From Biped to Strider: The Emergence of Modern Human Walking, Running, and Resource Transport
Abstract
The inspiration for this volume of contributed papers stemmed from conversations between the editors in front of Chuck Hilton's poster on the determinants of hominid walking speed, presented at thel998 meetings of the American Association of Physical Anthropologists (AAPA). Earlier at those meetings, Jeff Meldrum (with Roshna Wunderlich) had presented an alternate interpretation of the Laetoli footprints based on evidence of midfoot flexibility. As the discussion ensued we found convergence on a number of ideas about the nature of the evolution of modem human walking. From the continuation of that dialogue grew the proposal for a symposium which we called From Biped to Strider: the Emergence of Modem Human Walking. The symposium was held as a session of the 69th annual meeting of the AAPA, held in San Antonio, Texas in 2000. It seemed to us that the study of human bipedalism had become overshadowed by theoften polarized debates over whether australo pithecines were wholly terrestrial in habit, or retained a significant degree of arboreality.
Chapters (11)
Functional-morphological analyses related to fossil and contemporary hominin locomotion are the focus of this volume. As locomotion is considered a key element in the overall behavior of living primates, allowing them to fulfill such basic needs as avoiding predators, foraging for food, and finding mates, biological anthropologists have generally agreed that it most likely served similar functions in earlier hominins as well. In primates, differing locomotor behaviors and their impact on other biological complexes have produced a diverse range of behavioral and anatomical configurations. In turn, primate locomotion studies are diverse in their scope. Anthropologists interested in hominin locomotion frequently draw on primate and other animal locomotor studies in efforts to understand the complexities associated with the evolution of hominin locomotion. Through comparative analyses on musculo-skeletal structures, positional behavior, and the kinematic and kinetic components of body motion in settings ranging from dissection rooms, laboratories, and in the field, researchers have developed a wide variety of approaches and techniques for investigating the intricacies of locomotor movement in living contemporary hominins and their closest relatives.
Functional analysis of fossil great apes and humans indicate that no known fossil taxon was a habitual knuckle-walker. However, the phylogenetic relations among hominoids suggests that the last common ancestor of the African apes and humans was in fact a knuckle-walker. Anatomical, fossil and molecular evidence of relations among the Hominoidea strongly suggest than Pan and Homo share a common ancestor not shared by any other living taxon. If this is correct, then knuckle-walking must have evolved once in the common ancestor of Pan, Gorilla and Homo (in which it was lost), or twice, independently in each African ape lineage. In addition to being less parsimonious, most multiple origins hypotheses for knuckle-walking also fail to account for characters shared by African apes and humans that are plausibly functionally related to increased terrestriality. These include vertebral, limb and intra-limb proportions, and limb long bone, carpal, tarsal and metapodial, and phalangeal morphology. In theory, knuckle-walking and obligate bipedalism could have evolved from an unknown type of terrestrial quadrupedalism, possibly associated with high frequencies of facultative bipedality. This would also account for characters and positional behavior shared by African apes and humans, the differences between Pan and Gorilla, and the apparent retention of primitive features of the trunk in humans. However, it implies a substantial increase in homoplasy as well as a hypothetical ancestral morphotype unkown in any group or out group. Functional anatomy and phylogeny together continue to suggest that humans are most likely to have evolved from a knuckle-walker. However, a functionally plausible, though less parsimonious facultative bipedality hypothesis is also possible. In this regard, hints of the unique functional morphology of Ardipithecus ramidus suggest that this taxon would serve to test these two alternatives.
Australopithecine foot bones from Hadar (Ethiopia) as well as ten fossil footprints from Laetoli (Tanzania) exhibit arboreal anatomical characteristics. About 3 Mya there were two genera in South Africa: a more human-like genus with bipedal locomotion and one Australopithecus genus with a more ape-like morphology of mixed features, i.e. bipedal for the talus and the distal epiphysis of the tibia, and arboreal for the other foot bones. The human hand is a primitive unspecialized organ whose axis lies on the third ray, suggesting that the hand was never used for specialized locomotion. A common ancestor of humans and apes and australopithecines is proposed. This ancestor was neither arboreal nor quadrudepal, but bipedal. Primitive bipedalism was a characteristic feature of “Protohominoidea.”
Examination of the Laetoli hominid footprints has already lead to a diversity of opinion on different topics. Recent reconstruction of the locomotor apparatus of australopithecines led to the hypothesis that their locomotor repertoire included a significant proportion of arboreal activity. While the structure of the foot of the earliest hominids may be partially gleaned from the study of its preserved skeletal parts from sites in Eastern and Southern Africa, such fossils lack information about the weight transfer during progression.
The most important external force that acts on the body during progression is the force exerted on the ground. This force is due to the reaction to gravity and to the momentary acceleration of the body. The relative distribution of pressure between the lateral and the medial portions of the foot is a crucial matter, not only for the functioning of the foot, but also for interpreting the fossil footprints fixed in the ash layers at Laetoli. In bipedal movement the fore-limb is no longer used to support against gravity or to accelerate the body. The forward swing of the arm contributes angular momentum to neutralize partially that of the advancing leg of the opposite side. The arms do not behave as pendulums in typical walking, but are subject to muscle action. The swinging of the arms is consequently not a purely incidental accompaniment of forward movement, but is an integral part of the dynamics of progression.
Consequently, we analysed the weight transfer of an individual in walking normally and also in walking with different constraints on arm and trunk motion during bipedal locomotion. The differences in the course of the gravitational force in the footprint can give some insight for the particular footprint morphology in the Laetoli tracks.
Fossilized footprints preserved in volcanic ash tuffs in the Hawaii Volcanoes National Park afford an exceptional opportunity to study footprints of traditionally unshod modern human pedestrians, laid down under conditions relatively similar to those associated with footprints made by Pliocene hominids at the east African site of Laetoli, Tanzania. The Hawaiian footprint area encompasses about 13 km2 of the Ka’u Desert. Two footprintbearing ash layers date to 200 and 400 years before present (ybp) respectively. The track localities were surveyed with GPS coordinates and photographed, including stereophotography. In many instances footprint clarity and preservation are exceptional, revealing anatomical details of foot shape, toe conformation and arch development. Footprints were contrasted with stereophotos and casts of the Laetoli tracks and with footprints made by a captive chimpanzee in a sand trackbox. The modern human footprints were distinct in the marked development of the ball of the foot and toe pads, indicative of differential weight bearing or traction by these structures. There is consistent expression of a well-developed arch and no indication of midtarsal flexion. In contrast, the Laetoli hominid tracks do not exhibit these adaptations. Instead, they display a tapering proximal heel outline, relatively narrow distal metatarsus, indistinct ball and poorly differentiated impressions of the lateral toes. Preservation of the ash layer is patchy throughout the Ka’u footprint area; however, several examples of tracks permit limited documentation of spontaneous gait parameters. Contrasts with the Laetoli tracks emphasize the short step length of the fossil hominid gait and the highly variable angle of gait and step width in both ancient hominid and modern human trackways.
When Mary Leakey and collaborators discovered the Laetoli footprints (Tanzania) in 1978-1979, they exhumed the direct evidence that a species of primate was able to walk bipedally 3.75 Mya. This evidence of an early bipedalism has also been corroborated by contemporary fossil bones, especially those of Australopithecusafarensis. But in what manner did these early hominids walk on two legs? This point remains the subject of discussion. Our purpose is to add pedal architectural data to the debate concerning the locomotor modalities in early hominids, especially in Australopithecus afarensis.
One of the cornerstones of modern evolutionary biology is the insight that an individual that is more tailored to his environment should have a higher survival and reproductive potential than his less adapted neighbors. Behavioral ecology attempts to explain behaviors as adaptive, or not, only in particular ecological contexts. And life history theory highlights that the developmental stage of an individual is an integral part of the environment and that development is an inherently sequential process. But how do these seminal ideas help us understand the evolution of hominid bipedality?
Bipedality can be thought of as a suite of possible styles, with different forms optimizing diverse traits. The locomotor form of an individual can be optimized for many characteristics, including 1) efficient use of energetic, thermal, temporal and water budgets; 2) range; 3) velocity or acceleration; 4) endurance, fatigue and injury protection; and 5) burden carrying. All could be important in different ecological circumstances and, indeed, many may act in concert with others, but which ones? when? how? and how can we tell from the fossil record?
While female australopithecines appear to have excelled at slow speeds and short distances, the locomotor form of Homo seems to be oriented toward relatively long distance travel and endurance walking and running. Understanding these aspects of the locomotor regime does not, however, inform about the other elements of the behavioral repertoire, nor does it elucidate why the transition took place and what the functional implications of it are.
The task of understanding bipedality as a fundamental adaptation of Hominidae can only be a truly fruitful endeavor if we keep in mind that males and females may have different ecological perspectives; children, adolescents, and adults may interact with the environment in different ways; and the environment is a complex set of interacting, dynamic factors.
A full understanding of the evolution of bipedalism requires consideration of the effects of body form on locomotor biomechanics. This is particularly important given the great range of body proportions found in fossil hominids. For example, although Homo ergaster had an essentially modern body form, it differed from most modern humans in having very long limbs, and particularly long distal limb elements, for its size. This study experimentally investigated the effects of crural index (tibia length relative to femur length) on the kinematics and kinetics of normal human walking. We hypothesized that a relatively longer tibia would lead to higher bending moments along the leg. We found, however, that modern humans with higher crural indices employ a series of postural adjustments that keep bending moments at comparable levels. An examination of the relevant fossil material suggests that early hominids with long tibiae, particularly Homo ergaster, likewise did not experience particularly high bending moments along the leg during locomotion. This implies that early hominids may have modified their locomotion behaviorally to moderate the bending stresses incurred during walking. Although an essentially modern human body form had evolved by the early Pleistocene, the form of walking that characterizes most modern humans may not have evolved until significantly later.
A suite of functional tradeoffs involving specialization for fighting versus locomotor economy is hypothesized to have influenced the evolutionary pathways of hominids. Characters such as pronounced forelimb strength, robust distal limbs, short stature, wide hips, robust head and neck, and fully bipedal stance and gait gave australopithecines a body configuration that is consistent with specialization for fighting with the forelimbs. This, plus a high level of sexual dimorphism in body and forelimb size suggest that australopithecines were specialized for male-male aggression. Nevertheless, traits that made australopithecines effective fighters would also have made them inefficient runners by modern human standards. Given the evidence of specialization for male-male aggression in australopithecines, the evolution of high locomotor stamina in Homo represents a dramatic change in evolutionary trajectory. I suggest that the evolution of improved locomotor stamina in Homo was made possible by the invention of new weapon technology that reduced functional conflicts between specialization for economical transport and specialization for male-male fighting. Invention of the first effective weapons would have shifted selection for male-male aggression from favoring greater physical strength and agility to favoring creative innovation, allowing independent evolution of cursorial specialization. In this scenario, the emergence of Homo (1) is dependent on the invention of new weapons, and 2) represents both greatly improved distance transport and increased lethality in a lineage already highly specialized for fighting.
Enhancing our understanding of the skeletal biology of modern hunter-gatherers and developing more sophisticated models of fossil and prehistoric hominin locomotor behavior and subsistence activities requires information on male and female forager mobility patterns. Unlike other primates, modern human foragers expend considerable energy in activities involving the transport of resources across the landscape. Although male foragers are often associated with high mobility in comparison to their female counterparts, female foragers are seen to engage in subsistence tasks incorporating a high frequency of burden carrying. This paper examines the influence of age and sex on mobility and resource transport in a group of Pumé foragers located in the savanna-wetlands of southwestern Venezuela.
One of the most important economic, social and biological transitions in human history is the shift from food collecting to food producing systems. Competing models regarding the interpretation of the archaeological evidence bring the economic organization of incipient Southwestern farmers into question. Were they committed agriculturalists occupying settled villages, or seasonally mobile groups using agriculture as a buffer to wild resources? Reconstructing the changing economic strategies accompanying the first archaeologically detectable evidence of increased residential stability can be approached from a biological perspective. Bone biology research indicates a clear link between habitual physical activities and skeletal form. Cross-sectional data derived from computed tomographic scans of femoral diaphyses provide a means to test hypotheses regarding relative mobility patterns accompanying the foraging to farming transition.
... A possible means of bridging gaps between the morphology and locomotor effectiveness lies in evidence from fossilized footprint trails. Fossilized footprints from a broad range of time periods [Laetoli [21], Ileret [22], Hawaii [23]] have augmented skeletal data by providing additional evidence corroborating and/or reshaping the interpretation of the skeletal data of a particular species. Footprints have been used to supplement stature and body mass estimations based upon skeletal segments because forensic data show quite clearly that footprint dimensions correlates well with stature [24] and unloaded body mass [25]. ...
... Additionally, particular aspects of foot morphology can be directly observable within fossilized prints and compared with reconstructions based on bony elements alone (e.g. toe pad shape and separation, toe length, and hallux position [22,23]). Finally, specific details of locomotor patterns are preserved in fossilized footprints. ...
... Finally, specific details of locomotor patterns are preserved in fossilized footprints. Footprints have been used to indicate the cadence at which the species walked [17], the stride lengths of the individuals [23,[26][27][28][29][30], the pattern of weight transfer while walking [31,32] and whether individuals were walking with other individuals [21,22]. Experimental data from extant populations with recorded stature, mass, cadence and speed can further confirm relationships between the footprint tracks and behavior of extinct hominins [31,[33][34][35]. ...
Human footprint fossils have provided essential evidence about the evolution of human bipedalism as well as the social dynamics of the footprint makers, including estimates of speed, sex and group composition. Generally such estimates are made by comparing footprint evidence with modern controls; however, previous studies have not accounted for the variation in footprint dimensions coming from load bearing activities. It is likely that a portion of the hominins who created these fossil footprints were carrying a significant load, such as offspring or foraging loads, which caused variation in the footprint which could extend to variation in any estimations concerning the footprint's maker. To identify significant variation in footprints due to load-bearing tasks, we had participants (N = 30, 15 males and 15 females) walk at a series of speeds carrying a 20kg pack on their back, side and front. Paint was applied to the bare feet of each participant to create footprints that were compared in terms of foot length, foot width and foot area. Female foot length and width increased during multiple loaded conditions. An appreciation of footprint variability associated with carrying loads adds an additional layer to our understanding of the behavior and morphology of extinct hominin populations.
... For example, the famous tracks attributable to an early bipedal hominid (Homo or Australopithecus) from the Laetoli site in Tanzania represents one of the most exciting scientific discoveries of the 20th century, which Mary Leakey herself regarded as the most significant of her career. The Laetoli hominid footprints have provided important information on human bipedalism and the evolutionary history of humankind (Leakey, 1979;Leakey and Hay, 1979;Day and Wickens, 1980;White, 1980;Charteris et al., 1982;Leakey, 1987;White and Suwa, 1987;Agnew and Demas, 1998;Meldrum, 2004aMeldrum, , 2007aTuttle, 2008). Thus, hominid footprints have the potential to reveal information on the size, stature, gait, and speed of both individuals and groups (populations). ...
... Day and Wickens (1980) reported that footprint contour patterns of modern and fossil hominids have remarkable similarities in heel and ball impressions, figure of eight contour patterns, and medial arch. However, Meldrum (2004a) considers this conclusion overstated. Unlike the cercopithecoid footprints, the longest, or at least most prominent, digit of the Laetoli hominid footprints is the great toe which is nearly parallel to the other toes and situated as in the human foot (Leakey and Hay, 1979). ...
... Unlike the cercopithecoid footprints, the longest, or at least most prominent, digit of the Laetoli hominid footprints is the great toe which is nearly parallel to the other toes and situated as in the human foot (Leakey and Hay, 1979). However, Meldrum (2004a) notes that digit II may be equally as long as digit I. The longitudinal medial arch or medial arch has long been considered to be diagnostic of hominid footprints (Elftman and Manter, 1935). ...
Although more than 60 ancient hominid track sites ranging in age from 3.7 million to less than 500 B. P. are recorded from all continents except Antarctica, no ichnotaxonomic names have ever been formally proposed for hominid tracks. There is no prohibition to the naming of fossil footprints of species that created tracks and trackways similar to those of living species. On the contrary, there is precedent for the naming of ichnotaxa corresponding to the dominant extant vertebrates classes: mammals = Mammalipedia and birds = Avipeda. The hominid track site sample includes only about a dozen sites where footprint preservation is good enough to show details of diagnostic foot morphology and typical trackway morphology. We infer that the Acahualinca Footprint Museum site in Nicaragua represents the most important ancient hominid track site that combines accessibility, a large sample of well-preserved trackways and reliable dating. For this reason, we select the Nicaraguan tracks as the type sample for the new ichnotaxon Hominipes modernus ichnogen., and ichnsp. et ichnosp. nov., which we infer to represent fully modern Homo sapiens. Our preliminary investigations of other track sites suggest that the majority also yield H. modernus. However, at many sites preservation is insufficient to make an ichnotaxonomic designation at the species level or to infer that the trackmaker was H. sapiens. Thus, at many sites including the famous Laetoli site, we apply the more general label of Hominipes isp. indet.
... The two alternate hypotheses can be generalized as: (1) the footprints are essentially indistinguishable from those of modern humans and represent an as yet unrecognized relatively derived hominin (e.g. Day and Wickens, 1980;Chartelis et al., 1981;Alexander, 1984;Lovejoy, 1988;Tuttle, 1985Tuttle, , 1996Tuttle et al., 1990Tuttle et al., , 1991Musiba et al., 1997;Schmid, 2004;Sellers et al., 2005;Harcourt-Smith and Hilton, 2005;Kimbel and Delezene, 2009); and (2) the footprints indicate a trackmaker with a foot architecture manifestly distinct, in their mosaic and/or intermediate nature, from modern humans (Stern and Susman, 1983;Susman et al., 1984;Deloison, 1991Deloison, , 1992Clarke, 1999;Meldrum, 2000Meldrum, , 2002Meldrum, , 2004aBerge et al., 2006;Meldrum and Chapman, 2007;Bennett et al., 2009). ...
... The advantage to naming ichnotaxa is that within the parataxonomy they can be referred to unambiguously based on morphology (the basis of the parataxon) without having to make a definite statement as to the tracemaker's identity, which is usually not known or debateable (e.g., Bertling et al., 2006). Impetus for naming the Laetoli hominin tracks arises in part from growing interest in hominin tracks (e.g., D'Aout et al., 2010;Raichlen et al., 2010;Bennett et al., 2009;Kim et al., 2008a;Lockley et al., 2007Lockley et al., , 2008Meldrum, 2004aMeldrum, ,b, 2007a and the recognition that none had ever been formally named, until Kim et al. (2008b) proposed the name Hominipes modernus, for well-preserved tracks unequivocally attributed to Homo sapiens. That ichnotaxon is based on the type footprints at the Acahualinca Footprint Museum, Managua, Nicaragua (Lockley et al., 2008). ...
At 3.6 Ma, the Laetoli Pliocene hominin trackways are the earliest direct evidence of hominin bipedalism. Three decades since their discovery, not only is the question of their attribution still discussed, but marked differences in interpretation concerning the footprints’ qualitative features and the inferred nature of the early hominin foot morphology remain. Here, we establish a novel ichnotaxon, Praehominipes laetoliensis, for these tracks and clarify the distinctions of these footprints from those of later hominins, especially modern humans. We also contrast hominin, human, and ape footprints to establish morphological features of these footprints correlated with a midtarsal break versus a stiff longitudinal arch. Original photos, including stereo photographs, and casts of footprints from the 1978 Laetoli excavation, confirm midtarsal flexibility, and repeatedly indicate an associated midfoot pressure ridge. In contrast, the modern human footprint reflects the derived arched-foot architecture, combined with a stiff-legged striding gait. Fossilized footprints of unshod modern human pedestrians in Hawaii and Nicaragua unambiguously illustrate these contrasts. Some points of comparisons with ape footprints are complicated by a variable hallucal position and the distinct manner of ape facultative bipedalism.
... Based on the markedly convex metatarsal surface on the medial cuneiform, the lack of hallucal metatarsal head and base flatness characteristic of humans, and the shape of the Laetoli prints with a divergent hallux and impression of the m. abductor hallucis, many conclude that Au. afarensis had a hallux capable of abduction (Stern and Susman, 1983;Susman, 1983;Susman et al., 1984;Deloison, 1991;Meldrum, 2004). Latimer and Lovejoy (1990b), on the other hand, suggest that Au. afarensis had an adducted hallux based on relatively parallel articular surfaces of the medial cuneiform and its anteriorly located groove for the m. ...
... Their conclusion is based on the presence of weight-bearing tubercles on the distal tarsal bones, a dorsiflexed calcaneal neck, an ape-like navicular morphology with dorsally inclined articulations for the cuneiforms, an ectocuneiform hamulus, proximodistally short cuneiforms, a groove for the m. abductor digiti minimi on the plantar aspect of the 5th metatarsal, a dorsally oriented tarsometatarsal joint on the hallucal metatarsal (Sarmiento, 1998;Berillon, 1998Berillon, , 2000Sarmiento and Marcus, 2000;Harcourt-Smith, 2002;Harcourt-Smith and Aiello, 2004;Mitchell et al., 2012), and the absence in some Laetoli footprints of a marked medial arch (Deloison, 1992;Meldrum, 2004; although it appears to be present in other prints; see for example; Day and Wickens, 1980;White, 1980;Day, 1985;Robbins, 1987;Tuttle, 1987;Tuttle et al., 1991;Schmid, 2004). ...
This paper presents an analysis of metatarsal torsion in apes, cercopithecoids and humans, compares australopiths with these species, and discusses their inferred foot morphology and function relative to prehensility, arboreality and the presence or absence of a longitudinal arch. Our results show that locomotor modes are reflected in metatarsal torsion values. Apes, which climb vertically with their foot inverted, have hallucal metatarsal heads that are turned toward the other toes and lateral toes that are inverted. Cercopithecoids, which tend to orient their feet in an axis more parallel to the line of motion, present signs of prehensility by having inverted 2nd metatarsals that oppose the hallux, while their two lateral-most metatarsals are strongly everted. Humans, with their rigid feet and longitudinal arches, have all toes that present their plantar surface toward the ground, resulting in hallucal and 2nd metatarsals that are relatively untwisted and the others that are strongly everted. Humans are different from all taxa only for the 2nd and 3rd metatarsal. It is hypothesized that the untwisted 2nd metatarsal reflects the lack of digit opposability of the medial foot and the strongly everted 3rd metatarsal reflects the longitudinal arch. Australopithecus afarensis was characterized by an everted lateral foot, the prerequisite for the development, but not necessarily an indicator, of a longitudinal arch. In Australopithecus africanus, torsion of fragmentary and complete 1st, 2nd, 3rd and 5th metatarsals suggest that the species did not have a foot with monkey- or ape-like prehensile capabilities and did not have a human-like longitudinal arch. In the Swartkrans remains, torsion is consistent with an unprehensile foot. The morphology of the fossils indicates that there was strong selection to orient the plantar surface of the toes facing the ground at the expense of a grasping foot and inversion ability.
... Furthermore, in males, it remained quadrangular in shape (i.e., a ratio of 1) between the Natufian hunter-gatherers and Chalcolithic farmers, and in females, it demonstrated mixed results (quadrangular in the Natufian and Chalcolithic samples and elongated horizontally in the PPN). It is well established that the calcaneocuboid joint plays a crucial role in restricting the range of motion and increasing the stability of the human foot, which is necessary for bipedal locomotion (Kidd et al., 1996;Meldrum and Hilton, 2004;Ginot et al., 2016). Furthermore, based on a study on rodents, it was reported that a wider facet on the horizontal plane enables a broader range of horizontal movement, and a taller facet on the sagittal plane facilitates a wider range of sagittal movement (Ginot et al., 2016). ...
The calcaneal morphology changed considerably during human evolution to enable efficient bipedal locomotion. However, little information exists regarding its adaptation to changes in habitual activities following the transition to a sedentary lifestyle. We aimed to examine changes in calcaneal morphology during the Pleistocene-Holocene Levant in light of sexual dimorphism. We studied three archaic Homo sapiens calcanei dated to the Middle and Upper Paleolithic, 23 Natufian hunter-gatherers, 12 Pre-Pottery Neolithic early farmers, and 31 Chalcolithic farmers. The calcanei were scanned via a surface scanner and measured, and bone proportions were calculated. Measurements included the height, length, and width of various calcaneal elements. The sex of each individual was determined using methods based on calcaneal morphology. The validity of these methods was tested in those individuals who had the pelvis (92.3% agreement rate). Accordingly, the sample included 59.4% males and 40.6% females. Most calcaneal indices were sex-independent, except for the relative width, relative anterior length, and the cuboid index. Temporal trends between the Natufian and Chalcolithic periods were more pronounced among males than females. While in the proximal calcaneus, the temporal trend was similar between males and females, it differed in the distal part and articular facets. The calcanei of archaic H. sapiens exceeded the average of the Natufian hunter-gatherer for most variables, though the trend varied. To conclude, males and females were affected differently by the changing environment. The calcanei of archaic H. sapiens were better adapted for activity involving high mobility, independent of sex. During the transition to a sedentary way of life, different factors probably designed the male and female calcaneus. These could include factors related to the sexual division of labor, adaptation to lengthy standing, and changes in footwear.
... During the evolution that led to Homo sapiens, our hominin ancestors developed new forms of cooperation that made it possible to organise their societies in new ways. It is generally agreed that hominins evolved in open landscapes in which the individual travelled over long ranges [119]. Cooperative foraging could have been caused by increased seasonality and variability in the environments. ...
The aim of this article is to provide an evolutionarily grounded explanation of central aspects of the structure of language. It begins with an account of the evolution of human causal reasoning. A comparison between humans and non-human primates suggests that human causal cognition is based on reasoning about the underlying forces that are involved in events, while other primates hardly understand external forces. This is illustrated by an analysis of the causal cognition required for early hominin tool use. Second, the thinking concerning forces in causation is used to motivate a model of human event cognition. A mental representation of an event contains two vectors representing a cause as well as a result but also entities such as agents, patients, instruments and locations. The fundamental connection between event representations and language is that declarative sentences express events (or states). The event structure also explains why sentences are constituted of noun phrases and verb phrases. Finally, the components of the event representation show up in language, where causes and effects are expressed by verbs, agents and patients by nouns (modified by adjectives), locations by prepositions, etc. Thus, the evolution of the complexity of mental event representations also provides insight into the evolution of the structure of language.
... Wood 1992). Erectus was the first in our lineage with modern human anatomy (Plummer 2004), allowing for enduring bipedalism (Meldrum and Hilton 2004). The cultural change also accelerated. ...
Rational agency is of central interest to philosophy, with evolutionary accounts of the cognitive underpinnings of rational agency being much debated. Yet one building block—our ability to argue—is less studied, except Mercier and Sperber’s argumentative theory (Mercier and Sperber in Behav Brain Sci 34(02):57–74, https://doi.org/10.1017/s0140525x10000968, 2011, in The enigma of reason. Harvard University Press, Cambridge, 2017). I discuss their account and argue that it faces a lacuna: It cannot explain the origin of argumentation as a series of small steps that reveal how hominins with baseline abilities of the trait in question could turn into full-blown owners of it. This paper then provides a first sketch of the desired evolutionary trajectory. I argue that reasoning coevolves with the ability to coordinate behavior. After that, I establish a model based on niche construction theory. This model yields a story with following claims. First, argumentation came into being during the Oldowan period as a tool for justifying information ‘out of sight’. Second, argumentation enabled hominins to solve collective action problems with collaborators out of sight, which stabilized argumentative practices eventually. Archeological findings are discussed to substantiate both claims. I conclude with outlining changes resultant from my model for the concept of rational agency.
... concluded that the gait pattern of the Laetoli hominins was similar to the modern humans' , whereas others (e.g. Meldrum 2004;Schmid 2004;Hatala et al. 2016) inferred that it was significantly different, qualitatively and/or quantitatively. However, all the aforementioned studies are equally biased, regardless of the methods used and the results obtained, because they all focus only on G1. ...
We currently have little archaeological and historical data about mining
areas of North Africa that were exploited in pre-Roman times, and even the
rare ancient proofs can be mostly dated to Roman period. However, it was the
searching for new metals that brought Phoenician to the western expansion:
North Africa was one of the richest Mediterranean areas and we believe that such
a small amount of information about this region has to be connected to the lack of
dedicated studies. Every time that the scientific interest focuses on this important
part of the economic and social life in the ancient world (as it was already made in
Spain and Sardinia), new data emerges and offers a bigger historical background.
Current researches of ‘Researches about Phoenicians in North Africa: archaeology,
numismatic and economic history’ aims, first of all, to define historical
and technological background of all the metal production cycle, the exploitation,
the manipulation techniques and the resources management of mining areas in
North Africa, Morocco and Algeria in particular
... Several thousand modern human footprints are embedded in a muddy ash at Hawaii Volcanoes National Park (HAVO), Hawaii (Moniz-Nakamura, 2003;Meldrum, 2004). The footprint-bearing ash dates to approximately 1780 A.D. The tracks are concentrated in an elongate passage between Kilauea and Mauna Loa apparently used by humans to traverse through this saddle . ...
... Kinematics and the functional morphology of nonhuman primates are 2 research fields that provide crucial information that can be used to evaluate early hominid locomotor modes (Coppens and Senut 1991;Crompton and Günther 2004;Franzen et al. 2003;Ishida et al. 2006;Kimura et al. 1996;Meldrum and Hilton 2004;Preuschoft 1970Preuschoft , 1971Preuschoft , 1973Strasser et al. 1998;this issue). Kinematic investigations regard primates mainly as completely integrated systems and document movements quantitatively. ...
Setups that integrate both kinematics and morpho-functional investigations
of a single sample constitute recent developments in the study of nonhuman primate
bipedalisms. We introduce the integrated setup built at the Primatology Station of the
French National Centre for Scientific Research (CNRS), which allows analysis of both
bipedal and quadrupedal locomotion in a population of 55–60 captive olive baboons. As
a first comparison, we present the hind limb kinematics of both locomotor modalities in
10 individuals, focusing on the stance phase. The main results are: 1) differences in
bipedal and quadrupedal kinematics at the hip, knee, and foot levels; 2) a variety of foot
contacts to the ground, mainly of semiplantigrade type, but also of plantigrade type; 3)
equal variations between bipedal and quadrupedal foot angles; 4) the kinematics of thefoot joints act in coordinated and stereotyped manners, but are triggered differently
according to whether the support is bipedal or quadrupedal. Although very occasionally
realized, the bipedal walk of olive baboon appears to be a habitual and nonerratic
locomotor modality.
... Homo ergaster/erectus was a long ranging species, fuelled by a high quality diet, and adapted to transporting fairly heavy burdens. The long legs, short broad trunk and short arms, in comparison to the predecessors, seem to be adaptations to endurant bipedalism, that is, long range walking or running (Preuschoft & Witte, 1991; Hilton & Meldrum, 2004). Ergaster/erectus's gracile physique and more prominent stature gave this hominid a thermoregular advantage (Wheeler, 1992), which implies a capability for long ranging day time excursions in hot open lands. ...
... Unfortunately, the trackways do not divulge what other behaviors were practiced by its makers, and whether they were habitual biped as are modern humans or also quadrupeds and climbers as are African apes. As regards the foot morphology corresponding to the Laetoli print, the conclusions of Meldrum (2004Meldrum ( , 2007, who recognizes the makers as having a flat flexible midfoot, are the most cautious. ...
Based on comparisons to non-statistically representative samples of humans and two great ape species (i.e. common chimpanzees Pan troglodytes and lowland gorillas Gorilla gorilla), Ward et al. (2011) concluded that a complete hominin fourth metatarsal (4th MT) from Hadar, AL 333-160, belonged to a committed terrestrial biped with fixed transverse and longitudinal pedal arches, which was no longer under selection favoring substantial arboreal behaviors. According to Ward et al., the Hadar 4th MT had (1) a torsion value indicating a transverse arch, (2) sagittal plane angles between the diaphyseal long axis and the planes of the articular surfaces indicating a longitudinal arch, and (3) a narrow mediolateral to dorsoplantar base ratio, an ectocuneiform facet, and tarsal articular surface contours all indicating a rigid foot without an ape-like mid-tarsal break. Comparisons of the Hadar 4th MT characters to those of statistically representative samples of humans, all five great ape species, baboons and proboscis monkeys show that none of the correlations Ward et al. make to localized foot function were supported by this analysis. The Hadar 4th MT characters are common to catarrhines that have a midtarsal break and lack fixed transverse or longitudinal arches. Further comparison of the AL 333-160 4th MT length, and base, midshaft and head circumferences to those of catarrhines with field collected body weights show that this bone is uniquely short with a large base. Its length suggests the AL 333-160 individual was a poor leaper with limited arboreal behaviors and lacked a longitudinal arch, i.e. its 4th MT long axis was usually held perpendicular to gravity. Its large base implies cuboid-4th MT joint mobility. A relatively short 4th MT head circumference indicates AL 333-160 had small proximal phalanges with a restricted range of mobility. Overall, AL 333-160 is most similar to the 4th MT of eastern gorillas, a slow moving quadruped that sacrifices arboreal behaviors for terrestrial ones. This study highlights evolutionary misconceptions underlying the practice of using localized anatomy and/or a single bony element to reconstruct overall locomotor behaviors and of summarizing great ape structure and behavior based on non-statistically representative samples of only a few living great ape species.
... This is characterized by a fully adducted hallux, large and robust calcaneus and tarsal region, a pronounced medial longitudinal arch and short toes (Griffin and Wood, 2006). Mediated by substrate material properties (Allen, 1997;Meldrum, 2004) they represent a record of peak foot pressure in the hindfoot, and a combination of peak pressure and pressure impulse in the forefoot (D'Aout et al., 2010). During normal walking, the weight-bearing foot undergoes a highly stereotypical movement and pressure distribution pattern in which the heel contacts the ground first, making a relatively deep impression on the substrate. ...
Verification of human footprints within the geological record provides critical evidence of presence as well as information on the biomechanics of the individuals who made those prints. Consequently, the correct identification of human footprints is important, but is something for which critical and objective criteria do not exist. The current paper attempts to address this issue by presenting a new statistically based approach to the verification of human footprints. The importance of this is illustrated by the recent controversy surrounding a series of marks identified as human prints in the Valsequillo Basin in Central Mexico dated originally to 40 000 years ago. The dating of these marks remains highly controversial with some teams placing their age at 1.3 million years old. Irrespective of this debate the crucial question that must be addressed is whether or not they represent evidence of human presence. Using an objective statistically based methodology developed here, these controversial marks are re-examined and found to be of questionable origin, as they are inconsistent with a suite of other, known human and hominin prints. Consequently, we argue that they should be removed as evidence in the ongoing controversy surrounding the colonization of the Americas.
... Kinematics and the functional morphology of nonhuman primates are 2 research fields that provide crucial information that can be used to evaluate early hominid locomotor modes (Coppens and Senut 1991; Crompton and Günther 2004; Franzen et al. 2003; Ishida et al. 2006; Kimura et al. 1996; Meldrum and Hilton 2004; Preuschoft 1970 Preuschoft , 1971 Preuschoft , 1973 Strasser et al. 1998; this issue). Kinematic investigations regard primates mainly as completely integrated systems and document movements quantitatively. ...
Setups that integrate both kinematics and morpho-functional investigations of a single sample constitute recent developments in the study of nonhuman primate bipedalisms. We introduce the integrated setup built at the Primatology Station of the French National Centre for Scientific Research (CNRS), which allows analysis of both bipedal and quadrupedal locomotion in a population of 55–60 captive olive baboons. As a first comparison, we present the hind limb kinematics of both locomotor modalities in 10 individuals, focusing on the stance phase. The main results are: 1) differences in bipedal and quadrupedal kinematics at the hip, knee, and foot levels; 2) a variety of foot contacts to the ground, mainly of semiplantigrade type, but also of plantigrade type; 3) equal variations between bipedal and quadrupedal foot angles; 4) the kinematics of the foot joints act in coordinated and stereotyped manners, but are triggered differently according to whether the support is bipedal or quadrupedal. Although very occasionally realized, the bipedal walk of olive baboon appears to be a habitual and nonerratic locomotor modality.
... Evidence of a thermoregulatory adaptation similar to humans (presumably including the same sweating capacity) suggests that they were active during the heat of the day, and by doing so could have minimized interactions with most large predators (Foley, 1987;Lewis, 1997). Femoral cortical bone thickness indicates that activity levels were high in early Homo (Ruff et al., 1993;Ruff, 2000), and the overall H. erectus body plan suggests that it shared a unique capacity with humans: the ability to endurance-run (Carrier, 1984;Hilton and Meldrum, 2004). Ruff et al. (1993) argued that high levels of femoral robusticity in early Homo reflect high activity levels, and that the decline in postcranial robusticity in Homo through the Pleistocene may reflect cognitive and technological advances, analogous to what has been argued for cheek tooth reduction through time. ...
The appearance of Oldowan sites ca. 2.6 million years ago (Ma) may reflect one of the most important adaptive shifts in human evolution. Stone artifact manufacture, large mammal butchery, and novel transport and discard behaviors led to the accumulation of the first recognized archaeological debris. The appearance of the Oldowan sites coincides with generally cooler, drier, and more variable climatic conditions across Africa, probably resulting in a net decrease in woodland foods and an increase in large mammal biomass compared to the early and middle Pliocene. Shifts in plant food resource availability may have provided the stimulus for incorporating new foods into the diet, including meat from scavenged carcasses butchered with stone tools. Oldowan artifact form varies with clast size, shape, raw material physical properties, and flaking intensity. Oldowan hominins preferred hard raw materials with good fracture characteristics. Habitual stone transport is evident from technological analysis, and raw material sourcing to date suggests that stone was rarely moved more than 2-3 km from source. Oldowan debris accumulation was spatially redundant, reflecting recurrent visitation of attractive points on the landscape. Thin archaeological horizons from Bed I Olduvai Gorge, Tanzania, were probably formed and buried in less than 10 years and document hominin processing of multiple carcasses per year. Transport beyond simple refuging behavior is suggested by faunal density at some site levels. By 2.0 Ma, hominin rank within the predatory guild may have been moderately high, as they probably accessed meaty carcasses through hunting and confrontational scavenging, and hominin-carnivore competition appears minimal at some sites. It is likely that both Homo habilis sensu stricto and early African H. erectus made Oldowan tools. H. habilis sensu stricto was more encephalized than Australopithecus and may foreshadow H. erectus in lower limb elongation and some thermoregulatory adaptations to hot, dry climatic conditions. H. erectus was large and wide-ranging, had a high total energy expenditure, and required a high-quality diet. Reconstruction of H. erectus reproductive energetics and socioeconomic organization suggests that reproductively active females received assistance from other group members. This inference, combined with archaeological evidence for acquisition of meaty carcasses, suggests that meat would have been a shared food. This is indirectly confirmed by nutritional analysis suggesting that the combination of meat and nutritionally dense plant foods was the likely diet fueling body size increase and encephelization in Homo. Most discussion of Oldowan hominin behavior and ecology, including that presented here, is based on materials from a few sites. There is a critical need to analyze additional large, primary-context lithic and faunal assemblages to better assess temporal, geographic, and environmental variability in Oldowan behavior.
... In contrast, the savanna Pumé, who are the focus of this paper, live between these major river courses and are mobile foragers . The first detailed studies of savanna Pumé occurred in the 1980s (Gragson, 1989) and in the 1990s (Greaves, 1997; Hilton and Greaves, 2004; Greaves, 2006 ). The following describes the savanna Pumé of Dora Aná , Yagurí, and Charakotó as they were living during the 2005–2006 study (seeFig. ...
Because humans have slow life histories, discussions of the optimal age at first birth have stressed the benefits of delayed reproduction. However, given the diversity of ecological, fertility, and mortality environments in which humans live, reproductive maturity is expected to be highly variable. This article uses reproductive histories to examine a pattern of early menarche and first birth among the Pume, a group of South American foragers. Age at menarche and first birth are constructed using both retrospective and cross-sectional data for females over the age of 10 (n = 83). The objectives are first to define these patterns and then discuss their reproductive consequences. On average, Pume girls reach menarche at age 12.9, and give birth to their first child at age 15.3-15.5 (retrospective and cross-sectional data, respectively). This populational average falls several years prior to what often is considered the human norm. Two questions are then considered. What are the infant mortality costs across a mother's reproductive career? How does surviving fertility vary with age at first birth? Results indicate that the youngest of first-time mothers (<14) are four times more likely to loose their firstborns than older first-time mothers (> or =17). Given parity-specific mortality rates, the optimal strategy to minimize infant mortality and maximize reproductive span is to initiate childbearing in the midteens. Women gain no additional advantage in surviving fertility by delaying childbearing until their late teens.
Humans evolved in the dynamic landscapes of Africa under conditions of pronounced climatic, geological and environmental change during the past 7 million years. This book brings together detailed records of the paleontological and archaeological sites in Africa that provide the basic evidence for understanding the environments in which we evolved. Chapters cover specific sites, with comprehensive accounts of their geology, paleontology, paleobotany, and their ecological significance for our evolution. Other chapters provide important regional syntheses of past ecological conditions. This book is unique in merging a broad geographic scope (all of Africa) and deep time framework (the past 7 million years) in discussing the geological context and paleontological records of our evolution and that of organisms that evolved alongside our ancestors. It will offer important insights to anyone interested in human evolution, including researchers and graduate students in paleontology, archaeology, anthropology and geology.
In humans, bipartite scaphoid still does not differentiate clearly from traumatic non-union of the scaphoid. To aid diagnosis, we sought to analyze the main geometrical similarities among bipartite scaphoids from primate species with fused and unfused scaphoid centrales. Four human embryos, four cases of adult humans with bipartite scaphoid, twelve adult specimens of other extant anthropoid primates, and two Neandertal scaphoid specimens were included in this study. Three-dimensional polygon models of the scaphoid and os centrale were generated from CT scan, micro-CT scan, or histological sections. A 3D comparative study of the morphological and morphometrical parameters was performed using the MSC Patran software. The os centrale was smaller than the scaphoid in all specimens and its shape was elongated in the anteroposterior scaphoid direction. The position of the os centrale centroid compared to the scaphoid using direction vectors had a strong orientation along the proximodistal axis in all species. The main morphological feature of bipartite scaphoid was the continuity of the scaphoid from its proximal pole to its tubercule along the anteroposterior axis. In all specimens, if the os centrale was removed, the scaphoid still appeared normal and whole. The bipartite scaphoid in adult humans shares geometrical analogies with monkeys and orangutans, human embryos, and Neandertals. Morphological and morphometrical features identified in this study are useful to differentiate bipartite scaphoid from scaphoid pseudarthrosis. All other criteria suggested in the past lead to misdiagnosis.
Fossil footprints are of great interest. A number of features help to identify their makers and can be used to investigate on biological and ecological issues. This is of crucial interest in palaeoanthropology, particularly in view of the emergence of our peculiar pattern of posture and locomotion. However, hominin footprints are rare and most of them are ascribed to the genus Homo. The only exception is represented by the trackways discovered in 1978 at Laetoli Site G, northern Tanzania, and referred to Australopithecus afarensis. These footprints were left on volcanic ashes about 3.66 million years ago by three bipedal creatures walking on a humid layer that was subsequently cemented. At Laetoli Site S (about 150 meters from Site G), we have unearthed new bipedal footprints of two different individuals, who were moving on the same palaeosurface, in the same direction and at the same speed as the three exposed at Site G. Our analysis based on advanced photogrammetric methods shows that the estimated stature and related body mass of one of the new individuals greatly exceed the estimates for those from Site G. This evidence supports marked intraspecific variation, pointing out the occurrence of a considerable difference in size between sexes and suggesting inferences on reproductive behaviour and social structure of these ancient bipedal hominins. A research project combined with conservation plans urgently needs to be developed and submitted to the Tanzanian Authorities for the knowledge, preservation and valorisation of such an extraordinary cultural heritage.
First off, I would like to express my appreciation to Patrick Huyghe and the members of the Tim Dinsdale Award Search Committee for this honor and privilege of addressing the members of SSE. I accept this Award, not so much in recognition of my modest accomplishments, but as acknowledgment of the import of the fundamental question -- Are there biological species, i.e. relict hominoids, behind the legends of man-made monsters? -- as a legitimate and timely question.
A series of capsules and boxes related to the evolution of the human lineage, as published in Andrea A.J. (general editor). World History Encyclopedia, 21 vols. Santa Barbara (CA), ABC-CLIO, Era 1.
The hominin footprint record spans ~3.6 Ma, from Late Pliocene to Holocene, and thus also spans a temporal duration corresponding to many of the major events in hominin evolution. While the oldest (~3.6 Ma) tracks from Laetoli (Tanzania) have been attributed, provisionally, to genus Australopithecus, all others are attributed to various species of the genus Homo, including H. erectus (H. ergaster), H. neanderthalensis, and H. sapiens.
Recent reviews of the previously neglected hominin track record have demonstrated that more than 60 sites are documented in the literature, and that these are found on all continents (excepting Antarctica). Based on age, geographic location, and to a lesser degree footprint morphology, it is possible to infer which post-Laetoli sites and footprint assemblages represent H. erectus (H. ergaster), and which are attributable to later Homo species. However, distinguishing between H. sapiens and H. neanderthalensis on the basis of footprint morphology is not demonstrated conclusively. All the older sites (~3.6- Ma to ~117,000 yBP), from Africa and Europe, including those that represent pre-H. sapiens species, are “open-air” sites, whereas a number of younger, pre-Holocene sites (~62,000 to ~10,000 yBP), especially in Europe, are cave sites. With the exception of a very controversial site in Mexico dated at ~40,000 yBP, no other New World footprint sites are more than ~12,500 years old, and the oldest Australian sites are ~19,000–23,000 yBP.
The extent to which significant modifications in the morphology of the hominin foot and corresponding footprints between 3.6 million and ~50,000 yBP has occurred continues to be debated, but there are two distinct polar morphologies (Praehominipes and Hominipes) now documented in the ichnologic literature. The question of whether transitions in such morphologic features as midfoot flexibility vs. a fully modern arch, and separation of the big toe from traces of lateral digits, and their inferred lengths, constitute evidence of major evolutionary changes may not be resolved to consensus without additions to pedal fossil remains and trace fossil record.
In most cases, sites reveal associated tracks and traces of other tetrapods, mostly mammals and birds, as well as, in some instances, other hominin-manufactured artifacts. Such contextual trace fossil evidence is important for understanding the ecology of early hominin habitats. As recent studies have noted, there is no well-defined line between the hominin track record, narrowly defined as footprints, and the broader ichnologic record, which includes cut marks on bone, handprints, paintings in caves, and even various artifacts. Paleolithic cave paintings that depict tracks and associated track makers could be considered as the earliest examples of vertebrate ichnology field guides, although the significance to the artists themselves likely differed from our modern notion of a guidebook. Although not normally thought of as part of the track record, footprints on the Moon, as well as the tracks of lunar vehicles, and robotic vehicles employed on Mars, represent the ichnologic signatures of recent major events in hominin evolution.
Based on comparisons to non-statistically representative samples of humans and two great ape species (common chimpanzees Pan troglodytes and lowland gorillas Gorilla gorilla), Ward et al. (2011a) concluded that a complete hominin fourth metatarsal (4th MT) from Hadar, AL 333-160, belonged to a committed terrestrial biped with fixed transverse and longitudinal pedal arches, which was no longer under selection favoring substantial arboreal behaviors. According to Ward et al., the Hadar 4th MT had (1) a torsion value indicating a transverse arch, (2) sagittal plane angles between the diaphyseal long axis and the planes of the articular surfaces indicating a longitudinal arch, and (3) a narrow mediolateral to dorsoplantar base ratio, an ectocuneiform facet, and tarsal articular surface contours all indicating a rigid foot without an ape-like midtarsal break. Comparisons of the Hadar 4th MT characters to those of statistically representative samples of humans, all five great ape species, baboons and proboscis monkeys show that none of the correlations Ward et al. make to localized foot function were supported by this analysis. The Hadar 4th MT characters are common to catarrhines that have a midtarsal break and lack fixed transverse or longitudinal arches. Further comparison of the AL 333-160 4th MT length, and base, midshaft and head circumferences to those of catarrhines with field collected body weights show that this bone is uniquely short with a large base. Its length suggests the AL 333-160 individual was a poor leaper with limited arboreal behaviors and lacked a longitudinal arch. Its large base implies cuboid-4th MT joint mobility. A relatively short 4th MT head circumference ii indicates AL 333-160 had small proximal phalanges with a restricted range of mobility. Overall, AL 333-160 is most similar to the 4th MT of eastern gorillas, a slow moving quadruped that sacrifices arboreal behaviors for terrestrial ones. This study highlights evolutionary misconceptions underlying the practice of using localized anatomy and/or a single bony element to reconstruct overall locomotor behaviors and of summarizing great ape structure and behavior based on non-statistically representative samples of only a few living great ape species.
This study investigates whether a flexible pole can be used as an energy-saving method for humans carrying loads. We model the carrier and pole system as a driven damped harmonic oscillator and predict that the energy expended by the carrier is affected by the compliance of the pole and the ratio between the pole's natural frequency and the carrier's step frequency. We tested the model by measuring oxygen consumption in 16 previously untrained male participants walking on a treadmill at four step frequencies using two loaded poles: one made of bamboo and one of steel. We found that when the bamboo pole was carried at a step frequency 20% greater than its natural frequency, the motions of the centers of mass of the load and carrier were approximately equal in amplitude and opposite in phase, which we predicted would save energy for the carrier. Carrying the steel pole, however, resulted in the carrier and loads oscillating in phase and with roughly equal amplitude. Although participants were less economical using poles than predicted costs using conventional fixed-load techniques (such as backpacks), the bamboo pole was on average 5.0% less costly than the steel pole. When allowed to select their cadence, participants also preferred to carry the bamboo pole at step frequencies of approximately 2.0 Hz. This frequency, which is significantly higher than the preferred unloaded step frequency, is most economical. These experiments suggest that pole carriers can intuitively adjust their gaits, or choose poles with appropriate compliance, to increase energetic savings.
The hunting and gathering lifestyle adopted by human ancestors around 2 Ma required a large increase in aerobic activity. High levels of physical activity altered the shape of the human body, enabling access to new food resources (e.g. animal protein) in a changing environment. Recent experimental work provides strong evidence that both acute bouts of exercise and long-term exercise training increase the size of brain components and improve cognitive performance in humans and other taxa. However, to date, researchers have not explored the possibility that the increases in aerobic capacity and physical activity that occurred during human evolution directly influenced the human brain. Here, we hypothesize that proximate mechanisms linking physical activity and neurobiology in living species may help to explain changes in brain size and cognitive function during human evolution. We review evidence that selection acting on endurance increased baseline neurotrophin and growth factor signalling (compounds responsible for both brain growth and for metabolic regulation during exercise) in some mammals, which in turn led to increased overall brain growth and development. This hypothesis suggests that a significant portion of human neurobiology evolved due to selection acting on features unrelated to cognitive performance.
Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil
record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers
dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human–like
foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The
size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and these prints are also morphologically distinct from the 3.75-million-year-old footprints at Laetoli, Tanzania. The Ileret
prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion.
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