Population Interaction in the Jōmon Society via 3D Data of Human Crania: Geometric Morphometric Study

Abstract Background The Jōmon period (14,000 to 800 cal BC), when people on the Japanese archipelago engaged mainly in hunting and gathering and experienced relatively more severe climate changes, is an important prehistoric period for investigating how people reacted to environmental fluctuations in human evolutionary history. Anthropologists have extensively discussed the population history of the Jōmon period of the Japanese archipelago via their morphological variations. Some have supported the notion of relative morphological uniformity within the Jōmon population, which could be sustained by widespread population interactions, although others have claimed that spatiotemporal morphological differences (especially geographical clines) may exist to some extent. Objective The aim of this study is to examine the morphological interphase and interregion variations among the Jōmon populations to investigate the population interactions during this period (ie, how widely and continuously they interacted). Methods This study used geometric morphometrics of a much larger sample of 3D data of Jōmon human crania than previous studies (n=363 from 97 sites, including 146 females, 215 males, and 2 unknown-sex individuals). The configurations of landmarks were processed with generalized Procrustes analysis and principal component analysis. The principal scores were statistically analyzed with the Steel-Dwass test. We also compared the Jōmon crania with the Yayoi crania in the same way. Results Notably, the results of statistical tests on the Jōmon crania show that principal component (PC) 1 did not show any significant differences both in spatial and temporal comparisons. Regional differences did not show geographical clines in PC1. PC2 indicated that statistically significant differences were found in some regions (eg, the Tohoku and Tokai regions: Z =6.375, P <.001; the Kanto and Tokai regions: Z =4.880, P <.001), and a gradual geographical cline was found among the different regions and in phases (eg, the Early and Final phases: Z =3.118, P =.02; the Middle and Final phases: Z =4.233, P <.001). Comparative results between the Jōmon and the Yayoi populations also showed that the Jōmon populations were spatiotemporally less varied than the Yayoi populations and that individual variation within a site was more variable in the Jōmon site than that of the Yayoi site. Conclusions This observation is consistent with the possibility that the population interactions of the Jōmon people had been widespread and continuous, which has an important implication for their resilience against severe climate changes at that time. It is possible that the relative stability of the Jōmon society was sustained by their frequent interactions with various populations, as suggested by insights from relevant archeological, ethnographic, and genetic research.