FREE ESSAY ON EVOLUTION

EVOLUTION

HUMAN EVOLUTION
Human evolution is the biological and cultural development of humans. A human is any
member of the species Homo sapiens, meaning "wise man." Since at least the Upper
Paleolithic era, some 40,000 years ago, every human society has devised a creation myth
to explain how humans came to be. Creation myths are based on cultural beliefs that have
been adopted as a legitimate explanation by a society as to where we came from. 
The science of paleoanthropology, which also tries to create a narrative about how humans
came to be, is deeply technical. Paleoantropology is the science of the evolution of
humans, and it is the base of all research in that field. Humans have undergone many
different changes during the last hundred million years, and it is the
paleoanthropologist's job to identify and explain these changes. In this research paper I
will examine: human physical traits that define their species, human origins from
pre-humans to modern humans, major discoveries and the history of human evolution, and
what the future may hold as far as evolution for the human species.
Homo sapiens are the only living representative of the family Hominidae. The Hominidae,
or hominids are a group of upright walking primates with relatively large brains. So all
humans are hominids, but not all hominids could be called human. Next all humans are
primates. The mammalian order of primates includes about 180 species of prosimians (lemur
like animals), monkeys, apes, and ourselves. Primates are unusual mammals for they have
evolved such distinctive traits as highly developed binocular vision, mobile fingers and
toes with flat nails instead of claws, a shortened snout with a reduced sense of smell,
and large brains relative to body size. If primates are unusual for mammals, humans are
even more unusual for primates. We are essentially elaborated African apes. We share
almost 99 percent of our genetic material with chimpanzees. Yet we have several traits
that are very different. Two legged walking, or bipedalism seems to be one of the
earliest of the major hominine characteristics to have evolved. To 
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accommodate this strange position, we have developed a specialized pelvis, hip and leg
muscles, and an S-shaped vertebral column. Because these changes can be documented in
fossil bone, bipedalism is seen as the defining trait of the sub family Homininae.
Much of the human ability to make and use tools and other objects stem from the large
size and complexity of the human brain. Most modern humans have a braincase volume of
between 79.3 and 91.5 cubic inches. In the course of human evolution the size of the
brain has more than tripled. The increase in brain size may be related to changes in
hominine behavior. Over time stone tools, and other artifacts became increasingly
numerous and sophisticated. It is likely that the increase in human brain size took place
as part of a complex interrelationship that included the elaboration of tool use and tool
making, as well as other learned skills, which permitted our ancestors to be increasingly
able to live in a variety of environments. 
The earliest hominine fossils show evidence of marked differences in body size, which may
reflect a pattern of the different sexes in our early ancestors. The bones suggest that
females may have been 3 to 4 ft in height and about 60 to 70 lb. in weight, while males
may have been somewhat more than about 5 ft tall, weighing about 150 lb. The reasons for
this body size difference are disputed, but may be related to specialized patterns of
behavior in early hominine social groups. This extreme difference between sexes appears
to disappear gradually sometime after a million years ago. 
The third major trend in hominine development is the gradual decrease in the size of the
face and teeth. All the great apes are equipped with large, tusk-like canine teeth that
project well beyond the level of the other teeth. The earliest hominine remains possess
canines that project slightly, but those of all later hominines show a marked reduction
in size. Also, the chewing teeth, the premolars and molars, have decreased in size over
time. Associated with these changes is a gradual reduction in the size of the face and
jaws. In early hominines, the face was large and positioned in front of the braincase. As
the teeth became smaller and the brain expanded, the face became smaller and its position
changed. Thus, the relatively small face of modern humans is located below, rather than
in front of, the large, expanded braincase. 
Evidence of immediate relatives of the human species begins about five million years ago
with the Australopithecus genus and leads in to the primitive Homo genus to modern
humans. The nature of the human's evolution before that is uncertain, but scientists have
hypothesized some ideas. What they do know is that between 7 and 20 million years ago,
primitive apelike animals were widely distributed on the 
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African and later on the Eurasian continents. Although many fossil bones and teeth have
been found, the way of life of these creatures, and their evolutionary relationships to
the living apes and humans, remain matters of strong disagreement among scientists. One
of these fossil apes, known as Sivapithecus, appears to share many features with the
living Asian great ape and the orangutan, whose direct ancestor it may well be. None of
these fossils, however, offers convincing evidence of being on the evolutionary line
leading to the hominid family generally. But they do help paint a picture of what early
human relatives could have been like. 
The convincing fossil evidence for human evolution begins with Australopithecus. Fossils
of this genus have been discovered in a number of sites in eastern and southern Africa,
and were first identified in South Africa in 1924. Earliest fossils show them existing
about 3.9 million years ago, and the genus flourished until it seemed to have become
extinct about 1.5 million years ago. All the australopithecines were efficiently bipedal
and thus indisputable hominines. In details of their teeth, jaws, and brain size,
however, they differ enough among themselves to warrant division into four species: A.
afarensis, A. africanus, A. robustus, and A. boisei. 
The earliest australopithecine is A. afarensis, which lived in eastern Africa between 3
and 3.9 million years ago. Found in the Afar region of what is now Ethiopia and in
Tanzania, A. afarensis had a brain size a little larger than those of chimpanzees. Some
of the species possessed canine teeth somewhat more projecting than those of later
hominines. No tools of any kind have been found with A. afarensis fossils. Between about
2.5 and 3 million years ago, A. afarensis apparently evolved into a later
australopithecine, A. africanus. Known primarily from sites in southern Africa, A.
africanus possessed a brain similar to that of its predecessor. However, although the
size of the chewing teeth remained large, the canines, instead of projecting, grew only
to the level of the other teeth. As with A. afarensis, no stone tools have been found in
association with A. africanus fossils. By about 2.6 million years ago, the fossil
evidence reveals the presence of at least two, and perhaps as many as four, separate
species of hominines. An evolutionary split seems to have occurred in the hominine line,
with one group evolving toward the genus Homo, and finally to modern humans, and the
others developing into australopithecine species that eventually became extinct. 
The australopithecine species that eventually became extinct includes the robust
australopithecines, A. robustus, that lived in southern Africa, and A. boisei, found only
in eastern Africa. 
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The robust australopithecines represent an unusual adaptation because their principal
difference from other australopithecines lies in the large size of their chewing teeth,
jaws, and jaw muscles. The robust australopithecines became extinct about 1.5 million
years ago. 
Although scientists do not agree, many believe that after the evolutionary split that led
to robust australopithecines, A. africanus evolved into the genus Homo. This was a
species called Homo habilis, or handy man. Appearing about 2.5 million years ago, the new
hominid probably didn't look terribly different from its predecessors, but it had a
somewhat larger brain. And, perhaps as a result of some mental connection other hominids
were unable to make, Homo habilis figured out for the first time how to make tools.
Earlier species had used tools like bits of bone for digging, or sticks for fishing
termites out of their mounds (something modern chimps still do). But Homo habilis
deliberately hammered on rocks to crack and flake them into useful shapes. The tools were
probably not used for hunting, as scientists once thought. Homo habilis, on average, was
less than 5 ft. tall and weighed less than 100 lbs., and it could hardly have competed
with the lions and leopards that stalked the African landscape. 
The hominids were probably scavengers instead, supplementing a mostly vegetarian diet
with meat left over from predators' kills. Even other scavengers like hyenas, jackals and
such were stronger and tougher than early humans. But Homo habilis presumably had the
intelligence to anticipate the habits of predators and scavengers, and probably used
tools to butcher leftovers quickly and get back to safety. Their adaptations to the
rigors of prehistoric African life enabled members of the Homo habilis species to survive
for 500,000 years or more, and at least one group of them apparently evolved, around 2
million years ago. 
Around 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 
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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 also 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 rare. Perhaps, the bands now carried firebrands 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, others, depending on the scientist's belief in what
happened, classify certain fossils from this period as late Homo erectus by some
scientists and as early Homo sapiens. 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 (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. 
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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 mitochondria 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. Most scientists, who consider the human race to be much older, do
not accept its results. 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 
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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.