RESUMEN
OBJECTIVES: A change in how children were treated and valued occurred in premodern Japan, as popularized ideas of an inheritance-based family system led to more careful and affectionate child-rearing practices by lower social-status groups. A number of books were written, advising that breastfeeding should last approximately 3 years. The objective of this study is to reconstruct and compare breastfeeding and weaning practices before and after the transition, to illuminate the impact of documented changes in child-rearing practices on subadults' lived experience. MATERIALS AND METHODS: Carbon and nitrogen stable isotopic data were obtained from 40 subadult skeletons excavated from the Sakai Kango Toshi 871 (SKT871) site (late 17th-19th century, Osaka, Japan). Isotopic results from SKT871 were compared with previously reported results from the Hitotsubashi site (AD 1657-1683, Tokyo, Japan). Hitotsubashi and SKT871 represent urban populations of lower status before and after the transition of societal perception of subadults. RESULTS: The most probable age at the end of weaning reconstructed in SKT871 was 1.9 years (1.4-2.7 years with a 95% credible interval) and was lower than that in Hitotsubashi (2.1-4.1 years with a 95% credible interval). DISCUSSION: The age at the end of weaning became younger after the transition of societal perception toward subadults, and this younger weaning age is inconsistent with written recommendations for the duration of weaning in premodern Japan. It is possible that an increased need for inheritors under the inheritance-based family system led to earlier weaning and shorter inter-birth intervals, but authorities recommended an ideal practice of a longer breastfeeding period.