  Nitrogen isotope analysis of bone collagen has been used to reconstruct the
breastfeeding practices of archaeological human populations. However, weaning
ages have been estimated subjectively because of a lack of both information on
subadult bone collagen turnover rates and appropriate analytical models. Here,
we present a model for analyzing cross-sectional delta-15N data of subadult
bone collagen, which incorporates newly estimated bone collagen turnover rates
and a framework of approximate Bayesian computation. Temporal changes in human
subadult bone collagen turnover rates were estimated anew from data on
tissue-level bone metabolism reported in previous studies. A model for
reconstructing precise weaning ages was then developed and incorporating the
estimated turnover rates. The model is presented as a new open source R
package, WARN (Weaning Age Reconstruction with Nitrogen isotope analysis),
which computes the age at the start and end of weaning, 15N-enrichment through
maternal to infant tissue, and delta-15N value of collagen synthesized entirely
from weaning foods with their posterior probabilities. A precise reconstruction
of past breastfeeding and weaning practices over a wide range of time periods
and geographic regions could make it possible to understand this unique feature
of human life history and cultural diversity in infant feeding practices.
