STABLE NITROGEN ISOTOPES AS EVIDENCE FOR THE AGE OF WEANING AT THE ANGEL SITE - A COMPARISON OF ISOTOPIC AND DEMOGRAPHIC MEASURES OF WEANING AGE

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 Valle y. The high proportion of infants in the Angel skeletal series appears to reflect high rates of infant mortality associated with weaning wit hin this sedentary society of maize agriculturalists. Age-related vari ations 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 sta ble N-isotope ratio prier to age 2 and a rapid decline in early childh ood is used to estimate the age of weaning. The isotopic data are comp ared with estimated mortality rates to evaluate the consistency and pr ecision of isotopic and mortality profiles as measures of weaning age. At Angel, weaning was not directly correlated with peak infant mortal ity. Non-linear equations that model prehistoric weaning behaviour are described. These equations produce estimates of both the timing and r ates of juvenile dietary change that are amenable to statistical compa risons between archaeological sites. The non-linear models provide an approach that is more realistic and more informative than determining a single age of weaning. (C) 1997 Academic Press Limited.