Chimpanzee Locomotor Energetics and the Origin of Human Bipedalism
Bipedal walking is evident in the earliest hominins [Zollikofer CPE, Ponce de Leon MS, Lieberman DE, Guy F, Pilbeam D, et al. (2005) Nature 434:755-759], but why our unique two-legged gait evolved remains unknown. Here, we analyze walking energetics and biomechanics for adult chimpanzees and humans to investigate the long-standing hypothesis that bipedalism reduced the energy cost of walking compared with our ape-like ancestors [Rodman PS, McHenry HM (1980) Am J Phys Anthropol 52:103-106]. Consistent with previous work on juvenile chimpanzees [Taylor CR, Rowntree VJ (1973) Science 179:186-187], we find that bipedal and quadrupedal walking costs are not significantly different in our sample of adult chimpanzees. However, a more detailed analysis reveals significant differences in bipedal and quadrupedal cost in most individuals, which are masked when subjects are examined as a group. Furthermore, human walking is approximately 75% less costly than both quadrupedal and bipedal walking in chimpanzees. Variation in cost between bipedal and quadrupedal walking, as well as between chimpanzees and humans, is well explained by biomechanical differences in anatomy and gait, with the decreased cost of human walking attributable to our more extended hip and a longer hindlimb. Analyses of these features in early fossil hominins, coupled with analyses of bipedal walking in chimpanzees, indicate that bipedalism in early, ape-like hominins could indeed have been less costly than quadrupedal knucklewalking.
[Show abstract] [Hide abstract] ABSTRACT: When carrying objects, nonhuman primates often show bipedal locomotion. Studies of primate bipedality, however, in both nature and captivity, have concentrated on locomotion on horizontal substrates, either terrestrially or arboreally. No observational or experimental study seems to have looked at non-horizontal bipedality, yet we show here that it occurs often in nature in Sapajus libidinosus, the bearded capuchin monkey. The context is transport of small food items from source to site of consumption, in which the monkeys usually carry handfuls of maize kernels over several meters’ distance, both on the ground and in the trees. Most impressively, over a fifth of such bouts are done vertically, when the tree trunk is fully upright. Such vertical bipedality, with or without transport, apparently has not been reported before.0Comments 0Citations
- "For living primates, at least, it might be assumed that bipedality's various manifestations in nature are well known, but here we report a previously-undescribed variant. So far as we can see, all prior descriptions of bipedal locomotion in primates have focused on behavior on horizontal or near-horizontal substrates—e.g., Hylobates (Vereecke et al. 2006); Macaca, (Nakatsukasa et al. 2004); Pan (Aerts et al. 2000; Sockol et al. 2007); Papio (Berillon et al. 2010). In nature, these may be terrestrial (on the ground's surface) or arboreal (on tree boughs), including non-experimentally induced situations, like the chimpanzees crop-raiding (Albrecht and Dunnett 1971) and bonobos branch-dragging (Kano 1992). "
[Show abstract] [Hide abstract] ABSTRACT: Bipedality evolved early in hominin evolution, and at some point was associated with hair loss over most of the body. One classic explanation (Wheeler 1984: J. Hum. Evol. 13, 91–98) was that these traits evolved to reduce heat overload when australopiths were foraging in more open tropical habitats where they were exposed to the direct effects of sunlight at midday. A recent critique of this model (Ruxton & Wilkinson 2011a: Proc. Natl. Acad. Sci. USA 108, 20965-20969) argued that it ignored the endogenous costs of heat generated by locomotion, and concluded that only hair loss provided a significant reduction in heat load. We add two crucial corrections to this model (the altitude at which australopiths actually lived and activity scheduling) and show that when these are included there are substantial reductions in heat load for bipedal locomotion even for furred animals. In addition, we add one further consideration to the model: we extend the analysis across the full 24 h day, and show that fur loss could not have evolved until much later because of the thermoregulatory costs this would have incurred at the altitudes where australopiths actually lived. Fur loss is most likely associated with the exploitation of open habitats at much lower altitudes at a much later date by the genus Homo.0Comments 0Citations
- "Bipedal locomotion is quite inefficient for chimpanzees due to their bent-hip/bent-knee posture: they consume ~25% more energy when walking bipedally than they do when walking quadrupedally (Sockol et al., 2007). Nonetheless, only a modest change in limb length and/or muscle fascicle length would have been sufficient to make hominin bipedalism more energy efficient than chimpanzee quadrupedalism (Sockol et al., 2007). Consequently, there might well have been an added efficiency benefit to bipedalism if the australopiths were making short forays out onto more open areas beyond the lacustrine/riverine gallery forests in search of new food sources (such as USOs). "
[Show abstract] [Hide abstract] ABSTRACT: Understanding the forces that have influenced the evolution of shape, size, and proportions of the human appendages, including both limbs and girdles (scapula and pelvis), have played an important part in paleoanthropology. This chapter outlines a framework to address evolutionary variation in the human appendages, specifically regarding key transitions from the last common ancestor (LCA) of chimpanzees and modern humans, which combines data from extant comparative models and fossil hominins to generate testable developmental hypotheses. For the scapula, pelvis, and then limbs, the chapter first describes the relevant skeletal anatomy and development, and then briefly discusses the tissues, signaling centers, and genes currently known to be involved in their morphogenesis. The chapter compares phenotypic variation in each element in a morphospace. It utilizes the idea that evolutionary trajectories through morphospace represent developmental transformations from putative ancestral morphotypes to living species.0Comments 1Citation
- "Humans are decidedly the outlier among catarrhine primates, having relatively short arms and long legs relative to each other and to trunk length. This unique pattern primarily reflects selection for bipedalism on hindlimb length (Bramble and Lieberman, 2004; Sockol et al., 2007; Pontzer et al., 2009), but also potentially selection for shorter forelimb elements in the Homo, perhaps due to demands associated with increased tool use and manipulation and/or reduced reliance on arboreal behaviors. "