From side to side: Symmetry in handaxes in the British Lower and Middle Palaeolithic

Highlights

• Symmetry in handaxes may be influenced by the extent/location of cutting edge.

• Symmetry is consistently present in handaxe assemblages in the later Acheulean.

• However the degree of symmetry varies from assemblage to assemblage.

• The reasons for this variability remain unclear.

• There are insights into cognitive development within these results.

Abstract

The Acheulean is defined by its iconic tool type, the handaxe, and a suite of other large cutting tools (LCTs). These tools retain information on technical and procedural practices concerned with the manufacture of these butchery tools and carcass processing knives. The Acheulean straddles the period in which more ancient hominin species (H. erectus and H. heidelbergensis) give way to archaic H. sapiens (sensu lato) amongst whom the ancestor of modern humans may be found. The roots of modern behaviour may be present in these handaxe making hominin species, and the handaxes themselves, through proxy data such as bilateral symmetry, may chart hominin cognitive evolution as researchers such as T. Wynn and F. Coolidge (2016), amongst others, have argued. But the search for the earliest consistent application of symmetry, and its persistence thereafter has been hampered by the lack of large datasets, spanning the temporal extent of the Acheulean, and analysed through a single consistent methodology.

Our paper has two aims. The first, and in the absence of a large comparative data set of earlier Acheulean handaxes, is to assess the degree to which symmetry is consistently applied to the making of handaxes in the later Acheulean (≤ 0.5 Mya), a time when bilateral planform symmetry should already be an integral component in handaxe making. The dataset we select is the British Acheulean from MIS 13 – MIS 3/4. To the best of our knowledge this is the first time handaxe symmetry has been assessed on a large body of British Acheulean handaxes. Our second aim is to present a relatively simple and low tech methodology for the analysis of handaxes and their symmetry that is widely available and does not require expensive equipment or specialist software/technical knowledge. It works from orthogonal handaxe photographs which many researchers will already have. From such data it may be possible to begin to construct the larger datasets necessary to answer symmetry related questions regarding cognitive evolution. This offers us the opportunity to raise a number of key methodological questions which we believe ought to be debated by researchers before the generation of appropriate datasets begins.

Introduction

The Acheulean is the name given to a stone tool assemblage type recognised by the presence of its iconic tool – the handaxe, one of a suite of large cutting tools (LCTs) which also includes cleavers, picks, trihedrals and unifaces (Clark, 1994, Wymer, 1968). However, the Acheulean is also defined by technological practices associated with the manufacture of LCTs, such as the making of large flake blanks often from cores with a prepared surface (Sharon, 2007), and marginal thinning, commonly with a soft hammer or billet to impose deliberate shape on the LCT (Newcomer, 1971). Good introductions to handaxes are present in a number of references (de la Torre, 2016, Emery, 2010, Goren-Inbar and Sharon, 2006, Machin, 2009, Newcomer, 1971).

The oldest Acheulean yet discovered is at Konso in Ethiopia and Kokiselei 4, West Turkana, Kenya, both of which date to 1.75 Mya (Beyene et al., 2013, Lepre, 2011). From this point onwards, handaxes become the defining artefact of the Acheulean found across the Old World from Spain to China, and from South Africa to the English Midlands. The appearance of Homo ergaster in Africa, (Lepre and Kent, 2015) at about c. 1.9 Mya (KNM-ER 2598), and its more widespread presence after c. 1.6 Mya (KNM-ER 3733; Lepre and Kent, 2015) is suggestive of a link between this new hominin and the Acheulean ‘package’ - a new tool technology to meet the needs of new behavioural adaptations. The emergence of the Acheulean may help fill the fossil gap which currently exists for the erectines between KNM-ER 2598 and 3733 (Lepre and Kent, 2015).

Traditionally, handaxes are thought to have been made in Africa by two hominin species, H. ergaster/erectus and H. heidelbergensis (= H. rhodesiensis). In Europe handaxes were made by H. heidelbergensis (Manzi, 2016, Profico et al., 2016), although the chronology of the Heidelbergs in Europe may be subject to change given recent palaeogenetic advances (Meyer et al., 2016, Meyer et al., 2014). H. neanderthalensis is also a European handaxe maker (Ruebens, 2014, Ruebens et al., 2013), but new cultural labels are applied to the Late Pleistocene Neanderthal handaxes (e.g. Mousterian of Acheulean Tradition rather than Acheulean). Anatomically modern humans may continue to make handaxes once they emerge in Africa (Clark et al., 2003), a pattern possibly seen elsewhere (Shipton et al., 2013).

This hominin evolutionary trajectory is often portrayed as a single upward cline, a slope of gradual development as for example in the iconic Social Brain graph (Dunbar et al., 2014, Gowlett et al., 2012), although a more punctuated interpretation is possible (McNabb and Cole, 2015, Shultz et al., 2012).

In these interpretations the Acheulean (here broadly defined as handaxe making by hominins other than Neanderthals and anatomically modern humans) is often seen as an evolving material culture accompaniment to biological development. Early handaxes are described as crude and poorly shaped, lacking much - if any - sense of symmetry in their planform (Hodgson, 2010, Hodgson, 2015, Wynn, 2002). Later Acheulean handaxes, appearing toward the end of the Acheulean, supposedly show much higher degrees of symmetry accompanying regularity in planform outline (Clark, 1994, Clark, 2001, Wynn and Coolidge, 2016). Potentially, these later Acheulean handaxes may reflect the increasing capacity of material culture to carry symbolic meaning (Lycett, 2008).

The Acheulean then, in its broadest definition, is a key period in human evolution as it sees the emergence of some of the cognitive faculties that will later contribute to the ‘modernity’ of Homo sapiens. Wynn has explicitly linked what he sees as stages in handaxe development to evolving hominin cognition and spatial awareness, connected with more sophisticated hunting (Wynn, 2002), and evolving hominin neural architecture (Wynn and Coolidge, 2016). He argues that a threshold was crossed at c. 1.8 Mya with the deliberate imposition of shape on raw material. Whereas the preceding Oldowan tools acquired form fortuitously through the production of flakes, the earliest Acheulean handaxes had clear form deliberately imposed upon them. This imposition of shape in its earlier stages was an ‘attention to shape’ (Wynn, 2004), through an awareness of the balance of surface area either side of a mid-line. By 1.0 Mya attendance to shape was becoming more prevalent. A second major threshold had been crossed by ≥ 0.5 Mya when that awareness of symmetrical balance reflects congruence, an exact mirroring of opposing edges. Wynn posits that from this point on bilateral planform symmetry is commonly accompanied by cross-sectional symmetry in long profile and across the width too (looking from the tip down). With a three dimensional concept of symmetry now present, knappers were even able to produce deliberately asymmetric LCTs on occasion – broken symmetry.

Persistent bilateral symmetry in planform down the long axis of a handaxe is then one of the hall-marks of cognitive evolution.

In light of the above, there are a number of research questions that could be asked of the Acheulean which would focus on temporal changes in its character over the 1.5 + Mya lifespan of this phenomenon. However, two of us (JM and JC) have elsewhere noted the difficulties in finding appropriate data in which to study long-term changes in handaxe symmetry over time (McNabb and Cole, 2015). Ideally, long sequences with large assemblages from single sites are necessary, and lots of them; but they are scarce. Currently some of the best are in the Awash Valley, Ethiopia, Melka Kunture, Ethiopia, and Oldupai Gorge, Tanzania (Beyene et al., 2013, Clark et al., 2003, de la Torre and Mora, 2005, de la Torre and Mora, 2014, Gallotti and Mussi, 2017, Leakey and Roe, 1994, Schick and Clark, 2003).