Dunmore, C., Skinner, M., Bardo, A., Berger, L., Hublin, J., Pahr, D., Rosas, A., Stephens, N. and Kivell, T. (2020). The position of Australopithecus sediba within fossil hominin hand use diversity. Nature Ecology and Evolution [Online]. Available at: https://dx.doi.org/10.1038/s41559-020-1207-5.
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.
Rodriguez, A., Pouydebat, E., Chacón, M., Moncel, M., Cornette, R., Bardo, A., Chèze, L., Iovita, R. and Borel, A. (2020). Right or left? Determining the hand holding the tool from use traces. Journal of Archaeological Science: Reports [Online] 31. Available at: https://doi.org/10.1016/j.jasrep.2020.102316.
Currently, approximately 90% of the human population is right-handed. This handedness is due to the lateralization of the cerebral hemispheres and is controlled by brain areas involved in complex motor tasks such as making stone tools or in language. In addition to describing the evolution of laterality in humans, identifying hand preference in fossil hominids can improve our understanding of the emergence and development of complex cognitive faculties during evolution. Several fields of prehistory like palaeoanthropology or lithic analysis have already investigated handedness in fossils hominins but they face limitations due to either the incomplete or the composite state of the skeleton remains or to results replication or method application failure. Wear analysis could provide new complementary data about hand preference evolution and the development of certain complex cognitive functions using indirect evidence (use traces, micro-scars in particular) of the hand holding the stone tool during use. Controlled experiment has been carried out in order to establish a reference collection of tools used with the left and tools used with the right hand. Wear analysis was performed on this corpus using “classical” microscopic approach and geometric morphometric analysis. A machine learning algorithm, the k-NN method, was applied to verify if use traces (micro-scars) could help determine the hand holding the tool during use. The best model, based on parameters referring to invasiveness of micro-scars, was able to correctly determine the hand holding the tool with 75% accuracy.
Georgiou, L., Dunmore, C., Bardo, A., Buck, L., Hublin, J., Pahr, D., Stratford, D., Synek, A., Kivell, T. and Skinner, M. (2020). Evidence for habitual climbing in a Pleistocene hominin in South Africa. Proceedings of the National Academy of Sciences of the United States of America [Online] 117:8416-8423. Available at: https://doi.org/10.1073/pnas.1914481117.
Bipedalism is a defining trait of the hominin lineage, associated with a transition from a more arboreal to a more terrestrial environment. While there is debate about when modern human-like bipedalism first appeared in hominins, all known South African hominins show morphological adaptations to bipedalism, suggesting that this was their predominant mode of locomotion. Here we present evidence that hominins preserved in the Sterkfontein Caves practiced two different locomotor repertoires. The trabecular structure of a proximal femur (StW 522) attributed to Australopithecus africanus exhibits a modern human-like bipedal locomotor pattern, while that of a geologically younger specimen (StW 311) attributed to either Homo sp. or Paranthropus robustus exhibits a pattern more similar to nonhuman apes, potentially suggesting regular bouts of both climbing and terrestrial bipedalism. Our results demonstrate distinct morphological differences, linked to behavioral differences between Australopithecus and later hominins in South Africa and contribute to the increasing evidence of locomotor diversity within the hominin clade.
Dunmore, C., Bardo, A., Skinner, M. and Kivell, T. (2019). Trabecular variation in the first metacarpal and manipulation in hominids. American Journal of Physical Anthropology [Online]. Available at: https://doi.org/10.1002/ajpa.23974.
Objectives: The dexterity of fossil hominins is often inferred by assessing the comparative manual anatomy and behaviors of extant hominids, with a focus on the thumb. The aim of this study is to test whether trabecular structure is consistent with what is currently known about habitually loaded thumb postures across extant hominids. Materials and methods: We analyze first metacarpal (Mc1) subarticular trabecular architecture in humans (Homo sapiens, n = 10), bonobos (Pan paniscus, n = 10), chimpanzees (Pan troglodytes, n = 11), as well as for the first time, gorillas (Gorilla gorilla gorilla, n = 10) and orangutans (Pongo sp., n = 1, Pongo abelii, n = 3 and Pongo pygmaeus, n = 5). Using a combination of subarticular and whole‐epiphysis approaches, we test for significant differences in relative trabecular bone volume (RBV/TV) and degree of anisotropy (DA) between species. Results: Humans have significantly greater RBV/TV on the radiopalmar aspects of both the proximal and distal Mc1 subarticular surfaces and greater DA throughout the Mc1 head than other hominids. Nonhuman great apes have greatest RBV/TV on the ulnar aspect of the Mc1 head and the palmar aspect of the Mc1 base. Gorillas possessed significantly lower DA in the Mc1 head than any other taxon in our sample. Discussion: These results are consistent with abduction of the thumb during forceful “pad‐to‐pad” precision grips in humans and, in nonhuman great apes, a habitually adducted thumb that is typically used in precision and power grips. This comparative context will help infer habitual manipulative and locomotor grips in fossil hominins.
Galletta, L., Stephens, N., Bardo, A., Kivell, T. and Marchi, D. (2019). Three-dimensional geometric morphometric analysis of the first metacarpal distal articular surface in humans, great apes and fossil hominins. Journal of Human Evolution [Online] 132:119-136. Available at: https://doi.org/10.1016/j.jhevol.2019.04.008.
Understanding the manual abilities of fossil hominins has been a focus of palaeoanthropological research for decades. Of interest are the morphological characteristics of the thumb due to its fundamental role in manipulation, particularly that of the trapeziometacarpal joint. Considerably less attention has been given to the thumb metacarpophalangeal (MCP) joint, which plays a role in stabilizing the thumb during forceful grasps and precision pinching. In this study we use a three-dimensional geometric morphometric approach to quantify the shape of the first metacarpal head in extant hominids (Homo, Pan, Gorilla and Pongo) and six fossil hominin species (Homo neanderthalensis Tabun C1 and La Chappelle-aux-Saints, Homo naledi U.W. 101-1282, Australopithecus sediba MH2, Paranthropus robustus/early Homo SK84, Australopithecus africanus StW 418, Australopithecus afarensis A.L. 333w-39), with the aims of identifying shapes that may be correlated with human-like forceful opposition and determining if similar morphologies are present in fossil hominins. Results show that humans differ from extant great apes by having a distally flatter articular surface, larger epicondyle surface area, and a larger radial palmar condyle. We suggest that this suite of features is correlated with a lower range of motion at the MCP joint, which would enhance the thumbs ability to resist the elevated loads associated with the forceful precision grips typical of humans. Great ape genera are each differentiated by distinctive morphological features, each of which is consistently correlated with the predicted biomechanical demands of their particular locomotor and/or manipulatory habits. Neanderthals and U.W. 101-1282 fall within the modern human range of variation, StW 418, SK 84 and U.W. 88-119 fall in between humans and great apes, and A.L. 333w-39 falls within Pan variation. These results agree with those of traditional linear analyses while providing a more comprehensive quantitative basis from which to interpret the hand functional morphology of extinct hominins.
Dunmore, C., Kivell, T., Bardo, A. and Skinner, M. (2019). Metacarpal trabecular bone varies with distinct hand-positions used in hominid locomotion. Journal of Anatomy [Online] 235:45-66. Available at: https://doi.org/10.1111/joa.12966.
Trabecular bone remodels during life in response to loading and thus should, at least in part, reflect potential variation in the magnitude, frequency and direction of joint loading across different hominid species. Here we analyse the trabecular structure across all non-pollical metacarpal distal heads (Mc2-5) in extant great apes, expanding on previous volume of interest and whole-epiphysis analyses that have largely focussed on only the first or third metacarpal. Specifically, we employ both a univariate statistical mapping and a multivariate approach to test for both inter-ray and interspecific differences in relative trabecular bone volume fraction (RBV/TV) and degree of anisotropy (DA) in Mc2-5 subchondral trabecular bone. Results demonstrate that while DA values only separate Pongo from African apes (Pan troglodytes, Pan paniscus, Gorilla gorilla), RBV/TV distribution varies with the predicted loading of the metacarpophalangeal (McP) joints during locomotor behaviours in each species. Gorilla exhibits a relatively dorsal distribution of RBV/TV consistent with habitual hyper-extension of the McP joints during knuckle-walking, whereas Pongo has a palmar distribution consistent with flexed McP joints used to grasp arboreal substrates. Both Pan species possess a disto-dorsal distribution of RBV/TV, compatible with multiple hand postures associated with a more varied locomotor regime. Further inter-ray comparisons reveal RBV/TV patterns consistent with varied knuckle-walking postures in Pan species in contrast to higher RBV/TV values toward the midline of the hand in Mc2 and Mc5 of Gorilla, consistent with habitual palm-back knuckle-walking. These patterns of trabecular bone distribution and structure reflect different behavioural signals that could be useful for determining the behaviours of fossil hominins.
Pouydebat, E. and Bardo, A. (2019). An interdisciplinary approach to the evolution of grasping and manipulation. Biological Journal of the Linnean Society [Online] 127:535-542. Available at: https://doi.org/10.1093/biolinnean%2Fblz058.
This paper is an introduction to a special issue of the Biological Journal of the Linnean Society (2019, volume 127: issue 3) focused on an interdisciplinary approach to the evolution of grasping and manipulation in tetrapods. Grasping is associated with pronounced morphological, dietary, social and locomotor differentiation, and this prompts several evolutionary questions, including the following. In primates, was the origin and evolution of grasping associated primarily with feeding or with locomotion and other social behaviours? Are some grasping and manipulative abilities unique to humans? What is the variability in grasping and manipulation among primates? What can we learn from other tetrapods? The special issue addresses some of these questions by exploring the ways in which the anatomy, functional morphology, ontogeny and biomechanics of tetrapods enable their hands to carry out diverse functions, such as locomotion and manipulation. We briefly review the possible origin and evolution of grasping and manipulative abilities in tetrapods and then introduce the ten other contributions to the special issue.
Bardo, A., Vigouroux, L., Kivell, T. and Pouydebat, E. (2018). The impact of hand proportions on tool grip abilities in humans, great apes and fossil hominins: a biomechanical analysis using musculoskeletal simulation. Journal of Human Evolution [Online] 125:106-121. Available at: https://dx.doi.org/10.1016/j.jhevol.2018.10.001.
Differences in grip techniques used across primates are usually attributed to variation in thumb-finger proportions and muscular anatomy of the hand. However, this cause-effect relationship is not fully understood because little is known about the biomechanical functioning and mechanical loads (e.g., muscle or joint forces) of the non-human primate hand compared to that of humans during object manipulation. This study aims to understand the importance of hand proportions on the use of different grip strategies used by humans, extant great apes (bonobos, gorillas and orangutans) and, potentially, fossil hominins (Homo naledi and Australopithecus sediba) using a musculoskeletal model of the hand. Results show that certain grips are more challenging for some species, particularly orangutans, than others, such that they require stronger muscle forces for a given range of motion. Assuming a human-like range of motion at each hand joint, simulation results show that H. naledi and A. sediba had the biomechanical potential to use the grip techniques considered important for stone tool-related behaviors in humans. These musculoskeletal simulation results shed light on the functional consequences of the different hand proportions among extant and extinct hominids and the different manipulative abilities found in humans and great apes.