Linear Enamel Hypoplasia in the Great Apes: Analysis by Genus and Locality Darcy Lee Hannibal, 1 * and Debbie Guatelli-Steinberg 2 1 Department of Anthropology, University of Oregon, Eugene, Oregon 97403 2 Department of Anthropology and Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, Ohio 43210 KEY WORDS dental defect; enamel hypoplasia; developmental stress; great apes ABSTRACT Most studies report a high prevalence of linear enamel hypoplasia (LEH) in the great apes relative to other nonhuman primates and some human popula- tions. It is unclear if this difference is a direct result of poor health status for the great apes, or if it represents differential incidence due to a lower threshold (sensu Goodman and Rose, 1990 Am. J. Phys. Anthropol. [suppl.] 33:59 –110) for the occurrence of enamel hypoplasia among great apes. This study uses the Smithsonian Na- tional Museum of Natural History’s great ape collection to examine the prevalence of LEH, the most common type of hypoplasia observed. Frequencies of LEH are reported, as well as analyses by taxa and provenience. The study sam- ple consists of 136 specimens and includes 41 gorillas, 25 chimpanzees, and 70 orangutans. Analyses of frequencies are presented for both individuals and teeth by taxonomic category and locality. Among the individuals in this study, 63.97% are affected by LEH. Overall, gorillas (29.27%) exhibit lower frequencies of LEH than chimpanzees (68.00%) and orangutans (82.86%). There is a marked difference in LEH frequencies between mountain and low- land gorillas. There is no difference in LEH frequencies between Sumatran and Bornean orangutans. A range of variation for the great apes in enamel hypoplasia frequen- cies is found when taxon and locality are considered. It is likely that both biological and environmental factors in- fluence the high frequencies of enamel hypoplasia exhib- ited in the great apes. Am J Phys Anthropol 127:13–25, 2005. © 2004 Wiley-Liss, Inc. Enamel hypoplasia is broadly defined as a defi- ciency in enamel thickness that results when phys- iological stress disrupts the formation of enamel (Goodman and Rose, 1990). Linear enamel hypopla- sia (LEH), the most common and widely studied form of enamel hypoplasia, is manifested as a de- pressed horizontal furrow in the enamel around the circumference of the tooth crown. Because hypoplas- tic defects can be caused by a variety of physiological stressors, including febrile disease, parasitic infec- tion, and nutritional deficiencies (Goodman and Rose, 1990), they have been used in numerous an- thropological contexts as nonspecific indicators of physiological stress (extensively reviewed in Good- man and Rose, 1990). Although Colyer (1936) pub- lished the first comprehensive assessment of nonhu- man primate enamel hypoplasia, only recently have researchers begun to explore the extent to which the study of enamel hypoplasia in nonhuman primates can provide insights into the physiological stress experienced by primate groups (Eckhardt, 1992; Eckhardt et al., 1992; Eckhardt and Protsch von Zieten, 1993; Guatelli-Steinberg, 1998, Guatelli- Steinberg and Lukacs, 1998; Guatelli-Steinberg and Skinner, 2000; Hannibal, 2000; Kelley and Buicek, 2000; Lukacs, 1999; Miles and Grigson, 1990; Moggi-Cecchi and Crovella, 1991, 1992; Newell, 1998; Skinner, 1986a,b; Skinner et al., 1995; Skin- ner and Guatelli-Steinberg, 1997; Stottlemire, 1998; Vitzthum and Wikander, 1988; Zhang, 1987). Most research on enamel hypoplasia in nonhuman primates has focused on establishing how LEH var- ies across the primate order (e.g., Guatelli-Stein- berg, 2000; Newell, 1998; Schuman and Sognnaes, 1956; Skinner and Guatelli-Steinberg, 1997; Vitz- thum and Wikander, 1988). These studies consis- tently find a high incidence of enamel hypoplasia among great apes and a low incidence in monkeys and prosimians. However, the manifestation of LEH is not only influenced by physiological stress but also by intrinsic attributes of enamel that vary system- atically across taxa. Thus, this broad taxonomic pat- tern in the distribution of LEH is not necessarily a direct, or even an indirect, reflection of broad taxo- nomic differences in stress experience. For example, Grant sponsor: AmeriCorps Education Award; Grant sponsor: Uni- versity of Oregon Graduate Student Research Award. *Correspondence to: Darcy Hannibal, PO Box 51254, Eugene, OR 97405. E-mail: dlhan@darkwing.uoregon.edu Received 7 April 2003; accepted 10 September 2003. DOI 10.1002/ajpa.20141 Pulished online 31 August 2004 in Wiley InterScience (www. interscience.wiley.com). AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 127:13–25 (2005) © 2004 WILEY-LISS, INC.