A comparative analysis of fetal to adolescent limb segment proportions of prehistoric Jomon hunter-gatherers and modern Japanese

Abstract

Upper and lower limbs of prehistoric Jomon adults are known to have relatively elongated distal segments (forearm and lower leg) compared with those of modern Japanese. In the present study, we compared limb segment proportions (e.g. brachial index, crural index, intermembral index) between 118 Jomon and 311 modern Japanese skeletons from the 5th fetal month to 19 years of age. Comparisons were made separately in fetal to infant periods (< 1.5 years), toddler to preadolescent periods (1.5–10 years), and adolescent period (>10 years). Results showed that, in all three age groups, both brachial and crural indices are significantly/near-significantly greater in the Jomon than in the modern Japanese, indicating that the distally elongated intralimb characteristics of the Jomon emerge early in development probably based on genetic factors such as limb pattern formation. In Jomon and modern Japanese, both brachial and crural indices reach the adult levels at least by the age of 1.5 years and remain almost constant throughout the subsequent (toddler to adolescent) development. Results also demonstrated that, in the toddler to preadolescent periods, humeri of the Jomon become elongated at a slower rate than those of the modern Japanese, possibly contributing to the adult Jomon condition of a comparatively short upper arm.