Christina Calcagno
BIO 3003G
Professor Bollinger
18 July 2017
Bipedalism in Humans
Humans today (Homo Sapiens) and other extinct species such as Homo Neanderthalensis, Homo Erectus, and Homo Naledi are all a part of Homo Genus. Homo Genus and the extinct Australopithecus Genus are all collectively referred to as hominins (Foot). Going back millions of years ago, it can be seen when the hominin species first began walking and why. The biological evolution behind these evolutionary changes reveal the purpose of why modern humans look and walk the way they do today. The hominin group has a common theme about it. This theme is that there is not an exact way of how things came to be. It is more a disorganized complicated process than everything happening at once. For example, the way that our head (skull) or hands came to be has a similarly messy history as the way modern humans came to walk on two feet (Foot). Essentially, walking on two feet has been a main influence on how the human body looks and functions today. Walking on two feet is also called bipedalism. The evolution of walking on two feet throughout time has both proven advantageous as well as having its draw backs. Throughout the course of this paper the many theories about how bipedalism has come to be and the changes it has caused the human body to undergo will be shown, ultimately proving how walking on two feet, rather than on all fours, was one of the greatest evolutionary changes for the human species.
Bipedalism is the act of walking, running, or jogging on two legs. Although many other animals occasionally stand or walk on two legs, few use bipedalism as their everyday way of locomotion. Many animals, such as the chimpanzee, use bipedalism occasionally, or temporarily but not on a permanent or regular basis. This type of bipedalism is called, facultative bipedalism. Meanwhile, humans walk on two legs everyday which categorizes them under the habitual bipedalism category. Habitual bipedalism is considered a rare phenomenon in which very few species have adapted to. Recent studies have suggested that early ancestors of the present-day human would have lived in a wooded area about seven or eight million years ago. Therefore, climbing up and down trees would have been a typical characteristic while foraging for food or hiding from predators. This typical behavior would have likely helped them gain and retain certain features such as longer arms or curved toes. These features would have helped the ancestors to utilize arboreal (living in trees) ways of locomotion while climbing around in trees (University). Around six to three million years ago early human ancestors were linked to ape like ways of moving around. Fossilized bones have been found that record a gradual transition from tree climbing to walking upright during this time period. The earliest humans known, called Sahelanthropusm, show significant evidence that walking on two legs would have been a common way of getting around. Transitioning from tree climbing to walking upright may have been to help this species to survive in changing habitats, such as deteriorating forests or wet grasslands (Smithsonian). The reason our ancestors evolved over time is rooted in environmental changes. These environmental changes impacted each generation, forcing them to evolve slowly overtime to overcome different challenges and adapt to rapidly changing lifestyles.
The transformation that occurred from arboreal lifestyle of the primates to very uniquely human way of walking, was one of the most important throughout the history of the species. The specific transfer of weight from four limbs to just two walking allowed for specific upper limbs to take on a different role which caused a chain reaction. For example, walking on two feet changed the way the teeth/jaw are used today. Another huge biological change would be the human spine and brain. The spine had to go through many changes in order to accommodate for human skeleton to become bipedal. The top of the spine was changed from the back of the skull to the middle of the skull, which has allowed for better stability of the head and more upright positioning when standing on two legs. The movement of the top of the spine to the center of the skull has also allowed for the facial muscles to focus solely on facial expressions, rather than supporting the head in an upright position. The spine has also adapted a more curved look. These curves allowed for the spine to bear the weight of the human body and help conserve energy and remain upright when standing on two feet (Gray). Around the time hominins stopped walking on all fours and began walking on two, the obstetric dilemma occurred. The locomotive change forced a reconfiguration of the human birth canal in females. The birth canal became narrower due to the new structure of the pelvis (Costandi). This change in the birth canal was present before the brain became bigger. Though the evolutionary venture of human brain growth is somewhat separate than bipedalism in humans, it is still worth noting because it is thought that bipedalism sparked this change.
Most of the main evolutionary changes that occurred due to walking on two legs happened to the lower limbs. The lower limbs not only changed in bone structure, but also joints and mobility as well (Lupu). Adaptations were made such as a shorter, more broad and curved pelvis, along with larger hip joints. This type of pelvis allowed/s for the back and forth motion walking requires along with help bearing the weight of the body (Gray). One of the most significant changes would have to be from flat to arched feet. The foot is considered the most important of all the evolutionary changes. The human foot is what sets our species apart from any other primate. Human feet become the platform to support its body weight. Rather than being a grasping limb, like it was in earlier hominids, feet have since adapted a different purpose. This changed purpose, called for smaller toes, in a line, and a non-opposable big toe to push off the ground when walking. Also, feet have evolved into having larger heels, in order to support more weight. When walking, the weight of the human body is transferred from the heel, through the side of the foot, to the ball of the foot, ultimately ending in the big toe when walking. This makes it essential for the human foot to be arched to propel the human body forward, rather than early hominids with flat feet that were flat and not specifically there for the purpose of bipedal walking but rather climbing or quadruped walking (Lupu). Although the foot is one of the most important biological changes in the hominid family, it is equally as important to consider why this species evolved in the first place.
Many scientific explanations of why human bipedalism occurred are deeply rooted in environmental adaptation. A majority of the explanations are centered around a single cause such as standing up on two legs to look over tall grass in the grasslands of the Savanna’s in Africa. This conclusion was drawn from the fact that early human ancestors were short in stature, making it hard to see over tall objects or reach for tall branches, unless they were on their hind legs (Johnanson). This is an example of early hominins adapting to the climate that was quickly changing. The once lush rainforests in Africa were becoming large savannahs and wild woodlands which would make it easier to walk on two legs (“Bipedalismâ€). Though, at first early hominins were clumsy on two legs, making them slow runners and easier prey. One of the most logical explanations of why early hominins became bipedal is because of the needs to expend a lesser amount of energy, higher quality of reproduction, foraging better food for themselves and others, and most importantly safety. For example, males were crucial to the survival of their partner and offspring. Therefore, being able to use bipedal habits, males would have been able to collect better quality foods, keeping their families healthy, along with being able to protect them better from any type of harm that may try to come their way. Becoming bipedal would have helped early ancestors to expand their horizons, carry food back to home base, along with other advantages (Johnanson). Many scientists, such as Darwin, have suggested bipedalism occurred to free the hands for tool usage. Again, this theory is hard to confirm due to the fact that the earliest stone artifacts only date back to approximately 2.5 million years ago, long after humans had become bipedal. Ultimately, there is a wide variety of theories suggesting why or how bipedalism has come to be, many have valid reasoning but many have been and will be ruled out as research continues on. (“Theoriesâ€).
The plethora of advantages as to why humans became bipedal is one of the reasons that present-day humans still utilize this trait. Walking on two feet allowed for early human ancestors to have complete use of their hands. Having hands free, the early hominids would have been able to create tools, grab food off of trees, and potentially use their hands as instruments of communication. Being able to stand upright would have allowed for bipedal hominids to forage for longer periods of time because they would be exposed to less sun, therefore would be able to conserve more energy (“Bipedalismâ€). Over time, standing on two feet in the sun explains why early humans thinned out their hair and became “naked apesâ€. Standing in the sun on two legs, means that only the upper part of the body needs to be protected from the sun, which allowed for the body to cool more efficiently (Richard). Another advantage of being bipedal would be the fighting advantage. Typically, the larger (or taller) being in a scuffle would be victorious. That being said, when our early ancestors became accustomed to being bipedal they would have a leg up on other creatures when threatened or provoked since they were able to utilize their hands as well as having the height advantage. Being able to fight standing upright has proven itself most advantageous when put to the scientific test. In a 2011 test conducted between humans in both a bipedal and quadrupedal posture it was found that the people who stood in a bipedal position had a forty to fifty percent higher force rate when fighting than those in quadrupedal positions. This advantage in fighting has also been linked to the advantage taller men today have over shorter men when seeking a woman’s preference. There have been numerous studies that have proven that women are more attracted to taller men than short. Also, it has been shown that woman who reproduce with tall men will most likely have tall offspring which is important when thinking about how the “good genes†will be passed on to further generations (David).
Although the advantages are plenty, there are also several disadvantages to walking on two feet. The biological evolution of hominids has allowed for greater pressure to be placed upon the spine. The pressure and weight put on the spine allows for more back injuries to occur. Whether that be bulging spinal discs, completely herniated discs, or arthritis the human spine is still at risk for severe damage due to walking on two feet. There is also the possibility that the veins of the leg deteriorate which cause bulging veins that are considered a high-risk injury. Also, if something were to happen to one foot early in the hominids bipedal adventures, it would have put them more at risk for survival and could have ultimately led to their demise due to the fact they could not get around well and could not get proper treatment for their injuries; modern medicine has helped improve these risks though (Larson).
Early hominids began walking on two feet for a variety of reasons. Though there is not an exact reasoning yet, research is underway and is providing many reasoning’s as to why humans became bipedal. Going back millions of years ago, it can be seen when the hominin species first began walking and why. The biological evolution behind these evolutionary changes reveals the purpose of why modern humans look and walk the way we do today. The hominin group has a messy lineage. This means that there is not an exact way of how one thing came to be, it is more disorganized and complicated than that. For example, the way that our head (skull) or hands came to be has a similarly messy history as the way modern humans came to walk on two feet (Foot). Ultimately, walking on two feet has been a main influence on how the human body looks and functions today. Bipedalism throughout time has both proven advantageous as well as having its draw backs. Throughout the course of this paper the many theories about how bipedalism has come to be have been shown as well as the changes the human body underwent to accommodate for the change, ultimately proving how walking on two feet, rather than on all fours, was one of the greatest evolutionary changes for the human species.