“This is not just about rock art”, says Hipólito Collado Giraldo. “It’s about understanding how people used caves and where they left their marks”.

Ancient human DNA which has survived for thousands of years on cave walls is opening up new ways to study prehistoric human activity. 

Researchers found traces of ancient human DNA in one pigmented calcite crust sampled in Escoural Cave (Portugal). To their surprise they also found ancient human DNA in several non-pigmented parts of the cave wall in Escoural as well as in Covarón Cave (northern Spain).

The interdisciplinary study was conducted within the framework of the First Art project, which is led by researchers from Spain and Portugal in collaboration with institutions across Spain, Portugal, the UK, China and Germany.

The study shows that human DNA can be preserved on cave walls long after the populations that visited the cave have disappeared.

Hipólito Collado Giraldo, an archaeologist and rock art specialist from the Extremadura Government in Spain, who brought together the First Art team, explained:

“We know that some of the art was applied to cave walls by blowing or rubbing pigment onto the surface. Given the enormous sensitivity of current ancient DNA analysis techniques, we were eager to see if this type of contact could leave traces of DNA in the rock art, potentially allowing us to obtain genetic profiles from the makers of the art.”

The human DNA of three of these samples comes mostly from females, one mostly from males, and one remains undetermined. Further analysis of the two unpigmented cave wall samples from Covarón revealed that their DNA belonged to modern humans, with nuclear DNA placing them within the Western hunter-gatherer genetic cluster. This is consistent with the findings for other ancient Iberian populations.

“Although we cannot directly connect the traces of ancient human DNA we have found to the creation of rock art, this is the first evidence for human DNA preservation on cave walls for thousands of years”, says first author Alba Bossoms Mesa, a doctoral researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

“It is exciting to think that we may have uncovered a new way to study prehistoric human presence”.

The team also tested a prehistoric bird bone airbrush from Altamira Cave that was used to blow red ochre onto the walls. Despite expectations of finding saliva-derived DNA, no ancient human DNA was recovered, most likely due to the extremely high contamination by present-day human DNA, combined with only minimal sampling. This highlights the fragility of DNA preservation, especially in material that has been heavily handled over decades of study.

“This study fundamentally changes how we think about where ancient DNA can be found”, says senior author Matthias Meyer, a palaeogeneticist at the Max Planck Institute for Evolutionary Anthropology who co-led the work with Hipólito Collado Giraldo.

“We were surprised to see that ancient DNA can be recovered not only from pigmented samples, but also from cave walls that show no visible evidence of past human activity.

“We can now ask new questions: Who touched this wall? Was it a man or a woman? Which population did they belong to? How far did ancient humans venture into deep cave systems?”

This discovery opens up new possibilities for studying prehistoric human behaviour without disturbing archaeological deposits. By analysing DNA found on cave walls, researchers can potentially now learn more about the occupants of the caves, determining for example their biological sex and genetic ancestry.

“This is not just about rock art”, says Hipólito Collado Giraldo. “It’s about understanding how people used caves and where they left their marks”.

Despite favourable conditions for ancient DNA preservation at many sites, pigment surfaces rarely retain enough DNA to survive for thousands of years, particularly if they are not protected by mineral crusts or sealed environments.

“The preservation of human DNA on cave walls is highly variable”, says Bossoms Mesa.

“But when it does survive, it tells a powerful story. And while these first results are promising, I think our priority now should be to refine the methods and to understand under what conditions we can expect a higher success rate”.

“This is just the beginning”, adds Meyer.

“We now know that cave walls are archives of past human presence. The next step is to test more sites, art styles and techniques, especially hand stencils and figurative art in caves with good molecular preservation, as far as minimally invasive sampling allows”.

With further work, it may become possible to reveal the makers of at least some pieces of cave art – and to put faces, or at least genetic identities, to the artists who created them.

Click on this link to access, Investigating ancient human DNA preservation on cave walls and in rock art, published in Nature Communications.