Isotopic evidence of breastfeeding and weaning practices in a hunter–gatherer population during the Late/Final Jomon period in eastern Japan

Abstract

Jomon hunter–gatherers in Japan commonly show Neolithic characteristics, such as intensive utilization of potteries, grinding stones, and many plant food sources. In this study, breastfeeding and weaning practices in a Jomon hunter–gatherer population are investigated to evaluate two hypotheses concerning the relations between utilization of potteries/plant foods and early weaning and children's diet around and after the weaning process. Stable carbon and nitrogen isotope ratios were investigated for 46 subadult and 47 adult human skeletons excavated from the Yoshigo site of the Late/Final Jomon period (approximately 4000–2300 years BP) in eastern Japan. A new analytical procedure was developed and residuals of nitrogen isotope ratios were calculated to cancel out the effect of positive correlation in the carbon and nitrogen isotope ratios. Age changes in the residuals showed that the age at the end of weaning in the Yoshigo population was 3.5 years (2.3–5.5 years in 95% credible interval), which is not younger than that in typical non-industrialized populations and the other skeletal hunter–gatherer populations. Furthermore, most infants were probably weaned using a combination of the same food sources as those eaten by adults. These results suggest that the utilization of pottery and plant food per se is not a sole determinant of the age at the end of weaning in past human populations, and a special diet was not always applied during and just after the weaning process.