Dental indicators of growth disturbance in a series of ancient Lower Nubian populations Changes over time.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 60463-470(1983) Dental Indicators of Growth Disturbance in a Series of Ancient Lower Nubian Populations: Changes Over Time JOEL D.RUDNEY Carialngy Postdoetoral Program, School of Dentistry, University of Minnesota, Health Sciences Unit A, Minneapolis, Minnesota 55455 KEY WORDS disturbance Nubia, Striae of Retzius, Meroitic, X-Group, Growth ABSTRACT Previous studies of accentuated striae of Retzius in tooth enamel suggest that early childhood growth disturbance tends to be severe in state-level agricultural societies. The present study investigates the diachronic stability of levels of growth disturbance with a series of Lower Nubian agricultural states broadly similar in terms of mode of subsistence and way of life. The sample consists of 114 first permanent molars from the Meroitic (100 B.C. to 300 A.D.) and X-Group(300 to 600 A.D.) cultures. These teeth were sectioned according to standard histological technique. Data on the frequency and severity of accentuated striae of Retzius were then used to derive estimates of the magnitude of individual growth disturbance. Populations were compared by means of a two-way ANOVA, with growth disturbance as the dependent variable, and age and population as the independent variables. The results show that those dying in childhood experienced significantly higher levels of early childhood growth disturbance than did those surviving to adulthood. The results also show a decline in growth disturbance levels over time. Both XGroup children and X-Group adults experience significantly less early childhood growth disturbance than their Meroitic counterparts. These results suggest an improvement in child health status from Meroitic to X-Group times. Tentative explanatory hypotheses imply an increase in village autonomy, an increase in helminthic disease related to a change in irrigation technology, or direct and indirect effects of consumption of naturally-occurring tetracyclines. These hypotheses are not mutually exclusive, and further research is needed before any of them can be tested. Growth disturbance in early childhood is a multifactorial syndrome. Its etiology is complex, incorporating both malnutrition and infectious disease (Scrimshaw et al., 1968). Synergistic interaction between these components often leads to systemic disruption of normal development, in which growth may slow down or cease altogether (De Maeyer, 1976; Susskind, 1977; Sieber and Lippman, 1980). Records of such disruption are often preserved in hard tissue, and that has made it possible to study growth disturbance in ancient populations. Such studies have employed a variety of skeletal and dental indicators of growth arrest, including Harris lines, enamel hypoplasia, bone turnover rates, and accentuated striae of Retzius (de- 0 1983 ALAN R.LISS, INC. velopmental microdefects in tooth enamel) (Rose and Boyd, 1978; Armelagos, Huss-Ashmore, and Martin, 1979; Clarke, 1980; Goodman et al., 1980; Rose et al., 1981). All of these growth arrest indicators are useful, but accentuated striae of Retzius have been shown to have some particular advantages. Enamel is unique among the hard tissues in that it does not remodel (Osborn and Ten Cate, 1976). Thus, a record of growth disturbance during the period of enamel formation is preserved for as long as the tooth continues to exist. That allows for the combination, within a sample, of both children and adults, which permits a more unbiased estimate of Received May 14,1982; accepted September 27, 1982. 464 J.D. RUDNEY the full extent of growth disturbance within an ancient population (Rose, 1973; Molnar and Ward, 1975; Rose, 1977; Rose and Boyd, 1978; Cook, 1981). Previous accentuated striae studies have shown a strong link between growth disturbance and cultural evolution. Diachronic comparisons of hunting and gathering populations with village and state-level agriculturalists indicate that levels of growth disturbance increase as the transition to agriculture is made, and peak at the state level of social organization (Rose, 1973,1977;Rose et al., 1978). These studies contribute to the understanding of biological consequences of major culture change, but give little attention to the possibility of fluctuation in levels of growth disturbance in the absence of such change. The purpose of the present research is to investigate growth disturbance levels in a series of populations broadly similar with respect to culture and subsistence. An accentuated striae of Retzius data base is used to evaluate the severity of growth disturbance in two successive state-level agricultural populations from ancient Lower Nubia. Biocultural interpretations of the pattern of variation between these two populations are discussed, and resulting hypotheses are then critically evaluated. Archeological background Lower Nubia is the portion of the Nile Valley immediately to the south of classical Egypt, between the First and Second Cataracts. This study deals with material from the Meroitic (100 B.C. to 300 A.D.) and XGroup (300 to 600 A.D.) cultural horizons (Adams, 1977). These periods display extensive similarities in settlement pattern, diet, food preparation techniques, and agricultural practices (Trigger, 1965; Adams, 1977). Differences are primarily political and economic in nature. During the Meroitic period, Lower Nubia is ruled by the Upper Nubian empire of Meroe. During the X-Group period, Lower Nubia becomes an autonomous kingdom, and trade also declines (Adams, 1977). Throughout both periods, the subsistence base consists of sorghum, supplemented by legumes, dates, mutton, goat, and other fruits and vegetables. Agricultural activity is intensive, with irrigation being provided by an animal-powered lifiing device, the saqia (introduced at the beginning of the Meroitic period) Chigger, 1965; Adams, 1977). The skeletal biology of these Nubian populations has been a topic of intensive study. Greene (19671, Carlson and Van Gerven (1977, 19791, and Nielsen (1970) have shown that the Meroitic and X-Group populations are biologically continuous, while Armelagos (1968,1969)and coworkers have given equal attention to the paleopathology of these groups. Reports have been published on mortality patterns (Meroitic and X-Group),gross skeletal pathology (Meroitic and X-Group), patterns of bone growth (X-Group),and bone histology (X-Group)(Armelagos, 1968, 1969; Armelagos et al., 1972; Martin and Armelagos, 1979). Of particular relevance to the present study are findings of porotic hyperostosis (Meroitic and X-Group), and juvenile osteoporosis (X-Group) (Carlson et al., 1974; Armelagos et al., 1979). Both are symptomatic of conditions (iron deficiency and parasite-mediated anemia; protein-energy malnutrition) that can promote growth disturbance with concomitant accentuated striae of Retzius formation (Kreshover, 1960;Roseand Pasley, 1980; Rose et al., 1981). MATERIALS AND METHODS Sample selection The sample was drawn from a collection of Lower Nubian dental material recovered from cemeteries in the vicinity of Old Wadi Halfa, Sudan (Greene, 1967). Previous accentuated striae of Retzius studies have relied primarily upon the canine, because its simple crown morphology makes it easy to section, and because its age 0.5 to age 4.5 period of crown development encompasses the ages at which growth disturbance typically occurs (Rose, 1973; Clarke, 1978). However, in this case, use of the canine was not feasible, because the Wadi Halfa dental collection consists mainly of posterior teeth. The first permanent molar, which has also been employed by Cook (1981), was selected as the most suitable alternative. This tooth is not so easy to section (Rudney, 1981), but its crown develops during the first 3 years of life (Fanning and Brown, 19711, a period when children are highly susceptible t o growth disturbance (Susskind, 1977; Thomson and Pollitt, 1977). The sample selected consists of 105 first permanent molars. The Meroitic cultural period is represented by 40 individuals from GROWTH DISTURBANCE IN NUBIA: CHANGES OVER TIME 465 junction. Since ante-mortem loss of occluding teeth sometimes resulted in curtailment of normal wear, it did prove possible to include a number of older adults in the sample (due to differential wear across the buccal and lingual cusps, most adults in the sample are represented by only a single cusp-see Table 1). The unavoidable exclusion of the very young from the sample means that the age-distribution within it may not be fully representative of the Meroitic and X-Group populations. However, the agedistributions within the Meroitic and X-Group components of the sample were compared with the Mann-Whitney U test and found not to be significantly different (Table 1). Interpopulation comparisons within the sample are thus not likely to be biased with respect to age. Sample preparation and data collection The teeth were bisected along a longitudinal plane running between the mesiobuccal and distolingual cusps, and acid-etched ground sections then made according to TABLE 1. Agedistributwn ofthe sample’ standard histological technique (Rose, 1973; Distolin a1 Mesiobuccal Clarke, 1978; Rudney, 1981). The sections Y cusps3 cusps were then examined for accentuated striae of Age-group2 Meroitic X-Group Meroitic X-Group Retzius (Rudney, 1981).A stria was classified as accentuated on the basis of histological 0 1 0 1 3Y evidence of unusually large fluctuation in 3 3 3 4 4Y 1 4 1 3 the shearing component of ameloblast mo5Y 4 3 4 4 6Y tion. Such evidence is manifested as a gross 3 3 3 4 7Y accentuation in the amplitude of prism cur0 0 0 0 8Y vature across the crest of the stria. In more 1 3 0 2 9Y 1 2 1 2 severe cases, accentuation of prism curvature 10 Y 0 2 0 2 11 Y is accompanied by blurring and obliteration 2 0 2 0 12 Y of prism boundaries. These discontinuities 0 1 13 v 0 1 indicate an interruption of secretory activity 2 0 2 0 14 $ 0 2 1 3 15 Y so prolonged as to completely disrupt the nor16 y 0 2 1 2 mal pattern of enamel matrix flow (Osborn, 1 0 1 0 17 Y 1973;Osborn and Ten Gate, 1976;Rose, 1977, 1 3 0 3 18 Y 6 15 10 14 1979;Rudney, 1979,1980,1981). 19-30 v _ _ _. 2 4 3 5 31-50 Such gradations in the severity of accen28 47 36 46 Totals tuated striae were taken into account during Mann-Whitney U test5:Age by population, Meaiobuccal cusps. data collection. Striae displaying both accenU = 619.0; z = -0.4328; p = 0.6652. tuated curvature and prism discontinuities Mann-Whitney U test5: Age by population, Distolingual cusps. were given a relative weight of 2, while striae U = 819.5;z = 0.0806; p = 0.9358. ‘Data given aa number of individuals contributing a cusp to a displaying only accentuated curvature reparticular agegroup. Persons contributing both a mesiobuccal ceived a lesser weight of 1.The weights of all and a distolingual cusp are represented twice. aAge groups 3 years to 18 years represent dental ages. Age accentuated striae found within each cusp of groups 19-30 years and 31-50 years combine persons aged by each tooth were summed to generate a subic, endmanial, and dental techniques. Due to differential wear or damage during sectioning, four “growth disturbance score” (Rudney, 1980, Meroitic and 19 X-Group individuals are represented by a 1981). These scores provided an estimate of mesiobuccal cusp alone. the amount of growth disturbance experi‘Due to differential wear or damage during sectioning, 12 Meroitic and 18 X.Group individuals are represented by a enced by individuals during the first 3 years dwtolingual cusp alone. of life, the period in which the M1 crown 6Siegel(1956). cemetery 6B16 at South Argin. The remaining 65 are from X-Group cemeteries 2413 (Serra West) and NAX (North Argin) (Greene, 1967). The criterion for inclusion of a tooth within the sample was the presence of a fully developed and unworn dentinoenamel junction in the mesiobuccal and/or distolingual cusp (see below). This criterion served to maximize inter-tooth comparability within the sample, although it did require the exclusion of very young and very old individuals (Rudney, 1981). Ages within the sample range from 3 to 50 years (Table 1). Those younger than three were excluded due to immature enamel which was histologically distinct from fully developed enamel and also subject to post mortem changes. Adults were excluded when the mesiobuccal and distolingual cusps of all their first permanent molars were worn below the tip of the dentinoenamel 466 J.D. RUDNEY develops (Massler et al., 1941;Fanning and Brown, 1971;Anderson et al., 1976). To control for any intra-observer error in the assessment of prism curvature, the scoring step was repeated until consistency was achieved. Additional control for error is provided by independent analysis of growth disturbance scores for the mesiobuccal and distolingual cusps (this step was mandated by the inclusion of differentially worn teeth in the sample). One-sample KolmogorovSmirnov tests indicate that the distribution of scores for either cusp is not significantly different from normality (Siegel, 1956).On that basis, it was deemed legitimate to use parametric techniques to make population comparisons. A two-way ANOVA was set up for each set of cusps (all statistical tests were run using the SPSS system of canned statistical programs) (Nie et al., 1975).Growth disturbance was taken as the criterion variable, with Population and Age-at-Deathas the categorical variables. Meroitic and X-Group represented the categories in Population. In order to provide adequate sample sizes for analysis, the original age-groupswere pooled into two categories, Children and Adults. Age 15 was made the dividing line between the two. RESULTS The results of the analysis are the same for both the mesiobuccal and distolingual cusps. Table 2 presents the mean values for growth disturbance scores within each category of population and age. These values suggest a difference in the level of growth disturbance between age groups. Within each population, those dying in childhood experience higher levels of growth disturbance (during the first 3 years of life) than do those surviving to adulthood. Moreover, there is also a clear differencebetween populations in terms of the magnitude of growth disturbance. X-Group children experience less early childhood growth disturbance than do Meroitic children, and X-Group adults experience less early childhood growth disturbance than do Meroitic adults. The ANOVA summary table (Table 3) indicates that the differences between age groups and populations are highly sisnificant (p gO.001) in all cases. It also shows that the effects of age and population on growth disturbance are independent and additive. Together, both variables account for about 30% of total variance in growth dis- turbance scores (as indicated by the value of R2). DISCUSSION The results show differences in the level of growth disturbance both within and between these ancient Lower Nubian populations. The observed difference between age groups can be related to mortality data collected for the Wadi Halfa skeletal populations (Armelagos, 1968, 1969). The mortality curves for both the Meroitic and X-Group population peak during infancy and early childhood. Those experiencing less growth disturbance in early childhood would be expected to be more likely to survive beyond that critical period. The lower early childhood growth disturbance scores seen in Meroitic and X-Group adults would appear to be a reflection of this. Armelagos' (1968,1969)mortality data can also be related to the decline in growth disturbance scores observed between the Meroitic and X-Group populations, as his findings show a corresponding decline in mortality rates between the Meroitic and X-Group periods. Taken together, the mortality data and the growth disturbance data strongly suggest an improvement in the relative health status of Wadi Halfa area children during the X-Group period. This change is difficult to account for, in view of the extensive similarities between the Meroitic and X-Group periods. Two possible explanations for the X-Group improvement in child health have thus far been proposed. Armelagos (1968,19691,writing in reference to the Wadi Halfa mortality data, has suggested that the improvement may be related to an increase in local village autonomy during X-Group times. A reduction in the demands of central authority could have led to an increase in the amount of food available for local consumption, and a similar effect might also have been engendered by the decline in trade with Egypt (this trade did involve an exchange of Nubian foodstuffs for manufactured goods) (Adams, 1977).Such changes might conceivably have led to a relative improvement in child nutrition (although a recent study of bone turnover rates in X-Groupchildren does suggest that proteinenergy malnutrition was not unknown in XGroup times) (Armelagos, et al., 1979). A question posed by this hypothesis pertains to the degree of local autonomy actually experienced in the Wadi Halfa region. Sites found 467 GROWTH DISTURBANCE IN NUBIA: CHANGES OVER TIME around Wadi Halfa include the X-Group royal tombs at Ballana and Qustul, and a large settlement at Faras believed by some to be the X-Group capital (although others favor the site of Qasr Brim, farther to the north) (Adams, 1977).These sites suggest a substantial governmental presence in the Wadi Halfa region during the X-Group period. The effect such a presence may have had on the autonomy of local villages needs to be evaluated before the autonomy hypothesis can be fully accepted. An alternative (though not antithetical) explanation for the X-Group improvement in child health is based on endemic disease (Rudney, 1981). The helminthiases hookworm and schistosomiasisare known to have been present in Egypt for several millenia (Foster, 1965;Ruffer, 19671,and high levels of porotic hyperostosis strongly suggest their presence in Lower Nubia during Meroitic and X-Group times (Carlson et al., 1974). These diseases are known to contribute growth T ABU 2. ANOVA cell meam-growth disturbance by disturbance in children, and a strong positive population by age at death relationship between high prevalences of A. Mesiobuccal cusps hookworm and schistosomiasis and yearPopulation Age group round irrigation has also been established - Children Adults Memitic x = 15.13(n = 16) = 12.08(n = 12) (May, 1958;Van der Schalie, 1960;Malek, S.D. = 4.161 -S.D. = 5.282 1961;Scrimshaw et al, 1968;Miller, 1979). X-Group X = 11.09 (n = 23) X = 6.58(n = 24) The intensification of Nubian agriculture S.D. = 5.964 S.D. = 3.412 engendered by the introduction of the saqia B. Distolingual cusps at the beginning of the Meroitic period could Population Age P U P thus have led to increased local prevalences - Children Adults Meroitic X = 16.18(n = 17) = 12.47(n = 19) of hookworm and schistosomiasis (Rudney, 1981). A possible consequence of the deleteS.D. = 5.114 S.D. = 4.858 X = 11.82(n = 22) Z = 7.79 (n = 24) X-Group rious health effects associated with such a S.D. = 5.491 S.D. = 3.867 shift could have been natural selection in TABLE 3. ANOVA summary table-growth disturbance by population by age at &ath A. Mesiobuccal cusps sourceof variation sum of squares Main effects 737.087 386.606 Population Age at death 292.400 9.253 Interactions: Pop. with age Explained 746.341 variance 1614.326 Residual variance Total 2360.667 variance Multiple R = 0.559;Multiple R2 = 0.312 D.F. Mean square 2 1 1 1 368.554 386.606 292.400 9.253 16.209 17.003 0.407 0.001 0.001 0.001 0.526 3 248.780 10.942 0.001 71 22.737 74 F 12.860 R. 13.901 B. Distolingual cusps 718.4U Main effects 414.094 Population 308.582 Age at death 0.528 Interactions: Pop. with age Explained 718.940 variance Residual 1820.438 VarianCe Total 2539.378 variance Multiple R = 0.532;Multiple R2 = 0.283 2 1 1 1 359.206 414.094 308.582 0.528 15.391 17.743 13.222 0.023 0.001 0.001 0.001 0.881 3 239.647 10.268 0.001 78 23.339 81 31.350 468 J.D. RUDNEY favor of those more resistant to these diseases (May and Anderson, 1979). The improvement in child health seen several hundred years later in the X-Group period might thus be related to a gradual increase in the biological resistance of the Lower Nubian population to helminthic disease (Rudney, 1981).This hypothesis is not dependent on the degree of local autonomy in the Wadi Halfa region, but it in turn presents other difficulties. One problem is that the biochemistry and genetics of innate mechanisms for resistance to helminthic disease is not well understood. There is strong evidence for the existence of such resistance, but no accepted means for the identification of genetically resistant individuals (May, 1958; Malek, 1961;Wakelin, 1978;Miller, 1979).This lack of specific information presently precludes independent testing of the endemic disease hypothesis through genetic analysis of living Nile Valley populations differing in their exposure to helminthic disease. The hypotheses considered above are complete in themselves, but a full discussion of growth disturbance in Lower Nubia requires mention of the Bassett et al. (1980)report of tetracycline in labeling in bone sections from Wadi Halfa X-Group remains. Exposure to this antibiotic is thought to have occurred through consumption of grain contaminated by tetracycline-producingbacteria of the genus Streptomyces (Bassett et al., 1980).It can be argued that tetracycline might have contributed to the X-Groupimprovement in child health by ameliorating some bacterial, rickettsial, and chlamydia1 infections (tetracycline is not therapeutically effective against viral or helminthic agents) (Kastrup and Boyd, 1979). However, such an hypothesis must be evaluated in light of the known capacity of pathogenic organisms to become resistant to tetracycline (Connamacher, 1976). It can as easily be argued that any potential benefits of tetracycline would have been nullified by the evolution of resistant bacterial strains. An additional complication is provided by reports which suggest a deleterious effect of tetracycline on dental development. Findings in experimental animals include ultrastructural changes in ameloblasts, which may be accompanied by accentuated striae of Retzius formation, or frank enamel hypoplasia. Such effects are dose dependent, and may also vary according to the type of tetracycline administered (Lofgren et al., 1968;Nylen et al., 1972;Kruger, 1975).The effect of tetra- cycline on dental development in humans is not well understood, because it is difficult to isolate the effect of the drug from that of the disease it was used to treat. However, accentuated striae of Retzius have been reported in association with tetracycline-labeledbands in dentin, and the clinical literature contains repeated suggestions that tetracycline may act to compound effects of systemic disease on dental development (Brearley, et al., 1968; Baker and Storey, 1970; Baker, 1972; Primosch, 1980;Kotsanos, 1982). Thus, the results of the present study may be influenced by a possible tetracycline effect on accentuated striae of Retzius formation (Rudney, 1981).A test of that hypothesis will require at least minimal information on levels of tetracycline exposure in the dental tissues of both the Meroitic and X-Group populations. Research that is currently in progress may supply some of the needed data. At present, the most that can be said is that a tetracycline effect cannot be ruled out. On the basis of current knowledge, all the hypotheses discussed above are best regarded as tentative. Further research will be needed to determine the relative strengths of each. Since these hypotheses are not mutually exclusive, it is possible that each may have a contribution to make to succeeding stages of explanation. At present, the importance of the current study lies chiefly in the finding of a significant difference in the level of growth disturbance between two biologically continuous populations that are very similar with respect to culture and environment. This finding suggests that the relationship between early childhood growth disturbance and culture is complex and multifactorial. The Nubian data do nothing to contradict the general impression that child health tends to be poor in ancient state-level agricultural societies (Cassidy, 1980). They do, however, suggest that local epidemiological or historical factors may induce fluctuations in the level of growth disturbance seen. Comparisons with diachronic series of populations from other areas may help elucidate the extent to which such fluctuation in levels of growth disturbance may be characteristic of agricultural populations in general. ACKNOWLEDGMENTS An earlier version of this paper was presented at the 50th Annual Meeting of the American Association of Physical Anthropologists, Detroit, Michigan, April 25,1981.The author would like to thank Dennis P. Van GROWTH DISTURBANCE IN NUBIA: CHANGES OVER TIME Gerven and David L. Greene for their valuable advice and criticism during the course of this research. Thanks are also due to Jerome C. Rose and Steven K. Clarke for their advice on the manufacture and observation of dental thin sections, and to George J. Armelagos, for access to data collected by the first University of Colorado Nubia expedition. Finally, thanks to the University of Colorado Department of Geology for use of their petrographic thin section lab, and to Geoff Reed and Bob Lanham for instruction in the use of the equipment. LITERATURE CITED Adams, WY (1977)Nubia. Princeton: Princeton University Press. 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