Figure 2.

Image analysis of the wear patterns on the Swartkrans fossils and on experimental bone tools. (A) Variability (Upper) and mean (Lower) in the orientation of the striations on the Swartkrans tools (S) and on experimental tools used to dig termite mounds (T), to excavate the ground in search of tubers and larvae (G), and to extract bulbs (B) [Brain's experimental tools (7)]. An unpaired t test has shown the orientation of the striations on the Swartkrans and termite digging tools to be the most similar, and significantly different from the other experimental tools. (B) Striation width as measured at 40× magnification on all of the striations visible. A nonparametric statistical test has shown the striation widths on all of the experimental tools to be significantly different from each other, but with the closest similarity recorded between the Swartkrans and termite digging tools. This figure is shown in color as Fig. 8 in the supplemental data on the PNAS web site, www.pnas.org.