Bipedal Locomotion Essay

Bipedalism “Humans are habitually bipedal” (Du Brul 1962), “bipedalism is one of a few characteristics that separates us from our pre-human ancestors” (Jablonski and Chaplin 1992) and according to R.F. Ewer “the most important” (Ewer 1965). Ewer also makes the very obvious point that monkey’s present existence in a quadrupedal state presents us with the steep evolutionary question of “why did we evolve bipedal locomotion and monkeys did not?” (Ewer 1965) ‘Plenty of other creatures are bipedal, few are habitually bipedal, the kangaroo is one such exception, but few others exist, the main difference between us and those other non-habitually bipedal creatures is that their anatomy needed little alteration from ancestral species in order to allow for bipedal locomotion’ (Du Brul 1962). Therefore our anatomy and that of our pre-human ancestors are substantially divergent, at least those parts directly related to our upright posture (Du Brul 1962). The fact that there is such a high level of divergence with regards to the anatomy of our quadrupedal pre-human ancestors and us, bipedal humans, is intriguing. Does this speak to adaptions that weren’t initially for upright posture that eventually became useful to us as a means to more efficiently move around, or were these changes specifically for upright posture all along and if so what could necessitate such a dramatic change in our means of locomotion? (Ewer 1965) “The adaptation of a major evolutionary novelty in a population requires that the novelty confer a survival advantage and greater reproductive success to individuals in the population even during the course of its development” (Jablonski and Chaplin 1992). This tells us that the first question isn’t likely to be a plausible line of thinking if for no other reason than that the adaptations required, and present, in human and hominid anatomy are, in a fundamental way, in complete opposition to quadrupedal locomotion. The degree of anatomical divergence is evidence that something in our ancient past made bipedal locomotion, an “evolutionary novelty,” a “survival advantage” over quadrupedal locomotion and therefore granting bipedal individuals more “reproductive success” (Jablonski and Chaplin 1992). Ewer believes that the ecology of the pre-human environment at the time of this adaptation was such that it necessitated a terrestrial lifestyle rather than an arboreal one (Ewer 1965). The ecological change presumed to be the culprit here according to Ewer, and many others, is a recession of the forests, which would render a quadrupedal arboreal lifestyle impractical although not disallowing a quadrupedal terrestrial existence such as baboons, and the growth of expansive grasslands which is what finally makes bipedal locomotion a survival and reproductive advantage (Ewer 1965). The grasslands are also important for the evolution of upright posture due to it being “a habitat where bipedal walking is relatively easy and, moreover, one which confers considerable visual advantage” (Ewer 1965). Ewer points out that not all terrestrial environments make for easy bipedal travel citing the difficulty one would experience trying to traverse dense jungle or stony hillsides on only two feet (Ewer 1965). E. Lloyd Du Brul talks about another advantage of bipedal movement “Man’s body axis has been reoriented 90 degrees to the vertical position in the gravitational field, this has completely freed the hands from postural commitments to be used for food gathering and feeding” (Du Brul 1962). Ewer corroborates this with the following; “gorillas spend roughly one third of the day in a vertical position on their hind limbs with their hands freed for such tasks as feeding and grooming” (Ewer 1965). In conclusion to his

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