Neanderthals used tar extracted from birch bark not only to glue tools together, but may have also used the dark, sticky substance as an antimicrobial to treat wounds and skin infections, research shows. A recent study published in the academic journal "PLOS One" pointed out that past archaeological evidence showed that Neanderthals would use tar made from birch bark (birch tar) to fix stone tools on wooden or bone handles, like an "ancient glue." But new experimental results show that the substance also has the potential to inhibit bacterial growth, providing new clues that Neanderthals may have mastered rudimentary "medicinal" uses.
Tjaark Siemssen, the first author of the paper and an archaeologist at the University of Cologne in Germany, said that some indigenous groups today, such as the Mi'kmaq people in eastern Canada, use birch tar extract as a medicinal substance to combat various microbial activities. This inspired the research team to wonder whether the birch tar produced by Neanderthals also had antibacterial properties.
To verify this, the team selected the bark of two birch trees that were widely distributed in Europe in the late Pleistocene - European white birch (Betula pendula) and downy birch (Betula pubescens). They used three different processes to produce tar: metal pot distillation, elevated pottery structure distillation, and condensation. The researchers then used the tar obtained to target two common pathogenic bacteria: the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli.
The results showed that no matter which preparation method was used, birch tar did not show obvious inhibitory effect on E. coli. In contrast, tar made from European white birch has the most significant antibacterial effect on Staphylococcus aureus through an elevated ceramic structure. The only tar produced by condensation from Betula tomentosa had no measurable effect on either strain.
Siemssen explained that this difference is likely related to the bacterial cell structure. The outer layer of E. coli has an additional membrane structure, which acts as a protective barrier and can block the antibacterial components of tar, thereby weakening or even negating its bactericidal effect.
In another related experiment, the research team also used the bark of paper birch (Betula papyrifera) to produce tar in an anoxic environment. This tar exhibits a "broad-spectrum" antibacterial effect, inhibiting both Gram-positive and Gram-negative bacteria. Siemssen concluded that the difference in oxygen conditions during the preparation process is likely to be a key factor affecting the antibacterial efficacy of birch tar.
The researchers also cautioned that any inference about ancient humans' use of organic materials must consider the impact of "preservation bias." Plant extracts, resins or bark themselves are highly susceptible to decomposition over time, and their residues are also significantly disturbed by changes in soil chemistry and temperature, which may affect archaeologists' judgment of their original use.
Ella Been, an anthropologist at the Ono Academic Institute in Israel, points out that although birch bark itself has some antibacterial properties and Neanderthals did use it to produce tar, this in itself does not directly prove that they intentionally used it as a medicine in a medical setting. In other words, there are still gaps in the chain of evidence from "having medicinal effects" to "consciously being used as medicine."
Some scholars tend to believe that Neanderthals had already recognized the multiple uses of this substance. Andrew Sorensen, an archaeologist at Leiden University in the Netherlands, said he has reason to believe that most archaeologists have accepted or are accepting the idea that Neanderthals used birch tar as some form of medicine. In his view, it would be unreasonable for humans to maintain such a long-term and close relationship with a certain material if they only stay in the single use of "adhesive".
Currently, this research has been officially published in "PLOS One" and has been reviewed and fact-checked by independent scientific editors. Although there is still controversy surrounding whether Neanderthals systematically used birch tar as a "medicine," new evidence at least suggests that humans may have been exploring ways to use natural materials to fight infections in ancient times.