Darwins Evolutionary Theory

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Darwins Evolutionary Theory
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The THEORY Of Evolution
Evolution (like many scientific discoveries) is
still a theory, and is not a proven scientific
fact -- A theory is a well-supported, testable
explanation of phenomena that have occurred in
the natural world -- because we will never be
able to see the process of evolution happening
(it takes too long), we will never be able to
prove the evolution of a single species However,
because we are in science class, it is important
not just to understand what scientists believe
happened, but understand the SCIENTIFIC reasoning
behind why evolution makes scientific sense
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What is Evolution?
More importantly than what evolution is, it is
important to understand what evolution is NOT --
Evolution is NOT, humans descended from
monkeys -- Evolution IS based on several
scientific facts, we can assume that humans and
monkeys at one point in history had a common
ancestor Evolution, in its simplest definition,
is change over time -- evolution is the process
by which modern organisms have descended from
ancient organisms
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Macroevolution vs. Microevolution
There are two kinds of evolution which relate to
one another Macroevolution the large-scale
evolution of how a new species develops from an
existing species -- this is the classic
evolution that we think of Microevolution the
small-scale genetic changes (often caused by
mutation) that the offspring of one generation
inherits from previous generations -- this leads
to what we called genetic variability If enough
genetic variability occurs between generations,
eventually the two generations will no longer be
genetically compatible and will be unable to
mate, creating a new species -- therefore,
microevolution causes macroevolution
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Charles Darwin
Charles Darwin was a British scientist during the
mid -1800s -- in 1831, he set sail around the
world on the boat the H.M.S. Beagle -- during
stops on the Beagle, Darwin went onshore and
collected samples of species and made
observations -- Darwin discovered an
extraordinary diversity of life on Earth From
his discovery of the diversity, Darwin theorized
as to how the great diversity of species on Earth
developed
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What Darwin Observed
Organisms seem remarkably well-suited to their
environment -- all organisms were able to
survive to reproduce in whatever conditions they
lived Similar environments in different locations
contained different species of organisms -- the
grasslands environment in Australia, Argentina,
and England were all similar, but all had
different animals -- for example, why are
there no kangaroos in Argentina, even though
the environmental conditions were almost
identical to Australia?
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What Darwin Observed, continued
Some fossilized organisms looked similar to
modern organisms, while some looked completely
different -- Darwin wondered what happened to
the species that had died out -- Darwin also
wondered how modern species were related to
those fossils of organisms that no longer existed
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The Galapagos Islands
Most of Darwins important discoveries came from
observations of the organisms of the Galapagos
Islands -- Tortoises had specific shell-shapes
based on the island that they lived on -- Birds
had different shaped-beaks based on the island
on which they lived -- Mockingbirds from
different islands looked different On the way
home, Darwin wondered if all of the different
varieties of each species all came from the same
common ancestor. . .
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Fighting Traditional Beliefs
When Darwin returned to England, many people
disagreed with and mocked his theories The
traditional view was that Earth and all life were
only a few thousand years old and that since the
original creation, no living species had
changed Even when the fossil record challenged
this idea, Darwins opponents changed their ideas
to say that there were several periods of
creation which were preceded by catastrophic
events that killed off all previous life. .
. Finally, studies (not all of evolution) of
other scientists helped Darwin to gain support
for his theory. . .
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Hutton and Lyells Geologic Theories
In 1795 James Hutton published a theory of how
geologic forces shaped Earth -- rocks are pushed
up to form mountains, and also eroded and
buried -- most geologic forces take millions of
years, therefore the Earth must be at least
millions of years old In the early 1800s,
Charles Lyell published a book that showed how
Earth is constantly changing -- the geologic
process that shaped Earth in the past are still
occurring From this, Darwin theorized that
evolution could have happened over millions of
years and is still occurring
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Thomas Malthus and Population Growth
In 1798, Malthus argued that if the human
population of the world continued to grow
unchecked, there would eventually not be enough
resources (or food) for everyone -- the only
factors that controlled human population growth
were war, famine, and disease Darwin took this
theory into other organisms, to which he said it
factored even more strongly -- plants and other
animals produce more offspring than humans, and
very few survive The big question from this for
Darwin was what determines which individuals
survive to reproduce and which ones dont
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Jean Lamarcks Theory
Before Darwin, Jean-Baptiste Lamarck published
his own theory of how traits are passed on to
offspring, causing evolution Lamarck proposed
that organisms acquire traits during their
lifetime and pass those traits onto their
offspring -- for example, if a human works out
and gets big muscles during his lifetime, than
all of his offspring will have big muscles This
is known as the theory of evolution of acquired
traits also called the theory of use and
disuse -- obviously, this theory does not make a
lot of sense
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Image of Lamarcks Theory
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On the Origin of Species
In 1859, almost 30 years after the voyage of the
Beagle, Darwin published a book with his theory
of evolution -- he title the book On the Origin
of Species In his book, he presented several
ideas, including -- evolution had taken place
for millions of years -- evolution is still
occurring -- the mechanism for evolution is
called natural selection
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Natural Variation
Darwin argued that individuals of the same
species are all different -- some cows give more
milk, some plants give bigger fruit Darwin
called this observation natural variation Darwin
also noticed that farmers breed individuals to
get the most desirable trait (most milk, biggest
fruit) -- Darwin called this artificial
selection In artificial selection, nature
provided the variation and humans selected the
variations that they found useful to pass on to
the offspring
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Natural Selection
Darwin argued that nature does the same thing as
humans, based on the following ideas Struggle for
Existence -- organisms of the same species fight
for the same resources Survival of the
Fittest -- the organisms best adapted to their
environment will compete the best for the
resources and therefore will survive to
reproduce -- over time, natural selection will
select for individuals with the greatest fitness
for their environment
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Common Descent
Because of natural selection, two organisms may
end up competing for different niches in their
environment -- one set of individuals is better
at exploiting one resource and another set is
better at using another resource Over time, the
sets of individuals are different enough that
they no longer need the other resource Eventually,
the generations become so different that they
become new species This is known as common
descent According to common descent, all species
came from common ancestors
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Darwins Evolutionary Theory

• Individual organisms of the same species differ
  from one another, some of this variation is
  inherited.
• Organisms in nature produce more offspring than
  can survive
• Members of each species compete for limited
  resources
• Each individual is unique, and has different
  advantages to compete
• Individuals best suited to their environment
  survive and reproduce most successfully. These
  characteristics that make them survive are passed
  onto offspring.
• Species change over time
• Species alive today descended with modifications
  from species alive in the past.
• All organisms on Earth are united by common
  descent