Biomass tar, Podocarpus leaves and the diversity of southern African Stone Age adhesives – new data from Elands Bay Cave

Adhesives are among the most informative archaeological artefacts for understanding the behaviour of Stone Age forages. In the southern African Middle and Later Stone Age, the botanical origin of most adhesives was identified as conifers of the genus Podocarpus. One of these identifications of Podocarpus adhesives comes from Elands Bay Cave. However, it has recently been shown that similar adhesives can be, and were, produced from many plants available on the southern African subcontinent, opening important questions about the role of Podocarpus within these plants. Here, we re-investigate the Elands Bay Cave adhesive record and compare it to natural and experimentally produced adhesive substances, using infrared spectroscopy and mass spectrometry. We find that Elands Bay Cave artefacts were made from the leaves of several plant species including Podocarpus spp using the condensation method. We also identify the oldest archaeological record for an adhesive based on water-soluble plant gum. These findings have important implications for our understanding of Stone Age adhesives as proxies for human evolution and the dynamics of invention.