Lower Paleolithic bipolar reduction and hominin selection of quartz at Olduvai Gorge, Tanzania: What's the connection?

Abstract Numerous researchers have noted that at Lower Paleolithic sites in East Africa hominins largely exploited quartz toolstone with the bipolar reduction technique. The choice to pursue bipolar knapping on quartz is often attributed to raw material constraints. Thus, at some East African Lower Paleolithic sites the abundance of bipolar knapping may have simply constituted a response to the local absence of lithic resources other than small quartz pebbles. However, at Olduvai Gorge, Tanzania, where a variety of other stone raw materials were available, the hominin use of bipolar reduction is still predominately tied to quartz. While quartz raw material constraints may explain the use of bipolar reduction on quartz at Olduvai, what they do not explain is the virtual absence of bipolar reduction on non-quartz toolstones. Thus, we ask here two separate, but related questions: (1) why did hominins use bipolar on quartz?; and (2) why did hominins avoid bipolar on non-quartz? To begin to understand this tight technology-toolstone connection, we formulated two simple hypotheses, which we tested via experimental stone tool replication: (1) Quartz bipolar reduction produces flakes that possess “superior” functional characteristics to those produced via non-quartz bipolar reduction; (2) Bipolar reduction is more expedient on quartz than on non-quartz toolstones. Our experimental tests indicated that while quartz and basalt bipolar reduction yield flakes with similar attributes, bipolar reduction on quartz is significantly more expedient than it is on basalt. As such, the close technology–toolstone association between quartz and bipolar can be explained by constraints and advantages of both quartz and basalt alike. Bipolar reduction is already widely acknowledged to be an expedient technology requiring little to no skill. By applying bipolar reduction exclusively to quartz, hominins at Olduvai appear to have only enhanced this reduction strategy's features. Overall, our experimental results are consistent with the widely-held notion that Lower Paleolithic hominins recognized the differences in the physical properties of different types of raw material, and that it is the interplay between raw material and reduction strategy that governed hominin association between bipolar reduction and quartz at Olduvai.