The Human Evolution Theory Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Human Evolution. In this research paper we are going to examine the human evolution theory. Hominids is the most highly organized family of apes. It includes the modern man, his predecessors: paleanthropines and archanthropines as well, according to the most scientists - australopithecines. Some scholars restrict the family of hominids only by people, starting with the archanthropines. The proponents of an expanded interpretation of the family include two subfamilies into it: australopithecines and actually people (Homininae) with one genus Homo, and three species - Homo habilis, Homo erectus and Homo sapiens. According to many authors, Homo sapiens is divided into two subspecies - Neanderthal and modern humans. Some researchers attribute Pithecanthropus, Neanderthal and modern humans to the genus Homo as separate species. According to the prevailing view about the origin of hominids, they are the branch of the anthropoid apes, which, after separation from a common trunk with Pongidae led to the emergence of Homo sapiens.

The most accepted in modern science is the separation of two subfamilies in the family Hominidae :

- Australopithecinae - hominids with many typical Pongidae features;

- Homininae - hominids without Pongidae features.

The greatest value to create a clear picture of the immediate ancestors of the family of hominids are numerous and well-preserved finds in South Africa. Now in Southern and Eastern Africa there are several fossil anthropomorphic primates that are combined into three types - Australopithecus, Paranthropus and Plesianthropus - stand out in the subfamily or family of australopithecines.

Africa is the most likely an ancestral of hominids. Australopithecines were a very peculiar group. They appeared about 6-7 million years ago, and the last of them died out only about 900 thousand years ago, during the existence of more progressive forms. It is known that australopithecines had never left outside Africa, although some finds from the island of Java, are sometimes referred to this group.

The complexity of australopithecines location among the primates is that their mosaic structure combines features characteristic for both modern apes and humans.

The skull of Australopithecus is like a chimpanzee skull. It is characterized by large jaw and massive bony ridges for the attachment of chewing muscles, small brain and a large flattened face. Australopithecine teeth were very large, but fangs were short, and structural details of the teeth were more like human than ape.

The structure of the skeleton of Australopithecus is characterized by a broad low, relatively long legs and short arms, grasping hand and ungrasping foot, vertical spine. This structure is almost human, the differences are only in details of structure and in small amounts.

The height of Australopithecus ranged from a meter to one and a half. The brain size was about 350-550 ccm, like modern gorillas and chimpanzees. For comparison, the brain of modern man has a volume of about 1200-1500 ccm. The structure of Australopithecus brain was also very primitive. They lived in tropical forests and savannas, nourished mainly by plants. However, later australopithecines hunted antelopes or took prey of large predators - lions and hyenas. Australopithecus lived in groups of a few individuals and, apparently, constantly roamed the expanses of Africa in search of food.

Australopithecus can be divided into three main groups, each of which allocates a number of species: Early australopithecines - existed 7 - 4 million years ago, possessed the most primitive structure. Several genera and species of early australopithecines are identified.

Australopithecus gracilis - existed 4 - 2.5 million years ago, had a relatively small size and modest proportions. One genus Australopithecus with few species is usually distinguished.

Massive Australopithecus - existed 2.5 - 1 million years ago, were very massive highly specialized forms with developed jaws, small front and huge back teeth. Massive australopithecines are allocated in a separate genus Paranthropus with three species.

Let us consider in more details each of them.

The remains of ancient apes, which can be attributed to the early Australopithecus, were discovered in Chad and Toros-Menalla and were named Sahelanthropus tchadensis. The whole skull was popularly called "Tomai". The dating of the finds of is about 6-7 million years ago. More numerous discoveries in Kenya and Tugen Hills are dating 6 million years ago. They were called Orrorin tugenensis. In Ethiopia, in two locations - Alayla and Aramis - were found numerous skeletal remains, called Ardipithecus ramidus kadabba (about 5.5 million years ago) and Ardipithecus ramidus (4,4 million years ago).

Findings in two locations in Kenya - Kanapoi and Allia Bay - were named Australopithecus anamensis. They date from 4 million years ago.

We do not know much about early australopithecines. Judging by the skull, thighs, limb bones and the remains of the pelvis, early australopithecines were already bipedal primates. However, judging by the bones of hands they retained the ability to climb trees, or even were four-legged creatures resting on phalanx of fingers, like modern chimpanzees and gorillas. The structure of teeth of early Australopithecus intermediate between apes and humans.

Ardipithecus ramidus, who lived 4.4 million years ago was an early hominid. The remains of this species were found in presumably forested territories, but these creatures could be bipedal. (Woldegabriel, Haile-Selassie, Renne, Hart, Ambrose, Asfaw, Heiken & White, 2001; White, Suwa & Asfaw, 1994). The fact that Orrorin and Ardipithecus lived in relatively moist and wooded habitats, calls into question the theory that the ecological changes led to human evolution, having pushed out early hominids in open savanna, where bipedalizm gave key adaptive advantage. Ardipithecus teeth have more similarities with the human than the chimpanzee teeth. It is possible that there were no soft leaves in Ardepithecus menu.

Since about 4 million years ago the paleontologic record is sufficiently complete and consistent.

In Kenya, Tanzania and Ethiopia in many localities the fossils of gracile australopithecine called Australopithecus afarensis were discovered. This species existed from about 4 to 2.5 million years ago. The best known are finds from the area in Hadar, Afar desert, including the skeleton, nicknamed Lucy. Also, in Tanzania, there were discovered the fossilized footprints of bipedal creatures in the same layers, which are the remains of Australopithecus afarensis.

In addition to Australopithecus afarensis, in the East and North Africa during the interval 3-3,5 million years ago, probably other species inhabited. In Kenya, Lomekwi a skull and other fossils, described as Kenyanthropus platyops were found.

In Chad, in the Koro Toro (East Africa), the only fragment of jaw, described as Australopithecus bahrelghazali was found.

In South Africa, in some localities numerous fossils, known as Australopithecus africanus were discovered. The first record of Australopithecus - a baby's skull, known as the Taung Baby belongs to this species.

Along with all these advanced features, "early Homo» retained in their morphology very primitive set of features, including the structure of hand and brain. Because of this, some scientists consider them a kind of progressive late gracile australopithecines. Two types are the most distinguished among them: smaller one - Homo habilis and bigger one - Homo rudolfensis.

In 1959 in Tanzania (East Africa), in the gorge Olduvaya the married couple Leakey found fragments of bones of the primacy, which was named Zinjanthropus boisei by Louis Leakey. In sediments with Zinjanthropus remains crude tools from pebbles, as well as the bones of reptiles, birds and mammals were found. Among the guns choppers, guns treated bilaterally, and polyhedrons prevailed. Age of the finds is 1.75 million years.

Initially, the author of finds was convinced that guns of Olduvai culture were the handiwork of the substance, and it was concluded that Zinjanthropus was one of the oldest members of the human race. However, a small brain volume (530 ccm) and other primitive features of this being sown doubt among scientists in the possibility of producing stone tools by him. Further discoveries have shown that these doubts were not unfounded.

In 1960, in the same layer, but at 60 cm deeper horizon with the remnants of Zinjanthropus, Louis Leakey discovered the skeletal remains that belonged to the being different from Zinjanthropus and australopithecines in general. Initially, this creature was named "prezinjanthropus" (predecessor of Zinjanthropus). Later the bones of "prezinjanthropus" were found in the horizon with the remnants of Zinjanthropus and later sediments. The absolute age of the most ancient remnants of prezinjanthropus is about 2 million years. It was determined by careful study of fossil remains that they belonged to creatures more progressive than Zinjanthropus and australopithecines in general. This is indicated by the brain volume (650 ccm) and other features, including the bone structure of the foot and hand, revealing about two-legged gait, as well as the ability of his hand to "force clamp". All this allowed to consider "prezinjanthropus" as a being worthy of a place in the genus of "man" and give him the name of the species Homo habilis («handy man"). The value of this species name is primarily due to the fact that along with the rests of this hominid a large quantity of guns of Olduvai culture is found.

Louis Leakey's son, Robert Leakey on the shores of the Lake Rudolf (Kenya), found the bones of anthropoid beings, whose lifetime the scientist attributed to the second million years before our time.

But the most sensational discovery was the one by Donald Johanson in Hadera (Ethiopia). There, in 1974, almost complete skeleton of female mice, similar to the type of Australopithecus was found. "Lucy" (as Johanson dubbed this creature) had a vertical gait, differed by quite slender physique with height of about one meter, but her skull had completely ape traits. Scientists dated the find to 3-3,5 million years. It is likely that "Lucy" gives us an idea of the biological forms that gave rise to the genus Homo.

As to the Australopithecus afarensis movement professionals has not yet reached a consensus. Some, including American anthropologists O. Lovejoy, D. Johanson and B. Latimer, believe that Lucy has already perfectly mastered bipedal locomotion, and the structure of her pelvis and thigh muscles, even impeded the movement of the trees. (Latimer, B.M., T.D. White, W.H. Kimbel, D.C. Johanson and C.O. Lovejoy, 1981). Other, no less well-known American experts, such as R. Sasman and Dzh.Stern prove that Lucy and her relatives were still walking legs with knees a little bent. The Swiss P. Schmidt is confident that Australopithecus afarensis could not run for long distances, as evidenced by the shape of the Lucy chest - long and cylindrical. According to him, moving on two legs Lucy strongly rotated body, as gorillas do. Peculiarities of the structure of fingers and big toe, elongated proportions of the hands seem to say about a quite long pastime of these creatures in the trees, which they apparently used to be the safest place to sleep and rest. (D.C.Johanson, M.A.Edeg. Lucy`s Child: The discovery of Human Ancestor. Viking. Press, London. 1990).

Hominids moved from herbivorous to carnivorous. Probably at first they took away prey from predators or picked the remains of their feasts. This is evidenced by the traces of stone tools on bones printed over the traces of the teeth of lions and hyenas. "Early Homo» learned to manufacture stone tools. At first it were just shingles chopped in half, then the first people became to beat the stones for a few chips, making out a sharp cutting edge. Such primitive weapon was called pebble, or Olduvai one, according to the place of the first finds.

Perhaps "Early Homo» were able to do the simplest screens of the wind from the branches, pinned to the ground with stones. Further development of culture went with accelerating pace.

Systematic division of Hominids is very confusing. In older studies, it was customary to distinguish several stages of human evolution - archanthropines, paleanthropines and neanthropines. Archanthropines immediately preceded the australopithecines, or at stadial terminology - protantropy. At present, almost all scholars are inclined to think of a more complex - "Network" - character of evolution. However, the terms "archanthropines", "paleanthropines" and "neanthropines" are easy to use.

Sometimes all Hominids are united in one genus Homo, to which the modern man also belongs. However, the difference of the most ancient representatives of the subfamily - archanthropines - from modern man is so striking that many anthropologists are inclined to allocate a special kind of Pithecanthropus to them.

These include, among the other ancient African finds - "Man working» (Homo, or the Pithecanthropus, ergaster). These early humans produced guns of Olduvai type, among which gradually improved forms appear. Aboud the time of 1-1,5 million years ago, guns were improved so much that they already belonged to a new archaeological culture - Acheulean. A typical instrument of the Acheulian culture is a hand-ax - heavy, with rough cutting edge.

The first finds of Pithecanthropus were made on the island of Java (Indonesia) at the end of the XIX century by a Dutch physician E. du Bois-Reymond. (C. Gradmann, 2000). These archanthropines represent the most massive representatives of the ancient people and belong to the species "man rectified» (Homo, or the Pithecanthropus, erectus).

Some populations of Africa synchronous to European Neanderthals were much more similar to modern humans. Many researchers even refer them to the modern mind. The people of Klasies River in South Africa had a mental protuberance, head was rounded, and the skull was high. The size and shape of the brain of these people were almost indistinguishable from modern ones. The dates are well in excess of 100 thousand years.

In several African localities with the dating from 200 to 100 thousand years ago the bones of people who did not have a strongly exposed neck, large brow ridge, and possessed with the very large brain, and protruding chin were discovered.

Since about 40 thousand years ago, people of completely modern look, only slightly more massive than we are - neanthropines - are being known almost throughout the populated universe - from Africa, Europe, Asia and Australia.

About the people of Africa in the time Upper Paleolithic far less is known than about the population of Europe. However, fundamentally, they were similar both biologically and culturally.

As it was shown by studies in recent decades, the australopithecines were the direct evolution precursors of human. It is from the representatives of these advanced bipedal primates, about three million years ago in East Africa beings, having made the first artificial tools, having created an ancient paleolithic culture - Olduvai and having marked the beginning of the human race stood out.

On the African continent in the period from 1 to 4 million years creatures that in the way of their movement (bipedal) and on the structure of the dental system (small teeth) were much closer to humans than to the anthropomorphic apes lived. However, the shape of skull and brain volume were more similar to chimpanzees. Their foot was very similar to the human one, but the hand still had quite a few archaic characteristics. The significance of these findings is that they fill a gap in the chain of creatures leading from animals to humans, and enhance the arguments in favor of recognition Africa as an ancestral home of mankind.