Bipedalism of Human Evolution and Caused Changes

What is human evolution? Before answering the question of human evolution we must first answer what is a human? A human as defined by the Merriam-Webster dictionary is a bipedal primate mammal (Homo sapiens). Humans are a distinct species because of their abilities to stand and walk upright on two legs, reason using their larger much more complex brains, continuously create and implement tools, and their ability to communicate via language. In layman’s terms if your reading this and have a heart beat I’m talking about you, human! Human evolution is the lengthy process of change by which people originated from apelike ancestors (6). Homo sapiens share a proven and undeniable relationship with the great apes such as the chimpanzees and gorillas of Africa (6). In that they both share a common ancestor, for which the Homo sapiens owe a great deal of gratitude to. If not for their unrelenting will to survive and evolve humans, as we know them today would not exist. Scientists now estimate that humans have proliferated the earth for over six million years, a span of over 7,500 generations since the rise of the first Homo sapiens (6). Without question the human is the most remarkable species on earth. So my curiosity leads me to ask like so many who have come before me. Where exactly did we originate? How did we manage to survive for six million years? And of course how have we changed? “ Is evolution a theory, a system, or an hypothesis? It is much more: it is a general condition to which all theories, all hypotheses, all systems must bow and which they must satisfy henceforward if they are to be thinkable and true.” (1). A great take away for me with this paper would be, for my knowledge on the above stated topic of human evolution to evolve providing a better understanding of the ancestral origins of humans.

The evolution of Homo sapiens has gone through considerable changes during the course of evolution to what is now recognized as the modern day Homo sapiens. Such changes that have occurred through evolution are bipedalism, changes in features of the body like brow ridges, and of course brain size and capability. Bipedalism is a use of movement that is on two feet upright and is a significant aspect that distinguishes humans from other sorts of hominoids. The original bipeds are of thought to have existed in Africa between five and eight million years ago (2). The evolution to bipedalism brought about several anatomical changes. For the ability, stability and benefits offered by balancing on two legs, the skull must be fixed over the spinal column. As bipeds slowly evolved, the foramen magnum, the opening gap at the center of skull for the spinal column, moved from the rear of the skull to over the center. The spinal column also evolved from a continuous curve to a spine with four concave and convex curves (2). Additional changes such, as was the broadening of the pelvis, which gives a wider level stance for more stability when walking on two legs.

Many different dynamics could have played a role in the evolution to bipedalism; the need to adapt to the ever-changing environment and the need to have unrestricted hands to grip and manipulate tools and weapons. These dynamics were the foundation of Charles Darwin's theory of the evolution of quadrupeds to bipeds (3). Benefits of bipedalism also include the ability to view farther and observe broader ranges because you can now see from a better vantage point; the ability to transport several necessities like food, tools, and weapons; and expend less energy because movements where now more efficient than before.

Bipedalism undoubtedly had many advantages, but it also had various drawbacks and posed risks to early hominids. Some of these drawbacks some still present today in humans -Include back pain, instability (similar to a child learning to walk), and complications with childbirth. The movement on four-leg supports provides more stability than two legs. The risk of falling was increased (head now being farther from the ground) and could have even resulted in death for early humankind.

The spine, formerly devised as a supportive arch, now is composed of four curves and is responsible for carrying the entire mass of the human frame. Though this type of spine works well for the motion of bipedalism is not entirely sensible for the everyday duties of humans. Heavy lifting can produce a strain on the back and can lead to back problems and further complications. Other back problems such as scoliosis, herniated disks, and pinched nerves are all results of bipedalism (4).

The evolution to bipedalism lead to the thinning of the pelvis of the Homo sapiens. This sort of narrowing was crucial for upright motion, but it added to the difficulty of childbearing for women. In other primates, birth is comparatively easy. Babies come through a straightforward canal and are born directionally facing their mothers. The mother then can pull the child out during birth without inflicting injury to spine of the baby. The human female pelvis is now quite smaller in diameter and babies are forced to be born facing away from their mothers’- requiring aid during childbirth to prevent damage to the baby's spine. The birth canal is now curved in such away that there is just enough room for the passing of the child’s head and shoulders.

Three adaptive characteristics of early humans that are no longer present in modern-day humans are heavy brow ridges, sagittal crests, and facial prognathism. Facial prognathism is the positional relationship of the mandible or maxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line the coronal plane of the skull. All of these characteristics were influenced by the changes in the nourishments consumed by humans. Heavy brow ridges, or supraorbital ridges, are the scrawny ridges located above the eyes. It is believed that early humans had very pronounced brow ridges to strengthen the facial structure during chewing. As humans evolved, their diets changed to softer more pliable foods and the amount of force needed in chewing significantly declined. The large brow ridges ultimately vanished and are almost completely absent in modern humans (7).

The sagittal crest is a line of bone that goes along the middle of the skull. The heavy chewing muscle, the temporalis, were attached to this crest. Modern humans no longer have a sagittal crest, but they are still visible in certain primates such as adult male gorillas (3). Like the heavy brow ridges, as man's diet evolved, the need for intensive chewing and crushing of the jaw lessened. The muscles in the face and head that were utilized for heavy chewing were no longer needed so the composition of humans changed and the sagittal crest went extinct. Facial prognathism is the projection of the mouth area of the face (5). Early humans had this facial structure to contain his large teeth and muscles, which were used to break and tear his food for consumption. As the size of the teeth lessened the facial prognathism followed suit and decreased.

We have come to learn that a growth in brain capacity has played a significant function in the evolution of modern humans. The Homo sapiens main competitors on earth were the Neanderthals. The Neanderthals had bigger brain capacities than modern humans, but yet only Homo sapiens persisted. The disappearance of Neanderthals approximately 40.000 years ago was a direct result of Homo sapiens and their prolific spread of their kind outside the continent of Africa, because these modern humans had evolved brains that were better at resolving problems, they had the ability to interact and properly communicate, and their bodies were more suited for their survival. Homo sapiens were better outfitted than the Neanderthals for survival so while they flourished, the Neanderthals vanished into history (7).

Conclusion:

There might never be a conclusive answer as to why or how we first adapted to bipedalism, but researchers are still looking for and finding fossils of our early ancestors that deliver evidence of how their bodies evolved to walking upright on two legs. It is however, certain that if Hominids had not freed up their hands they would have never been able to achieve the progress that defines humanity. Although walking a few feet seems like a normal thing to do for us now, six or seven million years ago it was the most significant achievement that our human ancestors could have ever done.