The Skills of Handaxe Making: Quantifying and Explaining Variability in 3D Sinuosity and Bifacial Asymmetry

Journal of Archaeological Method and Theory https://doi.org/10.1007/s10816-025-09705-9 (2025) 32:35 RESEARCH The Skills of Handaxe Making: Quantifying and Explaining Variability in 3D Sinuosity and Bifacial Asymmetry Antoine Muller1,2 · Gonen Sharon3 · Leore Grosman1 Accepted: 6 March 2025 © The Author(s) 2025 Abstract Observations about handaxe techno-morphology, like their symmetry, refinement, and fine edges have long been used to reconstruct the evolution of hominin cognition, skills, and technological decision making. However, these interpretations about the cognitive and technical abilities of Acheulean hominins often rely on the most ‘beautiful’ or supposedly ‘archetypical’ looking handaxes. But how often do these finely made handaxes actually occur in assemblages and how can we identify handaxes that were more skillfully made than others? Instead of seeking to estimate the skill level of individual past knappers, a trait that is oftentimes obscured in the archaeological record, we approach the question of knapping skill from the other direction. We instead ask how much skill was required to manufacture a handaxe? We explore, not the skill level of a handaxe’s maker, but how skillfully an individual handaxe was made. We put forth a suite of novel 3D methods of handaxe analysis for calculating their 3D edge sinuosity and 3D asymmetry. Using these methods, we quantify traits that are difficult to achieve during handaxe-making, providing an estimate of the requisite amount of ability, experience, attention, and effort demanded by their manufacture. Among our large sample of handaxes from the later Acheulean of the southern Levant, we find that blank size and tool-/site-use best explain the presence of more skillfully-made handaxes. Handaxes made on larger original blanks appear to afford more volume with which to enact longer and more skillfully demanding reduction sequences. Moreover, handaxes occurring at more recurrently occupied sites demanded less skill investment and appear geared towards the more expedient fulfilment of quotidian tasks. In the later Acheulean of the southern Levant there appears to be a great diversity in how skillfully handaxes were made, likely reflecting a diversity in the goals of handaxe making. Keywords Handaxes · Acheulean · Lower Paleolithic · Computational Archaeology · 3D Lithic Analysis Extended author information available on the last page of the article Vol.:(0123456789) 35 Page 2 of 33 A. Muller et al. Introduction Variability in stone tool technology and morphology is one of the most common and powerful ways of reconstructing past hominin behavior. This is especially true for Acheulean handaxes, a type of bifacial large cutting tool (LCT), whose morphology is at least partly determined by an intentional imposition of shape and symmetry (Ashton & White, 2003; García-Medrano et al., 2019; Gowlett, 1984, 1995; Hodgson, 2015; Shipton & Clarkson, 2015; Shipton & Nielsen, 2015; Shipton et al., 2019; White & Foulds, 2018; Wynn, 1995). This intentional imposition of shape allows us to reconstruct past hominin decision making, cognition, and skills. However, the spatiotemporal variability of handaxes remains hotly contested. For instance, some large trans-regional comparisons have supported the idea of temporal trends in the Acheulean (e.g. Hodgson, 2015; Shipton, 2013; Wynn & Tierson, 1990), while other studies found surprising homogeneity (e.g. Cole, 2015; McNabb & Cole, 2015; McPherron, 2000). There is even disagreement over whether chronological patterns exist in handaxe morphology. The longstanding view that handaxes moderately improve over time (Beyene et al., 2013; Gilead, 1977; Grosman et al., 2011; Hodgson, 2015; Klein, 2000; Saragusti et al., 1998; Shipton, 2018) has been questioned in recent years (Cole, 2015; Hoggard et al., 2019; McNabb & Cole, 2015; McNabb et al., 2018; Saragusti et al., 2005). After decades of research attempting to understand variability in handaxe morphology, one might expect the discipline to be approaching a consensus on the question of Acheulean variability. Instead, Isaac’s (1977) original characterization of the Acheulean as a period of “variable sameness” remains as relevant as ever and is often reiterated as simultaneous unity/conservatism and diversity/variability (e.g. Key, 2019; Lycett & Gowlett, 2008; Sharon et al., 2011; Shipton et al., 2023). It appears the study of Acheulean handaxes has reached an impasse, requiring new tools of measurement to further our understanding of Acheulean technological variability. Here, we develop a new analytical toolkit for measuring a suite of technological features of handaxes. We focus on 3D attributes that have previously been linked to the quality, difficulty, and skill of handaxe production, but have been understudied due to the difficulty of measuring them reliably. Handaxe‑Making Skill Handaxes, especially later Acheulean ones, have been shown to involve hierarchical sub-goals (Gärdenfors & Högberg, 2017; Mahaney, 2014; Muller et al., 2017; Stout, 2011; Stout et al., 2008; Wynn & Gowlett, 2018), including tasks like shaping, thinning, and sharpening (Newcomer, 1971). In the archaeological record, these features of handaxe-making are fulfilled with varying levels of skill. Stone toolmaking skill is determined by a myriad of factors. First, millennia of cognitive (Putt et al., 2017; Schoenemann, 2006; Stout et al., 2000, 2008, 2015; Uomini & Meyer, 2013) and physical (Marzke, 1997, 2013; Rolian et al., 2011; Susman, 1994) evolution establish the upper threshold on the ability level The Skills of Handaxe Making: Quantifying and Explaining… Page 3 of 33 35 achievable by a hominin knapper. This upper limit can be approached via learning knowledge and practicing know-how, which are governed mostly by our declarative and procedural memories respectively (Muller et al., 2023; Pargeter et al., 2020; Pelegrin, 1993; Sumner, 2011). How skillfully a handaxe is made also depends on the amount of time, attention, and effort imparted by the knapper. The importance of attention during knapping skill acquisition has recently been experimentally demonstrated (Bayani et al., 2021). Additionally, a highly skilled knapper may accidentally produce a less skillful-looking handaxe beneath their potential capability. Handaxemakers are also not always striving for the best looking handaxe and may intend to achieve a ‘cruder’ one for expedient or practical purposes. All these factors obscure the individual skill level of handaxe makers in the past. Thus, instead of seeking to estimate the individual skill level or ability of past knappers, we aim to quantify how skillfully an individual handaxe was made. In other words, how much skill (a combination of ability, experience, attention, effort, and intention) was required to manufacture a particular handaxe. We thus aim to measure the ‘minimum necessary competence’ (Wynn, 1985) required for each handaxe. Exper (...truncated)