Neanderthals and other early humans were able to produce a tarry glue from birch bark; this was long considered proof of a high level of cognitive and cultural development. Neanderthals used birch tar as an adhesive to attach stone scrapers or points to wooden handles to make tools. Researchers long believed that birch tar could only be produced in a complex process in which the bark of the tree had to be heated in the absence of air. However, an international research team led by Dr. Patrick Schmidt and Dr. Claudio Tennie from the Institute of Early Prehistory and Quaternary Ecology at the University of Tubingen has shown that there is a very simple way to make this useful glue.
Experimental set-up for the production of birch tar. Researchers burned birch bark near flat surfaces that Neanderthals would have used [Credit: University of Tubingen, Matthias Blessing] |
The researchers experimented instead with ordinary materials which were around in the Stone Age. They collected cut fresh birch bark or collected dead bark in the forest and burned it near flat river stones. After three hours, the process yielded a usable amount of a black sticky material.
After burning the birch bark on stone, the stone is covered with tar [Credit: University of Tubingen, Claudio Tennie] |
In order to test its adhesive strength, the researchers used the pitch to stick a stone scraper to a wooden handle; they were able to use it to scrape the tough outer membrane from the thigh bone of a calf.
A robot that used force-control technology developed by Ludovic Righetti and Johannes Pfleging tested the adhesive by scraping a block of wood 170 times [Credit: NYU Tandon, Johannes Pfleging] |
All that was needed was a fire and birch bark over a smooth surface of stones or bones. “It may be that this knowledge was not passed on directly, but that adhesive effect of the birch residues was re-discovered several times,” Claudio Tennie speculates.
The study has been published in the latest edition of Proceedings of the National Academy of Sciences.
Source: Eberhard Karls Universitat Tubingen [August 20, 2019]
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