Evolution Of Bipedal Locomotio Essay Research Paper

Evolution Of Bipedal Locomotio Essay, Research Paper

Subject: Evolution of Bipedal Locomotion

What are we. To the biologist we are members of a sub-species called Homo sapiens sapiens, which represents a division of the species known as Homo sapiens. The most interesting aspect about our species is that we are able to and can walk upright on our hind legs at all times. This is defiantly not the usual way of getting around for a mammal. The view of evolution is to see it as the product of steady environmental pressure exerted on each species, improving its adaptation to its habitat. This pressure, which has been termed natural selection is responsible for this. Natural selection works on the premise that in any population, no two individuals are exactly alike. Most of the differences between them are inherited from their parents, and are thus capable of being passed along to the next generation. Each generation will be slightly different from the one before it, and a little better adapted to the prevailing condition (Hand, 1993).

Habitually walking around on the hindlimbs, leaving the forelimbs free for other jobs, is an unusual mode of locomotion. Once our ancestors had adopted an upright stance, many things associated with being human became possible, such as fine manipulation with the hands, and the carrying of food back to a base camp (Leakey, 1981). This does not suggest that some four million years or so ago primitive hominids evolved upright walking in order to use their hands in refined ways or to develop a food-sharing economy. Indeed, this cannot be the case, because these behaviors did not arise until several million years after the development of upright walking. Nevertheless, the origin of bipedalism must be seen as one of the major steps, if not the major step, in human evolution.

A principle characteristic of the earliest hominids was probably the adoption of an upright posture and a certain way of walking with the posture. When looking at why these changes occoured, it is important to realize that these changes did not occour as in inevitable trend towards modern man. Why did our ancestors start to walk upright and when did they start to, are questions which need to be examined when figuring out the Evolution of Bipedal locomotion. Upon examination of all the evidence, there seems to be many different explanations.

The most significant claim is that Autralopithecus afarensis is probably the first ancestor to all homonids. When studying the bones of A. afarensis they look very modern below the neck. For example, the knee looks very much like a modern human joint; the pelvis is fully adapted for upright walking; and the foot with both modern and primitive features, is adequately structured for bipedalism. Some of the bones in the feet are slightly curved, and look like the bones you would expect to see in a human ancestral who climbed trees (Hunt, 1993). The adoption of upright walking, combined with an analysis of the environments in which hominid bones are found, implies that our ancestors of two million years ago lived in much more open country than did their forebears (Hand,1993). It is Probably at this point in human evolution with respect to bipedalism, A. afarensis was starting to leave behind its arboreal habits. Even still A. afarensis was probably capable of climbing trees in times of danger, and it is likely that they slept in trees, as baboons do, in areas where there are no caves for shelter. However, the body skeleton of these early humans was very different from ours, most notably in their limb proportions. For example Lucy a almost complete skeleton of an A. afarensis, shows clearly that while the arms of A. Afaresis were proportioned pretty much like ours, the legs were rather short (Hand,1993).

With more time being spent on the ground, and the animals moving at a faster speed than before, entirely new demands were made upon the foot. In the foot anatomy, when comparing early hominids and humans, there is a difference between the ways in which weight is transmitted along early hominids and human feet. In an early hominid moving bipedally, the weight is carried along the side of the foot, and the push is passed through the middle of the row of toes. In a human, body weight is transmitted along the outside of the foot, then internally across the ball of the foot, and finally push-off is made by the big toe, a much more efficient arrangement for striding (Hunt, 1993). The choice of aligning all of the toes might have been influence by the basically ape-like hominid s tendency to stand and monitor his surroundings. This would have helped develop strong hind feet capable of taking the entire body s weight. The keeping of a permanently upright stance probably came before rather than after the foot s reorganization for fast movement along the ground. Given some reorganization of muscles and bones it can be as economical of energy to stride on two legs as to run on four (Kingdon,1993). Some curvature in the foot bones as shown before, probably indicated that early humans had retained some climbing abilities. This was probably the middle step between primitive and modern features in an evolving foot which would be perfect for bipedalism. In Lucy s feet it has been found that there are subtle but significant differences. For example, the contours are human like but the ankle joints are still chimplike in the flexibi