Compound specific isotope evidence points to use of freshwater resources as weaning food in Middle Neolithic Paris Basin

Objectives
A clear understanding of past weaning practices can provide invaluable insights into social issues such as infant care, fertility rate, and demographic patterns in past societies. This study presents the first archeological research employing compound specific isotope analysis (CSIA) for the reconstruction of past weaning practices.

Methods
Weaning practices of two Middle Neolithic communities in the Paris Basin region: Balloy (BLR) and Vignely (VPB), are evaluated by combining previously published bone collagen stable carbon, nitrogen, and sulfur (n = 66) isotope analysis with new compound specific carbon and nitrogen isotope compositions of bone collagen (n = 10).

Results
Our results demonstrate that the diets of individuals from BLR and VPB likely incorporated freshwater resources. The signals of freshwater resources consumption are even stronger among subadults, suggesting that freshwater resources were used as weaning food at these sites.

Conclusions
The implications of our result are threefold. Currently many CSIA studies in archeology only involve either carbon or nitrogen. Our data shows that it is important to conduct CSIA on both carbon and nitrogen for a more integrated picture. Secondly, our data demonstrates that the use of a protein-based weaning food—instead of a starch-based weaning food (such as cereal gruel)—was likely more prevalent among the Middle Neolithic communities in the Paris Basin Region than previously thought. The finding thus prompts a rethinking of the role of protein-based weaning food in other archeological contexts. Lastly, the common assumption that weaning foods and adult diets share similar isotopic compositions can be problematic, as the use of protein-based, high trophic-level weaning foods can skew the δ15N weaning curve and produce an erroneously late estimation for weaning ages.