title: Weaning age in an expanding population: stable carbon and nitrogen isotope analysis of infant feeding practices in the Okhotsk culture (5th-13th centuries AD) in Northern Japan.
abstract: OBJECTIVE
  The Okhotsk people were sedentary hunter-gatherer-fishers who lived and prospered in Sakhalin, Hokkaido, and the Kurile Islands during the 5th to 13th centuries AD. They expanded rapidly along the northeastern coast of Hokkaido. We reconstructed infant feeding practices of the Moyoro population of the Okhotsk culture in eastern Hokkaido, Japan.
  
  
  METHODS
  Stable isotope ratios in 58 subadult human skeletons were measured.
  
  
  RESULTS
  The results suggest that complementary foods with a relatively low carbon isotope ratio were consumed during and after weaning, as observed in ethnographic descriptions of northern human populations such as the Ainu and isotopically suggested in ancient northern hunter-gatherer-fisher populations. Nitrogen isotope ratios of subadults showed that the age at the end of weaning in the Moyoro population was 1.8 (1.4-2.2 in 95% credible interval) years, which is earlier than that in other northern hunter-gatherer-fisher populations.
  
  
  CONCLUSIONS
  Because weaning age is one of the most important determinants of fertility, a shorter breastfeeding period suggests increased fertility. Furthermore, better nutrition would further promote the population increase, and thus populations of the Okhotsk culture could expand into new regions. These findings are consistent with recent emerging evidence of great contributions of the Okhotsk to the formation of later Ainu populations and culture.
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, the University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8561, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Tsutaya
authors.affiliation: Department of Human Biology and Anatomy, Graduate School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa, 903-0215, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Ishida
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, the University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8561, Japan.|The University Museum, the University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo, 113-0033, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Yoneda
mesh_terms: D000293:Adolescent; D001942:Breast Feeding / Q000266:history*; D002247:Carbon Isotopes / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005298:Fertility; D049691:History, Medieval; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007564:Japan / Q000208:ethnology; D008297:Male; D009587:Nitrogen Isotopes / Q000032:analysis*; D012272:Ribs / Q000737:chemistry; D012886:Skull / Q000737:chemistry; D014886:Weaning / Q000208:ethnology*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes
keywords: Hokkaido; breastfeeding; complementary food; fertility; hunter-gatherer-fisher