Biface Knapping Skill in the East African Acheulean: Progressive Trends and Random Walks

C Shipton

doi:10.1007/s10437-018-9287-1

Abstract

Over the 1.5-million-year duration of the Acheulean, there is considerable variation in biface finesse. It is not clear, however, if there is an improvement in biface knapping ability over time, or if variation between sites is largely unrelated to their age. The diversity and duration of the East African Acheulean presents an opportunity to examine this issue. Variables that reflect difficult aspects of biface knapping, and which were likely important goals for Acheulean hominins, were measured in order to assess skill. These variables—refinement (thinness), edge straightness, and symmetry—were compared across four East African Acheulean sites: Olduvai Gorge, Olorgesailie, Kariandusi, and Isinya. The influence of rock type, blank type, reduction intensity, aberrant scar terminations, and invasive flaking on these variables was assessed. Over relatively short timescales, confounding factors, including ones not possible to control for, tend to obscure any temporal signature in biface knapping skill. However, over the vast timespan of the Acheulean at Olduvai Gorge, a temporal trend was indeed apparent. Possible factors influencing this trend include the invention of new knapping techniques, the addition of adolescence as a life history stage, and evolving hominin cognition.

Highlights

For nearly 150 years, scholars of the Acheulean have speculated that there may be chronological patterns within the period (de Mortillet 1873), but the issue remains controversial (McNabb and Cole 2015)
The results show no difference in the percent of aberrant terminations, but an increase in the invasiveness of flaking and scar density, suggesting the latter two may in part underpin the increases in refinement, edge straightness, and symmetry between the beds
The results indicate a significant influence of rock type on refinement and edge straightness but not symmetry, with cryptocrystalline materials being less refined and with fewer straight edges than microcrystalline

Summary

Introduction

For nearly 150 years, scholars of the Acheulean have speculated that there may be chronological patterns within the period (de Mortillet 1873), but the issue remains controversial (McNabb and Cole 2015). East Africa is the original homeland of the Acheulean with the earliest sites documented c. In Louis Leakey’s (1951) original study of the Olduvai Gorge bifaces, he divided them into no less than 11 progressive stages (Fig. 1): BThe culture sequence – from the base of the deposits of Bed I to the top of Bed IV – reveals a slow and gradual evolution from the simple pebble tools of the Oldowan to the most beautifully made small hand-axes and cleavers of the Late Acheulean type^ In Louis Leakey’s (1951) original study of the Olduvai Gorge bifaces, he divided them into no less than 11 progressive stages (Fig. 1): BThe culture sequence – from the base of the deposits of Bed I to the top of Bed IV – reveals a slow and gradual evolution from the simple pebble tools of the Oldowan to the most beautifully made small hand-axes and cleavers of the Late Acheulean type^ (Leakey 1951, p. 158)

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