Did the lateral enamel of Neandertal anterior teeth grow differently from that of modern humans? Debbie Guatelli-Steinberg a,b, * , Donald J. Reid c , Thomas A. Bishop d a Department of Anthropology, The Ohio State University, Columbus, OH 43210, U.S.A. b Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH 43210, U.S.A. c Department of Oral Biology, School of Dental Sciences, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4BW, U.K. d Department of Statistics, The Ohio State University, Columbus, OH 43210, U.S.A. Received 16 February 2006; accepted 4 August 2006 Abstract The formation of lateral enamel in Neandertal anterior teeth has been the subject of recent studies. When compared to the anterior teeth of modern humans from diverse regions (Point Hope, Alaska; Newcastle upon Tyne, England; southern Africa), Neandertal anterior teeth appear to fall within the modern human range of variation for lateral enamel formation time. However, the lateral enamel growth curves of Neandertals are more linear than those of these modern human samples. Other researchers have found that the lateral enamel growth curves of Neandertals are more linear than those of Upper Paleolithic and Mesolithic modern humans as well. The statistical significance of this apparent difference be- tween Neandertal and modern human lateral enamel growth curves is analyzed here. The more linear Neandertal enamel growth curves result from the smaller percentage of total perikymata located in the cervical halves of their teeth. The percentage of total perikymata in the cervical halves of teeth is therefore compared between the Neandertal sample (n ¼ 56 teeth) and each modern human population sample: Inuit (n ¼ 65 teeth), southern African (n ¼ 114 teeth), and northern European (n ¼ 115 teeth). There are 18 such comparisons (6 tooth types, Neandertals vs. each of the three modern human populations). Eighteen additional comparisons are made among the modern human population samples. Sta- tistically significant differences are found for 16 of the 18 Neandertal vs. modern human comparisons but for only two of the 18 modern human comparisons. Statistical analyses repeated for subsamples of less worn teeth show a similar pattern. Because surface curvature is thought to affect perikymata spacing, we also conducted measurements to assess surface curvature in thirty teeth. Our analysis shows that surface curvature is not a factor in this lateral enamel growth difference between Neandertals and modern humans. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Enamel growth; Perikymata; Striae of Retzius Introduction The growth periods of Neandertal and modern human ante- rior teeth have been the subject of recent investigations into life-history differences between these two groups (Ramirez Rozzi and Bermudez de Castro, 2004; Guatelli-Steinberg et al., 2005, in press). These studies have focused on lateral enamel (i.e., enamel on the sides of teeth), on which it is pos- sible to count growth increments, known as perikymata, on enamel surfaces. The assumption underlying these studies is that the formation times of the lateral enamel of anterior teeth provide insight into the length of a species’ growth period. Actual lateral enamel formation times cannot currently be assessed in Neandertal teeth because they cannot be sectioned to determine their periodicities (i.e., the number of days repre- sented by perikymata). By applying an average periodicity de- rived from great apes and humans to all teeth in their samples, Ramirez Rozzi and Bermudez de Castro (2004) found that Neandertals had lateral enamel formation times that were * Corresponding author. Department of Anthropology, The Ohio State Uni- versity, Columbus, OH 43210, U.S.A. E-mail addresses: guatelli-steinbe.1@osu.edu (D. Guatelli-Steinberg), djreid@ncl.ac.uk (D.J. Reid), tab@stat.ohio-state.edu (T.A. Bishop). 0047-2484/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jhevol.2006.08.001 Journal of Human Evolution 52 (2007) 72e84