Ancient Hands, Dual Lives: Fossils Reveal Early Human Relatives Climbed and Crafted

New “Science Advances” study on Australopithecus sediba and Homo naledi finger bones shows a complex, non-linear evolution of hand use, challenging simpler narratives of our ancestors’ journey from tree-dweller to tool-maker.

Our hands tell stories of our lives – the calluses of a laborer, the nimble fingers of a musician. For our ancient human ancestors, too, their hands are now revealing intricate tales of survival and adaptation, thanks to cutting-edge analysis of their fossilized bones. A new study published this week in the prestigious journal Science Advances provides compelling evidence that two early hominin species, Australopithecus sediba and Homo naledi, skillfully used their hands for both adept climbing and sophisticated object manipulation, activities often seen as pulling in different evolutionary directions.

The research, led by Dr. Samar Syeda, a postdoctoral researcher at the American Museum of Natural History, along with a collaborative team from institutions including the Max Planck Institute for Evolutionary Anthropology, the University of the Witwatersrand, and the University of Kent, delves deep into the internal structure of finger bones. The team focused on nearly complete hand skeletons from two significant South African fossil finds: the MH2 specimen of Australopithecus sediba, which lived approximately 2 million years ago, and the Hand 1 specimen of Homo naledi, a more recent relative dated to around 250,000 to 300,000 years ago.

Decoding Behavior from Bone

The scientists employed 3D scanning techniques, likely micro-CT scans, to meticulously measure the thickness and distribution of cortical bone, the dense outer layer, within the phalanges (finger bones). This method is based on a fundamental biological principle: bone remodels and thickens in response to repeated mechanical stress. Just as weightlifting builds muscle and bone density, activities like gripping branches, climbing cliffs, or fashioning tools leave an indelible signature in the skeletal structure.

“The internal architecture of the bone reflects the loads it experienced during the individual’s lifetime,” explained Dr. Tracy L. Kivell of the University of Kent, a senior author often involved in such functional morphology research. “By analyzing these patterns, we can reconstruct how these ancient hands were habitually used, offering us a window into their behavior.”

A Tale of Two Hominins: Different Grips, Different Lives

While both species showed this dual capability for climbing and manipulation, the specifics of their hand use, as revealed by their bone structures, differed interestingly:

Australopithecus sediba: This 2-million-year-old hominin, known from the Malapa site, presented a fascinating mosaic. The cortical bone in most of its finger segments (proximal and intermediate phalanges) showed an ape-like pattern, suggesting significant loading consistent with climbing or suspensory behaviors. However, its thumb and pinky finger bones told a different story, exhibiting a more human-like pattern.

This indicates these digits were frequently used for precise manipulation, potentially for tool-related tasks or other dexterous activities. This finding is particularly compelling given A. sediba‘s remarkably long, human-like thumb, though some previous studies have noted it might have been somewhat gracile, perhaps limiting the force of its precision grips.

Homo naledi: The hand of this enigmatic species, discovered deep within the Rising Star Cave system, revealed an even more unique pattern. Its proximal phalanges (the finger bones closest to the palm) displayed a human-like loading signature, suggesting they were well-adapted for forceful manipulation, perhaps akin to tool use. Yet, moving further down the fingers, the intermediate phalanges showed an ape-like stress pattern, indicative of climbing.

This unexpected combination has led researchers to propose that H. naledi may have utilized specialized grips, such as the “crimp grip” familiar to modern rock climbers. Such a grip, where the fingertips bear significant weight with the middle part of the finger acutely angled, would be consistent with the observed bone patterns and could have been vital for navigating the treacherous, narrow passages of the cave system where its remains were found, or for scaling rock faces. This interpretation aligns with H. naledi‘s known anatomy: a robust, manipulative thumb and human-like wrist, paired with surprisingly long, curved fingers ideal for grasping.

Rewriting Hand Evolution

The implications of these findings are profound, further challenging the traditional, linear view of human hand evolution—a simple march from an ape hand primarily for locomotion to a human hand specialized for toolmaking.

“What we’re seeing is a much richer, more complex picture,” commented Smithsonian paleoanthropologist Dr. Rick Potts, who was not involved in the new study but has reviewed similar research. “There wasn’t a single moment or a straight line where hands stopped being for climbing and started being for tools. Different hominins were clearly using their hands in diverse ways, balancing the demands of their environments.”

Indeed, both A. sediba and H. naledi are known to possess other ape-like features in their upper limbs that would have been advantageous for climbing. This new study adds functional evidence from the hands themselves, suggesting that arboreal activity remained an important part of their behavioral repertoire, even as they developed enhanced manipulative skills.

“Neither of these hominin species has been found in direct association with stone tools at their respective sites,” Dr. Syeda noted. “However, the morphology of their hands, particularly the internal bone structure, strongly suggests they possessed the dexterity for such activities. It highlights that the potential for tool use may have evolved multiple times and in different ways across the hominin family tree.”

Erin Marie Williams-Hatala, a paleontologist at Chatham University not involved in the project, emphasized the importance of such finds. “Complete fossil hands are incredibly rare. Each one gives us an invaluable opportunity to understand how these individuals interacted with their world. Hands are one of our primary interfaces with our environment, and this research beautifully illustrates the diverse ways our ancestors ‘got a grip’ on theirs.”

Ultimately, this research underscores that the path to modern human hands was not straightforward. It was a journey marked by versatility, with different ancestral species striking unique balances between the ancient necessity of climbing and the emerging advantages of manual dexterity—a testament to the adaptability that is a hallmark of human evolution. These fossil fingers, once animated by the struggles and successes of ancient lives, continue to speak to us, revealing the nuanced story of how we came to be.