Technological adaptations of early humans at the Lower Pleistocene Nihewan Basin, North China: the case of the bipolar technique

The Nihewan Basin in North China has proved to be a key area for the study of human evolution outside of Africa due to its continuous record of hominin occupation since the Early Pleistocene. Lower Paleolithic lithic assemblages at Nihewan are attributed to the East Asian Mode 1 techno-complex, which is often defined by the widespread use of freehand knapping techniques. However, our ongoing investigation of several early Pleistocene archaeological sites at Nihewan has revealed a higher prevalence of bipolar stone artifacts than previously considered, which may have been underestimated in the past due to the disparity of analytical techniques applied to Early Stone Age assemblages and the poor quality of the Nihewan Basin raw materials. This has constrained the identification of bipolar attributes and their differentiation from freehand knapping products. This study aims to investigate technological and economical differences between the two techniques based on experimental results of chert from the Nihewan Basin, creating a referential framework for the study of bipolar artifacts that we apply, to the Early Pleistocene assemblages of Xiaochangliang and Cenjiawan. Our results not only highlight morphological and technological differences between bipolar and freehand products but also demonstrate that both techniques share significant similarities in terms of dimensions and productivity. Overall, our results help to contextualize the technological flexibility of East Asian Mode 1 assemblages in the Nihewan Basin, where early hominins employed alternative flaking techniques, often in the same assemblage, to overcome constrains imposed by the poor quality of most of the raw materials available.