Bipedalism is an ability of an organism to walk on two rear limbs. Many organisms use bipedalism in different situations, but most of them are accustomed to quadrupedalism (Hunt, 1996). Bipedalism is usually used for different purposes such as reaching out for food, scaring the predators, running faster, and so on. The history of evolution of a man suggests that he initially walked on all fours. In the course of evolution, the posture has gradually changed, and the men eventually started to walk on the rear limbs. The use of four limbs for locomotion would lead to the increased usage of energy. Studies have shown that it is harder to move on two limbs than on four. It is, therefore, difficult to determine the reasons that led to the preference of the usage of two limbs, which required much energy (Lovejoy, 1981). There were a lot of attempts to explain the reasons behind the switch. Two hypotheses will be the main object of this discussion.
The Postural Feeding Hypothesis
Hunt developed the postural feeding hypothesis in 1996. He asserted that the food gathering process was much easier when the hominids stood on two rear limbs (Hunt, 1996). Hanging on the trees and climbing up the trees was also easier. Thus, there was a need for the hominids to adapt to this posture. There is a belief that it was quite necessary for the hominids at that time, because they survived thanks to fruit gathering and hunting. Such a model was developed on the basis of the fact that the early men needed to move, and feeding was among the most important aspects of their lives. Hunting was the main task of the day, and there was a need to have a highly credible feeding pattern.
Credibility of the Hypothesis
First, the model explains that the hominids adapted to bipedalism in order to make their moving more expedient. The idea is quite probable, because everyone wanted to be competent enough with regard to climate, habitat, and eating habits among others. In addition, it is likely that feeding was a factor that led the hominids to get a better way of reaching for their food. Secondly, the model is based in regard to the extant apes (Hunt, 1996). However, this is not common for the rest of the models that try to explain their assertions without a tangible back up. Hunt used the extant apes from Tanzania while developing his hypothesis. This ensures that whatever evidence he offered to assert his suggestions was credible and could be used for his hypothesis. Thirdly, Hunt suggests that there is a strong co-relation between the habitats of the chimpanzees and those of the Australopithecus species.
The Behavioral Model
The behavioral model was based on the fact that there were many differences in behavior among the hominids. The hypothesis was developed by Lovejoy, in 1996, with a special focus on the survival and daily living of the hominids. The birth rate was highly significant, and sexual behavior asserted the polygamous nature of the setting (Lovejoy, 1981). The male was responsible for providing for the family. Therefore, the males needed to carry food home and be able to easily get it from the trees.
Credibility of the Hypothesis
The upright movement of the early hominids was highly probable, because it had many advantages. For instance, fighting between the men became much compared to the times when they used four limbs to scare away their predators (Lovejoy, 1981). Further, it was much easier to move, because the territory was flat and there was an even height in the savanna vegetation. It, is believed to be the first harbor of Australopithecus species. Thus, the hominids needed to see as far away as possible in order to protect and feed themselves.
Another piece of supporting evidence to this model was the climatic deterioration of the habitats of the hominids. As the regions became more humid, it was quite uncomfortable for the hominids and they started to look for ways to avoid vegetation. However, it was possible to do it only through the use of bipedalism in their locomotion.
Comparison between the Hypotheses
The two hypotheses have several issues in common. Apart from their common attempt to explain the reasons why Australopithecus started moving on two limbs, they also have some contextual similarities. For instance, both hypotheses agree that the hominids needed to change their style of walking in order to increase their efficiency (Lovejoy, 1981). Both models focus on the vital survival facts. While the postural feeding hypothesis focuses on the feeding habits, the behavioral one focuses on another vital aspect such as reproduction. It suggests that there was a need for the hominids to help each other search for food. It was geared towards the protection of their race from extinction.
Another major similarity was an agreement that gathering was a major way of getting food. The first model suggests that early man started to walk on two limbs because he tried to reach out for the food that was on the high branches of shrubs and trees. Such an idea is also approved by the second model. It suggests that the head of the then social groupings went out to look for food. He needed to carry the food home, to the rest of the family (Lovejoy, 1981). In both cases, therefore, gathering was a major factor that led to the switch. Finally, the two models are based on behavior of the early man. Feeding and general behavior are the fundamental aspects discussed by the both models.