Among hominins, the degree of curvature observed in the phalangeal shaft correlates with the frequency of arboreal behavior. Species that spend a lot of time grasping or suspending from curved branches have dramatically curved fingers and toes which allows for a more powerful grip. Non-arboreal primates, such as humans, have relatively flat manual and pedal phalanges, an adaptation reflecting a lack of regular arboreal activity. This, in turn, has facilitated the evolution of precise hand movements necessary for making and using tools. Highly curved phalanges reduce the capacity for precision grips.
Australopith phalanges are intermediately curved between those of modern humans and great apes, suggesting that climbing and arboreal behavior continued to play some role in the lifestyle of these early hominins6,9,12.
