Archaeological adhesives made from Podocarpus document innovative potential in the African Middle Stone Age

Studying the earliest archaeological adhesives has implications for our understanding of human cognition. In southern Africa, the oldest adhesives were made by Homo sapiens in the Middle Stone Age. Chemical studies have shown that these adhesives were made from a local conifer of the Podocarpaceae family. However, Podocarpus does not exude resin, nor any other substance that could have been recognized as having adhesive prop-erties. Therefore, it remains unknown how these adhesives were made. This study inves-tigates how Podocarpus adhesives can be made, comparing their mechanical properties with other naturally available adhesives. We found that Podocarpus tar can only be made by dry distillation of leaves, requiring innovative potential, skill, and knowledge. This contrasts with our finding that the Middle Stone Age environment was rich in substan-ces that can be used as adhesives without such transformation. The apparent preference for Podocarpus tar may be explained by its mechanical properties. We found it to be superior to all other substances in terms of its adhesive properties. In addition, the con-densation method that allows producing it can be recognized accidentally, as the pro-cesses take place above ground and can be triggered accidentally. Our findings have implications for establishing a link between technology and cognition in the Middle Stone Age.

Automated summary

Studying earliest archaeological adhesives provides insights into human cognition. The oldest adhesives recorded in southern Africa were made by Homo sapiens during the Middle Stone Age. However, the production method of these adhesives remains unknown. This study explores the production of adhesives from a local conifer and finds that the use of Podocarpus tar requires innovation and skill. The preference for Podocarpus tar may be attributed to its superior adhesive properties, which can be accidentally discovered through above-ground processes.