Archaeological Podocarpus tar supports the cognitive complexity of Neanderthals

Team Joris Di

Identifying Palaeolithic birch tar production techniques: challenges from an experimental biomolecular approach

The intentional production of birch bark tar by European Neanderthals as early as 190,000 years ago plays an important role in discussions about the technological and behavioural complexity of Pleistocene hominins. However, research is hampered because it is currently unknown how Neanderthals were producing birch tar. There are several different techniques that could have been employed, but these differ in their apparent production complexity, time and resource efficiency. Identifying production processes in the archaeological record is therefore paramount for furthering research on the technical behavioural repertoire. Organic biomarkers, identified with Gas Chromatograph–Mass Spectrometry (GC–MS), have been used to identify possible production processes during the Neolithic. Here we test whether these biomarkers can also distinguish Palaeolithic (aceramic) tar production methods. We produced tar using five different methods and analysed their biomolecular composition with GC–MS. Our results show that the biomarkers used to distinguish Neolithic tar production strategies using ceramic technology cannot be reliably used to identify tar production processes using aceramic Palaeolithic techniques. More experimentation is required to produce a larger reference library of different tars for future comparisons. To achieve this, complete GC–MS datasets must also be made publicly available, as we have done with our data.Team Joris DikChemE/O&O groe

Measuring ancient technological complexity and its cognitive implications using Petri nets

We implement a method from computer sciences to address a challenge in Paleolithic archaeology: how to infer cognition differences from material culture. Archaeological material culture is linked to cognition, and more complex ancient technologies are assumed to have required complex cognition. We present an application of Petri net analysis to compare Neanderthal tar production technologies and tie the results to cognitive requirements. We applied three complexity metrics, each relying on their own unique definitions of complexity, to the modeled production processes. Based on the results, we propose that Neanderthal technical cognition may have been analogous to that of contemporary modern humans. This method also enables us to distinguish the high-order cognitive functions combining traits like planning, inhibitory control, and learning that were likely required by different ancient technological processes. The Petri net approach can contribute to our understanding of technology and cognitive evolution as it can be used on different materials and technologies, across time and species.Team Joris Di

Scaling Palaeolithic tar production processes exponentially increases behavioural complexity

Technological processes, reconstructed from the archaeological record, are used to study the evolution of behaviour and cognition of Neanderthals and early modern humans. In comparisons, technologies that are more complex infer more complex behaviour and cognition. The manufacture of birch bark tar adhesives is regarded as particularly telling and often features in debates about Neanderthal cognition. One method of tar production, the ‘condensation technique’, demonstrates a pathway for Neanderthals to have discovered birch bark tar. However, to improve on the relatively low yield, and to turn tar into a perennial innovation, this method likely needed to be scaled up. Yet, it is currently unknown how scaling Palaeolithic technological processes influences their complexity. We used Petri net models and the Extended Cyclomatic Metric to measure system complexity of birch tar production with a single and three concurrent condensation assemblies. Our results show that changing the number of concurrent tar production assemblies substantially increases the measured complexity. This has potential implications on the behavioural and cognitive capacities required by Neanderthals, such as an increase in cooperation or inhibition control.Team Joris Di

Lap Shear and Impact Testing of Ochre and Beeswax in Experimental Middle Stone Age Compound Adhesives

The production of compound adhesives using disparate ingredients is seen as some of the best evidence of advanced cognition outside of the use of symbolism. Previous field and laboratory testing of adhesives has shown the complexities involved in creating an effective Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different adhesive recipes are, how much specific ingredients influence their performance, and how difficult it may have been for those ingredients to be combined to maximum effect. We conducted a series of laboratory-based lap shear and impact tests, following modern adhesion testing standards, to determine the efficacy of compound adhesives, with particular regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing additives of beeswax and ochre in varying ratios. During both lap shear and impact tests compound rosin adhesives performed better than single component rosin adhesives, and pure acacia gum was the strongest. The large difference in performance between each base adhesive and the significant changes in performance that occur due to relatively small changes in ingredient ratios lend further support to the notion that high levels of skill and knowledge were required to consistently produce the most effective adhesives.Adhesion Institut

Reply to: Problems with two recent Petri net analyses of Neanderthal adhesive technology

Team Joris Di

Laboratory strength testing of pine wood and birch bark adhesives: a first study of the material properties of pitch

Adhesives are an important yet often overlooked aspect of human tool use. Previous experiments have shown that compound resin/gum adhesive production by anatomically modern humans was a cognitively demanding task that required advanced use of fire, forward planning, and abstraction among other traits. Yet the oldest known adhesives were produced by Neandertals, not anatomically modern humans. These tar or pitch adhesives are an entirely different material, produced from a distinct, albeit similarly complex process. However, the material properties of these adhesives and the influence of the production process on performance is still unclear. To this end we conducted a series of laboratory based lap shear and impact tests following modern adhesive testing standards and at three different temperatures to measure the strength of pine and birch pitch adhesives. We tested eight different recipes that contain charcoal as an additive (mimicking contamination) or were reduced by boiling for different lengths of time. Lap shear tests were conducted on wood and flint adherends to determine shear strength on different materials, and we conducted high load-rate tests to understand how the same material behaves under impact forces. Our results indicate that both pine and birch pitch adhesives behave similarly at room temperature. Pine pitch is highly sensitive to the addition of charcoal and further heating. Up to a certain extent charcoal additives increases performance, as does extra seething. However, too much charcoal and seething will reduce performance. Similarly, pine pitch is sensitive to ambient temperature changes and it is strongest at 0°C and weakest at 38°C. Adhesive failures occur in a similar manner on flint and wood suggesting the weakest part of a flint-adhesive-wood composite tool may have been the cohesive strength of the adhesive. Finally, pine pitch adhesives may be better suited to resisting high-load rate impacts than shear forces. Our experiments show that pitch production and post-production manipulation are sensitive processes, and to obtain a workable and strong adhesive one requires a deep understanding of the material properties. Our results validate previous archaeological adhesive studies that suggest that the manufacture and use of adhesives was an advanced technological process.Adhesion Institut

Lap Shear and Impact Testing of Ochre and Beeswax in Experimental Middle Stone Age Compound Adhesives

The production of compound adhesives using disparate ingredients is seen as some of the best evidence of advanced cognition outside of the use of symbolism. Previous field and laboratory testing of adhesives has shown the complexities involved in creating an effective Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different adhesive recipes are, how much specific ingredients influence their performance, and how difficult it may have been for those ingredients to be combined to maximum effect. We conducted a series of laboratory-based lap shear and impact tests, following modern adhesion testing standards, to determine the efficacy of compound adhesives, with particular regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing additives of beeswax and ochre in varying ratios. During both lap shear and impact tests compound rosin adhesives performed better than single component rosin adhesives, and pure acacia gum was the strongest. The large difference in performance between each base adhesive and the significant changes in performance that occur due to relatively small changes in ingredient ratios lend further support to the notion that high levels of skill and knowledge were required to consistently produce the most effective adhesives.Adhesion Institut

Archaeological Adhesives

An adhesive is any substance that bonds different materials together. This broad definition includes materials used in everything from hafted stone tools to monumental architecture. In addition, the combination of bonding, plasticity, and insolubility meant that some adhesives were exploited for waterproofing and sealing of materials, as self-adhering inlays and putties, and as paints, varnishes, and inks. Adhesives have a history of at least 200,000 years. Throughout (pre)history and around the world, people used materials, including bitumen/ asphalt, carbohydrate polymers such as starches and gums, natural rubbers, mortars, proteins (from casein, soy, blood, and animal connective tissue), insect and plant resins, and tars made from various barks and woods. Adhesives thus are very diverse and have widely varying properties: they can be tacky, pliable, elastic, brittle, water-resistant, fluid, viscous, clear, dark, and much more. They are a plastic avant la lettre. These properties can and were tweaked by mixing ingredients or by further processing. In the study of archaeological adhesives, their characterization is essential and this is best done with chemical and spectroscopic methods. When larger coherent samples as opposed to single finds are analyzed, adhesive studies can provide data on past technologies, socioeconomic organizations, and environments and raw material availability. Through sourcing and mapping of ingredients and adhesive end products, travel and transfer of materials and knowledge can be illuminated. Additionally, experimental reproductions provide data on technological aspects that otherwise are lost in the archaeological record. An archaeology of adhesives can reveal the transport networks, subsistence, mobility strategies, division of labor, and technological know-how that held societies together.Accepted Author ManuscriptTeam Joris Di

Complicating the debate: Evaluating the potential of gas-chromatography-mass spectrometry for differentiating prehistoric aceramic tar production techniques

Birch bark tar was used extensively throughout human history. While later ceramic-based production technologies are known, prehistoric aceramic techniques leave little to no archaeological evidence. Experimental tar production attempts to fill this gap and suggest potential techniques. However, their archaeological relevance is unclear. Through an in-depth biomolecular analysis using Gas Chromatography-Mass Spectrometry, this study attempts to differentiate tars produced using four experimental aceramic techniques: condensation, ash mound, pit roll, and raised structure. In doing so we publish the largest collection of GC-MS results of aceramic birch tars. The results show that pentacyclic triterpenoids, characteristic of birch bark, vary between the production techniques in relation to heating exposure and perhaps the tar collection method. This allows for a tentative identification of tars produced through the condensation and ash mound techniques, which were formed consistently using short periods of heating and collected systematically by scraping. In contrast, tars produced using the pit roll and raised structure techniques do not have consistent molecular signatures. Despite the partial success of Gas Chromatography-Mass Spectrometry, the archaeological relevance is questioned because this technique is only applicable to samples from optimum lipid preservation conditions when a high number of pentacyclic triterpenoids are preserved. Therefore, using Gas Chromatography-Mass Spectrometry to determine the transformation methods of organics, like birch bark, may not be an appropriate standalone technique to fairly discuss the technological capabilities of past populations.Team Joris DikChemE/O&O groe