The Human Tree - Essay Example

?The Human Tree There is debate whether man’s direct ancestor is Australopithicus Afarensis or Ramidus, because there is not enough evidence to be certain if Afarensis was in a direct line or a secondary line from Ramidus. In either case the hominid line certainly descended from one or the other or both. Australopithicus Ramidus was the earlier about 4.5 million years ago. Afarensis appeared around 3.3 million years ago and probably was ancestor to both the other Australopithecus and homo lines. The main indication of divergence from apes is the size and location of the hole called the Foramen Magnum, the place where the spinal column enters the brain. This space was small and at the rear of the skull in quadrapedal animals. It moved a little forward and grew to about 6 times the earlier one for knuckle walkers, like gorillas. For bipedal animals it moved even further forward and nearly doubles in size. This makes sense, as the place where the spinal column enters the skull would govern the angle at which the head is carried (Howells 77-205). Lucy from Oldivai Gorge in South Africa is the most complete skeleton of this genus, which walked upright and may have used very simple tools. It probably lived in trees, but hunted or scavenged on the ground, as the curvature of fingers and toes indicates it could climb trees. The pelvis in the female is the same as modern man. The long forehead slopes at about 45 degrees from the bony ridge over the eyes, and there is no real chin. Two sets of footprints preserved by volcanic action and found by Mary Leakey show human toes, and they prove that Australopithecus Afarensis walked on two feet habitually, though the placement of feet show a more splayed gait and suggests that this ape was not quite upright ("Early Human Evolution: Early Transitional Humans."). One of the difficulties with the fossil records is that there is no way of knowing how many species exhibiting changes came between one recovered fossil and the next. This is why there is disagreement about exactly where the branches might be. Without DNA evidence it is not possible to know for sure which hominid is the ancestor of which others. Even with DNA evidence it would not be certain, as it would requires some from all the fossils in the line. Australopithecus Africanus followed next. However, it is not certain where homo branched off. It could have been from Aferensis, Africanus, Robustus or even a separate Paranthropus Robustus. All of these were inhabiting the same area as contemporaries. There might even have been interbreeding, which would indicate that the breeds were not really separate. The Robustus definitely had larger bones and brain cavity, and it seems to have gone extinct. That leaves either Afarensis or Africanus as being separate lines or branching to Australopithecus Bahrelghazali which then branched to Homo. Only lower jaw bones have been found thus far, but the dentition puts this species closer to Homo than the others. There may have been other branches of Australopithecus, but there is not enough fossil evidence that they were around very long before going extinct. Cross breeding could also have eliminated some differences ("Hominidae_filogenia.png (PNG Image, 1025 ? 979 pixels)."). So me theorists eliminate all of these australopithecines from the homo line of ancestry, believing that homo lines branched off independently from either Ardipithecus Ramidus or A. Garhi. However, one might question this based upon the lack of fossils and the latest find in Georgia on the Black Sea of five Homo Habilis types with a great deal of variation among them. It is possible they are all one species with variation, just as we have today. Speciation generally includes an inability to procreate successfully between species. A recent discovery of what seems to be a new species of Australopithecus, A. Garhi, in Ethiopia is a candidate for early human. This illustration shows the pitifully few pieces that have been found, and the Georgian discovery makes it worth further investigation before ascribing a new species name to it. If we look at small current populations now, a great deal of variety can be found . Why say ok for now and not ok for then? Homo Habilis is widely accepted as the first hominid in the human line of descent, appearing between 2.4 and 1.5 million years ago. Some researchers favour adding another line between H. Habilis and H. Erectus: Homo Ergaster. While many are convinced, as am I, that this species was the direct ancestor of the rest of the homo line, there is not enough fossil proof, as yet, to be certain. H. Habilis used and made tools, but they were not very sophisticated. He is the first to visibly diverge from previous hominids. The skull is rounded with the chin directly under the brain cavity. The forehead is smaller as is dentition. This species ate pretty much anything, but probably scavenged, using the primitive tools he created to cut up carcases to take with him. The foot of H. Habilis is definitely human, with different sized non-prehensile toes with no tree climbing curvature. The triangular foot is well established. He eventually became extinct, but not before fathering at least two lines leading to Homo Sapiens. It is thought that H. Ergaster is the direct ancestor of Homo Erectus, or may be the African version of H. Erectus after the migration to Asia. H. Ergaster, may have been followed by H. Antecessor, leading to H. Heidelbergensis and H. Neanderthalis. This is based upon very few fossils, but it is logically possible. Whether or not there is any connection between H. Antecessor and H. Sapiens is merely guesswork at this point. What has been found of H. Antecessor is at least 780,000 years old. Above is the entire collection of H. Antecessor fossils. The next hominid in line is the very familiar Homo Erectus, named so, because it is shown to have walked totally upright. The curvature of the spine has begun to approach modern types. The forehead is shortened and there is a more human dentition and chin. The cranial cavity is larger, but still only half the modern size. The genus ate anything organic. The dentition allowed for grinding grains and grasses, biting and ripping meat and mashing vegetables. They also had a primitive version of the modern human cochlea balance mechanism, enabling them to run long distances and remain balanced. Homo Erectus made very sophisticated tools, as did Homo Neanderthalis. There is evidence that Homo Erectus and Neanderthalis both used fire to cook their food("The emergence of humans."). H. Neanderthalis genes are found in modern man to a percentage of about 4%, so it is likely that when H. Neanderthalis disappeared, it was due to interbreeding with modern humans, probably those previously designated as Cro Magnon from Africa about 80,000 and 50,000 years ago. Homo Heidelbergensis may be another variation on Neanderthalis, or its ancestor, as there is some similarity in the brain case elongation and the prominent brow ridges. However, they also share many characteristics with modern humans. They were only slightly smaller than modern man and had 90% of the brains size of H. Sapiens Sapiens. These fossils are found everywhere, so they did migrate in all directions. In Europe their body styles conserved heat. In hotter climates they seem to have been smaller boned. The first Homo Sapiens appeared in Ethiopia about 160,000 years ago. In other places they developed, or arrived, between 100,000 and 40,000 years ago. The differences between Homo Sapiens and its immediate predecessors or contemporaries are small when considering the whole range from Australopithecus. Much is a matter of size and balance. The more modern the species the more streamlined and balanced proportions became and the symmetry increased. We may never know the whole truth, and may never find the evidence to prove all points of the line of the descent of Homo Sapiens Sapiens. Modern humans have larger brains, more vertical foreheads, smaller brow ridges, smaller jaws and molars, more prominent chins and more balanced and symmetrical bodies, conforming to the golden ratio of 1-1.618. Works Cited "Early Human Evolution: Early Transitional Humans."Web. 12/9/2013 . "The emergence of humans."Web. 12/9/2013 . "Hominidae_filogenia.png (PNG Image, 1025 ? 979 pixels)."Web. 12/9/2013 . Howells, William. Mankind in the Making: The Story of Human Evolution. Revised ed. Garden City, NY: Doubleday, 1967. Questia. Web. 9 Dec. 2013. P77-205. APPENDIX A: Phylogenic Tree   Read More