Anyone who touches a cave wall, steadies themselves against it while passing, or sneezes near it leaves behind tiny traces of themselves. Researchers have now shown for the first time that such traces can survive for tens of thousands of years: in caves in Spain and Portugal, they found ancient human DNA directly on the walls – in some places where Stone Age people made art.
The study grew out of the international "First Art" project, led by research groups in Spain and Portugal together with the Max Planck Institute for Evolutionary Anthropology in Leipzig and partners from several countries. The samples were originally meant only to determine the age and chemical make-up of the paint pigments. A fraction of each sample was enough to also search for DNA.
Five hits among 120 samples
Of 120 samples taken, only five yielded unambiguously ancient human DNA. They come from the Escoural Cave in Portugal – including a pigmented calcite crust from so-called Panel 11 – and from the Covarón Cave in northern Spain. Surprisingly, two of these samples contained no animal DNA at all. That strongly suggests humans deposited the genetic material directly, through saliva or sweat, for instance.
It is especially notable that DNA also turned up on unpainted sections of wall that had actually been intended as negative controls. The material, at least 2,000 and probably far older, shows that cave walls themselves can preserve biological traces for very long periods.
A new tool – with open questions
For archaeogenetics, this opens up a new source. Until now the field relied mainly on bones and teeth, which are rare, or on cave sediment, in which human and animal DNA are mixed. Now the walls themselves come into view as a "genetic archive" – even where no skeletal remains survive.
For now, though, the DNA cannot be assigned to any single person, let alone a particular artist. And the approach has a downside: every sample intrudes on fragile cultural heritage. Experts therefore caution weighing carefully which questions truly justify taking a sample. The findings appeared in the journal Nature Communications.