Changes of Structure of Anatomy as Human Evolution Evolves Essay Sample

Changes of Structure of Anatomy as Human Evolution Evolves Essay Sample

Introduction

 One of the controversial subjects in the world is about the origin of animals and in deed the origin of the whole universe.  There have been several theories attempting to explain the origin of the universe.  From the big bang theory to the religious theories, the origin of the universe still remains unknown. One of the earliest scientific theories that tried to explain the origin of species in the universe is the Darwin’s theory of evolution. In his book The Origin of Species, Darwin gave an account of evolution and genetic variation which could be used to explain the existence of different species. Darwin evolution theory has been cited as one of the most important theories that give an account of existence of different species of animals in the universe. One of the interesting accounts of this theory is the path of bipedalism human evolution. This theory claims that the modern human species shared a common ancestry with apes but through bipedalism, human species evolved to an upright movement through evolution.

In this paper, we are going to review the changes of structure of anatomy as human evolved.  We are going to review how over the years, human species has changed its bipedal structure to a form of terrestrial locomotion.

Anatomical evolution of human species

Since Darwin proposed the theory of human evolution, there has been a lot of interest to understand the course of the evolution. This interest has  been stirred by the discovery of the genetic structure which  showed that there could be evidence that theory of evolution by Darwin could be unravel  the mystery of existence of animals in the universes.

There have been concerted efforts from all the concerned quarters on the course of evolution. However one of the most important discoveries has been made by paleontologist and historians who have scavenged for all possible fossil sites that can add piece together to give a timeline evolution and changes in the anatomical structure of human being (Harcourt and Aiello, 2004; Heglund and Taylor 1982).

In the last 80 years or so, there have been many theories which have addressed the question of hominid bipedalism through comparative anatomy.  There are theories which have concentrated on the observation of the extant hominid taxa while the second group of theories has looked at the fossil materials (Wheeler, 1994).  However these theories have generically accept that the evolution of the bipedalism happened in a linear fashion  starting with brachiating ancestor  through a large bodied stage vertical climbing ancestor then to a terrestrial knuckle walking ancestor and finally coming to an obligate bipedalism where man walked on  two legs (Heglund and Taylor 1982).  All theories however agree there was an immediate apelike ancestor who later gave rise of the modern man but the use of tools played a key role in the evolution.

There is a controversy surrounding the bipedal evolution of human which is centered on two factors. First it is the development of the motor sense which is used to support the bipedalism.  The other issue is about the reasons why the bipedal structure actually evolved compared to that of apes. As we shall see later, the foot of Australopithecus Africanus remains controversial since this species is known to have existed before man learnt to use tools but the feet show it was fit for bipedalism. Those supporting the fact that bipedalism developed to support use of tools argue that the foot of this hominid was fit of arboreal purpose(Harcourt and Aiello, 2004; Czarnetzki and Jacob, 2003)..

The history of evolution of man dates more than 85 million years ago to one of the oldest surviving placental mammal group.   Paleontologists have indeed shown that there is a possibility that man shared the same ancestry with bats. However the earlier existence of human species can be traced to the existence of hominid which was a large family that housed the great apes and humans.  The word hominid describes the earliest ancestor for both man and apes before they evolved in different paths.

The history of evolution of man begins with the discoverer of a fossil which was named Ramapithecus.  This is believed to have been the early hominid. Ramapithecus is however believed to be the ancestor of the modern apes.  The earliest evidence on the   evolution of man from a common ancestry with apes is the Ardipithecuse ramidus   which is date more than 4.4 million years go.  This hominid is thought to have been bipedal and was about 4 feet tall (Jablonski, 1993). Let us look at two major genuses in the cours of bipedal evolution of human beings.

(i) Australopithecus

The next in the line of evolution of human species was Australopithecus which was discovered in Kenya and is thought to have lived more than 4.2 million year ago. Unlike the Ardiphithecus, Australopithecus anamnesis had improved bipedal features but its skull was like that of ancient ape (Wood and Collard, 1999).  Australopithecus afrensis who lived more than 3 million year ago had an apelike faces which has a sloping forehead with a distinct ridge over the eyes. It had a flat nose and chinless lower jaw. This hominid was 3.6 feet tall. It was like the modern human in many aspect but the head and the face were much larger.

The next in linage was Australopithecus africanus which was very similar to afernsis. This as also bipedal and had a large body size and a large brain size.  However this brain was not advance for speech and the molars were little larger. However the jaw was shaped like that of modern human.  The next was Australopithecus aethipicus which lived 2.6 million years ago.  This is thought to have been the ancestor of robustus and boisei. It has a huge molars and jaws which had a saggital crest and massive chewing muscles. Australopithecus robustus had a body similar to that of the africanus but had a massive skull and teeth (Wood and Collard, 1999; Heglund and Taylor 1982). This hominid had a huge face which was flat without a forehead.  It also had a large brow ridges and suggital crest but had not developed speech function.  The last hominid in the Australopithecus genus was boisei which lived 2.1 to 1 million years ago.  This was very much like robustus but had a massive face.  It also had huge molars which were more than 0.9 inches across (Harcourt and Aiello, 2004; Jablonski, 1993). On terms of bipedal evolution, there is a lot of controversy souring the Australopithecus afarenses foot bones which were found in Hadar in Ethiopia. Some argue that  the foot anatomy showed complete compliance with bipedal locomotion while there are others who argue that  the feet was fit for terrestrial and arboreal locomotion.

(ii) Homo

The next stage lead to the evolution of the Homo habilis otherwise known as handy man due to the tools they used which were found with their fossil remains.  This species had a form of speech but it is believed that they were like the Australopithecus in the body structure.  However the brain structure had evolved and was larger compared to earlier species (Harcourt and Aiello, 2004).  Homo habilis was still living on trees.  They could not walk on their four legs like the modern man. In term of bipedal structure, homo habilis was more like the australophithecus walking on all fours but different on the Australopithecus in that he had a large brain size. However the start of the use of tools meant the bipedal structure was becoming more relevant since most tools could be used while standing on two legs. Therefore it is believed that by the end of the evolution period, Homo habilis could have started developing a bipedal structure.

Homo erectus lived more than 300,000 years ago.  This species had a large brain size and had a form of speech. Its brain size was almost the same size like that of modern man. H was also a skilled user of tools and made fire to cook food. The species is also believed to have developed some form of clothing and hunted for food. He had a bipedal structure and resembled the modern man in different aspects except the face and the brow ridge.  However the species is thought to have been sturdier and stronger as compared to the modern man (Wood and Collard, 1999). Home erectus is though to have been the first hominid that assumed a complete upright structure.  He was the size of the modern man and could stand straight though a times they used all fours.  Homo sapiens archaic emerged more than 200,000 years ago.  This species had a large brain size and had a speech function.  He had a round skull but which had smaller features.  He also had smaller molars and brow ridges compared to other species.  He had a stronger skeleton compared to the modern man (Wood and Collard, 1999).  Homo sapiens had a bipedal structure and could walk upright. He was tall with muscles and more knowledgeable. Homos sapiens had already a bipedal structure but different with the other species in the application of their skills.  This is believed to be the ancestor of the modern and made complicated tools

The recent studies have linked human evolution with that of gorillas in terms of bipedal evolution. The gorillas do not only have brain size close to that of human but the anatomy of the ape has shown that it bipedal structure is similar to that of man. Therefore, many paleontologists have argued that in the course of evolution, the pre-human foot could have been the same as that of gorillas but it evolved to a broader one due to the effect of exerted body force. There are two explanations that are given for the development of the bipedal structure (Hunt, 1994).

First explanation is the use of tools was the first factor that leads to the development of an upright structure. This happened in the sense that when man started using the tools by hand, the rest of the limb were adapted to support the rest of the body (Wood and Collard, 1999).  The second explanation is that while all the limbs were similar at first, they evolved to function properly in their contemporary functioning. Therefore the hands became more adapted to handling tools while the legs became adapted to supporting the rest of the body. This gave rise the upright bipedal structure.  The urpright strcutre was enbld man to walk on two legs instead of four legs.

The anatomical evidence showing that hominid had bipedal locomotion was discovered in the pre-Neanderthal hominid like Homo erectus and some earlier species like Australopithecus africanus.  This was one of the reasons why they were eventually accepted as hominids.  However one of the arguments that had been used to refute bipedalism in the Australopithecus genus is that the pelvic structure showed increased inability to transfer body weight from one foot to the other as compared to the later Homo genus (Spoor et al., 1994).  The comparative anatomy of the pelvic and femoral morphology has become an important aspect in studying the human bipedal gait.

Although there is continued discovery of new materials, the debate about whether the development of the bipedal locomotion will remain controversial due to the presence of different paleontologists who use different methods to test their hypotheses.  However the debate will remain constrained by the general agreement on the existence of locomotors repertoire which precede bipedalism and the theoretic debate on the reasons why bipedalism evolve (Hunt, 1994).

Conclusion

The theory of human evolution which was put forward by Darwin has been instrumental in understating the origin of species. There is an agreement among the paleontologist that human beings would have evolved from ape ancestry.   One of the most controversial issues in the course of evolution is bipedlism where man was able to walk on two legs. However it is agreed that the use of tools would have been one the main factor the led to the use of two legs.

Work cited:

Czarnetzki, A. & Jakob, T. (2003). Palaeopathological and variant conditions of the Homo heidelbergensis type specimen. Journal of Human Evolution, Vol. 44 (4): 479–95.

Harcourt, W. & Aiello, L. (2004) Fossils, feet and the evolution of human bipedal locomotion. Journal of Anatomy, Vol. 204(5): 403-416

Heglund, G. & Taylor, C. (1982). Energetic and mechanics of terrestrial locomotion. Journal of Experimental Biology, Vol. 97:1

Hunt, K.D. (1994). The Evolution of Human Bipedality. Journal of Human Evolution, Vol. 26

Jablonski, N. (1993). Origin of habitual terrestrial bipedalism in the ancestor of the hominidae. Journal of Human Evolution, Vol. 24

Spoor, F.,Wood, B. & Zonneveld, F. (1994). Implications of early hominid labyrinthine morphology for evolution of human bipedal locomotion. Nature, Vol. 369: 645–8

Wheeler, P. E. (1994). The evolution of bipedality and loss of functional body in Hominoids. Journal of Human Evolution, 13, 91-98, (1984)

Wood, B. & Collard, M. (1999). The changing face of Genus Homo. Evolution  Anthropology, Vol. 8(6):195-207