Neanderthal-style birch tar holds back a common wound bacterium in lab tests

To make the tar, the team used tree species that grew during the Neanderthal era and production methods reconstructed from archaeological evidence, instead of modern industrial processes ^[5]. That choice keeps the question narrow. A positive result for commercial birch tar would have said little about the material Neanderthals could actually have made.

Running both production routes adds a useful check. The researchers set out to learn whether tar from different techniques would have similar antibacterial properties ^[12]. Tar from the sealed pit and tar condensed on stone both inhibited Staphylococcus aureus ^[13], a bacterium commonly associated with wound infections ^[3]. So the activity does not depend on the more demanding of the two processes.

How large the effect was is harder to judge from the University of Cologne's release ^[11]. It does not say how many samples were tested, how strongly growth was held back, or whether the tar was compared with an untreated control or a standard antibiotic. Its summary says "every sample" could inhibit bacteria responsible for dangerous wound infections, while its main text says every type of tar the team produced inhibited S. aureus ^{[14] [1]}. Those two wordings can describe different counts. The same summary says birch tar "may have doubled as a surprisingly effective natural medicine" ^[14].

The case for medicine leans on evidence from outside the experiment. Tjaark Siemssen of the University of Cologne and Oxford, who leads the study ^[9], said, "Alongside these findings, there is also growing evidence of medicinal practices and the use of plants among Neanderthals, which is why we were interested in the use of birch tar in this context" ^[10].

The thing this doesn't tell you is whether any Neanderthal ever put tar on a wound. Antibacterial activity is a property of the material. Medical use is a behaviour, and the record so far consists of tar traces found at Neanderthal sites across Europe, often still attached to stone tools and long read as hafting glue ^[6].

We think the study supports its capability claim well: tar made two Neanderthal ways held back a common wound pathogen ^{[13] [3]}. The medical reading is now a plausible hypothesis, and testing it will take residue evidence from those sites.