Estimation of skeletal adult age distribution of Okhotsk people in northern Japan

Abstract

The demographic structure of prehistoric hunter-gatherer societies has contributed to our understanding of the life history patterns of past human populations. The purposes of this study are to examine the human skeletal remains associated with the Okhotsk culture, to estimate age-at-death distribution using the Buckberry-Chamberlain system of auricular surface aging and the Bayesian approach, and to discuss whether paleodemographic estimates can yield an appropriate mortality profile of prehistoric hunter-gatherers in Japan. The application of the Bayesian theorem to the age-at-death estimation was based on the modern Japanese and Spitalfields known-age collections, assuming uniform, reference, and model prior probabilities. The age distributions of the Okhotsk had low proportions of young adults and high proportions of elderly adults. The results indicated that 24.4-51.3% of individuals were above the age of 55 years. The newly employed technique of the Bayesian estimation yielded the age distributions with significant numbers of elderly individuals, which are contrary to usual paleodemographic estimates. The results of this study suggest direct and plausible evidence of demographic traits in the Okhotsk people and allow us to reveal the mortality schedules of the prehistoric hunter-gatherers that otherwise could not be reconstructed from historical or ethnological records.

Demographic and pathological characteristics of the medieval Japanese: new evidence from human skeletons from Kamakura, Japan

“…Comparative samples for this study were cited from the literature on paleodemography (Nagaoka et al, 2006(Nagaoka et al, , 2012bNagaoka andHirata, 2007, 2008), dental caries (Sakura, 1964;Fujita, 1995;Ohshima, 1996;Todaka et al, 2003), enamel hypoplasia (Sawada, 2010), and violent behavior (Suzuki et al, 1956;Hirata et al, 2004;Nagaoka et al, 2009Nagaoka et al, , 2010Nagaoka, 2012) (Table 1). The chronological ages used in the comparative samples are the Jomon (14500-300 BC), Yayoi (300 BC-300 AD), medieval (1185-1573 AD), and Edo (1603-1687 AD) periods.…”

“…The contingency tables of age and Buckberry and Chamberlain's auricular surface stage for Japanese reference samples (Nagaoka et al, 2012b) were used to calculate the posterior probability of being a particular age conditional on being in a particular state of an age indicator. The prior probabilities used in the calculation are uniform ones, where an equal prior probability is assigned to each age category, because in this assumption the estimated age-at-death distribution of the target sample is independent of that of the reference one (Nagaoka et al, 2012a).…”

“…Table 3. Proportion of individuals classified into subadults and adults from the YCSB-SI and comparative samples (Nagaoka et al, , 2012b All Japan Jomon 6 14 17 17 18 11 3 ns Edo (Nagaoka andHirata, 2007, 2008) Tokyo Edo 6 5 14 31 28 11 4 ns 1 Fisher's exact test between YCSB-SI and comparative samples. ns: not significant.…”

“…Paleodemographers have sought solutions to overcome the difficult problem of age-at-death estimation and a consensus on procedures for estimating age at death from a skeletal sample, the 'Rostock Manifesto,' advocated using the Bayesian theorem to provide a methodological basis for adult aging techniques (Hoppa, 2002). Nagaoka et al (2012b) estimated the age-at-death distribution of the human skeletal remains associated with the Okhotsk culture using the Buckberry-Chamberlain system of auricular surface aging and the Bayesian approach, and obtained an appropriate mortality profile of the prehistoric huntergatherers with a high proportion of elderly individuals.…”

“…Based on the methods and reference sample employed by Nagaoka et al (2012b), this study estimated the age-at-death distributions of YCSB-SI and comparative samples. The distributions obtained here exhibit a high proportion of elderly individuals (17-29%), which is likely to be plausible, since these distributions do not depart from the realistic demographic structures of preindustrialized societies in historical or ethnological records (Kobayashi, 1956;Weiss, 1973;Howell, 1979;Kito, 2000).…”