The evolution of humans

The evolution of humans

The evolution of humans is characterized by essential aspects such as the development of the cranium capacity, development from quadrupedalism, and alteration of other anatomical features that distinguish. Bipedalism in early humans could be traced back from four to three million years ago. The Australopithecus fossils establish that the genus of early humans might have been the first crop to walk in twos (Kingdon, 2003). Initially, other preceding hominids were walking in all the four limbs. However, owing to the continuous evolution process that translated to the alteration and modification of the spinal cord and the foramen magnum during the evolution process, there was a gradual modification of the limbs to suit the newly acquired body frames (Kingdon, 2003). Consequently, the development and subsequent use of bipedalism resulted in the change in routine as early humans were able to effectively grasp objects, move straight in bipedal, and have altered anatomy. During the evolution process, one distinctive feature is that the female and male early hominids had varied anatomical development resulting in sexual dimorphism.

To adequately explain how the changes of human anatomy leading to bipedalism resulted in enhanced motions in early humans, various changes abilities of man have been pointed out in that regard. For instance, several studies attributed the emergence and ability of man to use his hands to bipedalism freely. Several forces could have attributed to this phenomenon changes in human development. Some scholars argue that climate change needs to adapt, and merely spontaneous evolution of the early hominids could have played essential roles leading to bipedalism in early humans (Walter, 2004). In adaptation, several assumptions are owing to lack of trees and the need for man to use his hands effectively in making tools, cooking, and other routine activities that require the use of front limbs, early humans promptly started using the arms regularly.

Several theories, hypotheses, and models have been put in place by various scholars to explain the origin of bipedalism in early humans. Such assumptions also highlight several forces that could have contributed to such instances in the past. Though these theories, hypotheses, and models have entirely different explanations and suppositions of what might have transpired, there is a general agreement that the development of bipedalism by early humans could have started with the Australopithecus genera (Walter, 2004). The existing hypotheses take into account the fact that bipedalism remains part of the evolution process, and several early hominids could have undergone such transformations to counter the needs for adaptation and other climatic demands (Kingdon, 2003). However, there is also an agreement that early humans did not just develop the aspect of bipedalism within a short period and that the activities related to bipedalism got learned over a prolonged period.

Though the theories and hypotheses in existence often try to explain the origin of bipedalism in early man, there are selected seven theories and hypotheses that remain relevant to the study. Hence, the study would critically examine the selected seven theories, assumptions, and models to evaluate their probable authenticity, suppositions, and weigh whether such theories effectively assess the magnitude of the issue at hand. The study would also take into account the criticism and the opposing views regarding the theories, models, and hypotheses that several critics put across as far as such suppositions are concerned.

Savannah-Based Theory

The theory anchors in the belief that early humans dot compelled to be bipedal to adapt to the changes in the savannah. The theory holds that when humans descended from trees, the life in the savannah involved walking with erect posture, forcing them to change their walking styles (Ko, 2015). There were no more trees which they could hope on from one place to the other, so it was a requirement that they became bipedal to adapt to their new and changed life as far as locomotion is concerned. Further, the theory derives most of its assertions from the knuckle-walking hypothesis that alluded that as evident in both the cases of Australopithecus anamensis and Australopithecus afarensis forelimbs, early humans walked in fours, but, through evolution, it changed (Kingdon, 2003). The hypothesis further highlights that the first humans underwent evolution to acquire the erected posture due to the tall savannah grass and the need to survive on the grass. The upright position they adopted as a means of survival as they watched over to see the potential prey. Consequently, as a routine practice and evolution, the early humans started adopted bipedal walking and upright posture to watch over the prey and remain safe in the long grass.

Further, the Savannah-based theory is backed up by a turnover pulse hypothesis. The proponent of the hypothesis is Elizabeth Virba, who hypothesized that bipedalism among early humans emanated to the climate changes that subsequently altered the usual lifestyle and living of early man (Ko, 2015). According to the turnover pulse hypothesis, early humans assumed bipedalism due to the shrinking forests that resulted from global warming and climate change in general. Subsequently, the shrinking forested areas and the extreme impacts of climate change forced the animals to move into the open grasslands. The occupation of the grasslands and subsequent need to adapt to their new habitat forced them to adopt bipedalism since there were no trees to aid their locomotion (Walter, 2004). Therefore, to align to the tenets of the theory, this hypothesis traces the origin of bipedalism of early humans on climate changes that pushed early humans to the grasslands, further forcing them to walk in bipedal to survive.

However, several archeological evidence points out to various findings that, to a great extent, renders the Savannah-based theory and other hypotheses supporting it doubtful. According to the existing archeological evidence, early hominids’ hands still supported grasping ability as evident in the current primates (Kingdon, 2003). The hands never divided into fingers, showing that the primates always used their hands in grasping objects. Therefore, though bipedalism developed in the savannah, there is no evidence ruling out the belief that lack of forests compelled early humans to adopt bipedalism. Thus, according to the archeological evidence in place, early humans might have developed bipedalism and at the same time, continued using their hands in the forest (Ko, 2015). The argument borrows from the findings in Ethiopia regarding the famous fossil Lucy. According to the archeological findings based on the fossil, it had curved fingers that gave them the ability to grasp objects as also walked in bipedal (Kingdon, 2003). Therefore, though there was no evidence of existing fossil of humans in the forest, the above findings dispel any assertion that early hominids wholly embraced bipedalism, ignoring the role that hands play. The adoption of bipedalism could have emanated from multiple aspects. The assertion that forest got depleted or lack of it resulted in bipedalism in early humans could not be valid to a great extent since various archeological evidence point out to the existence of curved hands among early humans.

The Travelling Efficiency Hypothesis

The hypothesis emanates from the finding that established that the energy costs in the quadrupedalism and bipedalism are equal. The result also concluded that the transition of the hominids to their current state could not have been considerably costing in terms of energy (Watson et al., 2008). The hypothesis derives its explanation from both the belief that the existence of savannah and the emergence of scattered forests increased the travel among the early humans in the terrestrials. Therefore, to enhance efficiency in the walking process, the man had to abandon quadrupedalism and assume bipedalism. Thus, according to the hypothesis, early humans’ aspect of bipedalism emanated from the desire to enhance their walking efficiency due to the scattered forests and expansive savannah grassland (Ko, 2015). Over some time, they fully embraced the aspect of bipedalism that formed their integral part to a great extent. Thus, the hypothesis significantly borrows from the tenets of the savannah-based theory.

The Provisioning Theory

The theory attributes bipedalism in early humans to monogamy. Based on the tenets of the argument, bipedalism in humans is more behavioral than something that emanated from the need by these early hominids to adapt to the environment, as in the case of the savannah-based theory (Latimer & Lovejoy, 1989). The proponent of the theory, Owen Lovejoy, notes that since apes were experiencing low birth rates and long birth intervals, the apes engaged in bonding activity among them that gave rise to monogamy. However, to bond, especially during the cold periods, the apes had to stand upright and remain erect. Again, the upright posture was essential for the male during its quest to search for food for the female and the offspring to improve their survival. Latimer & Lovejoy (1989) note that balancing the food collected required the male ape to stand and move upright, leading to bipedalism. The theory draws its backing from the archeological evidence that established that there existed the feminization of the male teeth, especially the canines among the Ardipithecus ramidus and Sahelanthropus tchadensis (Latimer & Lovejoy, 1989). Such evidence translated to the reduction of the male antagonistic behavior that got associated with sharp and long canines. Hence, such evidence much supported this theory. Again, the open ovulation and high sperm competition also characterized the monogamous reproductive system of these early humans, leading to the justification of this theory that due to monogamy (Ko, 2015). The first primates developed bipedalism to effectively fend for their mates, protect them as well as gain warmth through supposed cuddling.

However, the theory is subject to several shortcomings that threaten its validity. There is archeological evidence pointing out to the fact that early humans who were bipedal were indeed polygamous. The fossil evidence points out that the Australopithecus afarensis, who are believed to be monogamous, were polygamous. The aspect is evident since they were living in groups suggesting that there was a collective effort to fend for the young ones. Therefore, just like the current apes in their new habitat, early humans were polygamous, had multiple mating partners, and lived in groups. Thus, any assertion of monogamy could not be substantiated. Again, Lovejoy’s theory hypothesizes that increased size in males could be due to their constant quest to find food to fend for the family (Ko, 2015). However, the increased volume could be due it being a defense mechanism to wade-off the potential prey and also protect the territory. Finally, the masculinized canines among female primates were nothing to do with their sexual dimorphism. Instead, it was meant for actively sharing the responsibility of defending their territories from the intruders. The females had strong jaws and powerful canines to actively contribute to protecting their areas and other essential aspects related to the group (Walter, 2004). Therefore, the reduction in the strength of the male human the theory suggests was consistent with less antagonistic behaviors among the females, making it easy to contain them and subsequently ensure that the male could effectively reign on them.

The Postural Feeding Hypothesis

The hypothesis highlights that bipedalism in early hominids was only evident when the first humans were eating. According to Hunt (1996), the proponent of this hypothesis, early humans will only be bipedal when they reach out for fruits hanging on the tree. Subsequently, when the hominids would be on the ground, they will arise, use their hands to pick fruits, and feed on them. Again, bipedalism was vital for grabbing the overhead branch to reach the fruits. Over time, the practice evolved into behavior and habits leading to the development of bipedalism among various primates. Therefore, as a result, the convenience and effectiveness of the pattern, early humans evolved into bipedal organisms, altogether abandoning the quadrupedalism that they exhibited in the past. Therefore, hanging of the arms, typical features in bipedalism even in the contemporary chimpanzees were essential for movement as well as the search for food.

The assertion of the hypothesis derives its argument from the existing archeological evidence that points out to the fossil anatomy, which found largely similar features pf Australopithecus afarensis to the features that Hunt (1996) has hypothesized, aspects that defines the early humans as per the Hunt’s perspective. The hands and hanging arms in Australopithecus highlighted various features that typify the early humans. On the other hand, several studies have pointed out that the current ape or even orangutan used their hands to hold on to trees and effectively support their balancing as they hope from one tree to the other (Rose, 1984). The study also established that the chimpanzees and the orangutans use their hands to stabilize themselves, especially in the cases where the forest was not dense (Hunt, 1996). Therefore, instead of assuming quadrupedalism as walking mechanisms, bipedalism offers them more stability in their locomotion and movement from one place to the other.

Warning Display Theory

The proponent of the theory, Joseph Jordania, asserted that bipedalism could have emanated from one of the defense strategies that the early hominids employed to scare away prospective prey and enemies (Australia, 2013). These defense mechanisms include intimidation of the potential predator, warning displays, and aposematic moves that gets accompanied by sounds and visual displays vital for scaring away the potential intruders. Therefore, according to Joseph, early humans were desperate to remain visible in the face of threats, an aspect which led to bipedalism. In that regard, the early humans had to stand on hind limbs to pose an intimidating posture to the potential threats compounded by different sounds that they made (Australia, 2013). Bipedalism was one of the morphological developments that were essential in achieving the defense mechanisms that were vital for its survival. These morphological changes compounded by the synchronous body movements, strong smell as well as slow locomotion, posed a significant threat to the potential predators and intruders.

However, the theory is not backed with any archeological evidence and remains one of the recent suppositions regarding the origin of bipedalism in early humans. Therefore, the validity of the theory remains questionable since it is not backed by any fossil evidence or any archeological discovery. Therefore, to a great extent, it remains a mere supposition or unproven hypothesis.

The Wading Model

The model basis its explanation on the assertion that just as current large primates such as chimpanzees and apes revert to quadrupedalism for of locomotion while on dry land and bipedalism while wading through water, early humans could have developed bipedalism as a mode to move through the waterside environments (Australia, 2013). The proponent of the model, Alister Hardy, asserts that there are high chances that humans first learned about bipedalism while on the water and subsequently evolutionarily developed through several years. Interestingly, an early human might have been wading through water source, learned to balance his body in two limbs, and subsequently found a way of maintaining an erect posture after coming ashore (Australia, 2013). However, over a period, man learned complex locomotion, such as running or jumping, leading to the complex development of bipedalism. The model was further buoyed through the hypothesis of Elaine Morgan. According to Elaine in the Aquatic Ape Hypothesis, bipedalism among early humans is akin to any other attributes and features of a man. These natural aspects include control of breathing, possession of subcutaneous fat, and hairlessness. Thus, according to the hypothesis, bipedalism is an innate attribute that the early man had voluntary control over even if they evolved. However, the assumptions of this model got rejected due to a lack of evidence to support the assertions (Ko, 2015). There are no established findings that these hypotheses draw from, nor do they point out any convergence to the current existence, especially Morgan’s theory.

Conclusion

Bipedalism in early humans remains a subject of discussion, and a myriad of theories, models, and hypotheses have been put across to try to shed light on the developments that could have effectively contributed to such instances. The savannah-based theory, for example, points out to the role of climate change leading to depletion of forest cover to bipedalism among early humans. Again, the traveling hypothesis also attributes bipedalism to the fact that it guaranteed initial humans efficiency and proved an essential aspect in their locomotion. On the other hand, postural feeding theory backed with other hypotheses as well point out to the assertion that such phenomena could have existed due to the need for the human to have a developed eating mechanism that required that they stand in an erect posture to pick the fruits and feed themselves. Though there exist other different theories and models, one underlying fact is that any supposition or conjecture ties the genesis of bipedalism to Australopithecus species. Therefore, in taking a close examination of the existing theories, one must delve on the archeological evidence that supports their assertions. Not all methods derive their backings from any archeological evidence in existence.