The Evolution of Human Beings
The evolution of our own species is no different, at least in principle, than that of any other species. Nevertheless, the subject holds an intrinsic interest for us that the evolution is that of, say the mayfly dose not. The general picture of human evolution is that our branch of the family tree broke off from that of other primates about 8 million years ago.
The oldest hominid, Australopithecus ramidus (“southern ape, root of humans”). It appears to be midway in form between later hominids and modern great apes. The best–known early human fossils are bones of Australopithecus afarensis (“southern ape from the Afar triangle region of Ethiopia”), better known as Lucy, after the name given by paleontologists to a nearly complete skeleton of the species. This fossil, discovery in 1974, received its name when the paleontologists played a tape of the Beatles song “Lucy in the Sky with Diamonds.” Radiometric dating established the age of “Lucy” at 3.5 million years. Australopithecus afarensis is a different species and different genus from our own “Homo Sapiens,” but is closer to us than to any other primate.
Lucy and her family walked erect, but had brains about the size of a modern chimpanzee's. They were also rather small (the adults probably weighted no more than 60 to 80 pounds), and their body was covered with hair. If you saw an example of Australopithecus afarensis, the only thing that might make you think it is related to modern human beings is its upright gait.
Scientists used to think that the development of large brains made human beings special, and that the brain's development led to up right walking. In fact, the evolutionary story seems to be the other way. These primates walked upright first, which freed the hands for use, and then the large brain developed. Some scientists suggested that the evolutionary advantage bestowed by hand–eye coordination provided the competitive edge for Australopithecus, and that led to the large brain.
The gap between the last common great–ape ancestor at 8 million years ago and the first member of the hominid family at 4.5 million years ago is unlikely to be filled any time soon. The period of 3 to 8 million years ago happens to be a time interval that is not well represented by geological formations at the earth's surface, and so few fossils are found from this period.
Following Lucy, the line of Australopithecine's developed larger and larger brains, and at various times there were several different species within the genus. Form our point of view, however, the most important event happened about 2.5 million years ago, when the first known member of the genus Homo appeared. Fossils of Homo Habilus (“man the toolmaker”) were discovered in East Africa in the mid–twentieth century. Homo Habilus had a larger brain and size than Lucy. Homo Habilus fossils include crude stone tools. The association of human beings with tool making starts with H. Habilus. Shortly thereafter, another member of our genus, Homo Erectus (“man the erect”) appeared. Homo Erectus fossils are found not only in East Africa but in Asia and the Middle East. Many of the famous fossils — Java Man and Peking Man, for example — were members of this species. Homo Erectus lived at the same time as some of the later Australopithecine's, and survived until about 500,000 years ago. Homo Erectus was the first line of human ancestors to use fire.
Fossils that scientists recognized as anatomically modern human began to appear in rocks about 200,000 years ago. A major debate emerged among paleontologists as to whether anatomically modern humans began in Africa and spread to the rest of the world, or whether they emerged at several different points around the world. This question is still subject of serious discussion. The debate will likely continue unless, major paleontologists can find new fossil hominids.
About the same time yet another type of human being appeared on the sense—Neanderthal man. Sometimes we use the term “Neanderthal” to denote something stupid. This use of the word come from the fact that early studies of Neanderthal fossils concluded that this species walked stooped over, knuckles swinging, and had the thick brow ridge we associate with gorillas. These early suggestions came from a study of a single skeleton of an old man with a bad case of arthritis. Modern studies on other fossils reveal that Neanderthals, although far from being identical to modern human beings, were not all that different. They tended to be short, with thick powerful arms and legs, and a skull that is much more elongated and pulled forward than that of modern Homo Sapiens.
On the other hand, Neanderthals brain were 10% larger than modern humans. They had a complex social structure, cared for elderly and infirm members of their tribe, and performed burial ritual—a fact that suggects the presence of both religious and a language. Thus Neantherdal was not too different from its contemporaries among the anatomically modern humans.
Several mysteries and controversies surround Neanderthal. The first puzzle is how closely Neanderthals are to human beings. Were they, as some scientists claim, a subspecies of Homo Sapiens? Scientists who adopt this view classify Neanderthal as Homo Sapiens Neanderthalenis. On the other hand, the traditional view (and the view of many modern scientists) is that Neanderthal, although our nearest relative, was a separate species. People who hold this view classify Neantherdal as Homo Neantherthalensis, to indicate that it is the same genus, but a different species, than modern humans. In 1997, scientists succeeded in extracting bits of DNA from Neantherdal fossils. The DNA sequences were markedly different from those in modern humans. The results of this work provide the best evidence to date that Homo Sapiens and the Neanderthal are separate species.
The second great mystery about the Neanderthals—is the question of what happened to them. In Europe, where the fossil record is most complete, it appears they flourished till about 35,000 years ago. Then they disappeared rather suddenly. Their disappearance coincided with the entry into Europe of modern Homo Aspens. Several theories try to explain the Neantherthals disappearance. One theory is that they were wiped out by invading members of out own species in what might be described as a prehistoric instance of genocide. Another scientists is that Neanderthals intermarried with the invaders. In that way a certain percentage of the genes of modern human beings are Neanderthal in origin. In order for this is to be true, Neanderthal, by definition must be a subspecies of (as opposed to a separate species from) Homo Sapiens. Finally, some suggest that Neanderthals could not compete with the technically advanced newcomers. Therefore, they just died out. In this case, the Neanderthal did not get wiped out by acts of war, but moved to newer settlements and then just died out. This would explain and is an example of how the displacement of one species by another. This is a common phenomenon in the history of life.
The descent of modern humans beings raised an important point. In the past, many different beings had “human classifications”—many members of the hominid family walked the face of the Earth. For whatever reason, none of them survived to this day expect ourselves. The branch of the family tree leading to human beings, was extensively pruned by the process of natural selection. This fact, scientists believe, made it easier for people in the nineteenth century to discount or misinterpret Darwin, and to believe that the human race was special and not related to the rest of the web of life that exists on our planet.
