The Theory of Evolution

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Chapter 13 The Theory of Evolution
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13-1 The Theory of Evoltuion by Natural Selection
The idea that life evolves was first Proposed by
Lucretius 1900 years ago!
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His idea was not fully considered until The
middle of the 1800s.
In 1859, the English naturalist Charles Darwin
published convincing Evidence that species
evolve, and He proposed a reasonable
mechanism Explaining how evolution occurs.
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Like all scientific theories, the theory Of
evolution has developed over Decades of
experimental data.
Today almost all scientists accept That evolution
is the basis for the Diversity of life on Earth.
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The theory of evolution has 4 parts

• Variation exists with the genes of
• Every population of species
• (the results of mutation)

2) In a particular environment, some Individuals
of a population or species Are better suited to
survive and Have more offspring than others.
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3) Over time, the traits that make Certain
individuals of a population Able to survive and
reproduce Tend to spread in that population.
4) There is clear proof from fossils And many
other sources that living Species evolved from
organisms That are extinct.
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In 1831, Darwin became the Naturalist for the
naval voyage of The HMS Beagle.
The purpose of the voyage was to Survey the
coast of South America.
Little did anyone know, that voyage Would change
the world.
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During his voyage on the Beagle, Darwin found
evidence that challenged The traditional belief
that species Are unchanging.
As Darwin visited the many places On his voyage,
he saw things that Seemed as if they could only
be Explained by a process of gradual change.
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On the Galapagos Islands, Darwin Discovered
different varieties of Finches that had different
beaks.
The birds looked similar, but had Evolved beaks
that suited the Environment where they ate.
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When Darwin returned from his Voyage, he
continued his lifelong Study of plants, animals,
and geology.
He didnt report his findings called evolution
until much later.
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In Biology, a population consists of all The
individuals of a species that Live together in
one place At one time.
For example, the alligators in the Everglades
make up a population Because they live together
in A particular area.
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After reading an essay by Thomas Malthus, Darwin
made a key association,
Individuals that have physical or Behavioral
traits that better suit Their environmental are
more likely To survive and reproduce than
those That do not have such traits.
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Darwin called this process by which Populations
change in response To their environmental natural
selection.
The changing of a species that results In its
being better suited to its Environment is called
adaptation.
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In 1859, Darwin finally wrote down His ideas of
evolution and natural Selection in a book
called On the Origin of Species by Means of
Natural Selection
Many people were deeply disturbed by It,
including the church because it Hints that
humans evolved from apes.
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Darwins ideas have been updated
Natural selection causes change Within population.
Such as, broccoli, cauliflower, Brussels
sprouts, and cabbage all Come from the same
plant!
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In other words, natural selection Causes the
frequency of certain Alleles in a population to
increase Or decrease over time.
Isolation leads to species formation.
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Isolation is the condition in which 2
populations of the same species Cannon breed with
one another.
This happens all the time, and is why There are
many different types of Squirrels, and is the
reason that Darwin saw different types of The
same bird!
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Extinction leads to species replacement.
Over long periods of time, events such As climate
changes and natural Disasters result in some
species Becoming extinct, which means That they
disappear permanently.
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13-2 Evidence of Evolution
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Fossils provide an objective record Of evolution.
A fossil is the preserved or Mineralized remains
or imprint Of an organism that lived long ago.
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Today Darwins theory is almost Universally
accepted, based on a Large body of supporting
evidence, Most scientists agree on the Following
3 points
1) Earth is about 4.5 billion years old.
2) Organisms have inhabited Earth for Most of
its history.
3) All organisms living today evolved From
earlier, simpler life-forms.
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Although the fossil record will never Be
complete, it presents strong Evidence that
evolution has Taken place.
Paleontologists, scientists that study Fossils,
can determine that age of Fossils fairly
accurately by using Radiometric dating.
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Biological molecules contain a record Of
evolution.
A common ancestor is a species From which 2 or
more species Have diverged.
A phylogenetic tree shows how organisms are
related through evolution.
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Anatomy and development Suggest common ancestry.
Comparisons of the anatomy of Different types of
organisms often Reveal basic similarities in
Body structures.
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For example, sometimes bones (or other
structures) are present In an organism but are
reduced in Size and either have no use or Have a
less important function.
Such structures are considered to be Evidence of
an organisms Evolutionary past.
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These structures are called Vestigial structures.
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Does evolution occur in spurts?
The model of evolution in which Gradual change
over a long period of Time leads to species
formation Is called gradualism.
The model of evolution in which periods Of rapid
change in species is separated By periods of no
change is called Punctuated equilibrium.
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13-3 Examples of Evolution
Darwin wrote Can we doubt that Individuals
having any advantage, However slight, over
others, would Have the best chance of surviving
And of procreating their kind?
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There are 5 main elements to Natural Selection
1) All species have genetic variation.
2) The environment presents many Different
challenges to an individuals Ability to
reproduce.
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3) Organisms tend to produce more Offspring than
their environment Can support thus, individuals
of a Species often compete with One another to
survive.
4) Individuals within a population that Are
better able to cope with the Challenges of their
environment tend To leave more offspring than
those Less suited to the environment.
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5) The traits of the individuals Best suited to
a particular Environment tend to increase In a
population over time.
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The key lesson scientists have learned About
evolution is that the Environment dictates the
direction And amount of change.
A well studied example of natural Selection in
action is Industrial melanism.
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Industrial melanism is the darkening Of
populations of organisms over Time in response to
industrial pollution.
The best known case is the European Peppered
Moth.
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The formation of new species Begins with small
changes.
The accumulation of differences Between groups is
called divergence.
Biologists call the process by which New species
form speciation.
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Overtime, populations of the same Species that
differ genetically Because of adaptations to
different Living conditions become
what Biologists call ecological races.
Eventually races may become so Different that
they can no longer Interbreed successfully,
biologists Then consider them a new species.
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What keeps a new species separate?
Reproductive isolation is the inability Of
formerly interbreeding groups To mate or produce
fertile offspring.
This may happen due to geographical Reasons,
environmental reasons, Or the fact that hybrid
offspring Are not attracted to each other.
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THE END