Date Published: October 19, 2016
Publisher: Public Library of Science
Author(s): Anne Delagnes, Patrick Schmidt, Katja Douze, Sarah Wurz, Ludovic Bellot-Gurlet, Nicholas J. Conard, Klaus G. Nickel, Karen L. van Niekerk, Christopher S. Henshilwood, Nuno Bicho.
Heating stone to enhance its flaking qualities is among the multiple innovative adaptations introduced by early modern human groups in southern Africa, in particular during the Middle Stone Age Still Bay and Howiesons Poort traditions. Comparatively little is known about the role and impact of this technology on early modern human behaviors and cultural expressions, due, in part, to the lack of comprehensive studies of archaeological assemblages documenting the heat treatment of stone. We address this issue through an analysis of the procedure used for heating and a technological analysis of a lithic assemblage recovered from one Howiesons Poort assemblage at Klipdrift Shelter (southern Cape, South Africa). The resulting data show extensive silcrete heat treatment, which adds a new dimension to our understanding of fire-related behaviors during the Howiesons Poort, highlighting the important role played by a heat treatment stage in the production of silcrete blades. These results are made possible by our new analytical procedure that relies on the analysis of all silcrete artifacts. It provides direct evidence of a controlled use of fire which took place during an early stage of core exploitation, thereby impacting on all subsequent stages of the lithic chaîne opératoire, which, to date, has no known equivalent in the Middle Stone Age or Middle Paleolithic record outside of southern Africa.
The intentional heat treatment of silica rocks constitutes a major technological milestone in prehistory since the earliest developments of stone tool-making. It provides the first evidence of a transformative technology, i.e. transforming the physicochemical properties of a material for technical purposes, and it marks the emergence of fire engineering as a response to a variety of needs that largely transcend hominin basic subsistence requirements. Heat treatment of stone has long been documented in the prehistoric record as an intentional technical process used to improve the working quality of silica rocks and to enhance the sharpness and straightness the tool edges [1–3]. This technological process was reinvented many times in the Upper Pleistocene and Early Holocene in various geographical contexts. Its first occurrence was recently pushed back to more than 70 ka (thousand years) ago in the South African Middle Stone Age (MSA) sequences from Pinnacle Point  and Blombos Cave . The heat-treated raw material was silcrete, a continental silica rock  of rather good quality that acquires even better knapping quality when heated. The development of a fire-based transformative technology adds a new component to the extensive list of inventive solutions introduced in the MSA, in particular by Still Bay and Howiesons Poort groups [7, 8]. However, southern African MSA heat treatment of stone still remains poorly documented and much of the debate has focused on the heating methods and on the induced physical transformations of the silcrete [4, 9–12]. Conversely, very little is known about the role and impact of this new technology on early modern human behaviors and cultural expressions. In other words, the role of heat treatment in the MSA technological repertoire still has to be determined. The question remains whether this early emergence of stone heat treatment responds to a new set of specialized technological skills or whether it is part of the domestic sphere of activities. In this paper we address this issue through the analysis of the heating technique and technological strategy developed in a recently discovered and excavated MSA site: Klipdrift Shelter (KDS) (southern Cape region, South Africa) , a site that indicates the extensive use of fire for the heat treatment of silcrete within one discrete occupation layer of this site.
Our data add a new dimension to the understanding of fire-related behaviors during the Howiesons Poort by demonstrating the major role played by heat treatment in the production of silcrete blades in layer PBD at KDS. It provides the first direct evidence of the intentional and extensive use of fire applied to a whole lithic chaîne opératoire, based on an analytical approach that has allowed the analysis of all heated lithics from layer PBD. The heat treatment of silcrete in this layer has impacted all stages of core reduction and all subsequent operations of tool manufacturing. For the artisans, the benefits of heat treatment performed in an early stage of the chaîne opératoire were multiple. The Howiesons Poort groups considerably developed and optimized a technology that had possibly emerged from the early MSA , and continued in the Still Bay (c. 77–72 ka) in relation to the Still Bay point manufacturing process.