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_Evolution _
By: Anonymous
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 paleoanthropologists 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 Snell 2 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 humans 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 Snell 3 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.
Snell 4 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 Snell 5
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 scientists 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. Snell 6 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 Snell 7 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.
Word Count: 3008
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