now, researchers had recovered ancient DNA from cave bones, floor sediments and a Stone Age pendant. Never from the walls themselves.

Working with the Spanish-Portuguese First Art project, researchers at the Max Planck Institute for Evolutionary Anthropology sampled 24 rock art panels in 11 caves across Spain and Portugal.

The artworks varied considerably. Some were little more than dots and lines. Others included hand stencils and the painted ceiling of Altamira.

Five wall samples contained authentic ancient human DNA, although only one came from a painted surface. The remaining four were taken from bare rock, scraped as negative controls to establish what an unpainted wall might contain.

Escoural, where the painted sample was collected, had been sealed off for thousands of years. Quarrying finally broke into the cave in 1963.

Four of the Five DNA Finds Came From Walls Nobody Had Painted

Before collecting the control samples, the team photographed each patch of rock and used image software to enhance the colors, checking for traces of pigment too faint to see with the naked eye. None appeared. Yet two unpainted patches at Escoural and another two at Covarón Cave in Asturias, northern Spain, yielded ancient human DNA.

That complicated the question of where the genetic material had come from. Finding DNA exclusively on painted surfaces might have suggested a direct connection to the people who made the artwork. Instead, most of the positive results came from rock that showed no signs of having been painted.

To distinguish ancient DNA from modern contamination, the geneticists looked for deamination, a chemical alteration that accumulates as DNA ages. It leaves characteristic errors at the ends of genetic fragments. All five samples showed that damage.

Next came the animal DNA tests.

Cave floor dirt usually contains genetic material from numerous mammals, so a sample containing human DNA alone raises another possibility: somebody may have touched or rubbed against the rock, or deposited bodily fluids there. The painted crust at Escoural and one of its bare-rock samples contained only human DNA. The other three held genetic traces of felines, rabbits or hares, and large grazing animals such as deer. Dirt transferred by hands, or water moving through the stone, could account for that mixture.

“Who touched this wall? Was it a man or a woman?” asked senior author Matthias Meyer, a paleogeneticist at the institute.

The researchers turned to sex chromosomes for clues. In the three samples containing animal DNA, the human genetic material was predominantly female. The bare Escoural patch containing only human DNA was mostly male. As for the painted crust, there simply wasn’t enough DNA to determine sex.

A Portuguese Cave Stayed Sealed From the Copper Age Until 1963

Dating DNA recovered from a wall presents a particular problem. Unlike material buried in sediment, it has no surrounding soil layer to help establish when it was deposited.

The team instead compared the chemical damage in the wall fragments against 185 published ancient DNA samples. Their estimates put most of the wall DNA at a minimum of about 2,000 years old. One Covarón sample appeared to be at least 1,000 years old. Those are lower limits, not precise dates, and the DNA could be substantially older.

Escoural offers an unusually useful constraint. People could enter the cave until the Chalcolithic, or Copper Age, but afterward the entrance remained sealed until quarry workers broke through in 1963. The researchers therefore place the human DNA on its walls at no younger than 4,000 to 5,000 years.

There was another piece of evidence, though it came from a different source.

A bovid bone recovered from an older layer of Escoural may date back roughly 49,000 years. Its DNA showed about twice as much damage as the human fragments. On that basis, the authors consider an Upper Paleolithic origin for the wall DNA, or a later date. The Upper Paleolithic was the period associated with Europe’s celebrated painted caves.

The pigment itself cannot settle the question. Although the motif beneath the mineral crust resembles Paleolithic artwork, similar marks continued to appear during the Neolithic. The DNA and the painting need not be the same age. Thousands of years might separate them.

To investigate how widely the DNA was distributed, researchers examined 17 additional subsamples from the same panel. None contained ancient human DNA.

The entire positive result came from one tiny spot.

A Bird Bone Used to Spray Paint at Altamira Held Only Modern DNA

At Altamira in Cantabria, the researchers examined an object that seemed especially promising: a hollow bird bone, stained inside with red ochre and probably once used to blow pigment onto cave walls. If someone had used it as a spraying tool, saliva might have survived inside.

To avoid damaging the artifact, the researchers removed less than 1 milligram of pigment from its interior.

Six samples were analyzed. Each yielded between 1,050 and 17,122 human DNA fragments, but not a single sample showed the chemical damage associated with ancient DNA. According to the Max Planck Society, decades of handling had probably left so much modern contamination that any original genetic traces were buried beneath it.

The strongest genetic identification came from Covarón, though not from its artwork. DNA recovered from two bare-wall samples grouped with western hunter-gatherers, matching genetic clusters found among Europeans who lived approximately 16,700 to 5,200 years ago.

But the cave floor was packed with human DNA as well. One sediment sample contained as many as 26,946 unique human DNA fragments, and the researchers suspect that dirt, rather than direct contact with the wall, was responsible for the genetic traces recovered from the rock.

“The preservation of human DNA on cave walls is highly variable,” first author Alba Bossoms Mesa, a doctoral researcher at the institute, said in comments reported by Sci.News.

Only one of the 24 art panels produced ancient human DNA. A previous report of ancient DNA recovered from Texas rock paintings, published in 1996, has never been reproduced.

For the next round of research, the team plans to examine more hand stencils and figurative paintings, including works resembling Altamira’s painted ceiling. Such surfaces may offer another opportunity to investigate who came into contact with prehistoric cave art.

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