Identifying donkey domestication through changes in cross-sectional geometry of long bones

The initial phases of donkey domestication are difficult to identify in the archaeological record due to late and inconsistent changes in morphology and body size in the earliest domestics. Use of donkeys for load carrying and the management of captive herds resulted in a distinctive behavioral shift away from the free-ranging speed and mobility characteristic of wild asses toward slower, more steady pacing. Given the ability of bone to adapt to its mechanical environment, bone remodeling in the limbs of wild asses and donkeys are evaluated using cross-sectional geometry to determine whether weight bearing or locomotor differences between the wild and domestic forms may be used to recognize early domestication. Cross-sectional data were collected on the humeri, radii, metacarpals and metatarsals of eight wild ass and six donkey skeletons. Wild ass forelimbs have greater overall strength and more cylindrical humeral diaphyses, indicating better resistance to a varied locomotor repertoire. These results demonstrate that analyses of shaft geometry can provide information on changes in locomotor behavior during domestication. Our finding that shifts in gait had greater effects on the morphology of early domestic donkeys than did load-carrying places a new emphasis on understanding selection for gait changes in domestication dynamics.