Flake variation in relation to the application of force Matthew Magnani a , Zeljko Rezek a, b , Sam C. Lin a , Annie Chan c , Harold L. Dibble a, d, e, * a Department of Anthropology, University of Pennsylvania, 3260 South Street, Philadelphia, PA 19104-6398, United States b Department of Anthropology, Rutgers University,131 George Street, New Brunswick, NJ 08901-1414, United States c Department of East Asian Languages and Civilizations, University of Pennsylvania, 255 S. 36th Street, Philadelphia, PA 19104-6305, United States d Institute for Human Origins, School of Human Evolution and Social Change, Arizona State University, Box 874101, Tempe, AZ 85282-4101, United States e Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, D-04103 Leipzig, Germany article info Article history: Received 22 February 2014 Accepted 24 February 2014 Keywords: Lithic technology Flintknapping Force application Controlled experiment Experimental archaeology abstract The appearance of new force application techniques in the production of stone artifacts over the course of human evolution has been associated with the increasing technological capacity of hominin groups. Yet, the causal relationship between the knapping practice and the flake characteristics upon which these behavioral inferences rest remains largely untested under controlled settings. Here we present a recent controlled experiment examining the effect of various force application variables (hammer shape; location of force application; angle of blow; hammer displacement speed) on flake morphology. Results indicate that the independent variables interact with flake attributes in a complex way that makes simple analogies between particular attributes and specific force application techniques extremely difficult. However, trade-offs among the variables cast new light on the possible mechanisms underlying variation in force application techniques used in flintknapping. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction An important step toward the explanation of lithic assemblage variability is to understand the flaking techniques used by prehis- toric knappers. One of the major concerns is to distinguish the various kinds of force or load that were applied for flake produc- tion. Since the initial appearance of stone artifact production over two million years ago, the adoption of innovative knapping force applications (hammer type and percussion technique) have been associated with the increased cognitive complexity and techno- logical capacity of past hominins as well as evidence for cumulative cultural evolution (Ambrose, 2001; Mellars, 2006; Stout, 2011; Schick and Toth, 1993; Weaver, 2005). Novel percussion techniques also relate to innovations in sub- sistence, technological, and economic practices which likely incurred both new costs and benefits that were evolutionary sig- nificant to hominin evolution (e.g., Brown et al., 2009; Mourre et al., 2010; Hayden, 1987). For instance, the use of soft hammer per- cussion technology and the ability to exert fine control over artifact morphology and reduction trajectory has implications for artifact design and use-life, and by extension was likely inter-related with technological innovations as well as mobility and subsistence strategies (Bleed, 1986; Kelly, 1988; Kelly and Todd, 1988; Nelson, 1991). Indeed, such arguments have been made concerning North American biface technology (Morrow, 1995), blades and micro- blades of the Upper Paleolithic and later periods (Newcomer, 1975; Desrosiers, 2012), the Mousterian of Acheulian tradition in Middle Paleolithic Europe (Newcomer, 1971), the Acheulian industry of the Lower Paleolithic (Hayden, 1987; Bergman and Roberts, 1988), and, more recently, the Still Bay and Howiesons Poort industries of Southern African Middle Stone Age (Mourre et al., 2010; Villa et al., 2010; Soriano et al., 2007). In this context, it is essential to develop a better understanding of exactly how different variables related to the application of force affect particular aspects of flake morphology. This paper presents the results of a highly controlled experiment designed to address these issues. Previous research based on the current experimental design has focused on a number of independent variables that are under the control of a knapper, including the role of platform depth, exterior platform angle, angle of blow, hammer velocity, and exterior core morphology (Dibble and Rezek, 2009; Rezek et al., 2011; Lin et al., 2013). The set of experiments described in this paper focus on the application of force, including the material and shape of the hammer and the location of the strike. However, because some flake attributes are affected by the interaction of * Corresponding author. Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, D-04103 Leipzig, Germany. Tel.: þ49 215 898 7073. E-mail address: hdibble@sas.upenn.edu (H.L. Dibble). Contents lists available at ScienceDirect Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas http://dx.doi.org/10.1016/j.jas.2014.02.029 0305-4403/Ó 2014 Elsevier Ltd. All rights reserved. Journal of Archaeological Science 46 (2014) 37e49