Assessing human weaning practices with calcium isotopes in tooth enamel

Area of Science:

• Paleoanthropology
• Biogeochemistry
• Human Evolution

Background:

• Weaning practices vary across great apes, with significant divergence during human evolution.
• Reconstructing past weaning behaviors is challenging due to the lack of clear biomarkers in the fossil record.

Purpose of the Study:

• To investigate calcium (Ca) isotope ratios (δ⁴⁴/⁴²Ca) in human deciduous tooth enamel as a biomarker for early-life dietary transitions.
• To reconstruct the duration of breastfeeding and identify weaning patterns in modern humans.

Main Methods:

• Sequential microsampling of deciduous tooth enamel from individuals with known dietary histories.
• Analysis of Ca isotope ratios (δ⁴⁴/⁴²Ca) to track dietary changes from in utero to postnatal development.
• Comparison of enamel δ⁴⁴/⁴²Ca profiles between individuals with varying breastfeeding durations.

Main Results:

• δ⁴⁴/⁴²Ca variations in enamel accurately record the transition from placental nutrition to an adult-like diet.
• Ca isotope profiles correlate with breastfeeding duration: short/no breastfeeding shows a marked δ⁴⁴/⁴²Ca increase, while long breastfeeding shows stable values.
• This method provides a novel, independent approach to studying past weaning practices.

Conclusions:

• Ca isotope analysis of tooth enamel is a powerful tool for reconstructing hominin weaning strategies and early life history.
• This biomarker can help address challenging questions about past population dynamics and human evolutionary history.