The human lineage is marked by a transition in hand use, from locomotion towards increasingly dexterous manipulation, concomitant with bipedalism. The forceful precision grips used by modern humans probably evolved in the context of tool manufacture and use, but when and how many times hominin hands became principally manipulative remains unresolved. We analyse metacarpal trabecular and cortical bone, which provide insight into behaviour during an individual’s life, to demonstrate previously unrecognized diversity in hominin hand use. The metacarpals of the palm in Australopithecus sediba have trabecular morphology most like orangutans and consistent with locomotor power-grasping with the fingers, while that of the thumb is consistent with human-like manipulation. This internal morphology is the first record of behaviour consistent with a hominin that used its hand for both arboreal locomotion and human-like manipulation. This hand use is distinct from other fossil hominins in this study, including A. afarensis and A. africanus.
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The data used to generate the analyses and graphs are available at: https://data.kent.ac.uk/id/eprint/111
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We thank I. Livne (Powell-Cotton Museum), A. vanHeteren and M. Hiermeier (Zoologische Staatssammlung München), C. Boesch and U. Schwarz (Max Planck Institute for Evolutionary Anthropology), A. Ragni (Smithsonian Institution, National Museum of Natural History); M. Teschler-Nicola and R. Muehl (Natural History Museum, Vienna), J. Moggi-Cecchi and S. Bortoluzzi (University of Florence), F. Mayer (Museum für Naturkunde—Leibniz Institute for Evolution and Biodiversity Science, Berlin), B. Großkopf (Johann-Friedrich-Blumenbach-Institut für Zoologie und Anthropologie der Georg-August-Universität Göttingen), R. Macchiarelli (Museo Nazionale Preistorico Etnografico ‘Luigi Pigorini’), B. Zipfel (University of the Witwatersrand), E. Gilissen and W. Wendelen (Musée Royal de l’Afrique Centrale), V. Volpato (Senckenberg Museum of Frankfurt), D. Nadel (University of Haifa) and I. Herskovitz (Tel Aviv University) for access to specimens in their care. We also thank D. Plotzki (Max Planck Institute for Evolutionary Anthropology) and K. Smithson (Cambridge Biotomography Centre) for assistance in scanning these specimens, as well as M. Tocheri for assistance with landmarking software and L. Georgiou for discussions that enhanced this manuscript. For the Malapa project, we thank the South African Heritage Resources Agency and the Nash family for permissions, and the South African National Centre of Excellence in PalaeoSciences, the Lyda Hill Foundation, South African Department of Science and Technology, the South African National Research Foundation, the Evolutionary Studies Institute, University of the Witwatersrand, the University of the Witwatersrand’s Vice Chancellor’s Discretionary Fund, the National Geographic Society, the Palaeontological Scientific Trust, the Andrew W. Mellon Foundation, the Ford Foundation, the U.S. Diplomatic Mission to South Africa, the French embassy of South Africa, the Oppenheimer and Ackerman families, and Sir Richard Branson for funding. This research was supported by the Spanish MICINN/FEDER (CGL2016-75109-P), European Research Council starting grant no. 336301, European Union’s Horizon 2020 research and innovation programme (grant no. 819960), the Max Planck Society and the Fyssen Foundation.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
(a) An isosurface model of the metacarpus with inset parasagittal cross-section of the thumb metacarpal. (b) 3D isosurface showing inner trabecular structure of the metacarpus. (c) Segmented 2D cross-section of the thumb metacarpal (left), cortical and trabecular segmentation (centre), regular background grid overlaid on the isolated trabecular structure (right) and a close-up of this grid with a representation of the overlapping volumes of interest (VOIs) centred at each vertex of the background grid in purple (top). (d) Interpolation of BV/TV values, measured in overlapping VOIs, onto 3D trabecular meshes. (e) Anatomical landmarks (red), sliding semi-landmarks on curves (blue) and across the subarticular surfaces (green) on the smoothed surface of the trabecular models. (f) BV/TV values interpolated to each landmark and then divided by the mean value of each articular surface to produce RBV values on each landmark.
(a) A parasagittal cross-section image with its manual proximo-distal axis marked in blue and the computed eigenvector that best describes this axis marked in red. (b) The 3D image is rotated by the angle between the two axes (green arrows). (c) The cross-section of the rotated image shows the eigenvector now equals the proximo-distal axis of the bone and a 50% coronal cross-section, marked in orange, is orthogonal to the new axis. The position of this 50% diaphyseal mid-slice shown in 3D (d) and the anatomical axes used to calculate directional moments of inertia are radioulnar (RU), dorsopalmar (DP). The minimum (Imin) and maximum (Imax) moments of inertia calculated for this bone are depicted (f) and were averaged to generate the average area moment of inertia (Iavg, mm4).
(a) distal, (b) palmar and (c) dorsal views. Also, (d) depicts the average distributions of RBV across the thumb metacarpal (Mc1) base and (e) displays distal, palmar, dorsal and proximal views of individual fossil thumb metacarpals.
Supplementary Tables 1–7 and refs. 55–71.
An interactive 3D PCA depicting subchondral RBV variation across the finger metacarpals (Mc2–5). Each point represents the pattern of RBV across an associated metacarpus in one individual. Fossils are plotted in black and labelled.
An interactive 3D PCA depicting subchondral RBV variation across both subchondral surfaces on thumb metacarpals (Mc1). Each point represents the pattern of RBV across both subchondral surfaces in one individual. Fossils are plotted in black and labelled.
An interactive 3D PCA depicting subchondral RBV variation across the finger metacarpals (Mc2–4). Each point represents the pattern of RBV across an associated metacarpus in one individual. Fossils are plotted in black and labelled.
An interactive 3D PCA depicting subchondral RBV variation across the finger metacarpals (Mc2, 3 and 5). Each point represents the pattern of RBV across an associated metacarpus in one individual. Fossils are plotted in black and labelled.
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Dunmore, C.J., Skinner, M.M., Bardo, A. et al. The position of Australopithecus sediba within fossil hominin hand use diversity. Nat Ecol Evol 4, 911–918 (2020). https://doi.org/10.1038/s41559-020-1207-5
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