Supplementary material from "Modern stone tool users, from Northern Kenya, emphasize mass and edge length in the selection of cutting tools."

The production and use of informal flake cutting tools played an essential role in foraging across human history. While much is known about the production of these tools, the attributes that facilitate their selection and use remain underexplored. This is because there remain few opportunities for the use of such tools in a traditional setting. The Daasanach of East Turkana, Kenya, maintain a tradition of stone tool production and use, affording the opportunity to investigate tool selection in a natural setting. Through interview and video documentation, we observed 8 expert toolmakers complete butchery tasks, allowing us to link traditional technological knowledge that governs cutting tool selection with measurable lithic attributes. Our findings reveal that factors such as edge angle, mass, and grip significantly influence tool selection and cutting efficiency. These insights provide new perspectives on the functional relevance of informal cutting tools that have previously been understood only through experimentation. The outcomes of this study provide a venue for interpreting lithic variability in ancient contexts from the perspectives of traditional expert tool users. This research underscores the utility of detailed ethnographic studies to complement archaeological findings, enhancing our understanding of early human technological evolution.