Size of Apical Phalangeal Tufts
The distal ends of the distal phalanges of the human hand and foot possess flat, mediolateral expansions of bone known as apical tufts. The tufts support the fleshy volar pad (also known as the distal pulp) on the palmar (volar) surface of the finger, as well as the nail on the dorsal surface. Primate species vary in the size of their apical tufts, although none exhibit an expansion as great as that seen in humans. In general, primates engaged in suspensory locomotion tend to have smaller apical tufts, while quadrupedal primates tend to have larger tufts. Enlargement of the human apical tuft may reflect expansion of the digital pulp to enhance friction between the tips of the fingers and held objects (such as hammerstones and lithic cores) in the context of tool manufacture and use.
Tocheri et al., 2008. The evolutionary history of the hominin hand since the last common ancestor of Pan and Homo. J Anat 212: 544-562.