At the far end of South Africa's fossil record, two fossil hands recount the story of evolution as a twisted climb—literally, sometimes! New evidence about the fossil finger bones of Australopithecus sediba and Homo naledi, documented in a brilliant new study, is remaking the evolution of human dexterity, not as a smooth march toward tool-making precision, but as a more nuanced mosaic of manipulative and mobile adaptations.
Discovered in 2010 at the Malapa site, A. sediba lived about two million years ago. Its hand is an intriguing combination of characteristics—ape-like in some, but curiously human in others. Fast-forward over 1.7 million years to H. naledi, initially discovered deep in the Rising Star Cave system, and you have another mystery: a hand more human-like in some respects, but still possessing features well-adapted to climbing.
These two species, hundreds of thousands of years apart and subject to the whimsical forces of evolution, may have traversed the planet using a combination of grasp, grip, and grit.
Finger Anatomy: A Ledger of Human Labor
Most telling about this research is the approach. Directed by Samar Syeda, a postdoctoral researcher at the American Museum of Natural History, the researchers examined the internal make-up of the bones in the fingers—the cortical bone. Their finds have published in the latest edition of the journal Sciences Advances in an open access form.
This living tissue reconstructs according to stress throughout a person's lifetime and becomes denser where repeated stress or pressure is experienced. It's essentially a quiet ledger that keeps tabs on a lifetime of hand labor.
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In A. sediba, the thumb and pinky cortex pattern are similar to that of modern humans—suggesting that these fingers were used often in precision and manipulation tasks, maybe even in tool use. The rest of the fingers, however, retain an apelike pattern, suggesting continued use for climbing or suspension.
Living reconstruction in the Neanderthal Museum (Erkrath, Mettmann) of an Australopithecus sediba, locality Malapa, South Africa.
(Neanderthal-Museum Mettmann/CC BY-SA 4.0)
Combined with the species' unusually long and human-like thumb, the evidence suggests a two-purpose hand: one happy to grasp branches as much as it is to fashion stone.
H. naledi, however—literally—had a strange mix of traits in individual fingers. Its proximal phalanges (fingers' bones nearest the palm) showed a human-like pattern of loading, but its intermediate phalanges (mid-finger bones) showed evidence of ape-like stress.
"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," says senior author, Tracy Kivell, in a press release by the Max Plank Institute for Evolutionary Anthropology.
The Crimp Grip: Holding on For Dear Life
This strange internal anatomy suggests that H. naledi used grip patterns stressing the tips of the fingers—i.e., the "crimp grip" familiar to modern rock climbers. The implication? These ancient hominins may have climbed not just trees, but rocks or vertical cave walls, a behavior supported by the architecture of the Rising Star Cave, including steep slopes and narrow passages.
Palmar (left) and dorsal (right) views of the right-hand bones, found in situ in semi-articulation with the palm up and fingers flexed. (Tracy Kivell/CC BY 4.0 Wikimedia Commons)
Indeed, it's difficult to conceive that H. naledi ventured into its cave system with little climbing capability. Chamber entrances deep within the ground would have necessitated a high level of vertical mobility to access these areas. That its fingers evolved to such mechanical pressures while maintaining aspects related to manipulation is a testament to its adaptability—and a complication to any story that pictures a straightforward trade-off between climbing and tool-making, reports IFL Science.
What the research provides is a picture of hominin hand evolution as a series of intersecting experiments. Instead of a unique linear progression to more dexterous, tool-holding hands, the fossil record shows a diversity of forms—each balancing the mechanical demands of climbing, holding, and manipulating in a multitude of ways. Instead of a single route to the modern human hand, there were many routes across the ancestral landscape.
This evolutionary improvisation also suggests a higher truth: the hand anatomy of our ancestors not only tells us what they were capable of, but how they lived. Hands don't evolve independently—they evolve along with locomotion, environment, and behavior. And with both A. sediba and H. naledi, we're getting a glimpse of animals adapting to complex environments where survival demanded versatility, not specialization.
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While neither of these species has been directly associated with tools, their hand shape suggests that tool use potential was not limited to our immediate line. Dexterity might have evolved in different forms in different lines, from different combinations of necessity, opportunity, and anatomy.
Finally, these fossil fingers are not anatomical curiosities, but behavioral artifacts, and they tell us about the way early hominins moved around their world, what they held onto, what they climbed up, and even perhaps what they made. Not so much transitional intermediates along the way to us, these animals like A. sediba and H. naledi were pioneers in their own right—holding on for dear life to the trees, the cliffs, and even perhaps to the invention of culture.
"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," concludes Kivell.
Top image: The jaw and right hand of a Homo naledi at the Natural History Museum in London, England. Source: Emőke Dénes, Wikimedia Commons (CC BY-SA 4.0)
By Sahir
References
Samar M. Syeda et al. 2025. Phalangeal cortical bone distribution reveals different dexterous and climbing behaviors in Australopithecus sediba and Homo naledi. Sciences Advances, 11. Available at: DOI:10.1126/sciadv.adt1201.
Taub, B. 2025. Homo Naledi Had Hands That Rock Climbers Would Be Jealous Of. Available at: https://www.iflscience.com/homo-naledi-had-hands-that-rock-climbers-would-be-jealous-of-79197.
