The Homo naledi shoulder girdle: An adaptation to boulder climbing

Homo naledi, a recently discovered hominin species from the Rising Star cave complex in Gauteng Province, South Africa, is a surprising species in more ways than one. The conditions of accumulation, as well as the location of these remains in the cave are intriguing, as is their age of approximately 300,000 years. Likewise, the number of remains as well as their state of preservation are exceptional. But the most astonishing discovery of all is represented by the general morphology of this new species, with an upper body adapted to climbing and the lower body presenting important adaptations to bipedalism. The shoulder joint, in conjunction with the overall morphology of the upper limb, indicates the ability to move on vertical supports. These characteristics have been interpreted as being the hallmark of arboreal behavior; however, the tree cover in the region 300,000 years ago was very similar to that of today that is to say, very sparse. Thus, we suggest that the morphology of the pectoral girdle and upper limb in H. naledi represents adaptations not to arboreal behavior, but to behavior related to movement across and climbing on rocky walls.