Researchers recovered ancient human DNA directly from the walls of a cave in Portugal, marking the first time genetic material was extracted from a rock surface rather than skeletal remains. According to the study, this technique utilizes environmental DNA (eDNA) to identify prehistoric inhabitants in sites where no fossils or bones were preserved.
The discovery changes how archaeologists track ancient human movement. For decades, paleogenetics relied on the “gold standard” of extracting DNA from teeth or the petrous bone of the skull. This new method, reported by researchers including those affiliated with the University of Copenhagen, proves that humans leave a genetic footprint on the very surfaces they touch.
How was DNA recovered from cave walls?
The team focused on the limestone surfaces of caves in Portugal, specifically targeting areas where ancient humans likely spent significant time. Unlike previous studies that analyzed soil or sediment on the cave floor, this research targeted the walls.
According to the research findings, the process involved several critical steps:
- Surface Sampling: Scientists used specialized swabs to collect biological residue from the rock faces.
- Limestone Preservation: The calcium carbonate in limestone acts as a natural preservative, trapping skin cells, sweat, and other biological markers in the rock’s pores.
- High-Sensitivity Sequencing: Researchers used advanced genomic sequencing to separate the fragmented human DNA from the overwhelming amount of microbial and environmental DNA present in the sample.
The team identified human mitochondrial DNA, which allows researchers to trace maternal lineages and determine the haplogroups of the individuals who visited the site thousands of years ago.
Why does this discovery matter for archaeology?
This technique solves a primary problem in prehistoric research: the “missing skeleton” gap. Many caves contain clear evidence of human activity—such as cave art, tool fragments, or hearths—but no actual human remains. Because organic matter decays quickly in many environments, the absence of bones previously meant a lack of genetic data.
By extracting DNA from the walls, scientists can now identify who was present in a cave even if they didn’t die there. This allows for a more accurate map of human migration and social interaction across the Iberian Peninsula. It also provides a way to link specific individuals or groups to the creation of cave art without needing to find a burial site nearby.
How does eDNA compare to traditional genetic sampling?
The shift from skeletal analysis to environmental DNA (eDNA) represents a significant change in methodology. While traditional sampling provides a complete genetic profile of one individual, eDNA provides a broader, though more fragmented, snapshot of a population.
| Feature | Traditional Paleogenetics | Wall-Based eDNA |
|---|---|---|
| Required Material | Teeth, bone, or soft tissue | Skin cells, sweat, biological residue |
| Data Yield | High-resolution individual genome | Fragmented genetic markers/haplogroups |
| Site Requirement | Must find a burial or remain | Only requires evidence of human presence |
| Preservation Factor | Mineralization of bone | Calcium carbonate trapping in limestone |
What are the limitations of this method?
Despite the breakthrough, the method isn’t a total replacement for skeletal DNA. According to the researchers, eDNA is highly susceptible to contamination. Modern humans visiting the caves can leave behind “fresh” DNA that masks ancient signals. To prevent this, the team used strict sterile protocols and focused on DNA fragments that showed the specific chemical degradation patterns typical of ancient material.
Furthermore, the amount of DNA recovered from a wall is minuscule compared to what’s found in a femur or a molar. This means researchers can often only identify the general group or lineage of the humans, rather than reconstructing a full personal genome.
The success of this Portuguese study suggests that thousands of other caves worldwide—particularly those with limestone compositions—could be “genetic libraries” waiting to be read. Future research will likely focus on whether this method can be used to identify the species of extinct animals that left traces on cave walls, further filling the gaps in the prehistoric record.