TAGS: Sustainability / Natural Adhesives
A research team from the Universities of Tübingen and Cape Town discovers how tar with good adhesive properties can be produced using stone-age methods – indications of the first technical innovations.
Early Homo sapiens in South Africa used glue from local stone yew trees in the Mesolithic to attach stone tools to wooden spears, for example. This adhesive has excellent adhesive properties and can only be produced using a complex process.
Turning Point in Human Cultural Evolution
The fact that early modern humans around 100,000 years ago did not resort to more readily available adhesives is a testament to their innovative skills and great skill. This may have been a turning point in human cultural evolution.
Dr. Patrick Schmidt and Tabea J. Koch from the University of Tübingen in a joint study with Professor Edmund February from the University of Cape Town, South Africa discovered adhesive made from stone yew trees. The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).
Holly yews, conifers of the genus Podocarpus, are tropical evergreen shrubs and trees. "
Adhesives have been discovered at several Mesolithic sites in South Africa, mostly as remains on stone tools such as scrapers or fittings, which were glued to handles or spears in this way," said Patrick Schmidt. Chemical analyzes would have shown that such glue was often obtained from stone yew. "
That's amazing because yew trees don't excrete any appreciable amounts of tree resin or any other sticky substance."
Superior Properties
The team investigated how the glue could be made using only Stone Age materials and tools. "
The leaves of the stone yew contain small amounts of resin that have to be distilled out," explains Schmidt.
The team discovered two production methods: "
It's really easy to burn the leaves right next to flat stones. Condensation creates tar that can be scraped off the stones. People could have discovered this process by accident.” The second option, in which the leaves have to be heated in a kind of underground distillation apparatus for several hours so that the tar drips into a collecting container, is more complex. It is not known which method was used.
In any case, it is astonishing that people at that time did not use any other plants than yew trees as glue suppliers. “
People could have just collected tree sap. In several species that occurred in their area, it flows noticeably from the trunk. For example, some plants release sticky latex when the leaves break off,” explains Tabea Koch.
The team found the explanation using standard laboratory tests used in the adhesives industry. "
Our tar distilled from stone yew trees had particularly good mechanical properties and proved to be stronger than all other naturally occurring adhesive substances from the Stone Age in South Africa, it could hold significantly greater loads,” said Smith.
The fact that modern people in southern Africa deliberately produced particularly good adhesives around 100,000 years ago was a turning point in the development of our direct ancestors, says Schmidt.
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People didn't choose materials based on their properties but changed the existing material." Such new engineering technology required higher cognitive abilities and innovative thinking.
Source: Universities of Tübingen