Assessing and comparing technological complexity of Neanderthal and modern human adhesives

Adhesives are essential components of everyday life and have been for thousands of years. The history of adhesives begins with a stone tool covered in birch tar found at Campitello Quarry, Italy, dating to around 200,000 years ago. This find demonstrated the use of adhesives by Neanderthals and their ability to manufacture materials through transformative processes. In Southern Africa, modern humans have been producing compound adhesives by mixing plant and mineral materials since at least 70,000 years ago, tailoring adhesives to different environments and uses. In recent years, the number of identified prehistoric adhesives has grown, and adhesive technology has become a proxy for discussing technological complexity across different hominin species. However, to fully evaluate and compare the adhesive technology of other human groups across space and time, more research is needed on the selection of adhesive materials, adhesive recipes, and the context in which adhesives and their tools were used.

With this dissertation, I contribute to enlarging the sample of identified prehistoric adhesives by analysing tools with adhesive residues from Steenbokfontein Cave (South Africa, Later Stone Age), Morín Cave (Spain, Middle-Upper Palaeolithic), and the Dutch North Sea (the Netherlands, Mesolithic). I employ a multi-analytical approach encompassing optical microscopy and experiments with the integration of data from chemical analysis of residues. The results of the analysis, combined with data from available literature, provide insights into several questions that enhance the debate on the technological complexity of Neanderthals and modern humans. What materials and additives were used by Neanderthals and modern humans to manufacture adhesives? Was there a difference in adhesive recipes depending on the context of use of the hafted tools? Was there a preference for hafting specific tools? Is there a difference between Neanderthal and modern human adhesive technologies in terms of raw materials exploited, use of additives, and context of use? Does adhesive technology reflect differences in technological complexity between Neanderthals and modern humans?

All the analysed adhesives were used by Neanderthals and modern humans to fasten their tools to organic handles. Adhesive residues have been identified on stone and organic projectile points, as well as on ‘common tools’ used in domestic tasks, strongly suggesting that adhesives were integrated into the domestic economy of Neanderthals and modern humans. No relevant differences in the use of adhesives were observed depending on the tools’ raw materials or functions.

Adhesives were mostly produced from natural resources available in the surrounding environment. At Steenbokfontein Cave, South Africa, adhesives were made using the resin or tar of conifer trees, specifically Podocarpus or Widdringtonia, both of which were available near the Cave and mixed with (mineral) additives. Similarly, at Morín Cave in Spain, the resin from a tree of the genus Juniperus, largely available in the environment, was likely used. However, there is evidence that some adhesives were selected over others equally available for their material properties. For instance, birch bark tar was preferred over pine resin for hafting bone points at the Dutch North Sea, a trend seen at many other Mesolithic sites. Furthermore, increasing evidence suggests that Neanderthals used additives, primarily iron oxides, to alter the material properties of their adhesives, similar to contemporaneous modern humans in Africa. This reflects Neanderthals' and modern humans' understanding of available natural resources, their distinct material properties, and the effects of their combinations.

Adhesive technology requires good knowledge of natural resources and their material properties, control of fire, enlarged cognitive functions, and forms of cultural transmission and social learning, qualifying it as a complex technology. The examination of adhesive remains in this thesis demonstrates that Neanderthals and modern humans share considerable technological parallels, highlighting Neanderthal technological sophistication. How Neanderthals selected, transformed, and employed adhesives suggests analogous procedures and reasoning to modern humans. Consequently, these insights likely reflect that Neanderthals had comparable cognitive and technological skills to anatomically modern humans.