The origin of Bipedalism

The emergence of bipedalism, a unique attribute of hominids, has been explained to be contributed by a number of competing theories. The three major theories that have been explored are: postural feeding theory, behavioral theory, and thermoregulatory theory. The postural feeding theory is based on the ecological framework (Hunt, p. 77). On the other, hand the behavioral theory attributes the origin of bipedalism to several factors such as the societal, sexual, and reproductive behavior of ancient hominids (Lovejoy, p. 341). Finally, the thermoregulatory theory argues that the increased energy loss and cooling, diminished heat gain and limited requirement of water presented by a bipedal stance position in a hot, humid weather are the attributing factors to the emergence of bipedalism (Wheeler, p. 107).

The Hunt’s theory of postural feeding argues that the arboreal food assembly position of arm-hanging as well as climbing vertically, a common adaptation and positional specialty of apes, is adequately a shared feature to support anatomy. This model of the origin of bipedalism is informed by both the conduct of chimpanzee and the structure of australopithecine. It is estimated that about 80 percent of bipedalism among chimpanzee is observed during feeding which is carried out by the hanging arms for the stabilization of the posture. This has also been estimated to comprise ninety three percent of the overall time taken in feeble branches and fifty two percent in other centrally placed parts of a tree. Trunk forms observed in australopithecines is characterized by adaptation to traits such as hanging of the arms, assuming the adaptation of australopithecines to arboreal seed accumulation bipedal. According to Hunt, the ancient and specialty emergence of bipedalism underwent evolution later to form the habitual bipedal movements (Hunt, p. 80).
The Lovejoy’s theory of behavior emphasizes on the societal behavioral characteristics and frameworks that affects the survival and birthrate of hominids. The human sexual conduct and culture are assumed as referring to a monogamous culture of mating, a societal structure viewed as a preliminary requirement for male provisioning. The provisional conduct of the males by the use of the upper arms is applicable in the transportation of food to females and the offspring is perceived as a solid factor in the direct selection of bipedalism through enhancing the survival rate of the offspring and improved rate of reproduction (Lovejoy, p. 350).

The Wheeler’s theory of thermoregulatory structures, as the discerning force, bipedalism bestowing decline in heat gain and the aiding of heat dissipation. According to Wheeler, bipedalism increases the average body surface slightly above the ground surface, a position where the speed of movement of wind is conductive and the prevailing temperatures are favorable. Increased flow of wind is translated in increased convective loss of temperature. Bipedalism results in reduced rate of evaporative cooling prerequisite and therefore preserves body water. The vertical orientation of the hominids is also important in maximizing the exposure to direct sunlight during the day, a time when the energy emanating from sunlight is most intense (Wheeler, p. 110).
In attempting to asses these competing theoretical perspectives of bipedalism, it is critical to observe the time of appearance. All these hypothesis yields credible selective forces necessary for any evolutionary change. These evolutionary processes include access to food, provisioning, assurance of survival, increased offspring reproduction rate, elimination of predatory sources and preservation of energy and water resources. The individual significance of the above mentioned pressures changes with different conditions. The fundamental concern is the prevailing condition at the moment of appearance of bipedalism in a fossil entry (Klein, p. 165).

The ancient footprints, an evidence of convergence of toe and fully established archway were discovered at Laetoli (Klein, p. 170). At this time, paleoecological modernization included bush land and marine life at Laetoli as well as an indoor woodland in Hadar. Proof of bipedalism in Australopithecus is dated back to 3.9 and 4.2 mya (Leakey, et. al., p. 566). An Australopithecus tibia found in Kenya has been established to possess bipedal features. Additionally, bipedalism is deduced for the 4.4 mya. A further proof of existence of bipedalism is observed in the pelvis and the nature of the body Australopithecus (White, et. al., p. 310).
Therefore, from the paleoecological theoretical view, there is no evidence to support thermoregulatory theory. Maybe thermoregulatory gave rise to the vertical orientation of the hominid evolution and therefore influencing increased height, but bipedalism was fully developed early enough before the drastic ecological changes in Africa. The hanging arm, short lower limbs and long forehead features are all in favor of ecological evidence. With regards to the behavioral theory which presents the argument of monogamous mating and decline in mating competition as transforming societal factors precursor to bipedalism, it is expected that canine sizes would reduce in tandem with the emergence of bipedalism (White, et. al., p. 315). Based on paleoecological perspective, the encephalization of the homo took place later after evolution of bipedalism. All the evidences of discussed above converge in favor of the Hunt’s theory of postural feeding.