Abstract
Experimental studies of hafting adhesives and modifications to compound tool components can demonstrate the extent to which human ancestors understood and exploited material properties only formally defined by science within the last century. Discoveries of Stone Age hafting adhesives at archaeological sites in Europe, the Middle East, and Africa have spurred experiments that sought to replicate or create models of such adhesives. Most of these studies, however, have been actualistic in design, focusing on replicating ancient applications of adhesive technology. In contrast, this study tested several glues based on Acacia resin within a materials science framework to better understand the effect of each adhesive ingredient on compound tool durability. Using an overlap joint as a model for a compound tool, adhesives formulated with loading agents from a range of particle sizes and mineral compositions were tested for toughness on smooth and rough substrates. Our results indicated that overlap joint toughness is significantly increased by using a roughened joint surface. Contrary to some previous studies, there was no evidence that particle size diversity in a loading agent improved adhesive effectiveness. Generally, glues containing quartz or ochre loading agents in the silt and clay-sized particle class yielded the toughest overlap joints, with the effect of particle size found to be more significant for rough rather than smooth substrate joints. Additionally, no particular ochre mineral or mineral mixture was found to be a clearly superior loading agent. These two points taken together suggest that Paleolithic use of ochre-loaded adhesives and the criteria used to select ochres for this purpose may have been mediated by visual and symbolic considerations rather than purely functional concerns.
Highlights
Evidence for hafted and composite tools in the Middle Stone Age (MSA) and Middle Palaeolithic (MP) archaeological record is frequently discussed as a potential signature of behavioral complexity or modern behavior, even by researchers with diverse points of view on the concept of ‘‘modernity’’ [1,2,3,4]
The Tukey-Kramer Honest Significant Difference (HSD) test is a multiple comparison procedure used to simultaneously compare all possible pairs of means from a data set with multiple groups; in effect it is a t-test that corrects for the increase in Type I error caused by performing multiple t-tests
Far the Phase 1 and Phase 2 results have been examined separately; lastly a combined analysis of both phases was run. This is perhaps better for interpreting the decision-making process of an individual constructing a compound tool since the loading agents used here were intended as proxies for widely available natural materials: quartz sand of various particle sizes and ochres of diverse mineralogy
Summary
Evidence for hafted and composite tools in the Middle Stone Age (MSA) and Middle Palaeolithic (MP) archaeological record is frequently discussed as a potential signature of behavioral complexity or modern behavior, even by researchers with diverse points of view on the concept of ‘‘modernity’’ [1,2,3,4]. The act of hafting, that is the construction of a composite tool from an insert which forms the working edge, a joint, and a handle, has been described as a complex technology. The individual components of such tools are of limited utility on their own, evidencing the cognitive complexity underlying their construction. Barham [5], citing cognitive neuroscientist Scott Frey [6], characterizes hafted tools as complex because they qualitatively alter the actions of our limbs and our perception of a tool as an extension of our arms. Ambrose [1] in particular has interpreted hafting through the lens of constructive memory, a proposed subset of working memory that he asserts co-evolved with planning and task coordination abilities Other authors have emphasized the construction of composite tools through additive processes, as opposed to the reductive activity of knapping, and have used such tools to infer the emergence of specific cognitive capabilities including abstract thought, recursion, and multitasking or cognitive fluidity [1,3].
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