Evolution Of Humans

.. this time, East African mammals adapted to drier more open grassland conditions. It was about this time that the new form of human emerged in Africa, a hominid with a much larger brain, excellent vision, and limbs and hips fully adapted to an upright posture. Paleoanthropologists call this hominid Homo Erectus, a human much taller than its diminutive predecessors, standing on average five feet six inches tall, with hands capable of precision gripping and many kinds of tool-making. The skull is more rounded than those of earlier hominids, but still had a sloping forehead and retreating brow ridges.

Homo Erectus was more numerous and more adaptable than Homo habilis, and, on present evidence, was a much longer lived species. Archaeological sites for this species appear at higher, cooler elevations in southern, eastern, and northern Africa. Homo erectus may have been a skilled big game hunter, capable of organizing quite elaborate hunting and foraging expeditions, and using multipurpose axes and cleaving tools. Like all hunters and foragers, Homo Erectus had probably learned to live with natural fires and was not afraid of them. In time, the new hominid may have made a habit of conserving fire, taking advantage of smoldering tree stumps ignited by lightning strikes and other natural causes to light dry bush.

Then came the biggest step of all, the making of fire. Perhaps as early as 1.5 million years ago, Homo erectus may have learned to create fire in East Africa, but scientists still debate the issue. Fire offers not only warmth, but protection against predators and an easy way of hunting game, even insects and rodents. The toxins from many common vegetable foods can be roasted or parched out in hot ashes, allowing people to use a wider range of foods in their diet. Homo erectus was a much larger species than its predecessors meaning that the newcomers needed larger quantities of food to satisfy higher metabolic rates.

This meant they had to range over much larger hunting territories perhaps moving into more open country, where trees were rarer. Perhaps, the bands now carried fire brands with them as a weapon that would enable them to operate safely away from trees, and to occupy dark caves where predators often lurked. It also enabled Homo erectus to settle and live in far cooler environments. It may be no coincidence that the earliest human settlement of Europe and Asia occurred after Homo Erectus could make as well as tame, fire. Somewhere between 200,000 and 300,000 years ago, Homo erectus evolved into Homo sapiens. There is no particular reason to identify why evolution happened during this period and exactly when it happened. In fact, certain fossils from this period are classified as late Homo erectus by some scientists and as early Homo sapiens by others, depending on the scientists belief in what happened.

Even though they are in the same genus and species as modern humans, these early Homo sapiens do not have identical physical traits to modern humans. New fossil evidence suggests that modern man, sometimes called Homo sapiens sapiens (a sub-species of Homo sapiens), first appeared more than 90,000 years ago. There is some disagreement among scientists on whether the hominine fossil record shows a continuous evolutionary development from the first appearance of Homo sapiens to modern humans. This disagreement has especially focused on the place of Neandertals (or Neanderthals), often classified as H. sapiens neanderthalis, in the chain of human evolution.

The Neanderthals (named for the Neander Valley in Germany, where one of the earliest skulls was found) occupied parts of Europe and the Middle East from 100,000 years ago until about 35,000 to 40,000 years ago, when they disappeared from the fossil record. Fossils of additional varieties of early Homo sapiens have been discovered in other parts of the Eurasia. The dispute over the Neanderthals also involves the question of the evolutionary origins of modern human populations, or races. Although a precise definition of the term race is not possible (because modern humans show continuous variation from one geographic area to another), widely separate human populations are marked by a number of physical differences. Most of these differences represent adaptations to local environmental conditions, a process that some scientists believe began with the spread of Homo erectus sometime after a million years ago.

In their view, human development since Homo erectus has been one continuous, in-position evolution, meaning, local populations have remained, changing in appearance over time. What they are trying to say is that the peopling of the world, the spreading of humans, has not changed since Homo Erectus. The Neanderthals and other early Homo sapiens are seen as descending from Homo erectus and are ancestral to modern humans. Other scientists view racial differentiation as a relatively recent phenomenon. In their opinion, the features of the Neanderthals which are a low, sloping forehead, large brow ridge, and a large face without a chin are too primitive for them to be considered the ancestors of modern humans. They place the Neanderthals on a side branch of the human evolutionary tree that became extinct.

According to this theory, the origins of modern humans can be found in southern Africa or the Middle East. Evolving perhaps 90,000 to 200,000 years ago, these humans then spread to all parts of the world, supplanting the local, earlier Homo sapiens populations. In addition to some fragmentary fossil finds from southern Africa, support for this theory comes from comparisons of mitochondrial DNA, a DNA form inherited only from the mother, taken from women representing a worldwide distribution of ancestors. These studies suggest that humans derived from a single generation in southern Africa or southeastern Asia. Because of the tracing through the material line, this work has come to be called the “Eve” hypothesis.

Its results are not accepted by most scientists, who consider the human race to be much older. Whatever the outcome of this scientific disagreement, the evidence shows that early Homo sapiens groups were highly efficient at exploiting the sometimes harsh climates of Ice Age Europe. Further, for the first time in human evolution, hominines began to bury their dead deliberately, the bodies sometimes being accompanied by stone tools, by animal bones, and even by flowers. Although the evolutionary appearance of modern peoples did not dramatically change the basic pattern of adaptation that had characterized the earlier stages of human history, some innovations did take place. In addition to the first appearance of the great cave art of France and Spain some anthropologists have argued that it was during this time that human language originated, a development that would have had profound implications for all aspects of human activity.

About 10,000 years ago, one of the most important events in human history took place, plants were domesticated, and soon after, animals as well. This agricultural revolution set the stage for the events in human history that eventually led to civilization. The next evolutionary stage, is modern humans as we know them. Early Homo sapiens developed the traits that were discussed earlier, and man as we know it, came to exist. But how do we know all these things occurred, and why? It all comes from several very important steps in paleoanthropology.

The earliest human skeleton ever found was discovered in 1974 in a remote region of Ethiopia, a very well preserved A. afarensis fossil. Nicknamed Lucy, paleoanthropologists have found out periods of millions of years through her, and have used that knowledge to speculate on other discoveries. Footprints, bones, teeth, etc. are all used to help piece together the puzzle. Human evolution may have reached a dead end, foreseeable for a while at least.

Despite the enormous changes that we have wreaked on our environment, major evolutionary changes in humans will not occur in the distant future. Scientists dismiss the idea that the species is “going somewhere” under natural selection and then describe how most successful species are stable through their geological lifetimes. Furthermore, given the relative pace of cultural change and lack of isolation of human populations, there is little chance for a new different human species. Modern understanding of human evolution rests on known fossils, but the picture is far from complete. Only future fossil discoveries will enable scientists to fill many of the blanks in the present picture of human evolution. Employing sophisticated technological devices as well as the accumulated knowledge of the patterns of geological deposition, anthropologists are now able to pinpoint the most promising locations for fossil hunting more accurately.

In the years ahead this will result in an enormous increase in the understanding of human biological history. Bibliography Edgar, Blake, and Johanson, Donald. From Lucy to Language. New York: Simon and Schuster, 1996. Fagan, Brian. The Journey from Eden – The Peopling of Our World. London: Thames and Hudson, 1990.

Gallagher, Richard B., Michael Murphy, and Luke ONeill. “What Are We? Where Did We Come From? Where Are We Going?” Science 14 Jan. 1994: 181-183 Gibbons, Ann, “When It Comes to Evolution, Humans Are in the Slow Class.” Science 31 March. 1995: 1907-1908 “Human Evolution.” Microsoft Encarta. 1996 ed. [CD-ROM] Leakey, Richard.

The Origin of Humankind. New York: Basic Books, 1994. Lemonick, Michael “New Thinking on Human Evolution” Time 14 March 1994: 81-87.

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