Structural properties of humeral diaphyses of East Asian modern humans from the Late Pleistocene to Early Holocene

Objectives This study aims to explore the structural properties along entire humeral diaphyses of Late Pleistocene and Early Holocene East Asian modern humans relative to the contemporaneous Neandertal specimen Regourdou 1 to provide insight into adaptive behaviors within temporal and regional hominin contexts. Materials and methods The humeri of three individuals from East Asia securely dated from the Late Pleistocene to Early Holocene were selected: Tianyuan 1, Zhaoguo M1, and Qihe M2. These specimens were scanned using microcomputed tomography to evaluate structural properties: cortical bone thickness (CBT), second moment of area (SMA), external radius (ER), and polar moment of area (J). Results The distribution patterns of CBT, ER, and J were similar across all specimens. However, the magnitude of these variables was notably large in Regourdou 1 right humerus. The SMA, ER, and J of left humerus of Tianyuan 1 were less than that of other East Asian specimens, whereas those from the right humerus of the Qihe M2 individual were slightly larger than two other East Asian individuals. Additionally, the humeral asymmetry of Tianyuan 1 was greater than that of Zhaoguo M1 and Qihe M2. Discussion Compared to Regourdou 1, East Asian specimens had reduced humeral robusticity. Within East Asia, the Late Pleistocene modern humans exhibit greater humeral asymmetry than the Early Holocene humans, indicating a universal reduction of humeral asymmetry related to technological changes across Eurasia during this time. The current study contributes to developing a more thorough understanding of intergroup humeral structural variation across Eurasia during the Late Pleistocene and Early Holocene.