The metabolic costs of 'bent-hip, bent-knee' walking in humans

The costs of different modes of bipedalism are a key issue in reconstructing the likely gait of early human ancestors such as Australopithecus afarensis. Some workers, on the basis of morphological differences between the locomotor skeleton of A. afarensis and modern humans, have proposed that this hominid would have walked in a 'bent-hip, bent-knee' (BHBK) posture like that seen in the voluntary bipedalism of untrained chimpanzees. Computer modelling studies using inverse dynamics indicate that on the basis of segment proportions AL-288-1 should have been capable of mechanically effective upright walking, but in contrast predicted that BHBK walking would have been highly ineffective. The measure most pertinent to natural selection, however, is more likely to be the complete, physiological, or metabolic energy cost. We cannot measure this parameter in a fossil. This paper presents the most complete investigation yet of the metabolic and thermoregulatory costs of BHBK walking in humans. Data show that metabolic costs including the basal metabolic rate (BMR) increase by around 50% while the energy costs of locomotion and blood lactate production nearly double, heat load is increased, and core temperature does not return to normal within 20 minutes rest. Net effects imply that a resting period of 150% activity time would be necessary to prevent physiologically intolerable heat load. Preliminary data for children suggest that scaling effects would not significantly reduce relative costs for hominids of AL-288-1's size. Data from recent studies using forwards dynamic modelling confirm that similar total (including BMR) and locomotor metabolic costs would have applied to BHBK walking by AL-288-1. We explore some of the ecological consequences of our findings.     

Paleoenvironmental reconstruction of middle Miocene paleosols bearing Kenyapithecus and Victoriapithecus, Nyakach Formation, southwestern Kenya

Paleosols in the middle Miocene (15 Ma) Nyakach Formation at Kaimogool, near Sondu, southwestern Kenya have yielded specimens of the early cercopithecoid Victoriapithecus macinnesi and the early kenyapithecine Kenyapithecus africanus, and can be used as evidence for the environmental mosaic occupied by these primates. Five distinct types of paleosols (pedotypes) are recognized in the Nyakach Formation section at Kaimogool South. The most common paleosols are reddish brown, silty calcareous profiles with blocky structure and large root traces (Ratong pedotype) which are interpreted as soils of well-drained, dry bushland or thicket (nyika). Weakly developed paleosols associated with paleochannels (Dhero pedotype) represent wooded grassland early in the ecological succession from streamside flooding. One of these paleosols has yielded a fossil flora of grasses and small-leaved dicots like those of modern semi-arid wooded grassland. Crumb structured, calcareous paleosols with iron-manganese nodules (Yom pedotype) are interpreted to represent seasonally waterlogged, wooded grassland (dambo or vlei). Thick, red clayey, calcareous paleosols with blocky ped structure and large root traces (Tut pedotype) are interpreted as soils of well-drained dry woodland. Other blocky-structured, gray to brown calcareous paleosols with iron-manganese nodules (Chido pedotype) are interpreted as soils of seasonally waterlogged, riparian dry woodland. Fossil soils, plants and gastropods are evidence of an unusually dry (300-500 mm mean annual precipitation) habitat for apes, consisting of a vegetational mosaic dominated by dry woodland, bushland and thickets with few areas of seasonally waterlogged grassland. Fossils of V. macinnesi are rare from Nyakach, but were found in paleosols representative of bushland and thicket habitats (Ratong). Fossils of the ape K. africanus were found within paleosols indicative of dry woodland (Tut). Other paleosol types representative of seasonally dry dambo grassland (Yom), colonizing grassland (Dhero) or riparian woodland (Chido) are also represented, but have not yet produced primate fossils.     

Vertebral pathology in the afar australopithecines

Ten vertebral elements from the AL-288 partial hominid skeleton and 11 elements from the AL-333 collection are described. The AL-288 column presents a marked kyphosis at the level of thoracic vertebrae 6 through 10, with pronounced new bone formation on the ventral surfaces of these vertebrae. These features, associated with narrowed disc space and minor osteophytosis, resemble Scheuermann disease in the human. Even though this diagnosis is consistent with a basically human, bipedal locomotor repertoire, the presence of Scheuermann disease suggests that lifting, climbing, or acrobatic activities may have been important in early hominids.     

Paleosols, stable carbon isotopes, and paleoenvironmental interpretation of Kanapoi, Northern Kenya

This study uses the interpretation of paleosol features at Kanapoi, Kenya (4.2-3.4 Ma) to reconstruct the ecosystem occupied by Australopithecus anamensis. The paleosols at Kanapoi provide a unique and fortuitous opportunity, in that the bulk of the hominid specimens derive from paleosols, providing direct evidence of the environment that the Kanapoi hominids occupied. Seven named types of paleosols are recognized at Kanapoi, each representing a trace fossil of the local ecosystem during soil formation. The hominid-bearing Dite paleosols provide evidence that A. anamensis inhabited areas of semi-arid, seasonal climate regimes with mean annual precipitation ranging from about 350-600 mm. The in situ hominid collections from Dite paleosols show that A. anamensis at least occasionally occupied relatively open low tree-shrub savanna vegetation formed in well drained settings, and may have preferred these conditions over other poorly drained soils. The relatively open conditions of Dite paleosols existed within a spatially variable ecosystem, characterized by a mosaic of environments, ranging from forb-dominated edaphic grassland to gallery woodland, providing a larger view of the mixed ecosystem in which A. anamensis lived. Synthesis of paleoenvironmental indicators of A. anamensis at Kanapoi and Allia Bay, Kenya suggests that as early as 4 Ma hominids thrived in varied ecosystems.     

Morphological affinities of the Australopithecus afarensis hand on the basis of manual proportions and relative thumb length

The hands of apes and humans differ considerably with regard to proportions between several bones. Of critical significance is the long thumb relative to other fingers, which is the basis for human-like pad-to-pad precision grip capability, and has been considered by some as evidence of tool-making. The nature and timing of the evolutionary transition from ape-like to human-like manual proportions, however, have remained unclear as a result of the lack of appropriate fossil material. In this article, the manual proportions of Australopithecus afarensis from locality AL 333/333w (Hadar, Ethiopia) are investigated by means of bivariate and multivariate morphometric analyses, in order to test the hypothesis that human-like proportions, including an enhanced thumb/hand relationship, originally evolved as an adaptation to stone tool-making. Although some evidence for human-like manual proportions had been previously proposed for this taxon, conclusive evidence was lacking. Our results indicate that A. afarensis possessed overall manual proportions, including an increased thumb/hand relationship that, contrary to previous reports, is fully human and would have permitted pad-to-pad human-like precision grip capability. We show that these human-like proportions in A. afarensis mainly result from hand shortening, as in modern humans, and that these conclusions are robust enough as to be non-dependent on whether the bones belong to a single individual or not. Since A. afarensis predates the appearance of stone tools in the archeological record, the above-mentioned conclusions permit a confident refutation of the null hypothesis that human-like manual proportions are an adaptation to stone tool-making, and thus alternative explanations must be therefore sought. One hypothesis would consider manipulative behaviors (including tool-use and/or non-lithic tool-making) in early hominines exceeding those reported among extant non-human primates. Alternatively, on the basis of the many adaptations to committed bipedalism in A. afarensis, we propose the hypothesis that once arboreal behaviors became adaptively insignificant and forelimb-dominated locomotor selection pressures were relaxed with the adoption of terrestrial bipedalism, human-like manual proportions could have merely evolved as a result of the complex manipulation selection pressures already present in extant non-human primates.Both hypotheses are not mutually exclusive, and even other factors such as pleiotropy cannot be currently discarded.     

Paleosols and paleoenvironments of the middle Miocene,Maboko Formation,Kenya

The middle Miocene (15 Ma) Maboko Formation of Maboko Island and Majiwa Bluffs, southwestern Kenya, has yielded abundant fossils of the earliest known cercopithecoid monkey (Victoriapithecus macinnesi), and of a kenyapithecine hominoid (Kenyapithecus africanus), as well as rare proconsuline (Simiolus leakeyorum, cf. Limnopithecus evansi) and oreopithecine apes (Mabokopithecus clarki, M. pickfordi), and galagids (Komba winamensis). Specific habitat preferences can be interpreted from large collections of primate fossils in different kinds of paleosols (pedotypes). Fossiliferous drab-colored paleosols with iron-manganese nodules (Yom pedotype) are like modern soils of seasonally waterlogged depressions (dambo). Their crumb structure and abundant fine root-traces, as well as scattered large calcareous rhizoconcretions indicate former vegetation of seasonally wet, wooded grassland. Other fossiliferous paleosols are evidence of nyika bushland (Ratong), and early-successional riparian woodland (Dhero). No fossils were found in Mogo paleosols interpreted as saline scrub soils. Very shallow calcic horizons (in Yom, Ratong, and Mogo paleosols) and Na-montmorillonite (in Mogo) are evidence of dry paleoclimate (300-500 mm MAP=mean annual precipitation). This is the driest paleoclimate and most open vegetation yet inferred as a habitat for any Kenyan Miocene apes or monkeys. Victoriapithecus was abundant in dambo wooded grassland (Yom) and riparian woodland (Dhero), a distribution like that of modern vervet monkeys. Kenyapithecus ranged through all these paleosols, but was the most common primate in nyika bushland paleosols (Ratong), comparable to baboons and macaques today. Mabokopithecus was virtually restricted to riparian woodland paleosols (Dhero), and Simiolus had a similar, but marginally wider, distribution. Habitat preferences of Mabokopithecus and Simiolus were like those of modern colobus monkeys and mangabeys. A single specimen of Komba was found in dambo wooded grassland paleosol (Yom), a habitat more like that of the living Senegal bushbaby than of rainforest galagids. A shift to non-forest habitats may explain the terrestrial adaptations of Victoriapithecus, basal to the cercopithecid radiation, and of Kenyapithecus, basal to the hominoid radiation. Both taxa are distinct from earlier Miocene arboreal proconsulines, oreopithecines and galagids.     

Some microbiological aspects of surface and buried soils on Mt. Kenya,East Africa

When numbers of microorganisms in profiles of surface and buried horizons on Mt. Kenya were estimated by dilution plate counting they were found to be consistently lower than those from other soils in different geographical regions as determined from the literature. The lower numbers are probably characteristic of the poorly weathered Inceptisols and Entisols usually found in the alpine zone.The A horizons of the soils studied contain proportionately fewer of the total numbers of organisms in the A, B and C horizons than observed in most soils. Estimates of organic matter were positively correlated with numbers of fungi and bacteria in the A horizons. However, other factors such as severe drought, high light intensity, low temperatures, diurnal frost heaving, low pH and paucity of clay minerals may be significant factors in suppressing the more luxuriant growth of microbial populations.Organic and inorganic horizons of buried soils sometimes exhibit higher counts of microorganisms than adjacent horizons of surface soils. However, the bacteria and fungi even in deeply buried paleosols exhibit characteristics of an unspecialized heterotrophic population. Among fungi the species were obviously the same as those isolated from one or more of the overlying horizons. Taken in conjunction with other evidence from the profiles it is concluded that the microorganisms were introduced and represent a transient or non-active population. Contamination of buried organic horizons may influence the estimated age as assessed by radiocarbon dating.     

Dental metric assessment of the omo fossils: implications for the phylogenetic position of Australopithecus africanus

The discovery of Australopithecus afarensis has led to new interpretations of hominid phylogeny, some of which reject A. africanus as an ancestor of Homo. Analysis of buccolingual tooth crown dimensions in australopithecines and Homo species by Johanson and White (Science 202:321-330, 1979) revealed that the South African gracile australopithecines are intermediate in size between Laetoli/hadar hominids and South African robust hominids. Homo, on the other hand, displays dimensions similar to those of A. afarensis and smaller than those of other australopithecines. These authors conclude, therefore, that A. africanus is derived in the direction of A. robustus and is not an ancestor of the Homo clade. However, there is a considerable time gap (ca. 800,000 years) between the Laetoli/Hadar specimens and the earliest Homo specimens; "gracile" hominids from Omo fit into this chronological gap and are from the same geographic area. Because the early specimens at Omo have been designated A. afarensis and the later specimens classified as Homo habilis, Omo offers a unique opportunity to test hypotheses concerning hominid evolution, especially regarding the phylogenetic status of A. africanus. Comparisons of mean cheek teeth breadths disclosed the significant (P less than or equal to 0.05) differences between the Omo sample and the Laetoli/Hadar fossils (P4, M2, and M3), the Homo fossils (P3, P4, M1, M2, and M1), and A. africanus (M3). Of the several possible interpretations of these data, it appears that the high degree of similarity between the Omo sample and the South African gracile australopithecine material warrants considering the two as geographical variants of A. africanus. The geographic, chronologic, and metric attributes of the Omo sample argue for its lineal affinity with A. afarensis and Homo. In conclusion, a consideration of hominid postcanine dental metrics provides no basis for removing A. africanus from the ancestry of the Homo lineage.     

Lucy's length: stature reconstruction in Australopithecus afarensis (A.L.288-1) with implications for other small-bodied hominids

New stature estimates are provided for A.L.288-1 (Australopithecus afarensis) based on (1) the relationship between femur length and stature in separate samples of human pygmies and pygmy chimpanzees and (2) model II regression alternatives to standard least-squares methods. Estimates from the two samples are very similar and converge on a value of approximately 3'6" for "Lucy." These results are compared to prior estimates and extended to other small-bodied hominids such as STS-14 and O.H.62. A new foot-to-stature ratio is also estimated for A.L.288-1, and its potential biomechanical significance for gait is evaluated in comparison to other groups.     

Recognizing hominoid-modified bones: the taphonomy of colobus bones partially digested by free-ranging chimpanzees in the Kibale Forest, Uganda

We present a taphonomic study of bones that have passed though the digestive tracts of free-ranging chimpanzees from the Kibale Forest in Uganda. The bone assemblage can be characterized as having a very low species diversity; low number of identifiable specimens (NISP) per scat; bones extremely broken up (very small size range); skeletal part frequencies similar in some ways to those resulting from carnivore partial digestion; and sometimes articulated specimens. Modifications to the bones include corrosion, tiny tooth scores and pits, cracking, and fraying of bone edges. Together, these characteristics suggest that hominoid bone digestion may be recognizable, despite some similarities with leopard-, canid-, and eagle-modified bone. Chimpanzees are well-documented hunters of medium-sized vertebrates such as monkeys. This is significant in the study of human evolution if, as it seems, the last common ancestor of chimpanzees and humans was chimpanzee-like. It suggests there was a pre-stone-tool-using hunting phase in human evolution, perhaps by australopiths or the last common ancestor. Taphonomically, pre-stone tool meat eating has been very difficult to detect in the fossil record. However, if chimpanzees leave a recognizable taphonomic signature on the bones of their prey, we will be able to look for analogous signatures in fossil bones associated with fossil hominoids and hominids.     

河南郑州老奶奶庙第3地点初步研究

老奶奶庙第3地点位于河南省郑州市,年代距今约4.5万年或稍早。2016年度的发掘,发现动物化石575件,石制品66件。从遗物的密度和分布情况来看,本遗址应为第1地点或其它中心营地外围的临时性地点,古人类曾在此活动,但并不频繁。动物化石的种属组合揭示出当时应为草原-疏林景观。石制品属于典型的华北地区小石片石器工业,与本区MIS3阶段其他遗址工业面貌相似,应属于同一技术体系。     

Ontogeny and phylogeny of the pelvis in Gorilla, Pongo, Pan, Australopithecus and Homo

To examine the evolutionary differences between hominoid locomotor systems, a number of observations concerning the growth of the pelvis among the great apes as compared to modern and fossil hominids are reported. We are interested in the size and shape of the coxal bones at different developmental stages across species that may elucidate the relationship between ontogeny and phylogeny (i.e., heterochrony) in the hominoid pelvis. Our hypotheses are: (1) do rates of absolute growth differ?, (2) do rates of relative growth differ?, and (3) does heterochrony explain these differences? Bivariate and multivariate analyses of pelvic dimensions demonstrate both the diversity of species-specific ontogenetic patterns among hominoids, and an unequivocal separation of hominids and the great apes. Heterochrony alone fails to account for the ontogenetic differences between hominids and the great apes. Compared to recent Homo,Australopithecus can be described as 'hyper-human' from the relative size of the ischium, and short but broad ilium. Australopithecus afarensis differs from Australopithecus africanus by its relatively long pubis. In multivariate analyses of ilium shape, the most complete coxal bone attributed to Homo erectus, KNM-ER 3228, falls within the range of juvenile and adult Australopithecus, whereas Broken Hill falls within the range of modern Homo, suggesting that the modern human ilium shape arose rather recently. Among the great apes, patterns of pelvic ontogeny do not exclusively separate the African apes from Pongo.     

The first human dispersal to Europe: Remarks on the archaeological and palaeoanthropological record from Orce (Guadix-Baza basin, southeastern Spain)

The chronology of the first arrival ofHomo in Europe is a rather controversial issue, with most scholars claiming until very recently that there were no permanent human settlements before the middle Pleistocene. However, new findings at Atapuerca, Dmanisi and Orce, as well as the re-evaluation of the evidence from Java, Israel and China indicate a protracted chronology for the arrival of hominids in Eurasia, during late Pliocene/lower Pleistocene times. The systematic study of the macrovertebrate assemblages from circummediterranean sites such as Orce and Dmanisi has shown a faunal replacement at the Plio-Pleistocene boundary, marked by the arrival in Europe of African immigrants such as the hippopotamus, an equid similar to modern grevy’s zebra, a large cercopithecoid and several carnivores, including a giant hyaena, a sabre-tooth and a wild dog. An analysis of the relative frequency of bones and teeth for those species of large mammals preserved in Venta Micena indicates the improbability thatHomo sp. is represented in the fossil assemblage by several bones and no tooth remain. Finally, new data on the stratigraphy of Barranco León are offered, with remarks on the discovery in this locality of lithic artefacts and molar tooth fragment BL5-0.     

Ecological implications of the relative rarity of fossil hominins at Laetoli

Hominins are a very rare component of the large-mammal fauna at Laetoli. Although no equivalent data are available for Hadar, the much higher count and relative abundance of hominins suggests that they may have been more common at the latter site. The apparent relative rarity of hominins at Laetoli may have significant implications for understanding the ecology of Australopithecus afarensis. However, it is essential to first assess the extent to which taphonomic variables might have been a contributing factor. Using data from fossil ruminants, we show that the survivability of skeletal elements at Laetoli relates to the extent to which they can resist carnivore scavenging and their likelihood of being entirely buried by volcanic ashes and tuffaceous sediments. The rarity of hominins at Laetoli is probably due in part to the influence of these two taphonomic factors. However, these factors cannot account entirely for the difference in hominin relative abundance between these two sites, and ecological differences were probably a contributing factor. The highest population densities of chimpanzees today occur in forest and closed woodland, with reduced densities in open woodland. If similar levels of population-density variation characterized A. afarensis, the differences between Hadar and Laetoli may relate to the quality/optimality of the habitats. Hadar was, in general, much more densely wooded and mesic than Laetoli, with permanent and substantial bodies of water. In contrast, Laetoli was predominantly a woodland-shrubland-grassland mosaic supported only by ephemeral streams and ponds. The apparent greater relative abundance of hominins at Hadar compared with Laetoli suggests that, like chimpanzees, A. afarensis may have been more successful in more densely wooded habitats. Compared with Hadar, Laetoli probably represented a less optimal habitat for the foraging and dietary behavior of A. afarensis, and this is reflected in their inferred lower abundance, density, and biomass.     

Comparative analysis of the functional activity and composition of hydrolytic microbial complexes from the lower Volga barrow and modern chestnut soils

The structure and specific characteristics of the hydrolytic microbial complexes from chestnut paleosols buried under the barrows of different ages (～4500 and ～3500 years) was compared with their modern analogue in microcosm experiments. Potential activity of the hydrolytic complex of the microbial community of the barrow paleosols was found to be higher than in the modern soil complex. The share of metabolically active cells revealed by FISH after the introduction of a growth-stimulating polysaccharide into the paleosol microcosm was 50% of the whole prokaryotic cell number. The paleosol community exhibited a more pronounced response to addition of the substrate than the modern soil community. The differences in the phylogenetic taxonomic structure of the prokaryotic metabolically active hydrolytic complex in the buried and modern soils were revealed. The hydrolytic complex of modern soil was more diverse, while the dominant hydrolytic organisms revealed in paleosols were unicellular and mycelial Actinobacteria, as well as Proteobacteria.     

From apes to humans: locomotion as a key feature for phylogeny

If bipedalism has often been considered to be of a crucial interest for understanding hominid evolution, the acceptance of locomotor features to build phylogenies is still far from being a reality in the field. Especially for hominid evolution, it still seems to be difficult to accept that traits, other than craniodental ones, can be useful for defining the major dichotomies. The recent discovery of Australopithecus anamensis suggests a challenging view of the major dichotomy between apes and humans. Whilst it is widely accepted that Ardipithecus ramidus is ancestral to Australopithecus anamensis, which in its turn is ancestral to Australopithecus afarensis and then to later hominids, the postcranial adaptations, which should be taken into account, suggest another branching pattern. Based on the fact that by 4.0 million years two different locomotor patterns can be identified in hominids, two lineages would appear to be present: the "Australopithecine" lineage (with Australopithecus afarensis or Ardipithecus ramidus if the latter is really a hominid sensu stricto) and the "Hominine" lineage (with Australopithecus anamensis = Praeanthropus africanus).     

Forelimb segment length proportions in extant hominoids and Australopithecus afarensis

Forelimb proportions have been used to infer locomotor adaptation in Australopithecus afarensis. However, little is known about proportions among individual forelimb segments in extant or fossil hominoids. The partial A. afarensis skeleton A.L. 438-1 and the more complete skeleton A.L. 288-1 provide the opportunity to assess relative length of the arm, forearm, wrist, and palm. We compare scaling relationships between pairs of forelimb bones of extant hominoids and A. afarensis, and length of individual forelimb elements to a body size surrogate. Hylobatids, and to a lesser extent orangutans, have the longest forelimb bones relative to size, although the carpus varies little among taxa, perhaps due to functional constraints of the wrist. Pan species are unique in having long metacarpals relative to ulnar length, demonstrating that they probably differ from the common chimp-human ancestor, and also that developmental mechanisms can be altered to results in differential growth of individual forelimb segments. A. afarensis has no forelimb bones that are significantly longer than those of humans for its size. It falls within the range of variation seen in modern humans for all comparisons relative to size, but appears to differ from the typical human brachial index due to a slightly shorter humerus and/or slightly longer ulna. It has short metacarpals like humans only among hominoids. Thus, while Pan may have elongated its metacarpus relative to ulnar length, A. afarensis may have reduced the length of its metacarpals and possibly its humerus relative to body size from the primitive condition.     

Seed survival and persistence on a calcareous land surface after a 32-year burial

Abstract. Of 34 species of vascular plants recorded in an unimproved calcareous grassland community in 1960 and subsequently buried for 32 yr, just six spp. were recovered as viable seeds from the original land surface, following excavation of an experimental earthwork. Five of the six are known or suspected to form persistent seed banks; the status of Carex flacca as a persistent seed is now established. The exceptionally low density of viable seeds at 35 seeds/m² and the paucity of other plant remains confirm that these calcareous soils have supported rapid decomposition. The complete absence of viable seeds known to be short-lived indicated that the macrofauna has played no significant role in the introduction of viable seeds from the modern-day surface down to depths in excess of 1.6 m, at least not in recent years. Because of the precise dates of burial and excavation, the results offer a rare opportunity to confirm laboratory and other indirect observations of long-term seed persistence following burial in temperate climate calcareous soils.     

Soils,time, and primate paleoenvironments

Soils are the skin of the earth. From both poles to the equator, wherever rocks or sediment are exposed at the surface, soils are forming through the physical and chemical action of climate and living organisms. The physical attributes (color, texture, thickness) and chemical makeup of soils vary considerably, depending on the composition of the parent material and other variables: temperature, rainfall and soil moisture, vegetation, soil fauna, and the length of time that soil–forming processes have been at work. United States soil scientists¹ have classified modern soils into ten major groups and numerous subgroups, each reflecting the composition and architecture of the soils and, to some extent, the processes that led to their formation. The physical and chemical processes of soil formation have been active throughout geologic time; the organic processes have been active at least since the Ordovician.² Consequently, nearly all sedimentary rocks that were deposited in nonmarine settings and exposed to the elements contain a record of ancient, buried soils or paleosols. A sequence of these rocks, such as most ancient fluvial (stream) deposits, provides a record of soil paleoenvironments through time. Paleosols are also repositories of the fossils of organisms (body fossils) and the traces of those organisms burrowing, food–seeking, and dwelling activities (ichnofossils). Indeed, most fossil primates are found in paleosols. Careful study of ancient soils gives new, valuable insights into the correct temporal reconstruction of the primate fossil record and the nature of primate paleoenvironments.     

Energy transformation during erect and 'bent-hip,bent-knee' walking by humans with implications for the evolution of bipedalism

We have previously reported that predictive dynamic modeling suggests that the 'bent-hip, bent-knee' gait, which some attribute to Australopithecus afarensis AL-288-1, would have been much more expensive in mechanical terms for this hominid than an upright gait. Normal walking by modern adult humans owes much of its efficiency to conservation of energy by transformation between its potential and kinetic states. These findings suggest the question if, and to what extent, energy transformation exists in 'bent-hip, bent-knee' gait.This study calculates energy transformation in humans walking upright, at three different speeds, and walking 'bent-hip, bent-knee'. Kinematic data were gathered from video sequences and kinetic (ground reaction force) data from synchronous forceplate measurement. Applying Newtonian mechanics to our experimental data, the fluctuations of kinetic and potential energy in the body centre of mass were obtained and the effects of energy transformation evaluated and compared. In erect walking the fluctuations of two forms of energy are indeed largely out-of-phase, so that energy transformation occurs and total energy is conserved. In 'bent-hip, bent-knee' walking, however, the fluctuations of the kinetic and potential energy are much more in-phase, so that energy transformation occurs to a much lesser extent. Among all modes of walking the highest energy recovery is obtained in subjectively 'comfortable' walking, the next highest in subjectively 'fast' or 'slow' walking, and the least lowest in 'bent-hip, bent-knee' walking. The results imply that if 'bent-hip, bent-knee' gait was indeed habitually practiced by early bipedal hominids, a very substantial (and in our view as yet unidentified) selective advantage would have had to accrue, to offset the selective disadvantages of 'bent-hip, bent-knee' gait in terms of energy transformation.