Early modern human remains from eastern Asia: The Yamashita-cho 1 immature postcrania

One of the oldest, well-dated, early modern human specimens from eastern Asia is the Okinawan Yamashita-cho 1 juvenile (ca. 6 year old) femur and tibia, ¹⁴C dated to > 32,000 BP. The diaphyses of the specimen are compared with recent human and archaic Homo juveniles using cross-sectional geometric parameters (areas and second moments of area obtained through external molding and multiple plane radiography) to assess axial and bending strengths. Despite an incipient femoral pilaster (not seen in archaic Homo but predominant among early modern humans), the Yamashita-cho 1 femoral and tibial midshafts fall close to the archaic humans and at the limits of recent human variation in terms of diaphyseal cross-sectional shape [I_x/ I_y, I_max/ I_min, % cortical area (CA)] and robusticity [CA-STD and polar second moment of area (J)-STD]. In contrast, the Yamashita-cho 1 femoral neck-shaft angle of 136° and its predicted adult value of ca. 132° place it well above those of archaic Homo, and close to the values for African, Near Eastern and more recent eastern Asian early modern humans. In this respect, Yamashita-cho 1 is aligned with early modern humans. These data provide a mosaic pattern, in which diaphyseal robusticity and the cross-sectional distribution of bone parallel those seen in archaic Homo, whereas the presence of an incipient pilaster and the high neck-shaft angle align the specimen with early modern humans. Given that most of these features are developmentally plastic, these imply a changing ontogenetic pattern of lower-limb loading regimes in eastern Asia associated with the emergence of modern humans.