QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Schmitt, D. Search for Related Content PubMed PubMed Citation Articles by Schmitt, D. Social Bookmarking                         What's this?

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

Daniel Schmitt

Department of Biological Anthropology and Anatomy, Duke University, Durham NC, USA

View larger version (19K): [in a new window]   Fig. 1. Summary of the commonly accepted differences that are believed to distinguish the walking gaits of most primates from those of most nonprimate mammals. Nonprimates generally use (A) lateral sequence walking gaits (LH, RH, left and right hindlimb; LF, RF, left and right forelimb), (B) have a humerus that at ground contact is retracted relative to a horizontal axis passing through the shoulder, and (C) have greater peak vertical forces F on their forelimbs than they do on their hindlimbs. Primates show the opposite pattern. From Schmitt and Lemelin (2002), with permission.

View larger version (36K): [in a new window]   Fig. 2. The skeleton of one individual of Australopithecus afarensis. Members of this early hominid species were relatively small and short, with females weighing approximately 30 kg and standing about 1.05 m tall (McHenry 1991b, 1992). These early hominids were gracile with small and loosely stabilized limb and vertebral joints and distinctly curved phalanges (Stern and Susman, 1983), features that are also found in many extant apes. Like living apes, they also had relatively long upper limbs compared to the lower limbs, a condition that is also found in later australopithecines (McHenry and Berger, 1998). Many of the ape-like features of the postcranial skeleton are also found in earlier australopithecines (Ward et al., 1999). Exactly how these features should be interpreted is the subject of considerable debate (Susman et al., 1984; Latimer, 1991; Stern, 2000; Lovejoy et al., 2002; Ward, 2002), although the joint morphology suggests a different loading pattern from that found in modern humans (Stern and Susman, 1983; Schmitt et al., 1996, 1999). The image is modified from Fleagle (1999).

View larger version (12K): [in a new window]   Fig. 3. Illustration of the walking postures (at heel-strike, midstance and toe-off) and vertical ground reaction forces (expressed as % body weight) in a human (A) and a chimpanzee (B). The chimpanzee uses a more flexed hip and knee posture throughout stance phase, has lower oscillations of the center of mass, and generates a flatter, lower vertical peak force curve. Human and chimpanzee redrawn from Elftman (1944); force traces re-drawn from Kimura et al. (1979).

View larger version (24K): [in a new window]   Fig. 4. Angular values for the lower limb joints of humans walking normally and compliantly compared with bipedal walking gaits of the gibbon (Hylobates lar) and the pygmy chimpanzee (Pan paniscus). The data for the humans were collected at SUNY Stony Brook using the same sample as was used for the maximum walking speed and stride length data presented in Table 2. The data for the gibbon are a composite of data from Prost (1967) and Yamazaki and Ishida (1984). The data for the chimpanzee are from D'Aout et al. (2002).

View larger version (47K): [in a new window]   Fig. 5. Electromyographic activity of gluteus medius in spider monkeys (Ateles sp.) and chimpanzees (Pan troglodytes) during terrestrial quadrupedalism, terrestrial bipedalism, and climbing a large vertical support. The data for the spider monkey are from Fleagle et al. (1981), and for the chimpanzee from Stern and Susman (1983). The graphs follow the approach of Stern et al. (1980). The x-axis represents stance and swing phase. The y-axis represents activity (expressed as a percentage of maximum muscle recruitment) that occurred 75% of the time during the respective activity. Muscular recruitment increases in both magnitude and duration from quadrupedalism to bipedalism. The recruitment patterns during bipedalism and vertical climbing are similar to each other. The same pattern is found for the orangutan (Pongo pygmaeus) for all three behaviors and for the gibbon (Hylobates lar) during bipedalism and vertical climbing (Stern and Susman, 1983).

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter