Human evolution
Human evolution is the lengthy
process of change by which people originated from apelike ancestors. Scientific
evidence shows that the physical and behavioral traits shared by all people
originated from apelike ancestors and evolved over a period of approximately
six million years.
One of the earliest defining
human traits, bipedalism -- the ability to walk on two legs -- evolved over 4
million years ago. Other important human characteristics -- such as a large and
complex brain, the ability to make and use tools, and the capacity for language
-- developed more recently. Many advanced traits -- including complex symbolic
expression, art, and elaborate cultural diversity -- emerged mainly during the
past 100,000 years.
Humans are primates.
Physical and genetic similarities show that the modern humanspecies, Homo sapiens, has a
very close relationship to another group of primate species, the apes. Humans
and the great apes (large apes) of Africa -- chimpanzees (including bonobos, or
so-called “pygmy chimpanzees”) and gorillas -- share a common ancestor that
lived between 8 and 6 million years ago. Humans first evolved in Africa, and
much of human evolution occurred on that continent. The fossils of early humans
who lived between 6 and 2 million years ago come entirely from Africa.
Most scientists currently
recognize some 15 to 20 different species of early humans. Scientists do not
all agree, however, about how these species are related or which ones simply
died out. Many early human species -- certainly the majority of them – left no
living descendants. Scientists also debate over how to identify and classify
particular species of early humans, and about what factors influenced the
evolution and extinction of each species.
Early humans first migrated out
of Africa into Asia probably between 2 million and 1.8 million years ago. They
entered Europe somewhat later, between 1.5 million and 1 million years. Species
of modern humans populated many parts of the world much later. For instance,
people first came to Australia probably within the past 60,000 years and to the
Americas within the past 30,000 years or so. The beginnings of agriculture and
the rise of the first civilizations occurred within the past 12,000 years.
Paleoanthropology
Paleoanthropology is the
scientific study of human evolution. Paleoanthropology is a subfield of
anthropology, the study of human culture, society, and biology. The field
involves an understanding of the similarities and differences between humans
and other species in their genes, body form, physiology, and behavior.
Paleoanthropologists search for the roots of human physical traits and
behavior. They seek to discover how evolution has shaped the potentials,
tendencies, and limitations of all people. For many people, paleoanthropology
is an exciting scientific field because it investigates the origin, over
millions of years, of the universal and defining traits of our species.
However, some people find the concept of human evolution troubling because it
can seem not to fit with religious and other traditional beliefs about how
people, other living things, and the world came to be. Nevertheless, many
people have come to reconcile their beliefs with the scientific evidence.
Early human fossils and
archeological remains offer the most important clues about this ancient past.
These remains include bones, tools and any other evidence (such as footprints,
evidence of hearths, or butchery marks on animal bones) left by earlier people.
Usually, the remains were buried and preserved naturally. They are then found
either on the surface (exposed by rain, rivers, and wind erosion) or by digging
in the ground. By studying fossilized bones, scientists learn about the
physical appearance of earlier humans and how it changed. Bone size, shape, and
markings left by muscles tell us how those predecessors moved around, held
tools, and how the size of their brains changed over a long time. Archeological
evidence refers to the things earlier people made and the places where scientists
find them. By studying this type of evidence, archeologists can understand how
early humans made and used tools and lived in their environments.
The process of
evolution
The process of evolution
involves a series of natural changes that cause species (populations of
different organisms) to arise, adapt to the environment, and become extinct.
All species or organisms have originated through the process of biological
evolution. In animals that reproduce sexually, including humans, the term species
refers to a group whose adult members regularly interbreed, resulting in
fertile offspring -- that is, offspring themselves capable of reproducing.
Scientists classify each species with a unique, two-part scientific name. In
this system, modern humans are classified as Homo sapiens.
Evolution occurs when there is
change in the genetic material -- the chemical molecule, DNA -- which is
inherited from the parents, and especially in the proportions of different
genes in a population. Genes represent the segments of DNA that provide the
chemical code for producing proteins. Information contained in the DNA can
change by a process known as mutation. The way particular genes are
expressed – that is, how they influence the body or behavior of an organism --
can also change. Genes affect how the body and behavior of an organism develop
during its life, and this is why genetically inherited characteristics can
influence the likelihood of an organism’s survival and reproduction.
Evolution does not change any
single individual. Instead, it changes the inherited means of growth and
development that typify a population (a group of individuals of the same
species living in a particular habitat). Parents pass adaptive genetic changes
to their offspring, and ultimately these changes become common throughout a
population. As a result, the offspring inherit those genetic characteristics
that enhance their chances of survival and ability to give birth, which may
work well until the environment changes. Over time, genetic change can alter a
species' overall way of life, such as what it eats, how it grows, and where it
can live. Human evolution took place as new genetic variations in early
ancestor populations favored new abilities to adapt to environmental change and
so altered the human way of life.
REFERENCE
http://humanorigins.si.edu/resources/intro-human-evolution
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