Stable Nitrogen Isotopes as Evidence for the Age of Weaning at the Angel Site: A Comparison of Isotopic and Demographic Measures of Weaning Age

Abstract

Stable N-isotope ratios are used to estimate the age of weaning in the prehistoric (AD 1300-1450) population that inhabited the Angel site, a Middle Mississippian civic-ceremonial centre in the lower Ohio Valley. The high proportion of infants in the Angel skeletal series appears to reflect high rates of infant mortality associated with weaning within this sedentary society of maize agriculturalists. Age-related variations in stable N-isotope ratios of 23 juveniles are used to measure changes in childhood diet associated with breast-feeding after birth, weaning, and with the onset of adulthood. A pronounced peak in the stable N-isotope ratio prior to age 2 and a rapid decline in early childhood is used to estimate the age of weaning. The isotopic data are compared with estimated mortality rates to evaluate the consistency and precision of isotopic and mortality profiles as measures of weaning age. At Angel, weaning was not directly correlated with peak infant mortality. Non-linear equations that model prehistoric weaning behaviour are described. These equations produce estimates of both the timing and rates of juvenile dietary change that are amenable to statistical comparisons between archaeological sites. The non-linear models provide an approach that is more realistic and more informative than determining a single age of weaning. © 1997 Academic Press Limited.