Age-Related Variation in Isotopic Indicators of Diet at Medieval Kulubnarti, Sudanese Nubia
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International Journal of Osteoarchaeology Int. J. Osteoarchaeol. 17: 1–25 (2007) Published online 22 September 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/oa.862 Age-related Variation in Isotopic Indicators of Diet at Medieval Kulubnarti, Sudanese Nubia B. L. TURNER,a* J. L. EDWARDS,b E. A. QUINN,c J. D. KINGSTONa AND D. P. VAN GERVENd a Department of Anthropology, Emory University, 1557 Dickey Drive, Atlanta, GA 30322, USA b Department of Anthropology, University of Massachusetts at Amherst, Amherst, MA 01003, USA c Department of Anthropology, Northwestern University, Evanston, IL 60208, USA d Department of Anthropology, University of Colorado at Boulder, Boulder, CO 80309, USA ABSTRACT This study compares trends in dietary composition in two large cemetery populations from the site of Kulubnarti (AD 550–800) in Sudanese Nubia. Bone collagen and bone apatite carbonate were analysed to characterise stable carbon, nitrogen and oxygen isotopes. Previous research on these cemeteries has suggested marked differences in nutritional status and health between the populations. Contrary to expectations, there were no significant relationships between any isotopic indicators related to sex or cemetery of burial, suggesting no isotopically-measurable differences in diet. However, collagen 13C and 15N were significantly related to age, suggesting age-related differences in protein intake or other factors. Weaning trends are gradual and variable, with the range in 15N values exceeding 4% among infants/young children (0–3 yrs) and standard deviations exceeding 1% in collagen 13C and 15N for both infants/young children and subadults (4–17 yrs). This suggests varied weaning strategies among both populations and variable diets prior to adulthood. Also observed was a distinct range of isotopic carbon and nitrogen values among individuals classified as subadults (4–17 yrs), who are depleted in collagen 13C and 15N relative to adults. However, both infants/young children and subadults are slightly enriched in 18O relative to adults, which suggests the presence of non-local individuals or age-related variation in water sources. While most isotopic studies of age-related dietary trends have focused on reconstructing the weaning process, this study presents findings that indicate tripartite isotopic trends distinguishing infancy, subadulthood and adulthood as separate dietary categories. Broad similarities are evident between the results presented here and those from several earlier studies of smaller populations and to nutritional studies of modern communities. These findings suggest that further research into health disparities at Kulubnarti should focus on non-dietary causal factors, and more generally, that greater attention should be paid to subadulthood in palaeodiet studies. Copyright ß 2006 John Wiley & Sons, Ltd. Key words: Kulubnarti; weaning; subadult; diet; Nubia; isotopes; collagen; apatite Introduction of bioarchaeological research, utilising biochem- ical measures of the relative importance of consti- Isotopic reconstructions of palaeodiet in archae- tuent food types to individual diets (DeNiro ological populations constitute an important area & Schoeninger, 1983; Schwarcz & Schoeninger, 1991; Katzenberg, 1992; Schoeninger & Moore, 1992; Ambrose, 1993; Katzenberg et al., 1995; * Correspondence to: Department of Anthropology, Emory University, 1557 Dickey Drive, Atlanta, GA 30322, USA. Fogel et al., 1997). Such techniques provide e-mail: [email protected] insights into patterns of subsistence and resource Copyright # 2006 John Wiley & Sons, Ltd. Received 4 April 2004 Revised 2 August 2005 Accepted 28 November 2005 2 B. L. Turner et al. utilisation, and measure inter- and intra-group Weber, 1999; Aufderheide & Santoro, 1999; variation in dietary composition, such as the White et al., 2001; Richards et al., 2003; Papatha- relative abundance of different forms of protein nasiou, 2003; Yoneda et al., 2004). Oxygen iso- and carbohydrate in the overall diet (reviewed topes in bone and enamel apatite, expressed as in Katzenberg & Harrison, 1997). 18O, reflect the isotopic composition of sources Palaeodietary analyses using stable isotopes of consumed water, and can be used to recon- have grown increasingly sophisticated with the struct seasonality, geographical origin and pat- refinement of analytical techniques, increased terns of migration in several species of animals resolution and greater understanding of the com- (Koch et al., 1989; Kohn et al., 1998; Gadbury plex and variable cycling of stable isotopes et al., 2000) and humans (Fricke et al., 1995; White in biological systems. Carbon isotopes in bone et al., 1998, 2002). 13 and tooth apatite, expressed as CAP, generally Isotopic markers of dietary composition reflect the relative abundance of 13C:12C related to developmental age or assigned sex in the overall diet (Ambrose & Norr, 1993). are useful in discussing less tangible cultural Carbon and nitrogen isotope ratios in bone characteristics such as gender variation in diet 13 collagen, expressed respectively as CCOL and (Reinhard et al., 1994) and constructions of dif- 15N, primarily reflect the contribution and ferent life stages within a context of differential source of dietary protein. Nitrogen isotopes subsistence strategies. An example is the distinct also reflect trophic-level effects in protein intake range of isotopic values commonly found in the associated with the position of organisms in food tissues of infants who subsist primarily on protein webs (Lee-Thorp et al., 1989; Ambrose & Norr, sources such as breastmilk or herbivore milk 1993; Ambrose et al., 1997). Calculated offsets during the first months of life. Preserved infant 13 13 15 between apatite and collagen C( CAP- tissues commonly show an enrichment of N 13 18 CCOL, i.e. ÁAP-COL) estimate the relative and O in their skeletal tissues by as much as dependence on animal versus vegetable protein 3–5% relative to the tissues of juveniles and and is used to measure the extent of carnivory in adults (Jenkins et al., 2001; Bocherens & Drucker, the diet or changes in dietary macronutrients 2003), reflecting trophic-level fractionation (Lee-Thorp et al., 1989). Early interpretations of effects between the maternal diet, breastmilk these offsets suggested that values of 4% or less and infant tissues. Population-specific weaning indicated diets in which the bulk of carbon was trends in humans and other animals can be drawn from animal protein, indicating a more characterised isotopically as the introduction of carnivorous subsistence pattern, while values of supplementary foods through enrichment in 6–7% indicated a more herbivorous diet, and 13C and the cessation of breastfeeding through values intermediate between the two indicated an depletion of 15N as the diet becomes more like omnivorous diet (Krueger & Sullivan, 1984). that of associated adults (Katzenberg, 1992; More recent interpretations, however, suggest Schoeninger, 1995; Katzenberg et al., 1996; that dietary differences only account for part of Balasse et al., 2001). Recently, 18O has been this herbivore–carnivore effect and must be con- characterised in human enamel carbonate to sidered along with processes such as methano- track changes in water intake associated with genesis and bone formation (Hedges, 2003), the weaning process, as infants are supplemented pointing to the need to consider metabolic varia- with water directly after getting their water tion across taxa when interpreting offset values. exclusively from maternal milk during breastfeed- From these premises, carbon and nitrogen iso- ing (Wright & Schwarcz, 1998, 1999). topes have been used to explore further the The importance of infant and weanling diets as trophic-level effects between isotopic signatures correlated to short-term and long-term health in tissues of consumers and their prey (Sullivan & outcomes is well documented in clinical literature Krueger, 1983), the metabolic effects of water (Cunningham, 1995; Oddy, 2002), and the tim- stress (Ambrose, 1991), and human subsistence ing of the process as well as the composition of variation in a wide variety of ecological contexts weaning foods often influences rates of infant (Larsen et al., 1992; Pate, 1997; Katzenberg & morbidity and mortality (McDade & Worthman, Copyright # 2006 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 17: 1–25 (2007) Age-related Isotopic Variation in Nubia 3 1998). Isotopic studies of archaeological popula- Sudan (Figure 1). The samples are from riverine tions have demonstrated shifts in 15N and 13C cemeteries less than 1 km apart, both dated to AD among the remains of the very young and 550–800 and encompassing the Early Christian allowed researchers to estimate the timing and phase of the medieval period (Adams et al., 1999). nature of introduced supplemental foods (Kat- Previous studies have suggested differential nutri- zenberg et al., 1996; Schurr, 1997; Herring et al., tional and occupational stress between the two 1998; Dupras et al., 2001). Such studies have samples, possibly reflecting differential status, brought new dimensions to studies of the detri- based on pathological indicators such as cribra mental effects of dietary change in archaeological orbitalia and reduced cortical thickness (Mittler & populations, measured primarily through ana- Van Gerven, 1994; Van Gerven et al., 1995). The lyses of enamel hypoplasia and other dental non-specific nature of these indicators and the pathology (Katzenberg et al., 1996). number