Hands from two hominin species show the path to dexterity and tool use was gradual

American Association for the Advancement of Science (AAAS)—Hand remains from two ancient hominins found in South Africa have human-like finger characteristics useful for object manipulation, even though both species still regularly climbed trees, a new study* finds. However, the human-like hand features in each species – Australopithecus sediba and Homo naledi – differ from each other. The findings ultimately support the hypothesis that musculoskeletal hand evolution – a necessity for learning to use tools – was not a linear journey in Plio-Pleistocene hominins. Learning to use tools was a pivotal event in the history of the genus Homo. Until now, it’s been debated whether hominin hands lost traits adapted for climbing in trees before they developed object manipulation traits, or if manipulation and human-like dexterity emerged more gradually. Samar Syeda and colleagues examined two near-complete hand remains from these two hominins. Both had human-like traits in their fingers that differed from each other. The thumb base of A. sediba showed features that likely supported manipulation, while H. naledi’s hand had human- and Neanderthal-like features in its radial carpometacarpal joints, which connect the fingers to the carpal bones in the wrist. Each species’ hands also had traits to help them climb trees. The work shows that key traits for manipulation and tool use evolved while early humans were still climbing, suggesting that the road to human dexterity was anything but straightforward.

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3D color maps of cortical bone distribution in fossil and extant hominin phalanges.  Syeda et al., Sci. Adv. 11, eadt1201 (2025)

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Standardized average J and phalangeal curvature of A. sediba and H. naledi in relation to an extant and fossil comparative sample. (B) Phalangeal curvature measured via included angle, with images depicting proximodistal
curvature of the dorsal shaft in a representative third proximal and intermediate phalanx for each taxon. Reported curvature values represent the average of
digits 2 to 5 for the proximal and intermediate phalanges.  Syeda et al., Sci. Adv. 11, eadt1201 (2025)

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Article Source: AAAS news release