The structure and function of the hand and foot of Homo naledi are described in two separate papers published online in Nature Communications this week. Taken together, the findings indicate that H. naledi may have been uniquely adapted for both tree climbing and walking as dominant forms of movement, while also being capable of precise manual manipulation.
Modern humans (Homo sapiens) and extinct human species, including Homo neanderthalensis, Homo erectus, Homo habilis and Homo naledi, are part of the Homo genus. The Homo genus and the Australopithecus genus (extinct, close relatives of Homo) are together referred to as hominins.
In the first paper, Tracy Kivell and colleagues describe the H. naledi hand based on nearly 150 hand bones, including a nearly complete adult right hand, uncovered from the Dinaledi Chamber of the Rising Star cave system in South Africa. The H. naledi hand shares a long, robust thumb and wrist architecture with Neanderthals and modern humans. However, the finger bones are longer and more curved, suggesting the hand was used for movement and climbing through trees in combination with the forceful, precision manipulation required to use tools.
In the second paper, William Harcourt-Smith and colleagues describe the H. naledi foot based on 107 foot elements from the Dinaledi Chamber, including a well-preserved adult right foot. They show that the H. naledi foot shares many features with a modern human foot, indicating that it is well-adapted for standing and walking on two feet. However, the authors note that it differs in having more curved toe bones (proximal phalanges).
When considered together, these papers indicate a decoupling of upper and lower limb function in H. naledi, providing an important insight into the skeletal form and function that may have characterized early members of the genus Homo.