Phalangeal cortical bone distribution reveals different dexterous and climbing behaviors in <i>Australopithecus sediba</i> and <i>Homo naledi</i>

The evolution of the human hand is marked by a transition from a hand primarily used for locomotion to one primarily used for dexterous manipulation. The hand skeletons of Plio-Pleistocene hominins have different mosaics of human-like features associated with enhanced dexterity and ape-like features associated with locomotor hand use. However, the functional relevance of the ape-like features is debated, particularly due to a lack of complete and associated hand remains. Here, we investigate the internal phalangeal cortical structure of the nearly complete <i>Australopithecus sediba</i> MH2 hand and <i>Homo naledi</i> hand 1 to provide both insight into the manual behaviors of these fossil hominins and functional clarity regarding the mosaic features found within their hands. The phalangeal cortical structure demonstrates diversity in Plio-Pleistocene hand use, with <i>A. sediba</i> and <i>H. naledi</i> each indicating different dexterous abilities and different climbing strategies, supporting the functional importance of the ape-like features.