Bilateral Asymmetry of the Humerus in Jomon People and Modern Japanese.

Abstract

In the present study, I examined the bilateral asymmetries of several morphological characters of the humerus of 63 modern Japanese (male 46, female 17) and 40 Jomon people (male 20, female 20) with the aim of distinguishing between metric features that are strongly affected by mechanical loading and those that are not, and to discuss the loading conditions of the upper arms of Jomon people. The results were that the bilateral asymmetries of humeral length and all other measurements except for proximal epiphyseal breadth did not correlate significantly with asymmetries of diaphyseal geometric properties. Since the longitudinal growth of a long bone stops when its epiphyses are fused with the metaphyses while corticla remodelling goes on for life, the present results can be interpreted as follows: 1) Bilateral asymmetries in the longitudinal direction is likely to reflect the cumulative loading conditions to around an age of 20 years, and 2) bilateral asymmetries in the tranverse direction reflects loading conditions relatively close to the time of death. Regarding the loading conditions inferred for the upper arms of Jomon people, it is suggested that they were stronger than in modern Japanese and some hunter-gatherers (Amerindians). The loading conditions of the upper arms of Jomon people were also likely to be less asymmetric than in other populations, while differing considerably between sexes.

A Study on the Asymmetry of the Human Left and Right Pubic Symphyseal Surfaces Using High‐Definition Data Capture and Computational Shape Methods

“…It is already well‐established that different skeletal elements and bone features exhibit different degrees of asymmetry . Particularly, it is known that biomechanical stress, one of the causal factors for skeletal asymmetry, has greater impact on bone diaphysis rather than epiphyses , suggesting there is less environmental plasticity in the epiphyseal/articulating region and that variation in this region is more genetically constrained . In line with these findings, the lack of both directional and absolute asymmetry in age‐estimates observed in the paired pubic symphyses in our study is possibly due to the bone's resilience to biomechanical stress/physical loading, a conclusion supported by the low correlations between individual body size and age‐at‐death observed for the sample.…”

Analyses of sexual dimorphism of reconstructed pelvic computed tomography images of contemporary Japanese using curvature of the greater sciatic notch, pubic arch and greater pelvis

“…Several investigations of asymmetry in the lower body, such as in the lower limbs, lumbar spine and articular facet, have been reported [35][36][37][38][39]. These studies demonstrated that bilateral asymmetries were mainly attributable to differential loading to the left-sided bones resulting from right-handedness.…”

Limb bone bilateral asymmetry: variability and commonality among modern humans

“…Therefore, arcsine transformations did not produce normal distributions (Sokal and Rohlf, 1995) and most analyses were conducted using nonparametric tests on non-transformed data. For this reason, we also emphasize median asymmetry values in our summary statistics, although we also include mean asymmetries for comparison with previous studies that employed this statistic (Ruff and Jones, 1981;Sakaue, 1998;Mays, 2002).…”

“…Specifically, several studies have found less asymmetry in lengths or articular dimensions than in diaphyseal breadths or cross-sectional dimensions of the same skeletal elements (Ruff and Jones, 1981;Trinkaus et al, 1994;Churchill and Formicola, 1997;Sakaue, 1998; but see Krahl et al, 1994). This finding appears to be consistent with experimental evidence for less environmental plasticity of bone length or epiphyseal size compared to cross-sectional diaphyseal morphology (Lanyon, 1980;Lieberman et al, 2001).…”