Secular Change: Confounding Factor or Causative Factor of Inter-population Differences in Modern Japanese Crania?

Abstract

Basic statistics on cranial measurements from 15 modern Japanese populations were compiled by the Commission of Anthropological Investigation of Modern Japanese Crania. These data were analyzed in order to evaluate the magnitude of inter-population differences and the influence of secular change on the interpopulation differences. Cranial measurements taken for four populations from the late Edo period were used to estimate the inter-population differences that can be caused by systematic inter-observer measurement errors and by the bias in the sampling. The distance measures based on the measurement items with small intraand inter-observer measurement errors indicate that the inter-population differences in modern Japanese crania are much greater than the differences caused by the measurement error. However, the differences caused by sample bias are as large as some of the inter-population differences. The results of cluster analyses indicate that the influence of secular change can not be ignored. According to the results of discriminant analysis, the key characteristic in determining inter-population difference is maximum cranial breadth. Since secular change is observed in seven out of 13 measurement items with significant inter-population differences, a considerable part of so-called geographic differences among modern Japanese crania is likely to be due to the secular change that took place during the 100 year period required to collect the materials.