Right-Handed Neandertals Figure 6. SEMs of striations on left I2 and right C. Left: Lower medial portion of the labial aspect of the left second incisor of Regourdou 1 (left) showing (a) some V-shaped, relatively thick sub-horizontal scratches associated with a few thinner secondary striae occurring within the major striae. The medial margin of the tooth is on the left. Right: Central portion of the labial aspect of the right canine showing a network of mostly sub-vertical thin scratches (b), which we identify as an occlusal scratch. (c) is an abrasion spot associated with a major oblique scratch of taphonomic origin, most likely from a sediment particle. Scale bar is 100 mm. doi:10.1371/journal.pone.0043949.g006 incisor. Conversely, in both lateral incisors, the striations are concentrated on the mesial portion of the labial aspect, close to the neck. This evidence supports the interpretation of striae produced by the occasional hit of a stone tool across the labial tooth face. Finally, the striae on both lateral incisors are deeper and superimposed, indicating they were made at different times. The canines carry fewer scratches with more on the right (n = 57) than the left (n = 28). Moreover, the scratches on both canines tend to be shorter, thinner and less expressed than the scratches on the incisors. Scratches were quantified using the intervals first proposed by Bermu´ dez de Castro et al. [7]. Appearing exclusively on the labial face of canines and incisors, 382 scratches were scored into these teeth. Right oblique marks (.22.5u267.5u %) were the most common (45.0%) and left oblique (.112.5u–157.5u) the least common (10.2%) for all teeth. Vertical striations (.67.5u–112.5u) accounted for 27.5% and horizontal striations (0u–22.5u, .157.5u–180u) for the remainder (17.3%). We illustrate the distribution of the marks by mosaic plots (Figure 5), where percentages of the four intervals are given for each tooth (see Data Files S1, S2, S3, S4, S5 and S6). The dominant pattern for all four incisors is right oblique ranging between 47.1% and 66.0% of all marks. These are all significantly different from an equal probability of occurring at the ..001 level with chi2 (Table S3). While each incisor shows an array of angled marks, in these teeth the ‘‘right oblique category’’ consistently has the highest incidence of the four intervals. At least for the four lower incisors, the pattern shows consistent right-hand manipulations. For the incisors, the right oblique pattern is the most common (48.1%) and the left oblique the least common (10.2%), with the other categories intermediate. Unlike all other specimens we have analyzed [5,9], the canines preserve a different pattern, indicating that another action was performed on these teeth. In both canines vertical scratches are the most common, representing 68.4%–75.0% of the striations. In these cases right oblique marks are the next most common orientation (15.8%–21.4%), but these are far less frequent than the vertical marks. We suspect these scratches are related to mastication, lending no information to handedness. They do not contradict the consistent right-hand pattern on the four incisors, since in both canines left-handed scratches are rare (0%–7.0%). The labial aspect of the Regourdou 1 second left mandibular incisor shows deep and relatively thick sub-horizontal micro-traces clustered towards its mesial inferior region. As revealed by both stereo-microscopic and SEM analyses (Fig. 6a), their typical V- shaped outline and the presence of secondary striae occurring within the major microfeatures are indicative of the repeated passage of a hard object, likely a lithic tool across the labial face. Compared to cutmarks produced by stone tools on bone [9,39– 40], striations on the teeth tend to be fainter, with fewer sharp, secondary striae. Unlike the cutmarks on bone, which are associated with butchering dead animals, these enamel striations occur in the living individual with the oral environment and saliva having a smoothing effect on the marks over the lifetime of the individual. At other sites like Krapina [5] and Sima de los Huesos [17], labial scratches occur in newly erupted permanent and in deciduous anterior teeth, indicating the cutting activity begins early in life, which accounts for the overstriking and smoothing of marks. In contrast to the pattern characterizing the lower incisors, the SEM image of the labial aspect of the right canine shows a group of mostly vertically-oriented relatively thin, short scratches with the longest reaching ca. 1 mm length (Fig. 6b), The presence of an abrasion spot associated with a major scratch that runs obliquely mesio-distally and partially overprints the sub-vertical labial network likely results from a post-depositional (taphonomic) action by sedimentary particles. We have not seen this pattern of vertical striations in other Neandertal canines. Conclusions Regourdou 1 joins 16 of 18 European Neandertals (88.9%) who were clearly right–handed, along with their likely ancestors from Sima de los Huesos, all of whom were right-handed [9,17]. This predominant right-handed frequency (,90.0%) has implications beyond simple hand preference, since handedness is a uniquely human trait [41,42] with right-handers outnumbering left-handers in all world-wide cultures occurring in approximately a 9:1 ratio PLOS ONE | www.plosone.org 4 August 2012 | Volume 7 | Issue 8 | e43949