Paper short abstract:

To date, several anthropologists have estimated the life expectancy of Jomon people. However, those estimations are all skeptical due to possible sampling biases and the erroneous age estimations of the skeletal remains. I estimated the life expectancy by using their teeth and the Bayesian approach, to circumvent those problems.

Paper long abstract:

According to several reports of demographic survey on the modern hunter-gatherer populations, their life expectancies at age 15 range between 32 and 55 years. Contrarily, the life expectancy of Jomon people was once estimated as about 16 years, based on estimated ages of the skeletal remains. There are, at least, two errors that may have caused the estimation for Jomon life expectancy to be too short. One is the sampling bias preferring young skeletons to old ones. The other is the biased age estimation caused by the age distribution of reference samples dominated by young skeletons. Sampling tends to prefer young-adult skeletons because young adults have more durable skeleton and, after the death, more likely preserve their skeletal parts for the age estimation than old ones. The reduction of bone-remodeling activity in the old age is presumably the cause for the differential preservation. To circumvent this problem, I used the tooth as the age indicator; the dental pulp volumes were measured and the shrinkages were regarded as showing the progress of age. Unlike in bones, remodeling process does not occur in teeth; thus, the sampling bias caused by differential preservation was expected to be minimized. To circumvent the second problem (the biased age estimation), I employed Bayesian approach; this approach can avoid influence of the age distribution of reference samples. Bayesian approach was employed once before to estimate Jomon life expectancy, but the manner of application was inappropriate. I used and suggest in this paper an appropriate application of Bayesian approach. The result showed that life expectancy of Jomon people at age 15 should have been in between 29 and 42 years, the lower range of the modern hunter-gatherer populations.