Ancient Hands Reveal Diverse Gripping Abilities in Early Hominins

New research has shed light on the gripping abilities of early human ancestors in South Africa, revealing distinct differences in hand function and dexterity. Scientists from the Max Planck Institute for Evolutionary Anthropology, along with colleagues from the American Museum of Natural History, the University of the Witwatersrand, University of Kent, Duke University, and the National Geographic Society, analyzed fossil hand bones to uncover insights into how these ancient hominins may have used their hands.

The study examined two nearly complete hand skeletons from South Africa, including the hand of Australopithecus sediba, discovered in 2010 at the Malapa site and dated to around two million years ago, and the hand of Homo naledi, first unearthed in 2015 deep within the Rising Star Cave system and estimated to be about 250,000 years old.

While neither species has been directly associated with stone tools, aspects of their hand and wrist structures suggest that both had a degree of manual dexterity more comparable to that of modern humans than to living great apes like chimpanzees and gorillas. "Since stone tools are found in South Africa by at least 2.2 million years ago (and in East Africa by as early as 3.3 million years ago), and many primates are all excellent stone tool users, it is not surprising that A. sediba and H. naledi would be dexterous tool users as well. However, how exactly they used tools and if they manipulated their tools in similar ways is unclear," said senior author Tracy Kivell.

The analysis focused on the internal structure of the finger bones, specifically the cortical bone, which adapts over a lifetime based on how an individual uses its hands. "We found that A. sediba and H. naledi show different functional signals in the cortical bone structure of their fingers," said lead author Samar Syeda. In A. sediba, the thicker cortical bone distribution in the thumb and pinky fingers suggests potential for fine manipulation, consistent with both tool use and climbing. In contrast, H. naledi displayed a unique pattern, with human-like traits in the bones that connect to the palm and more ape-like traits in the mid-finger bones, suggesting a gripping style similar to the crimp grip used by modern rock climbers.

This finding highlights the varied evolutionary experiments in hand use among early human ancestors, reflecting the diverse challenges faced as these species adapted to their environments. "This work offers yet more evidence that human evolution is not a single, linear transition from upright walking to increasingly better tool use, but is rather characterized by different 'experiments' that balanced the need to both manipulate and to move within these past environments," Kivell added.

Research Report:Phalangeal cortical bone distribution reveals different dexterous and climbing behaviors in Australopithecus sediba and Homo naledi