In primates, the degree of phalangeal shaft curvature is directly related to the frequency of arboreal behavior. Curved fingers and toes aid in the ability to grasp onto a curved branch. Species that spend a great deal of time in suspensory behaviors have more curved phalangeal shafts, while species not habitually suspensory have relatively flat phalangeal shafts. When comparing human phalanges with those of chimpanzees, the shaft of the human phalanx is relatively straighter than a chimpanzee. Lucy shows an intermediate curvature between those of modern humans and chimpanzees, which suggest that Lucy was still engaged in some amount of arboreal behaviors.