Climbing to the top: A personal memoir of Australopithecus afarensis

Stern, Jack T.

doi:10.1002/1520-6505(2000)9:3<113::aid-evan2>3.3.co;2-n

Cited by 82 publications

(152 citation statements)

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“…For example, partial foot remains recovered at Hadar, Ethiopia, suggest that, by 3.6 million years ago, the lateral phalanges of A. afarensis were shorter than in the African great apes, but approximately 40% longer and more curved than in modern humans (Latimer et al, 1982;Susman et al, 1984) (Table 1). This intermediate phalangeal morphology is thought to reflect a mixed behavioral repertoire comprising substantial arboreality and facultative terrestrial bipedalism Stern, 2000). It has been suggested that this pedal morphology would have compromised efficient bipedal walking in Australopithecus, requiring an energetically costly 'high-stepping' gait to clear the toes from the ground at the end of stance (Jungers and Stern, 1983;Stern and Susman, 1983).…”

Section: Implications For Human Evolutionmentioning

confidence: 99%

Walking, running and the evolution of short toes in humans

Rolian

Lieberman

Hamill

et al. 2009

Journal of Experimental Biology

135

118

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SUMMARYThe phalangeal portion of the forefoot is extremely short relative to body mass in humans. This derived pedal proportion is thought to have evolved in the context of committed bipedalism, but the benefits of shorter toes for walking and/or running have not been tested previously. Here, we propose a biomechanical model of toe function in bipedal locomotion that suggests that shorter pedal phalanges improve locomotor performance by decreasing digital flexor force production and mechanical work, which might ultimately reduce the metabolic cost of flexor force production during bipedal locomotion. We tested this model using kinematic, force and plantar pressure data collected from a human sample representing normal variation in toe length (N=25). The effect of toe length on peak digital flexor forces, impulses and work outputs was evaluated during barefoot walking and running using partial correlations and multiple regression analysis, controlling for the effects of body mass, whole-foot and phalangeal contact times and toe-out angle. Our results suggest that there is no significant increase in digital flexor output associated with longer toes in walking. In running, however, multiple regression analyses based on the sample suggest that increasing average relative toe length by as little as 20% doubles peak digital flexor impulses and mechanical work, probably also increasing the metabolic cost of generating these forces. The increased mechanical cost associated with long toes in running suggests that modern human forefoot proportions might have been selected for in the context of the evolution of endurance running.

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Section: Implications For Human Evolutionmentioning

confidence: 99%

Walking, running and the evolution of short toes in humans

Rolian

Lieberman

Hamill

et al. 2009

Journal of Experimental Biology

135

118

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“…Immediately prior to the appearance of hominids, the primate fauna of Africa and Asia was dominated by generalized arboreal quadrupedal primates with a mixture of ape-like and monkey-like traits (Begun et al, 1997). The earliest known hominids (members of the genus Australopithecus) were relatively small-bodied compared to modern humans and their skeletons contain a mosaic of features ( Fig.·2) (Stern and Susman, 1983;Susman and Stern, 1984;Lovejoy, 1988;McHenry, 1991a;Leakey et al, 1995;McHenry and Berger, 1998;Ward et al, 1999;Stern, 2000;Ward, 2002). Early hominids had primitive, more ape-like features such as relatively small lower limb and vertebral joints, curved fingers and toes, relatively long upper limbs and short lower limbs.…”

Section: Schmitt 1438mentioning

confidence: 99%

Insights into the evolution of human bipedalism from experimental studies of humans and other primates

Schmitt

2003

Journal of Experimental Biology

247

145

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SUMMARYAn understanding of the evolution of human bipedalism can provide valuable insights into the biomechanical and physiological characteristics of locomotion in modern humans. The walking gaits of humans, other bipeds and most quadrupedal mammals can best be described by using an inverted-pendulum model, in which there is minimal change in flexion of the limb joints during stance phase. As a result, it seems logical that the evolution of bipedalism in humans involved a simple transition from a relatively stiff-legged quadrupedalism in a terrestrial ancestor to relatively stiff-legged bipedalism in early humans. However, experimental studies of locomotion in humans and nonhuman primates have shown that the evolution of bipedalism involved a much more complex series of transitions, originating with a relatively compliant form of quadrupedalism. These studies show that relatively compliant walking gaits allow primates to achieve fast walking speeds using long strides, low stride frequencies, relatively low peak vertical forces, and relatively high impact shock attenuation ratios. A relatively compliant, ape-like bipedal walking style is consistent with the anatomy of early hominids and may have been an effective gait for a small biped with relatively small and less stabilized joints, which had not yet completely forsaken arboreal locomotion. Laboratory-based studies of primates also suggest that human bipedalism arose not from a terrestrial ancestor but rather from a climbing, arboreal forerunner. Experimental data, in conjunction with anatomical data on early human ancestors, show clearly that a relatively stiff modern human gait and associated physiological and anatomical adaptations are not primitive retentions from a primate ancestor, but are instead recently acquired characters of our genus.

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“…Of the many apelike arboreal traits of the early hominin skeleton (reviewed in McHenry, 1991; Stern, 2000), some of the more widely discussed features include curved fingers and toes, pronounced ridges for the insertion of forearm flexor muscles (e.g., flexor digitorum superficialis), upper limbs with well-developed muscle scars, and aspects of the shapes of the metatarsal heads related to mobility.…”

Section: Climbing (Antipronograde) Ancestormentioning

confidence: 99%

Origin of human bipedalism: The knuckle-walking hypothesis revisited

Richmond

Begun

Strait

2001

Am. J. Phys. Anthropol.

217

161

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Some of the most long-standing questions in paleoanthropology concern how and why human bipedalism evolved. Over the last century, many hypotheses have been offered on the mode of locomotion from which bipedalism originated. Candidate ancestral adaptations include monkey-like arboreal or terrestrial quadrupedalism, gibbon-or orangutan-like (or other forms of) climbing and suspension, and knuckle-walking. This paper reviews the history of these hypotheses, outlines their predictions, and assesses them in light of current phylogenetic, comparative anatomical, and fossil evidence. The functional significance of characteristics of the shoulder and arm, elbow, wrist, and hand shared by African apes and humans, including their fossil relatives, most strongly supports the knuckle-walking hypothesis, which reconstructs the ancestor as being adapted to knuckle-walking and arboreal climbing. Future fossil discoveries, and a clear understanding of anthropoid locomotor anatomy, are required to ultimately test these hypotheses. If knucklewalking was an important component of the behavioral repertoire of the prebipedal human ancestor, then we can reject scenarios on the origin of bipedalism that rely on a strictly arboreal ancestor. Moreover, paleoenvironmental data associated with the earliest hominins, and their close relatives, contradict hypotheses that place the agents of selection for bipedality in open savanna habitats. Existing hypotheses must explain why bipedalism would evolve from an ancestor that was already partly terrestrial. Many food acquisition and carrying hypotheses remain tenable in light of current evidence.

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Climbing to the top: A personal memoir of Australopithecus afarensis

Cited by 82 publications

References 0 publications

Walking, running and the evolution of short toes in humans

Walking, running and the evolution of short toes in humans

Insights into the evolution of human bipedalism from experimental studies of humans and other primates

Origin of human bipedalism: The knuckle-walking hypothesis revisited

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