What Is Human Evolution?
Human evolution, or anthropogeny, is the origin and evolution of Homo sapiens as a distinct species from other hominids, great apes and placental mammals. In 1856, a strange skull was found by some workmen in the Neander Valley in Germany. The odd appearance of the skull led some to believe that it had once belonged to a person who was afflicted with rickets. They did not believe it could have come from an ancestor of modern man. It did, however, form the notion that there could have been creatures that were half-human and half-ape. Ernst Heinrich, a German scientist, claimed that if such a creature were ever found it should be named Pithecanthropus Erectus, which means upright apeman.
Pithecanthropus Erectus
Even before the discovery of the skull, which is now known as Homo neanderthalensis, people hypothesized that there was some sort of transmutation that took place between species. This, however, was not widely accepted. On November 4, 1859, the view on evolution as a whole changed dramatically. This was the date that Charles DarwinThe Origin of Species. With the release of this work, the theory of human evolution became a bit more believable. The theory of natural selection was proposed by Darwin within The Origin of Species. This theory states that the physical traits of an organism are selected for according to the environment it lives in. published his work. Darwin's theory piqued the interest of many scientists who went out in search of evidence which would branch the gap between apes and humans. In 1890, a Dutch physician by the name of Eugene Dubois found a low, apelike skull on the banks of a river in Java. Dubois also discovered a humanlike thigh bone near the skull. He concluded that this creature was the link between apes and humans which Heinrich hypothesized about. Other fossils began to be found which appeared to be transitional.
As the amount of finds increased, so did the number of species. Today, the family Hominidae (Bipedal Primates) has grown to include the genus': Ardipithecus, the most apelike hominids. Australopithecus, small-brained gracile hominids with mixed fruit/vegetable diet. Paranthropus, smalled-brained robust hominids with a grassland vegetable diet. Homo, large-brained hominids with an omnivorous diet. These are just brief descriptions of the genus given above. Below are some examples of the genus Australopithecus and Paranthropus that eventually led to the view of the Hominidae family we have today.
* A. anemensis
* A. afarensis
* A. africanus
* A. aethiopicus
* P. robustus
* P. boisei
(A. is an abbreviation for Australopithecus)
(P. is an abbreviation for Paranthropus)
Even though these fossils had both human and ape characteristics, the apelike qualities outnumbered the human ones. Scientists sought to find fossils that were closer to modern man than the Australopithecines. In the early 1960's, Louis Leakey found what he thought was another P. boisei skull, however, the brain case was larger than previous finds. After collaboration with P.V. Tobias and J.R. Napier, he named the skull Homo habilis, which means "handy man". He came up with this name because of the tools found at the site of the skull. Leakey figured that the enlarged brain size made it possible for H. habilis to form tools according to how his/her mind perceived it should look like. Other species of this genus that were found include H. Eructus, H. neanderthalensis, and our own species, H. sapiens sapiens.
Some controversy concerning the labeling of H. neanderthalensis as H. sapiens neanderthalensis has arisen in past years, as to whether it should be considered part of the sapiens line. Previously, Neanderthals were considered to have been the transitory form from H eructus to H. sapiens sapiens. The ideology then shifted to a position that Neanderthals were not a transitory form, but were instead a genetic dead end. Their abrupt disappearance in the fossil record has yielded suggestions that Neanderthals were outcompeted and replaced by anatomically modern human beings. The current viewpoint among many people is that Neanderthals were in fact a separate species and have been labeled by some as H. neanderthalensis, dropping "sapiens" from the name.
Ardipithecus ramidus
Ardipithecus ramidus is considered to be the earliest member of the Hominoidea family, this is because it is the most ape-like hominid known. The initail fossils of this species were found in the Middle Awash area of Ethiopia. Total seventeen fossil fragments were found including, two skull bases, a child's mandible, teeth, and arm bones. The fossils were found by a research team headed by Dr. Timothy White, Professor of Anthropology at the University of California, Berkely, in 1992 and 1993.
In 1994 more fossils were also recovered in Ehtiopia, close to the original site. Total 90 fragments where found, which accumulated to be about 45 percent of the total skeleton. Included in these fragments were pieces of the pelvis, ankle, feet, and leg. This find still awaits official anylisis to draw conclusive evidence on whether or not Ardipithicus was bipedal, even though the foramen magnum and leg fragments initially indicate this species was bipedal.
Ardipithecus ramidus is dated to about 4.4 million years ago, and displays a combination of human-like and chimp-like features. First, the teeth of Ardipithecus has thiner enamal, which more closely resembles that of a gorilla or chimp. The canines are smaller than that of a chimp, but are still larger than that of later hominids. The molars are also relativly small and ape shaped. Second, the foramen magnum is more forward in position when compaired to that of apes. This indicates a progression towards bipedalism if not bipedalism itself. Third the arm structure of Ardipithecus ramidus is an intermediate between the great apes and later members of the hominid line.
Australopithecus afarensis
One of the earliest of modern man's ancestors, Australopithecus afarensis lived between 4 million and 3.2 million years ago in eastern Africa. The teeth and jaws of two dozen hominids where uncovered at Laetoli in Tanzania along with a now famous set of footprints where two early hominids once walked along the shore of an ancient lake around 3.6 million years ago. More individuals were also found at Hadar in Ethiopia and another at Lake Turkana in Kenya.
Among those discovered at Hadar was Lucy, a nearly complete (40%) skeleton of an Australopithecus afarensis. Weighing about 60 pounds and standing about 3 and 1/2 feet high, Lucy lived about 2.9 million years ago when the eastern region of Africa was semiarid savanna with rainy and dry seasons. Lucy was discovered in 1974 by Tim White and Donald Johanson.
Lucy and other skeletons found helped scientists to draw a clearer picture of what these early human ancestors looked like. They were short, the tallest male probably reaching less than five feet, with extremely thick bones, and elongated back and short legs. The hands and feet were probably more similiar to apes than modern man, but the big toe appears to lack the grasping ability common to apes. The orientation of the pelvis allowed A. afarensis to walk upright, though the length and grasp of their arms allowed them to continue to move through the trees.
Paranthropus robustus
Paranthropus robustus first appeared about 1.8 million years ago and disappeared around 1 million years ago. This species was first discovered and named by Dr. Robert Broom. The fossil was initially found by Dr. Broom, who made a habit of buying fossils from local quarry workers, on June 8th 1938. On this occasion Dr. Broom purchased a maxillary fragment containing a first molar, that he noticed was different than that of A. africanus. Dr. Broom, after noticing the difference, looked into the location the fossil was found, Kromdraai, and with this further investigation found several more cranial and mandibular fragments that were associated with the original specimen.
Paranthropus robustus lived mostly in eastern Africa. The first remains were found in the quarries of Kromdraai, South Africa. Later excavations revealed more fossils in Kromdraai, South Africa and Swartkrans, South Africa. P. robustus was noted to have a somewhat larger cranial capacity (450-530 cc) than earlier hominids and thicker jaws with larger molars and premolars but similar incisors. P. robustus also exhibited well-developed cranial crests and ridges to support heavier chewing action. This support may have been needed for the wider variety of nuts, roots, and seed that were included in the diet of P. robustus. P. robustus died out around 1 million years ago and is not ancestral to the Homo genus.
Australopithecus africanus
Australopithecus africanus lived between 3 and 2.3 million years ago mostly in South Africa although remains have been found else where. Fossil remains have been uncovered at many locations including Taung in South Africa, Sterkfontein in South Africa, Makapansgat in South Africa, and possibly at Lake Turkana in Kenya and Omo in Ethiopia.
The first Australopithecus africanus was discovered by Raymond Dart in 1925. The fossil itself was found in a limestone quarry at a site called Taung. It took dart many days to remove the fossil from the limestone in which it was incased, but once removed it revealed the face, braincase, and brain cast of a young primate. The fossil thus became known as "Taung Baby".
Australopithecus africanus has a cranial capacity of between 435cc and 530cc, and the average cranial capacity of 450cc. Males of the species are though to have possibly weighed up to 100 pounds. Females possibly weighed around 50 with a height around 3'6''. When compared to Australopithecus afarensis, Australopithecus africanus is less prognathous with a more rounded jaw and larger back teeth and canines. The body of A. africanus when compared to A. afarensis was similar but possibly with longer arms and shorter legs. A. africanus has no sagital crest. Also, this species was capable of facultative bipedalism.
Homo habilis
Homo habilis first appeared around 2.5 million years ago. Fossils of H. habilis were first discovered in Olduvai Gorge in Tanzania and named by Louis Leakey, Phillip Tobias, and John Napier. Fossils of this species were also found at Lake Turkana, Kenya, Omo Basin, Ethiopia, and Sterkfontein Cave, South Africa. Excavations at Olduvai Gorge also indicate that H. habilis lived at the same time and in the same place as P. boisei.
Tools have been found at the Olduvai site, at the same level as P. boisei and H. habilis. These tools are called Oldowan tools. They are simple pebble tools made from water worn cobbles about 3"- 4" in diameter. The Oldowan tools are made by knocking off a few flakes from one or two faces of the stone, thus creating a sharp edge. The tools were initially found at the same level as P. boisei and H. habilis, but "zinj" (P. bosiei) was thought to be to primitive to use the tools. H. habilis with a larger brain size was a more likely candidate to be using the tools. The tools were most likely used by hominids to make a scavenging lifestyle more efficient. Oldowan tools allowed hominid's to more easily and quickly remove meat and bones from a carcass. This made the addition of meat to their diet a more efficient practice. Also, the genus Homo is the only genus of hominid that evidence is found of tool use.
With a relatively larger brain, 680cc on average and up to about 800cc, than the Australopithecines, Homo habilis is the first definite human ancestor. Homo habilis is considered to be the first member of the genus homo because of two main reasons. First, their larger brain size, and second, the presence of tools indicates that the large brains were capable of more complex thought processes not seen in the Australopithecines. H. habilis marked a trend in hominid evolution toward larger brains and more intelligence. In addition to this larger brain size, H. habilis remains also have reduced molars and premolars and a clearly bi-pedal foot structure.
Homo neanderthalensis
In 1856, three years prior to Darwin's publication of The Origin of Species, a skullcap and fossilized bones were found in a cave in Neander Valley near Dusseldorf, Germany. Living around 50,000 years ago, the Neanderthal Man, as these bones came to be called, were short, thick-set people with strong arms and legs, a large, slightly sloping face with predominant brow ridges and a nearly nonexistent chin, and a braincase (more than 1450 cc) larger than that of modern humans (around 1350 cc). These features are believed to have been an adaptation to the cold weather and hunting lifestyle the H. neanderthalensis followed during his reign in the last ice age.
When first discoverd, the bones were dismissed as the remains of a diseased individual, or and imbecile. When similiar bones were discovered in France, Yugoslavia, Belgium, and other locations in Europe, these finds could no longer be dismissed as an oddity. Early bias analysis of these bones led to the popluar image of the H. neanderthalensis as a stoop shouldered brute with a bent knees and forward jutting head and neck.
Homo sapiens
Beginning around 300,000 years ago fossils that would be classified as Homo sapiens with near-modern or modern features appear. Around 100,000 years ago fossils that are considered fully modern in appearance start to appear. Fully modern Homo sapiens are often referred to as Homo sapiens sapiens. The fossils form between these periods are considered transitional fossils between archaic and modern Homo sapiens.
Fossils with modern features are the only fossils that are placed in the category of Homo sapiens. To be classified as a modern feature the fossils have to posses features that are common in humans today. The loss of a prognathous profile, no heavy brow ridges, globular skull shape, more vertical forehead, smaller narrower flatter faces, and protruding chin are some of the criteria that would fit a fossil into the modern category. The cranial capacity of a modern Homo sapiens is also around 1,400cc.The post cranial skeleton being less robust is also considered a modern characteristic.
The fossils of Homo sapiens appear earliest in Africa and later in Southwest Asia, Europe, and East Asia. Later than this modern humans migrated to Australia, the Americas, and the islands of the Pacific. As you move farther from Africa and Southwest Asia dates for modern Homo sapiens become more and more recent, this indicates that Africa is the birthplace for modern human.
The earliest fossil evidence for modern Homo sapiens sapiens is found in South Africa. At sites such as Klasies River mouth and Border Cave, fossil remains and artifacts date to around 100,000 years ago and represent fully anatomically modern humans.
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