Bipedalism: Characteristics And Evolutionary Factors

Evidence of Bipedalism in Fossil Records

Question:

Discuss about the Anatomical changes that are required for the transition to Bipedalism.

Bipedalism is the process where it explains the characteristics of modern human beings that have gone through the process of evolution over the years.  It tries to identify the evidence of the process in the fossil that helps to determine the pressure that the human beings have faced that has forced them to attain the process of evolution. There can be number of factors that have an effect on the process of evolution of human being. These factors are being analyzed by bipedalism (White et al., 2015).

Bipedalism refers to movement, amongst various numbers of species there are very few who can walk on two legs. There are some specific breeds who practice this process which is which is known as facultative bipedalism. There are times when octopus walks on their hands or practice bipedalism which is temporary in nature. In this process they put their six legs over their head and walk on rest of the two. They use this process in order to camouflage themselves (Barrett & Maidment, 2017).

Habitual bipedalism which is also known as obligate bipedalism is a rare characteristics means of transportation. There are very few species that are present at the current time who practice habitual bipedalism. The species that practice habitual bipedalism includes human beings and kangaroos. This species show characteristics where the species have used bipedalism but still they retain the arboreal behavior.

Around thousands of years of ago there was a massive change in the climatic condition of earth where there was a massive drop in temperature. During this period there was a massive reduction in sea level, which resulted in change of sea level. There was a scarcity of water which resulted in reduction of forest which dried up soon therefore there was a growth of wood land and plain territory (Dunbar et al., 2014).  

Extensive study has drawn a conclusion that the ancestors of human beings used to live in a habitat which was made up of wood. The study have also showed that there were some early bipedal features which were retained by human beings such as long arms which were used by our ancestors to climb trees while living in the woodland. The DNA evidence shows the proof that the human beings and the apes share the same DNA characteristics. This understanding has and will help in the future in the process of study of the evolution in the human beings (Granatosky, Tripp & Schmitt, 2016).

Factors Affecting Bipedal Evolution

Though bipedalism is not considered to be the best or the most effective structure for the position of form of running as well as walking but it does carry a numerous positive options, which can contribute immensely towards walking. It is still not very clear from the study why our ancestors went through and evolution and why they adopted bipedalism form of walking (Zeininger, Shapiro & Raichlen, 2017).

Hypothesis shows that the bipedalism can carry the food and other items to a longer distance  which is the freeing of forelimbs for foraging, tool use, or protection; moving more energy-efficiently than other forms of primate quadrupedalism; and the development of long distance running (Ingham et al., 2017). Bipedalism can easily cool their body temperature which is known as thermoregulation. Despite a lack of consensus about the origins of bipedalism, many if not most of these proposed hypotheses are not mutually exclusive. Some combination of different selection pressures may have been responsible for driving bipedal evolution (Langdon, 2016).

Feet

In this transition of bipedalism, the human feet have large and enlarged feet. The feet being large help to bear the amount of weight of the human body. The feet of the human helps to act as a platform in supporting the entire body weight .The humans now have proper toes and feet which are smaller than their bipedal ancestors. This includes a non-opposable hallux, which is relocated in line with the other toes (Machnicki et al., 2016). When the non-human hominids walk upright, the weight of the heel is transmitted to the foot and then along the outside of the foot and finally it is reached to the big toe.

Limbs

There is an increase in the length of the leg when there was a change from quadrupedalism to bipedalism and there has been a revolution and it has been seen that the leg muscles is functioned in upright gait. In humans the "push" for walking comes from the leg muscles which are acting at the ankle. The longer the leg, which allows the usage of the leg and the muscle of the limb have natural swing while walking. The result of which is that the human forelimb are not needed for the locomotion and it is used for holding or carrying or manipulating objects with great precision (Osborn,2013).

 The apes which used to exist many years ago could stand on the hind limbs but they cannot be do it for a longer period of time. The femurs are not adapted for the bipedalism.The apes have the vertical femurs but the humans have the femurs are angled in the medium position from the hip to the knee. The knees are held closer together and under the body’s center of gravity.

Advantages of Habitual Bipedalism

Skull

The human skull is that portion of the body which is balanced and it has a vertebral coloumn.The foramen magnum which is said to be inferiorly located under the skull. This helps the human body to stand upright; this puts the whole weight of the head behind the spinal cord. The human face helps in the maintaining of the occipital condyles (Pontzer, 2017). The muscles of the human forehead, helps the human in their expression. The size of the brain is also significant and helps to increase the brain size. The transition took place around 2.4 million years where modern level of the brain size could not be attained till 500000 years. The anatomy in human shows that the brains are quite larger than that of the normal size(Pontzer, Raichlen & Rodman, 2014).

Spinal Column

It is important to maintain the balance in between two legs.The vertebral or the spinal columns of the human is bend in the forward or the lumbar region or a backward bend in the thoracic (upper) region. The lumbar spine helps the body to be straight and it requires that the more the muscular effort for bipedal animals. The human body leans forward and they use less muscular efforts, so as to stand or walk straight and upright. Thus it is the work of both the lumbar and the thoracic curves which brings the curves of the body to the center of gravity directly over the feet. The body of the humans is inclined in such a way the body erection is significantly smaller so that it can conserve the energy

Pelvis

Today in the quadruped, the center of the gravity in humans is located near the torso. Thus it is near to the center of which the pelvis is located. When the human being is walking then it gravity shifts from one side of the pelvis to the other side. The biepedalism needs special adaption and the gluteal muscle is different in bipedal human and quad apes. Today the humans have very large hips and which have larger pelvic joints (Tardieu, Hasegawa & Haeusler, 2017)

References

Barrett, P. M., & Maidment, S. C. (2017). The evolution of ornithischian quadrupedality. Journal of Iberian Geology, 1-15.

Dunbar, R. I. M., Lehmann, J., Korstjens, A. J., & Gowlett, J. A. J. (2014). The road to modern humans: time budgets, fission-fusion sociality, kinship and the division of labour in hominin evolution. Lucy to language: The benchmark papers, 333-355.

Granatosky, M. C., Tripp, C. H., & Schmitt, D. (2016). Gait kinetics of above-and below-branch quadrupedal locomotion in lemurid primates. Journal of Experimental Biology, 219(1), 53-63.

Ingham, S. J. M., de Carvalho, R. T., Abdalla, R. J., Fu, F. H., & Lovejoy, C. O. (2017). Bony Morphology: Comparative Anatomy and its Importance for the Anterior Cruciate Ligament. Operative Techniques in Orthopaedics.

Langdon, J. H. (2016). Case Study 9. Reading the Bones (1): Recognizing Bipedalism. In The Science of Human Evolution (pp. 67-73). Springer International Publishing.

Machnicki, A. L., Spurlock, L. B., Strier, K. B., Reno, P. L., & Lovejoy, C. O. (2016). First steps of bipedality in hominids: evidence from the atelid and proconsulid pelvis. PeerJ, 4, e1521.

Osborn, M. L. (2013). The Shoulder suspension of bipedal humans and the head suspension of quadrupedal cats: a reconstruction of macroevolutionary changes of complex systems based on natural experiments, comparative anatomy, and biomechanical analyses of extant organisms (Doctoral dissertation).

Pontzer, H. (2017). Economy and Endurance in Human Evolution. Current Biology, 27(12), R613-R621.

Pontzer, H., Raichlen, D. A., & Rodman, P. S. (2014). Bipedal and quadrupedal locomotion in chimpanzees. Journal of human evolution, 66, 64-82.

Tardieu, C., Hasegawa, K., & Haeusler, M. (2017). How Did the Pelvis and Vertebral Column Become a Functional Unit during the Transition from Occasional to Permanent Bipedalism?. The Anatomical Record, 300(5), 912-931.

White, T. D., Lovejoy, C. O., Asfaw, B., Carlson, J. P., & Suwa, G. (2015). Neither chimpanzee nor human, Ardipithecus reveals the surprising ancestry of both. Proceedings of the National Academy of Sciences, 112(16), 4877-4884.

Zeininger, A., Shapiro, L. J., & Raichlen, D. A. (2017). Ontogenetic changes in limb postures and their impact on effective limb length in baboons (Papio cynocephalus). American Journal of Physical Anthropology, 163(2), 231-241.