Abstract
ABSTRACTThe use of incremental carbon and nitrogen isotopic analysis is gaining momentum as a way of establishing infant feeding practices in the past. Here we examine the differences in information gleaned through incremental isotopic techniques applied to individuals, relative to more commonly-used bulk isotopic sampling of a cross-section of a population. We use bulk sampling methods, which use bone collagen isotope values from multiple individuals, to construct Bayesian weaning curves for our samples. We then compare these results to individual weaning times established through incremental isotopic analysis of single deciduous teeth. Our results highlight that in contexts with high adult dietary variation it may not be possible to interpret weaning behaviour using cross-sectional techniques, and incremental isotopic analysis may be the only way of interpreting weaning behaviours. Our findings also suggest that cross-sectional analyses are the most useful way of creating population-scale interpretations of weaning behaviour within a sample. Incremental techniques, however, are necessary if we want to tell individual weaning stories and investigate the variation in infant-feeding present within the past.
Highlights
The investigation of breastfeeding and weaning practices in the past is significant for a number of reasons
The investigation of weaning in archaeological populations involves the bulk sampling of bone collagen from a sub-sample of differently aged infants and children within a cemetery population (reviewed in Tsutaya and Yoneda (2015))
The long time period and wide confidence intervals associated with this model reflect the high level of variation in isotopic results. This variability in infant and child bulk collagen results is likely linked to high adult dietary heterogeneity (King et al Early view; 2018) transferred to the infants through breastmilk, and reflected in maternal choices of weaning foods
Summary
The investigation of breastfeeding and weaning practices in the past is significant for a number of reasons. Isotopic techniques have long been used to establish weaning times in past populations (Fogel, Tuross, and Owsley 1989, Wright and Schwarcz 1998, Schurr 1998). While an infant is breastfeeding they are consuming their mother’s protein, placing them a trophic level above their mother. This translates as a 2-3‰ increase in δ15N values (Fogel, Tuross, and Owsley 1989) and 1‰ increase in δ13C values relative to maternal values (Fuller et al 2006). The investigation of weaning in archaeological populations involves the bulk sampling of bone collagen from a sub-sample of differently aged infants and children within a cemetery population (reviewed in Tsutaya and Yoneda (2015)). Comparison can be made with other groups or time periods to study changes to infant feeding practice
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