Human Evolution and Its Link to Bipedalism

Bipedalism – Human Evolution
Introduction
Human evolution takes into account the biotic as well as cultural development of humans. Human philosophies of the manner in which evolution of man came to be is ascertained by beliefs that have been espoused by scientists and societies dating as back as 400 decades ago. Human species, scientifically referred to as homo sapiens has extremely evolved in the last number of billion years. There have been numerous scientific developments and dissimilar events that gave rise to the ultimate evolution of mankind. One of the key changes that have taken place through evolution is bipedalism, which encompasses alterations in body features, for instance, increase in brain capacity. In particular, bipedalism is a kind of locomotion conducted on two feet and is the one aspect that that distinguishes humans from other kinds of hominoids (Ishida et al., 2006). The purpose of this paper is to examine and lay emphasis on the origination of bipedalism in terms of the different theories predominant regarding it and the manner in which it has given rise to numerous developments in the origin story of human being. In addition, the paper will undertake an analysis of the bodily adaptations that took place so as to endure bipedalism and the consequences this new means of locomotion came along with it.
Savannah and Mosaic Theories
The very first endeavor of trying to elucidate the aspect of evolution was by Darwin through the Savannah theory. Basically, this theory made the argument that an ape living on a tree starting subsisting in the open savannah for lengthier periods as the forest home started to decline owing to change in climate. As a result, the ape progressively developed and adapted a bipedal posture so as to permit its forelimbs to be utilized for exercising primitive weapons like stones as well as sticks. Nonetheless, taking into account that in the end it was acknowledged that all of the attributes aforementioned, as well as bipedalism, could have been chosen against the savannah ecology, a great of the proponents of this theory lacked merit. Moreover, there continues to be primates that presently live in that environment and they lack such attributes. Another theory that lacked merit in this regard at the time was the Mosaic theory. The argument in this model was the ape aforementioned started subsisting in a mixed environment consisting of forest, swamp and savannah. The downside to it is that failed to offer any convincing reason for the evolution of the ape into a bipedal form of locomotion (Kraak, 1991).
Postural Feeding Theory
Chimpanzee biology together with australopithecine functional morphology give the suggestion of a mutual land-dwelling and arboreal postural feeding origin for bipedalism amongst hominids. In accordance to Hunt (1996), bipedalism amongst chimpanzees usually appears whilst feeding fruits of trees in the forest. This is more often than not done through reaching up to pluck the fruits while erect or through attaining poise and balance in tree branches clutching on in a semi-arm dangling position. Some anatomical features of Australopithecus mutual with apes are modified for decreasing muscle action and physical exhaustion in the course of hanging by the arm. Additional features of apes amongst hominids, comprising for instance, assemblages and metacarpals that are curved, are adaptations to both upper limb hanging and erect climbing. The anatomy of the australopithecines especially with respect to the hind limb and hip regions, is suggestive of characteristic bipedal locomotion while on the ground. However, when likened to modern human beings, it is imperative to note that their movement was less efficacious and created increased strains in the hip. Taking this into consideration, it is posited that hominid bipedalism might have emanated as feeding position, with arboreal hanging of the arm, bipedalism, and erect climbing as significant means of gathering for food, that was only well ahead developed into an efficacious locomotor adaptation (Hunt, 1996).
This theory is further advanced by Skoyles (2006) who delineates that a novel model of the distinctiveness, nature, and evolution of human bipedalism is shown in the perspective of the etiology of the equilibrium dysequilibrium syndrome disorder. From a biological perspective, human bipedalism is newfangled in numerous noteworthy respects. To begin with, humans are obligate, characteristic and varied in their bipedalism, and they also embrace their body posture spinally vertical in a multi-segmental standing against gravity. Third, they utilize their forelimbs for other purposes aside from locomotion. In addition, human body weight is fully supported by vertical poise and such bipedalism is included with upper body movements that rapidly shift the physique's center of mass. “Due to the situation that humans are obligate erect terrestrial animals, two frameworks - the body- and gravity- defined frameworks - are in constant alignment in the vertical z-axis.” This allows human sense of balance to become accustomed to egocentric body perceptions to become aware of body deviances from the gravitational erect. The argument made is that cortical parts handling the three-dimensional and other intuitions required to permit vertical balance was a significant reason for brain size development of Homo erectus (Skoyles, 2006).
Behavioral Theory
The behavioral theory of the origin of bipedalism was developed by Owen C. Lovejoy. The main position advocated for by this theory is that the social behavior of human beings are precisely what impelled them to become bipedal. To be more specific, Lovejoy lay emphasis on the social behaviors that had an impact on human survival and birth. He further posited that the sexual behaviors of the early man together with his anatomy gave the implication that a monogamous arrangement of reproducing and that this was perceived as a common necessity for the male species. The mannerism of carefully choosing the suitable mates on the basis of their locomotion or the manner in which they walked was further advanced by having the notion that if a male utilized the body’s upper limbs to fetch and bring sustenance to a mate, then the companion perceived this as a significant selection element for the formation of offspring owing to the bipedalism. This is for the reason that it was an indication of a longer lifespan for the offspring and the ability to survive longer. It also indicated that the offspring would likely be more resilient and have a superior rate of procreation as compared to its parents. Therefore, it was necessary for all male species to use two limbs for locomotion in order to secure mates (Kinzey, 1987).
However, the shortcoming of this theory is its argument that hominids had a monogamous arrangement of mating as it is an aspect that is not in line with the sexual dimorphism in the size of hominids. Specifically, with respect to primates that are not human beings, sexual dimorphism with respect to the size of the body is ideally elucidated by sexual selection owing to sexual dissimilarities in procreative potential. It is hard to consent that bigger male size in hominids did not come along with superior difference in male than female procreative achievement and some magnitude of polygyny. Taking this into consideration, it can be argued that Lovejoy’s conceptions regarding dissimilarities in size to decrease competition in food are not completely resounding and definite. It is solely the orangutans and chimpanzees, as the primates that have noticeable magnitude of sexual separation in food utilization. This is largely for the reason that in both of these two non-human primates, sexual dimorphism in terms of the size of the body is in alignment with male procreation competition and mating arrangements that are polygamous (Kinzey, 1987).
Thermoregulatory Structures Theory
This is a theory of the origin of bipedalism developed by P. E. Wheeler. On the basis of this model, bipedalism causes an increase in gaining of heat and facilitating the dispelling of heat. Wheeler’s main argument is that human bipedalism causes a rise in the mean body surface to some extent above the surface of the ground, a posture in which the rapidity of how the wind moves is conductive and the existing temperatures are satisfactory. As a result, the augmented current and tide of wind is turned in increased convective temperature dissipation. According to this theory, bipedalism gives rise to a diminished rate of cooling in evaporation and as a result conserves water in the body. The upright alignment of hominids is also significant in making the most of being directly exposed to sunlight in the course of the day, a period when the energy arising from sunshine is most powerful and forceful (Wheeler, 1991).
A great deal of Wheeler’s deductions emanated from the measurement of body outlines and shapes in the vertical and frontal sides and approximating the same body shapes in Australopithecines. Moreover, he lays emphasis that mammals that have adapted to living in the savannah have a tendency of having a more developed number of features to preclude the overheating of the brain. Bearing in mind that human beings do not possess these features, a different approach for cooling the brain would be needed if our lineages had also evolved there. The argument made by Wheeler is that the upright position obtainable by bipedalism might have been an important element of a different kind of mechanism. The outcomes of the study undertaken by Wheeler is that the bipedalism position substantially decreased the amount of body surface experiencing exposure to sunshine, especially during the middle of the day (Wheeler, 1991). In accordance to Wheeler (1991), a fitting example of this form of evolution could also per perceived amongst the dinosaurs. The argument made is that a number of dinosaurs were able to cool their brains in the same manner. This is owing to the fact that they had big intravenous sinuses that could have the capability of having a direct cooling effect on the brain. Similarly, in others, there were ostentatious head and nasal structures that may have functioned as a thermoregulatory brain cooler. However, the significant argument against and shortcoming of this perspective is the lack of hyperthermia amongst these species at the time and also their lack of progressive evolution and adaptation to their ecology.
Analysis
As delineated, the origins of bipedalism, which is a significant and central characteristic of hominids, has been accredited different competing theories. As indicated, to begin with, Lovejoy using the behavioral theory accredits and endorses bipedalism to the social, sexual, and procreative mannerism and behavior of early hominids in the evolution structure. Secondly, the theory advanced by Hunt is an ecological one, which argues for the notion of postural feeding, which outlined the need for hominids to employ their arms to clutch food and have an upright posture. Third of all, there is the thermoregulatory theory advanced by Wheeler, which brings into play the upsurge in heat loss, augmented cooling, diminished gain of heat and decreased necessity for water, convened by a bipedal posture in a hot temperature giving rise to bipedalism (Wheeler, 1991; Hunt, 1996; Kinzey, 1987).
In comprehensively examining these contending theories on the origin of bipedalism, it is imperative to take the aspect of timing into great consideration. This is owing to the reason that the mannerisms and activities of hominids significantly varied on the basis of the time in which they existed in the world. Without a doubt, all the aforementioned theories delineate that human beings experienced numerous stresses that gave rise to the bipedal posture and feature. For example, some of these societal pressures comprised of the accessibility to food and nourishment, survival, provision of food to mates, and also the ability to procreate and generate strong offspring, all of which are sensible. As a result, bearing this in mind, the most ideal way of analyzing these theories, is through the acting on the fossil records. This is largely for the reason that it becomes conceivable to make comparisons of timings to these societal pressures and stresses that the different theories posit hominids to have experienced and if they took place in their parallel ages. Despite the fact that all of the rationales and arguments presented by the various theories are conceivable, with respect to evolution of humans to bipedalism through the societal stresses, the decisive element is considering the parallels of the situations they faced and endured to the period that bipedalism is perceived in fossil archives.
To begin with, Lovejoy’s theory of behaviorism faced reproach owing to different aspects. The shortcoming in the theory lies in its argument that bipedalism is linked to only one sexual category, being the male species. More importantly, fossil archives and accounts provide substantive proof that the early man in the societal context was not monogamous. Rather, these archives give the indication of sexual dimorphism. The inference of this is that the hominids at that particular point in time in history has more than one companion and in dissimilar expanses, thereby giving the indication that there was a polygamous procreating structure. In addition, there is also the lack of evidence that early man in the society was set in a predetermined position for his home but rather the archives give the indication that at the time hominids were incessantly moving from one area to another (Kinzey, 1987).
In accordance to Gaulin and Sailer (1984), there is criticism in this theory for the reason that it is hard to agree that bigger male size in hominids did come along with bigger variation in male than female procreative accomplishment and some extent of polygamy. In chimpanzees as well as orangutans, which are both non-human primates, there is a noticeable magnitude of sexual segregation with regard to food exploitation (Kinzey, 1987). Imperatively, both of these creatures have sexual dimorphism in body size that is in tandem with the male procreative competition and reproductive systems that are polygamous. In addition, it might be conceivable that a decreased level of competition between the sexual categories with respect for food is at times as a result of sex dissimilarities in the size of the body that has evolved over the course of time for various reasons. Nonetheless, the benefit to a certain male of decreasing food competition with a food can be accomplished solely if she is nurturing his offspring or are from the same family and the female and offspring survival is augmented. This benefit can be attained if a single male creature dismisses other different males from gaining accessibility to the females and the food they have, and this sort of exceptionality can take place in either polygamous or monogamous societal orders (Kinzey, 1987).
Secondly, the argument advanced in the thermoregulatory theory takes into account the change in the style of movement of human beings to one that is erect owing to changes in temperature. The theory also has its significant criticism. One of the key elements of the argument is that the bipedalism position substantially decreased the amount of body surface experiencing exposure to sunshine, especially during the middle of the day. Nonetheless, a fundamental denunciation of the theory encompasses the other times of the day when there are no extreme sun rays and also the times when the sunshine would significantly cover the body of a bipedal species as compared to the quadrupled species. In line with the same argument aspect, there have been major criticism as to why no other quadrupled species have eventually evolved as time has passed by to become bipedal with the main endeavor of avoid the extreme sun rays. Moreover, there is the reproach of the theory in the sense that the fossil archives gave the indication that a great deal of the early men subsisted in arboreal regions that comprised of woodland cover as well as foliage that safeguarded them from the scorching rays of the sun. In addition, the evolving species also subsisted in caves where they could similarly escape the severe effects of the sunshine during the day (Wheeler, 1991).
In addition, according to Ruxton and Wilkinson (2011), it has been shown that for a human being standing at rest, bipedalism decreases external heat burden and therefore would have decreased thermal challenge. The main variance of this perspective from that postulated by Wheeler is that external heat challenge is considerably less significant as compared to internally generated heat and therefore the effect delineated by Wheeler makes a negligent different to heat balance. The authors make the argument that it is considerably simpler to imagine circumstances whereby a walking human being would lack the ability to make the most of accessible shade devoid of negatively impacting their activity as compared to an individual that is standing. As a result, the argument is that protracted exposure to hot and sunny circumstances is significantly more conceivable for a person that is walking than the one standing (Ruxton and Wilkinson, 2011).
Third, there is the postural feeding theory that has also been greatly criticized. As aforementioned, the key argument of this theory is that bipedalism amongst hominids through the activity of climbing up trees and reaching out to their branches in order to obtain food and nourishment. Despite the fact that this conception appeared sensible as to the developed upright position of walking, there were a number of flaws in the theory that resulted in numerous queries. One of the main shortcomings is the fact that there were other species of creatures that were quadrupled in their body structure but at the same time managed to climb trees and reach out to branches to obtain their food as well. They were able to achieve this by standing using their hind legs when obtaining their meals. It is imperative to note that these creatures were not obligated to remain erect or in a vertical posture so as to obtain their food on a daily basis or even move in a bipedal manner. There is also the key aspect that in accordance to fossil archives, hominids subsisted in arboreal regions that were significantly vegetative. Therefore, these animals were not largely necessitated to climb up trees and move to upper locations as they would easily obtain food in the low regions near the ground.
In spite of these substantial criticisms of the different theories delineated, the one that is most sensible from my own perspective is the postural feeding theory. There are significant reasons that can provide backing and support to this particular theory outlining how human being evolved to bipedalism. To begin with, in relation to fossil archives, the ecological and real-world morphology of the early man gave the indication that he utilized different postures for feeding, being both land-dwelling and arboreal, which gives a reason as to where bipedalism in hominids originated. In addition, the chronicles of the fossils that have been obtain presented that hominids’ movements were largely bipedal, especially at the time of feeding on fruits and pods that were positioned high up on trees in the woodlands. This was conceivable and achievable by the hominids’ endeavors to reach up to the trees while at the same time being erect on the ground. This act of obtaining pose whilst on the branches was undertaken when standing on one of the lower located branches of the tree and concurrently holding the upper located branches in a somewhat erect posture. This perspective was supported by bone structures of early man, which demonstrated that he had an erect posture owing to the protracted Alternatively, the hominids opted to go up in the trees and attempting to have poise and counterbalance using the branches so as to pluck and eat the fruits and pods. straight vertebrae and narrow ribcages (Westergaard et al., 1998).
The standpoint that hominids’ adaptations to utilize their arms for hanging on trees and branches during times of seeking foods can also be backed by the actuality that this was not a once in a lifetime mannerism but rather a repetitive activity in order to survive. Notably, there was a significantly high incidence of this activity because food is a basic need for the survival of any creature in the course of evolution. Taking this into consideration, it can be argued that this bipedal posture might have initially began as a position for seeking food necessitating the creature to hang up arms together with erect climbing, but as time went by this posture evolved, became modified in order to suit the creature to efficacy (Westergaard et al., 1998). Moreover, the other theories discussed failed to have substantial proof that backed the circumstanced delineated and their frequency in order to have bipedal adaptations. Any creature in the course of evolution has been reliant on food in order to survive through generations. As a result, this activity can easily influence the way of life, environment, and also the physical features of the creature (Stanford, 1996).
There are different examples throughout evolution that can support this particular argument. For instance, there is the evolution of fins in fish in order to facilitate faster movement and locomotion in water. The pelvic and pectoral fins in fish were initially tetrapod limbs, as they are perceived in different species such as amphibians and vertebrates. Another fitting instance is the adaptation of the claws and teeth of carnivorous animals such as lions and cheetahs so as to grasp on to their prey and eat the meat. In addition, their bodies evolved in order to facilitate their speed of movement and increase their likelihood of catching and feeding on prey. In the same manner, different creatures have an increased sense of hearing, sight, as well as smell, which facilitates them to get their prey and survive. Taking this into consideration, regardless of whether it an amphibian, vertebrae, mammal or primate, these creatures have evolved in the course of time, through the development and adaptations of the different ecological situations to facilitate their ability to feed and therefore survive. In relation to this, the evolution of human beings shifted from being semi-quadrupled into a bipedal in order to be able to find food and survive (Wrangham, 1980).
Conclusion
Bipedalism is a unique feature of human beings. The evolution of this attribute is elucidated by different theories that seek to explain its origin and the way in which it has given rise to several adaptations and developments in the origin story of human beings. Notably, this paper discusses three particular theories including the behavioral theory, postural feeding theory and the thermoregulatory structures theory. Despite the fact that these three theories have advanced different arguments that may seem sensible to different individuals, they do have their shortcomings and incongruence to fossil archives. From my perspective, I consider the postural feeding theory to be the most sensible theory that delineates the origin of bipedalism and its developments in hominids. Lovejoy developing and advancing the behavioral theory endorses and links bipedalism to the social, sexual, and procreative characteristic and behavior of early hominids in the evolution structure. Secondly, the theory propagated by Hunt is an ecological one, which argues for the notion of postural feeding, which outlined the need for hominids to employ their arms to clutch food and have an upright posture.
In essence, the postural feeding theory outlines the need for hominids to employ their arms to clutch food and have an upright posture. The main reason why this theory is selected is largely for the reason that archives of fossils have shown that early man-made use of dissimilar positions for feeding, being both land-dwelling and arboreal, which gives a reason as to where bipedalism in hominids originated. This is linked to the endeavor of hominids to reach up to the trees while at one fell swoop being erect on the ground in search of food. On the other hand, the hominids chose to go up in the trees and endeavoring to have composure and balance using the branches so as to grasp and eat the fruits and pods. Moreover, this particular theory gives a better and more sensible origin of bipedalism amongst humans because there was the basic necessity of finding food in order to survive. Throughout the story of evolution, we have perceived different animals adopting and having their body features modified so as to be more effective in feeding and survive to successive generations.










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