Kathryn L. Ranhorn

Stone tools are the most numerous and lasting record of prehistoric behavior and cognition. However, interpreting lithic archaeological evidence requires an understanding of the processes of tool c...

The ubiquity and durability of lithic artifacts inform archaeologists about important dimensions of human behavioral variability. Despite their importance, lithic artifacts can be problematic to study because lithic analysts differ widely in their theoretical approaches and the data they collect. The extent to which differences in lithic data relate to prehistoric behavioral variability or differences between archaeologists today remains incompletely known. We address this issue with the most extensive lithic replicability study yet, involving 11 analysts, 100 unmodified flakes, and 38 ratio, discrete, and nominal attributes. We use mixture models to show strong inter-analyst replicability scores on several attributes, making them well suited to comparative lithic analyses. Based on our results, we highlight 17 attributes that we consider reliable for compiling datasets collected by different individuals for comparative studies. Demonstrating this replicability is a crucial first step in tackling more general problems of data comparability in lithic analysis and lithic analyst's ability to conduct large-scale meta-analyses.

Multiple lines of genetic and archaeological evidence suggest that there were major demographic changes in the terminal Late Pleistocene epoch and early Holocene epoch of sub-Saharan Africa^1–4. Inferences about this period are challenging to make because demographic shifts in the past 5,000 years have obscured the structures of more ancient populations^3,5. Here we present genome-wide ancient DNA data for six individuals from eastern and south-central Africa spanning the past approximately 18,000 years (doubling the time depth of sub-Saharan African ancient DNA), increase the data quality for 15 previously published ancient individuals and analyse these alongside data from 13 other published ancient individuals. The ancestry of the individuals in our study area can be modelled as a geographically structured mixture of three highly divergent source populations, probably reflecting Pleistocene interactions around 80–20 thousand years ago, including deeply diverged eastern and southern African lineages, plus a previously unappreciated ubiquitous distribution of ancestry that occurs in highest proportion today in central African rainforest hunter-gatherers. Once established, this structure remained highly stable, with limited long-range gene flow. These results provide a new line of genetic evidence in support of hypotheses that have emerged from archaeological analyses but remain contested, suggesting increasing regionalization at the end of the Pleistocene epoch.