Essay, Research Paper: Evolution Of Humans 


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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 include 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
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, tusklike 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 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. 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
under 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 the 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 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.

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 O’Neill. “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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