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Durham University

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Publication details for Dr Andrew R Millard

Millard AR (2000). A model for the effect of weaning on nitrogen isotope ratios in humans. In Perspectives in Amino Acid and Protein Geochemistry. Goodfriend, GA Collins, MJ Fogel, ML Macko, SA & Wehmiller, JF New York: Oxford University Press. 51-59.
  • Publication type: Chapter in book
  • ISSN/ISBN: 0195135075
  • Keywords: weaning nitrogen isotopes humans breastfeeding

Author(s) from Durham

Abstract

Previous attempts to evaluate age-at-weaning from nitrogen isotope data are reviewed and shown to suffer from two faults: treating the process of weaning as an event, and estimating weaning age without accounting for the influence of growth on the body's nitrogen isotope ratios. In particular Schurr's (J. Archaeol. Sci. 24, 919-927, 1997) mathematical model for isotopic changes during weaning, is shown to use functions appropriate only for modelling an instantaneous switch in diet whilst maintaining a constant body weight.

This paper develops an improved model which takes account of the effect of changing body mass and an extended weaning period on the trajectory of isotopic change within juveniles. The model includes typical growth patterns for human infants, and a function which represents a gradual shift from sole dependence on the mother's milk to complete weaning. These are incorporated into isotope mass balance equations, which are then solved numerically. Comparison with longitudinal isotopic data from modern babies is not entirely unproblematic, but broadly confirms the model. Application to archaeological population data gives estimates of the average values of weaning parameters in these populations. Further work on the model and more controlled studies on modern and ancient populations are needed to fully quantify weaning ages.