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A model for the effect of weaning on nitrogen isotope ratios in humans.

Millard, AR



GA Goodfriend

MJ Collins

ML Fogel

SA Macko

JF Wehmiller


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.


Millard, A. (2000). A model for the effect of weaning on nitrogen isotope ratios in humans. In G. Goodfriend, M. Collins, M. Fogel, S. Macko, & J. Wehmiller (Eds.), Perspectives in Amino Acid and Protein Geochemistry (51-59). Oxford University Press

Publication Date 2000
Publisher Oxford University Press
Pages 51-59
Book Title Perspectives in Amino Acid and Protein Geochemistry
Keywords weaning nitrogen isotopes humans breastfeeding