In the version of this Article originally published, the authors mistakenly included duplicate entries in the flake datasets for the new Pech de l'Azé IV and Warwasi collections, resulting in minor errors in the statistical analysis. The authors have now repeated this analysis with the correct flake datasets. As a result, in the following two sentences, the number of flakes has been changed from 19,000 to 18,000: "Using more than 18,000 flakes from 81 assemblages spanning two million years..." and "We applied a comparative approach...on more that 18,000 complete and unmodified flakes." In addition, in Figs. 1-3 and Supplementary Fig. 1, some of the data points for the Pech de l'Azé IV and Warwasi collections have moved; the original and corrected figures are below. Supplementary Tables 1 and 2 have been updated to reflect the corrected statistics, and datasets 'Flake_data' and 'Summary_data' have been replaced with the corrected data files. Furthermore, the data availability statement has been updated with the text "Open access to these data and the R code generated for this study is provided at https://zenodo.org/record/1408081#.W6iyn84zaHs ". The authors would like to thank L. Premo at Washington State University for finding the duplicate entries in the published flake dataset.