Morphology and structure ofHomo erectushumeri from Zhoukoudian, Locality 1

Abstract

BackgroundRegional diversity in the morphology of theH. erectuspostcranium is not broadly documented, in part, because of the paucity of Asian sites preserving postcranial fossils. Yet, such an understanding of the initial hominin taxon to spread throughout multiple regions of the world is fundamental to documenting the adaptive responses to selective forces operating during this period of human evolution.MethodsThe current study reports the first humeral rigidity and strength properties of East AsianH. erectusand places its diaphyseal robusticity into broader regional and temporal contexts. We estimate true cross-sectional properties of Zhoukoudian Humerus II and quantify new diaphyseal properties of Humerus III using high resolution computed tomography. Comparative data for AfricanH. erectusand Eurasian Late PleistoceneH. sapienswere assembled, and new data were generated from two modern Chinese populations.ResultsDifferences between East Asian and AfricanH. erectuswere inconsistently expressed in humeral cortical thickness. In contrast, East AsianH. erectusappears to exhibit greater humeral robusticity compared to AfricanH. erectuswhen standardizing diaphyseal properties by the product of estimated body mass and humeral length. East AsianH. erectushumeri typically differed less in standardized properties from those of side-matched Late Pleistocene hominins (e.g., Neanderthals and more recent Upper Paleolithic modern humans) than did AfricanH. erectus, and often fell in the lower range of Late Pleistocene humeral rigidity or strength properties.DiscussionQuantitative comparisons indicate that regional variability in humeral midshaft robusticity may characterizeH. erectusto a greater extent than presently recognized. This may suggest a temporal difference withinH. erectus, or possibly different ecogeographical trends and/or upper limb loading patterns across the taxon. Both discovery and analysis of more adultH. erectushumeri are critical to further evaluating and potentially distinguishing between these possibilities.