History files that the earliest hominins were partly bipedal and that over time, they grew to be ever more bipedal. Bipedalism refers to the adaptation that the early human beings underwent in their skeletal adjustments by all the Hominin generations (Lovejoy 2010). In that regard, pupils have put forth several theories and hypotheses to give an explanation for the reason and magnitude of evolution of bipedalism in humans. Threat displays, freedom of hands, fingers and the thumb to carry and use tools, modifications in environment and climate, and sexual dimorphism in meals gathering are some of the reasons for the improvement of hominid bipedalism (Ayala 2009).
Several features of the early human beings inspired their survival, just like different species. Charles Darwin’s law of natural selection was the force behind bipedalism in humans (Ayala 2009). According to the principle, humans unconsciously became bipedal over millions of years; however, there was no particular reason for the evolution. Instead, scholars have maintained that the evolution happened merely because it was a favorable and more controlling trait by then. As a result, the unique noticeable characteristics in each species comprise the features that have persevered through natural selection by mutation. That is why Hunt (2011) observes that such characteristics manifested during the mutation phase of the species.
According to Ayala (2009), natural selection, or Darwinism, is complex to investigate because many factors got involved over millions of years. Those factors may have included the interaction with other animal species, the need to protect offspring, the avoidance of rivalry and competition for food, and the changes in environment. It should be noted, nonetheless, that the term ‘natural selection’ is ambiguous since it encompasses many factors. In contrast, Darwinism has a broad description, and thus natural selection does not necessarily have to be a distinct hypothesis or principle for it to provide a complete explanation of how survival occurred (Ayala 2009).
There are several hypotheses which try to expound on the origins of bipedalism. However, none is entirely satisfactory. These theories have looked at both the body shape and the habitation of the hominids (Lovejoy 2010). In that regard, movement speed can be disregarded at once since human beings are not the fastest runners.
The savannah-based hypothesis
Anthropologists first adopted this theory to explain how bipeds evolved from quadrupeds. The theory holds that early quadrupeds were compelled to relocate to savannah grasslands after abandoning the forests (Wheeler 2012). Accordingly, developing an upright posture would help the early hominids by watching over tall grasses for prowling predators, and hunting efficiently. Nonetheless, according to Lovejoy (2010), some anthropologists have expressed views contrary to the theory based on the paleoclimatological signs. The evidence suggests that early hominids evolved into bipeds while they were still in the forestlands and climbing trees (Jablonski and Chaplin 2013). In fact, many scholars have argued that bipedalism evolved in the jungles.
The postural feeding theory
This theory was proposed at Indiana University by Hunt Kevin. He claimed that bipedalism might have evolved as a result of early primates finding the upright posture easy to maintain balance and find and eat food (Hunt 2014). In support of the same, he observed that chimpanzees would stand on their hind legs while reaching for fruits hanging from plants and assume an upright posture while eating, and orangutans would maintain stability by their hands while climbing thin branches. In the same vein, scholars have argued that the primate Australopithecus afarensis’ shoulders and hands proved hanging traits, while their hind limbs and hips indicated upright posture (Jablonski and Chaplin 2013). Therefore, Hunt held that bipedalism was used for gripping from an overhead tree branch and gathering food and thus it developed less as a movement posture but more a feeding one (Hunt 2014).
The intimidation hypothesis
This theory holds that early primates evolved from quadrupeds to bipeds as a natural security device against predators. According to Jablonski and Chaplin (2013), these primates wanted to maintain visibility in order to intimidate or warn likely predators. They used the aposematism instincts to show threats. As a result, they developed many behavioral and morphological improvements aimed at improving their visual gestures and general body maneuverability. These developments included longer legs, bipedalism, and simultaneous body movements (Jablonski and Chaplin 2013).
The thermoregulatory theory
As the name suggests, this theory held that upright posture would raise the body surface area, thus lowering the amount of heat absorption by facilitating the dissipation of the same (Wheeler 2012). In other words, by increasing their height above the ground, the hominins were exposed to more air and winds which blew their sweats away. Apart from lowering the surface area uncovered from heat, blowing winds reduced their temperatures further, making them more relaxed (Wheeler 2012). Thermoregulation, according to Hunt (2014), refers to how the primates could store fat, pant, rest, and hibernate not only to facilitate their survival in the jungles and savannah grasslands but also how they exploited the same to develop a dominating and ‘civilized’ lifestyle. However, this theory does not clearly explain why only humans developed bipedalism whereas other animal species could also hibernate and regulate their body heat.
The provisioning theory
This theory was suggested by Lovejoy Owen who advocated for a revised version of Darwin’s hypothesis of natural selection. In his effort to give a better perspective of Darwin’s explanation, Lovejoy claimed that bipedalism was indispensable since humans had the inclination to pair-bond because bearing food with both hands was efficient for its transportation (Lovejoy 2010). In addition, he noted that sexual dimorphism implied that better hunting skills improved the offspring endurance levels. In other words, the males were to provide for the females, and the latter would be responsible for nurturing and protecting the young ones. The females instinctively knew which provisioning male to mate with, a factor which brought peace and harmony in their community since males would not fight one another over females (Lovejoy 2010). As a result, Lovejoy (2010) noted that the sharp, pointed male canine teeth disappeared as time went by. In that regard, scholars have shown that chimps can carry twice as many fruits in an upright posture as when quadrupedal (Jablonski and Chaplin 2013). Several anthropological evidence have supported this hypothesis. The decrease in the size of the teeth, decline in aggressive or violent behavior and general meekness, and the dimorphic reduction of body mass have validated Lovejoy’s hypothesis.
Ayala, F. J. “Darwin’s Greatest Discovery: Design Without Designer.” Proceedings Of The National Academy Of Sciences, vol 104, no. Supplement 1, 2009, pp. 8567-8573.
Hunt, Kevin D. “Positional Behavior Of Pan Troglodytes In The Mahale Mountains And Gombe Stream National Parks, Tanzania.” American Journal Of Physical Anthropology, vol 87, no. 1, 2014, pp. 83-105.
Jablonski, and George Chaplin. “Origin Of Habitual Terrestrial Bipedalism In The Ancestor Of The Hominidae.” Journal Of Human Evolution, vol 24, no. 4, 2013, pp. 259-280.
Lovejoy, C. Owen. “Evolution Of Human Walking.” Scientific American, vol 259, no. 5, 2010, pp. 118-125.
Wheeler, P.E. “The Evolution Of Bipedality And Loss Of Functional Body Hair In Hominids.” Journal Of Human Evolution, vol 13, no. 1, 2012, pp. 91-98.