The evolution of the human foot (original) (raw)
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Evolution and function of the hominin forefoot
Proceedings of the National Academy of Sciences, 2019
The primate foot functions as a grasping organ. As such, its bones, soft tissues, and joints evolved to maximize power and stability in a variety of grasping configurations. Humans are the obvious exception to this primate pattern, with feet that evolved to support the unique biomechanical demands of bipedal locomotion. Of key functional importance to bipedalism is the morphology of the joints at the forefoot, known as the metatarsophalangeal joints (MTPJs), but a comprehensive analysis of hominin MTPJ morphology is currently lacking. Here we present the results of a multivariate shape and Bayesian phylogenetic comparative analyses of metatarsals (MTs) from a broad selection of anthropoid primates (including fossil apes and stem catarrhines) and most of the early hominin pedal fossil record, including the oldest hominin for which good pedal remains exist, Ardipithecus ramidus. Results corroborate the importance of specific bony morphologies such as dorsal MT head expansion and "doming" to the evolution of terrestrial bipedalism in hominins. Further, our evolutionary models reveal that the MT1 of Ar. ramidus shifts away from the reconstructed optimum of our last common ancestor with apes, but not necessarily in the direction of modern humans. However, the lateral rays of Ar. ramidus are transformed in a more human-like direction , suggesting that they were the digits first recruited by hominins into the primary role of terrestrial propulsion. This pattern of evolutionary change is seen consistently throughout the evolution of the foot, highlighting the mosaic nature of pedal evolution and the emergence of a derived, modern hallux relatively late in human evolution. bipedalism | hominin evolution | metatarsals | Ardipithecus | functional morphology T he obligate terrestrial bipedalism of modern humans is unique among extant primates, and its ancient adoption by early hominins impacted subsequent evolutionary changes in social behavior and the development of material culture. A suite of morphological changes in the feet of early hominins is associated with the evolution of habitual bipedal locomotion in the human career and ultimately led to the energetically efficient gait used by modern humans (1-5). The forefoot skeleton includes the metatarsals (MT) and phalanges, and its functional anatomy is strongly tied to the evolution of bipedalism in hominins (5-9). Thus, hominin fore-foot fossils can offer key insights into when and how bipedalism evolved in the human lineage. During bipedal walking, modern humans dorsiflex (i.e., hyperextend) their forefoot joints, specifically at the metatarsophalangeal joints (MTPJs), as part of the push-off phase of gait, which tightens plantar soft tissues to convert the foot into a relatively stiff, propulsive lever (10) (also see ref. 11). Features of MT head morphology such as "dorsal doming" are thought to facilitate this stiffening mechanism (6, 12); doming occurs when the distal articular surface expands and becomes particularly pronounced dorsally. Comparative analysis of humans and chimpanzees has shown that dorsal doming is correlated with in vivo ranges of motion at the MTPJs, with humans displaying greater doming and a greater range of MTPJ dorsiflexion during bipedalism (9). The form and function of the hominin forefoot have been studied extensively (5, 6, 13-16), especially in light of more recent discoveries of hominin pedal fossils (17-19). However, a quantitative analysis of the hominin forefoot in a broad phylogenetic context is lacking, despite the theorized importance of these bony elements to the biomechanical demands of bipedalism (10, 20). To better understand the adaptive evolution of bipedalism in early hominins we investigated MTPJ morphology in Plio-Pleistocene fossil hominins (including species of Ardipithecus, Australopithecus, Paranthropus, and Homo) and a comparative sample of fossil and extant anthro-poids (including modern humans, apes, and monkeys) using shape analyses and phylogenetic comparative methods to test hypotheses about the nature and timing of forefoot evolution in the human clade. Three-dimensional geometric morphometric techniques were used to quantify MT1-MT5 head shapes, and a multioptima Ornstein-Uhlenbeck (OU) model was used to estimate the placement and Significance A critical step in the evolutionary history leading to the origins of humankind was the adoption of habitual bipedal locomotion by our hominin ancestors. We have identified novel bony shape variables in the forefoot across extant anthropoids and extinct hominins that are linked functionally to the emergence of bipedal walking. Results indicate a consistent and generalizable pattern in hominin pedal evolution that spans from Ardipithecus to early Homo-the relatively late derivation of a modern hallux in comparison with the lateral rays. These data provide novel morphological and macroevolutionary evidence for how and when the hominin pedal skeleton evolved to accommodate the unique biomechanical demands of bipedalism.
The Foot, 1998
When studying biological form and function, it is revealing to examine structure from an evolutionary perspective. The ape foot and that of modern humans differ in many areas, two of which are the absence of a divergent first ray and the reduced range of motion at the midtarsal joint. Two principle modifications are required to reduce the range of motion at the human midtarsal joint, one in each of the talo-navicular and calcaneo-cuboid articulations. A suite of data was obtained from the hindtarsus of humans, chimpanzees, gorillas, orangutans and the OH8 fossil foot. Multivariate analyses revealed the functional affinities of the fossil to be mixed, the medial column being ape-like while the lateral column was found to be human-like. Phylogenetic implications are that the lateral part of the foot became adapted for terrestrial bipedalism first with the medial column being subsequent. It is suggested that pathology resulting from disturbances of normal ontogeny should reflect this trend with mild disturbance affecting the medial column alone and severe disturbance affecting both medial and lateral columns.
Footprints and human evolution: Homeostasis in foot function
Human, and hominin tracks, occur infrequently within the geological record as rare acts of sedimentary preservation. They have the potential, however, to reveal important information about the locomotion of our ancestors, especially when the tracks pertain to different hominin species. The number of known track sites is small and in making inter-species comparisons, one has to work with small track populations that are often from different de-positional settings, thereby complicating our interpretations of them. Here we review several key track sites of palaeoanthropological significance across one of the most important evolutionary transitions (Australopithecus to Homo) which involved the development of anatomy and physiology better-suited to endurance running and walking. The sites include the oldest known hominin track site at Laetoli (3.66 Ma; Tanzania) and those at Ileret (1.5 Ma; Kenya). Tracks from both sites are compared with modern tracks made by habitually unshod individuals using a whole-foot analysis. We conclude that, contrary to some authors, foot function has remained relatively unchanged, perhaps experiencing evolutionary homeostasis, for the last 3.66 Ma. These data suggest that the evolutionary development of modern biomechanical locomotion pre-dates the earliest human tracks and also the transition from the genus Australopithecus to Homo.
The Functional Morphology of the Hominid Foot.
This is to certify that I am responsible for the work submitted in this thesis, that the original work is my own, except as specified in the acknowledgments and in references, and that neither the thesis nor the original work contained therein has been previously submitted to any other institution for a degree. Name: Francesca Campbell Signed: Date: 3 7 1. Abstract The functional morphology of the hominoid foot is reviewed with a particular emphasis on the comparison of the species Gorilla gorilla, Pan troglodytes and Homo sapiens. Collated measurements from specimens at the University of Sheffield and the Powell-Cotton Museum are compared using linear divisions of the foot. Linear divisions are compared using descriptive statistics using SPSS, average relative lengths using R, and finally analysed by PCA using SPSS. Attention is given to the second toe due to the unique morphology of the adducted H. sapiens hallux. From the comparative model of extant primates the foot bones of extinct homind bones are analysed, with special attention paid to the most complete foot specimen; Homo ergaster 'Narikotome Boy', Little Foot (STW 573) and OH 8 Homo habilis. This work supports the previous comparative work carried out by Adolph Schultz in the early 20th Century, the work of John Napier, John Robinson in the 1960's and Will Harcourt-Smith in the late 20th and early 21st Century. The wide range of human variation is demonstrated and the results are discussed in the context of there being a greater diversity in hominoid locomotion that the 'less uprightmore upright' model favoured for many years {fig1}. Recent developments in human walking style are discussed in the context of a closer link between extinct species than previously thought. 8 Francesca Campbell Figure 1. the 'less upright to more upright' model of evolution 9
Variation, mosaicism and degeneracy in the hominin foot
Evolutionary Human Sciences
The fossil record is scarce and incomplete by nature. Animals and ecological processes devour soft tissue and important bony details over time and, when the dust settles, we are faced with a patchy record full of variation. Fossil taxa are usually defined by craniodental characteristics, so unless postcranial bones are found associated with a skull, assignment to taxon is unstable. Naming a locomotor category based on fossil bone morphology by analogy to living hominoids is not uncommon, and when no single locomotor label fits, postcrania are often described as exhibiting a “mosaic” of traits. Here, we contend that the unavoidable variation that characterises the fossil record can be described far more rigorously based on extensive work in human neurobiology and neuroanatomy, movement sciences and motor control and biomechanics research. In neurobiology, degeneracy is a natural mechanism of adaptation allowing system elements that are structurally different to perform the same funct...
Journal of The Royal Society Interface, 2012
It is commonly held that the major functional features of the human foot (e.g. a functional longitudinal medial arch, lateral to medial force transfer and hallucal (big-toe) push-off ) appear only in the last 2 Myr, but functional interpretations of footbones and footprints of early human ancestors (hominins) prior to 2 million years ago (Mya) remain contradictory. Pixel-wise topographical statistical analysis of Laetoli footprint morphology, compared with results from experimental studies of footprint formation; foot-pressure measurements in bipedalism of humans and non-human great apes; and computer simulation techniques, indicate that most of these functional features were already present, albeit less strongly expressed than in ourselves, in the maker of the Laetoli G-1 footprint trail, 3.66 Mya. This finding provides strong support to those previous studies which have interpreted the G-1 prints as generally modern in aspect.
The foot in the Homo fossil record
In this article, the foot in the Homo fossil record throughout the world is reviewed. The main problem with the study of foot remains is the paucity of fossils from this anatomical area, in particular from the earlier members of the genus Homo. In spite of this, a comprehensive review of the morphology of the entire fossil record for the foot has been achieved. All the fossils belonging to the genus Homo are proposed to be biped due to the presence of longitudinal and transversal arches, the robusticity pattern of the metatarsals and an adducted hallux. Even in the early members of the genus Homo, the morphology of the foot is modern-like, with size being practically the only variation observed. Of the foot remains attributed to the genus Homo, two morphotypes become apparent: small-sized and large-sized individuals. It is important though to take into account that the earliest Homo feet belonging to smaller individuals could not belong to the genus Homo. Later, a new robust bauplan appears in the Homo fossil record for the foot represented by Homo erectus/ergaster, Homo antecessor, the hominins from Sima de los Huesos and Neandertals. Finally, modern humans display long feet that are gracile compared with their ancestors. An examination of the morphology of the Neandertal foot and of the foot from Sima de los Huesos confirms the evolutionary relationship between these two populations. However, enough differences exist between the two samples to indicate that they are in fact morphologically distinct. A parallel gracilization process is proposed in both modern humans and Neandertals.
Comparative forefoot trabecular bone architecture in extant hominids
2010
The appearance of a forefoot push-off mechanism in the hominin lineage has been difficult to identify, partially because researchers disagree over the use of the external skeletal morphology to differentiate metatarsophalangeal joint functional differences in extant great apes and humans. In this study, we approach the problem by quantifying properties of internal bone architecture that may reflect different loading patterns in metatarsophalangeal joints in humans and great apes.