Brief communication Diachronic investigation of linear enamel hypoplasia in prehistoric skeletal samples from Trentino Italy.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 119:283–287 (2002) Brief Communication: Diachronic Investigation of Linear Enamel Hypoplasia in Prehistoric Skeletal Samples From Trentino, Italy Andrea Cucina* Department of Anthropology, University of Missouri-Columbia, Columbia, Missouri 65211, and Department of Human and Animal Biology, University of Rome “La Sapienza,” 00185 Rome, Italy KEY WORDS environment enamel hypoplasia; Neolithic; Copper Age; Early Bronze Age; stress; Alpine ABSTRACT Linear enamel hypoplasia was scored on Neolithic, Copper Age, and Early Bronze Age samples from the Trentino region, Italy, in order to compare the extent of growth disruption in different biocultural subsistence systems (foragers with little agriculture, to agriculturists and agropastoralists). The Early Bronze Age sample shows a higher frequency of enamel defects and an earlier chronological onset than the early Neolithic sample. The higher frequency of defects in the Bronze Age sample could be linked to less diversified nutrition and, because of increased sedentism, a higher risk of disease. Am J Phys Anthropol 119:283–287, 2002. Skeletal markers of physiological disruption are biological markers that help us understand stressful processes. Linear enamel hypoplasia (LEH), a frequently used parameter in anthropological investigations, appears as macroscopic transverse areas of depression in the enamel as a consequence of the ameloblasts’ nonspecific response to physiological stress (Sarnat and Schour, 1941; Goodman and Rose, 1990). Unlike bony tissue, tooth enamel does not undergo remodeling after being laid down; thus, any event that is strong enough to slow down the ameloblasts’ activity and reduce the amount of enamel matrix during crown formation is permanently recorded (Kreshover, 1960; Goodman and Rose, 1990). The severity of stressful events varies according to several biological and cultural factors. Among them, technological innovations and change in subsistence patterns affect responses to environmental pressure (Goodman et al., 1980; Goodman and Rose, 1991). In Trentino, one of Italy’s northeastern Alpine regions, differential exploitation of the environment and changes in subsistence strategies to suit the needs of past populations are evident. The Alpine ecosystem has been utilized in a variety of ways through time in order to accommodate the prevailing lifestyle and economy (Bagolini et al., 1973; Riedel, 1994). Archaeological excavations in Trentino have unearthed human skeletal remains from several chronological periods, encompassing the Late Neolithic (ca. 3000 –2500 BC), the Copper Age (2500 –1800 BC), and the Early Bronze Age (1800 –1550 BC) (Barfield, 1971). Despite their small sizes, the samples provide insight into the different strategies of environmental exploitation and subsistence patterns in the region through time. Neolithic cultures based their subsistence on hunting and husbandry (Uerpmann, 1976; Pedrotti and Demetz, 1997). Agriculture, though present, does not appear as a primary source of nutrients. Hunting decreased over time, and during the Copper Age animal exploitation leaned toward pastoralism and use of animals’ secondary products (Riedel, 1994). With the invention of the animal-towed plow, agriculture and pastoralism became the major source of food (Bagolini et al., 1988). The present study focuses on hypoplastic enamel defects and their age of occurrence in skeletal samples from Trentino, Italy. It represents one further step in an ongoing investigation into lifestyle and living conditions of prehistoric populations in the area (Cucina et al., 1999). This paper describes the © 2002 WILEY-LISS, INC. © 2002 Wiley-Liss, Inc. Grant sponsor: Museo Tridentino di Scienze Naturali; Grant sponsor: C.N.R. Progetto Finalizzato Beni Culturali; Grant numbers: 96.01106.36, 97.00623.PF36; Grant sponsor: COFIN 97. *Correspondence to: Dr. Andrea Cucina, Department of Anthropology, University of Missouri-Columbia, 107 Swallow Hall, Columbia, MO 65211. E-mail: email@example.com Received 7 August 2001; accepted 14 May 2002. DOI 10.1002/ajpa.10135 Published online in Wiley InterScience (www.interscience.wiley. com). 284 A. CUCINA TABLE 1. List of sites and number of individuals forming the three groups Site Neolithic (3000–2500 BC) Copper Age (2500–1800 BC) Early Bronze Age (1800–1550 BC) 1 Solteri A Dos Trento La Vela Appiano Paludei di Volano Nogarole II Madonna Bianca Moletta Patone Romagnano Nogarole III Solteri Vezzano Number of individuals 1 2 9 3 1 1 6 MNI1 10 adults and 8 subadults 14 2 10 3 MNI, minimum number of individuals. occurrence of LEH in the Trentino area in terms of changing biocultural dynamics, and will contribute an ecological perspective to future investigations of skeletal pathological conditions. MATERIALS AND METHODS The Neolithic (NEO), Copper Age (CA), and Early Bronze Age (EBA) samples analyzed are listed in Table 1. Coeval specimens, coming from several small sites, were pooled in order to maximize sample sizes. The NEO sample consists of 12 individuals. The CA sample is represented by 11 individuals, plus loose teeth from the site of Moletta Patone that represent a minimum number of 10 adults and 8 subadults. A total of 29 individuals constitutes the EBA group. The presence or absence of linear enamel hypoplasia was scored on all available permanent teeth that had at least half of the crown present. Each tooth was examined under a tangential light spot, both by visual inspection and with the help of a ⫻4 magnifier. Then, number of defects per tooth and their position on the crown were recorded on anterior teeth only in light of their higher susceptibility to stress (Cutress and Suckling, 1982; Goodman and Armelagos, 1985; Goodman et al., 1987). For this undertaking, only teeth with at least two thirds of their crown were considered. Nonetheless, a few teeth were further excluded due to occlusal wear, which was not a major problem in these populations. To avoid double counting, the tooth showing more defects was used when both antimeres were present. Although two different categories of defects (slight and severe) were initially recognized following Corruccini et al. (1985) and Blakey et al. (1994), due to small sample size, all defects were considered regardless of their severity. The position of enamel hypoplasia on the crown surface was located by measuring the distances between the cemento-enamel junction (CEJ) and the upper and lower limits of each groove, using a thinpoint digital Mitutoyo sliding caliper. Chronological age at occurrence was determined based on the Trentino population-specific mean height of the crown (Hodges and Wilkinson, 1990; Cucina and Iscan, 1997) and the development chart in Reid and Dean (2000). The chronological age distribution of defects was assigned after analyzing all the anterior teeth of each individual. In order to avoid double counting, any age interval overlapping between different teeth from the same individual was included only once. The resulting age distribution must be considered just an estimate, for it cannot account for the actual age of formation of each tooth crown, the within-group variability, and the original crown height in the cases of even slight occlusal wear (Goodman and Song, 1999). The choice to use the developmental chart of Reid and Dean (2000) for crown development was driven by the need to use a more updated, precise, and accurate standard than those previously used, and the need to use one developed on a population geographically close to our Italian sample. Currently, no such accurate standards are available for Italian populations. Histological techniques such as counting the cross striations within the enamel (Fitzgerald and Rose, 2000) could not be applied because they require invasive sectioning of the teeth that was not allowed. Also, the sample-specific count of perikymatas (Fitzgerald and Rose, 2000) was not performed because of the partly worn teeth and the unknown hidden enamel formation time that still would have required application of the chart by Reid and Dean (2000). RESULTS Number and frequencies of enamel defects per type of tooth in the three samples are listed in Table 2. Lower frequencies occur in the earlier sample, while the EBA group shows higher values with minor differences from CA. Fisher’s exact test was performed for each tooth type between NEO-CA and NEO-EBA, and showed that differences were not statistically significant. When all of the tooth types are gathered into anterior (incisors and canine) and posterior (premolar and molars) groups separately for the upper and lower dentition, Fisher’s test and the chi-square test provide more significant results (Table 3). The increased occurrence of enamel hypoplasia in CA and EBA is also emphasized when the mean number of defects calculated on the two most representative teeth for LEH (i.e., the upper central incisor and lower canine) is considered (Goodman and Armelagos, 1985). In the incisors, mean values range between 1.3 defects in NEO to 2.2 in CA, with EBA evidencing 2.0 defects, while in the canines they range between 1.2 defects in NEO to 3.4 in EBA, with CA showing 2.6 defects. Differences are noteworthy, although a t-test did not provide statistically significant results. The chronological distribution of defects according to age class is shown in Figure 1. Each group tends to show major increases in the classes around the center of the age range (approximately between 2.5– 4.5 years). Notable differences occur in the earlier 285 ENAMEL HYPOPLASIA IN PREHISTORIC TRENTINO TABLE 2. Number of teeth affected by linear enamel hypoplasia, number of teeth present, and frequency of LEH, per type of tooth Neolithic Maxilla I1 I2 C P3 P4 M1 M2 M3 Mandible I1 I2 C P3 P4 M1 M2 M3 Copper Age Early Bronze Age Teeth affected Teeth present % Teeth affected Teeth present % Teeth affected Teeth present % 4 6 4 4 2 0 2 1 6 7 6 6 6 7 5 4 66.7 85.7 66.7 66.7 33.3 0.0 40.0 25.0 8 9 18 7 5 4 3 2 10 11 21 10 13 8 8 5 80.0 81.8 85.7 70.0 38.5 50.0 37.5 40.0 9 8 8 7 4 6 3 4 10 11 9 9 10 12 6 8 90.0 72.7 88.9 77.8 40.0 50.0 50.0 50.0 3 4 4 3 4 5 2 0 6 6 6 7 7 9 7 1 50.0 66.7 66.7 42.9 57.1 55.6 28.6 0.0 9 16 13 5 11 4 4 1 14 18 14 15 17 9 10 3 64.3 88.9 92.9 33.3 64.7 44.4 40.0 33.3 5 7 11 12 5 7 2 3 6 10 13 15 6 13 4 4 83.3 70.0 84.6 80.0 83.3 53.8 50.0 75.0 TABLE 3. P values from Fisher’s exact test and from chi-square test between Neolithic, Copper Age, and Early Bronze Age samples1 Fisher’s exact test Anterior-maxilla Posterior-maxilla Anterior-mandible Posterior-mandible NEO-CA NEO-EBA CA-EBA Chisquare2 0.49 0.22 0.10 1.00 0.06 0.09 0.19 0.053 1.00 0.67 0.76 0.033 0.07 0.20 0.17 0.043 1 Teeth were gathered into anterior (incisors and canines) and posterior (premolars and molars) groups, respectively, for maxilla and mandible. 2 Chi-square test was run on the three samples together (df ⫽ 2). 3 Difference significant a 95% level, P ⬍ 0.05. classes from 1.0 to 2.5–3.0 years, where the NEO population, relative to the others, is minimally represented or not represented at all. In particular, the Bronze Age group stands out for its early onset of lesions. DISCUSSION The results of the investigation of hypoplastic defects in the three prehistoric groups from the Alpine region of Trentino, Italy, show an increased frequency of enamel disruption from the earlier (NEO) to the later (EBA) population. Although the differences are not always significant, the trend of increase is consistent. However, because of the relatively small sample sizes, the results only suggest trends and must be treated with caution. Based on evidence that the groups do not differ between one another in terms of dental metric and nonmetric traits (Cucina et al., 1999), which indicates a biological continuity of the settlers, the differences encountered here should be interpreted mainly as consequences of environmental factors. The picture that emerges could result from a differential exploitation of environmental habitats, and could be the expression of cultural changes. The Neolithic groups appear to have settled open spaces at the bottoms of valleys, where archaeologists have encountered small camp sites. The associated faunal remains were mainly of wild game species, as in the group of La Vela, where deer-hunting was dominant (Pedrotti and Demetz, 1997). Although agriculture was known in this period, it did not represent an important contribution to subsistence. This interpretation is supported by the material record and by the low frequency of cavities (4.1%) reported in a previous study (Cucina et al., 1999). It seems that the Alpine valleys did not represent an ideal environment for this kind of subsistence activity (Bagolini et al., 1973). These valleys had been well-populated since Neolithic times and experienced a rapid population growth from the end of the Copper Age and the start of the Bronze Age (Barfield, 1971). Population expansion coincided with a shift in subsistence economy that emphasized intensive agropastoralism (Nicolis and Dal Ri, 1997), as supported by the higher rate of cavities in the Bronze Age group (16.1%; Cucina et al., 1999). The intensification of agriculture, along with population growth, might have led to two possible adaptive responses: population crowding in the valleys with epidemiological consequences (i.e., the spread of diseases), or incentive for some groups to move toward less hospitable highlands in search of new land to cultivate. Demand for land for pastoralism and decreased reliance on hunting increased this need (Riedel and Tacchiati, 1997). The chronological distribution of LEH also supports this evidence. The common occurrence of peaks after age 3 years can be explained by higher child mobility inside the settlement around that age, which increases the exposure to disease, and by the lack of maternal antibodies after weaning (Clarke, 1980; Katzenberg et al., 1996). In addition, the geometric structure of the enamel reduces the macroscopic manifestation of defects in the occlusal third of the crown (Hillson and Bond, 1997), whose forma- 286 A. CUCINA Fig. 1. Chronological distribution of defects per individual, calculated from anterior teeth. tion in anterior teeth lasts to around 2.5 years of age (Reid and Dean, 2000). The macroscopic presence of defects in this age range in EBA and CA and, in turn, their absence in NEO indicate that stress in the former groups was severe enough to overcome physiological and histological thresholds. Variability between groups in the initial appearance of defects seems to be due to actual differences between populations and not to attrition that reduced the occlusal portion of the crowns. The CA group is formed by a larger number of subadults than the other groups. This could explain the onset of defects in the CA population, but not the earlier onset in the EBA group. The conservative approach used here excluded all teeth that could have biased the results. The results could be interpreted in two ways. Either the CA and EBA groups faced more difficult environmental conditions than did the NEO group, or the NEO group faced such harsh conditions that individuals died before the onset of LEH. If the second alternative were the case, according to the osteological paradox of Wood et al. (1992), then one would expect to find other supportive evidence in the NEO group. While the small sample size precludes the use of demographic profiles as a reliable means to answer these questions, a previous study (Cucina et al., 1999) did not detect any substantive evidence. Dental metric traits should have been affected, resulting in smaller crowns in those Neolithic individuals who were capable of surviving the period of growth (Larsen, 1997). Instead, no statistical difference was noted (Cucina et al., 1999). For the time being, tying the frequency of hypoplastic defects to environmental conditions and cultural habits seems to provide a more parsimonious explanation, given the evidence at hand. In conclusion, this investigation points toward an increasing frequency of enamel disruption from the Neolithic to the Early Bronze Ages. The factors accounting for this trend may relate to nutritional changes (from a varied, animal-protein-based diet to a less varied, more carbohydrate-dependent one) and changing cultural habits. Although the small sample size limits generalization, the results are consistent with previous epidemiological findings (Cohen and Armelagos, 1984). Future studies are planned on skeletal pathologies. This paper and that of Cucina et al. (1999) will form the background for an epidemiological interpretation, which will provide a clearer insight into the living conditions in prehistoric Alpine populations. ACKNOWLEDGMENTS The present analysis is part of a wider project between the Museo Tridentino di Scienze Maturali, Trento, and the Department of Animal and Human Biology, University of Rome “La Sapienza.” the author thanks M. Lazinger and G. Dalmeri (Museo Tridentino di Scienze Naturali of Trento) and F. Nicolis (Archaeological Superintendency of Trentino) for permission to study the materials. I am grateful to A. Pedrotti (University of Trento) for valuable information. Special thanks go to V. Tiesler (Universidad Autonoma de Yucatan, Hérida) for her comments, R. 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