THEORY OF EVOLUTION Evolution explains the diversity

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THEORY OF EVOLUTIONEvolution explains the
diversity relatedness of life on earth 

• Standard Sets 7,8 Evolution (Population
  Genetics and Speciation)

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The Idea of Evolution Descent with Modification

• Living things share common characteristics
  because they are descended from common ancestors.
• Living things are diverse because each species is
  adapted to its own habitat and way of life.

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Who was Charles Darwin?

• 1831, became an unpaid naturalist on board the
  HMS Beagle.
• Observed plants and animals on the Galapagos
  Islands

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Darwins Investigations of the Galapagos Islands

• Each island had its own species of giant tortoise
  in response to the type of vegetation found on
  each island.
• Marine iguanas (only found on the Galapagos) have
  similarities to the land iguanas found in South
  America.
• The 13 species of finch on the islands are
  similar except for each having a beak adapted
  to a particular way of life.

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CHARLES DARWIN DEVELOPS A THEORYOn the Origin
of Species by Means of Natural Selection

• Darwins Observations
• 1) Individuals in a population are different
  from one another.
• 2) Organisms produce more offspring than the
  environment can support.
• 3) In spite of the large numbers of offspring,
  population size tends to remain the same.
• 4) Environments are constantly changing.

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CHARLES DARWIN DEVELOPS A THEORYOn the Origin
of Species by Means of Natural Selection

• 1) In each population there is a competition for
  available resources only some organisms survive.
• 2) Individuals with favorable variations are more
  likely to survive and reproduce. (survival of the
  fittest) 
• 3) The favorable variation that allows survival
  accumulates and eventually appears in the entire
  population. (adaptation)

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NATURAL SELECTION AT WORKNatural Selection
Provides a Mechanism for Evolution

• Natural Selection Check List
• aVariation exists between individuals.
• aOverproduction/struggle for survival.
• aSurvival of the fittest. (survive and
  reproduce)
• aAdaptation increases in the population.

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The maintenance of variation is beneficial
because populations that lack variation may not
be able to adapt to new conditions and may become
extinct.

• What causes Variation?
• Mutations and genetic recombination.
• Natural Selection reduces, but does not
  eliminate, the range of phenotypes.

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A Mutation is a change in the DNA sequence

• Spontaneous mutations affect the amino acid
  sequence of a protein. This new protein may be
  beneficial, harmful or have no affect at all.

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New mutations are constantly being generated in a
gene pool.

• A gene pool is all the genes in a population.
• Mutation is an important source of genetic
  variation within a gene pool.

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How does Natural Selection determine which
genetic traits are passed on?

• Beetles with brown genes escaped predation and
  survived to reproduce more frequently than
  beetles with green genes, so that more brown
  genes got into the next generation.

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Over the past 60 years penicillin has been used
to treat bacterial infections.

• Now, however, penicillin has become ineffective
  at killing many types of bacteria. What helped
  the bacteria become more resistant?

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Organisms Differ in Fitness

• What is Fitness?
• The most fit organisms reproduce and leave more
  offspring than the less fit organisms.
• Natural Selection is the change caused by the
  survival and reproduction of specific
  individuals.

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Natural selection causes change within populations

• Organisms best suited to their environment
  survive and pass on their traits through their
  genes.
• The frequency of these genes builds up in the
  population.
• When this genetic trait builds up in the
  entire population it is called an
  adaptation.
  

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Natural Selection determines the differential
survival of groups of organisms

• An adaptation is a trait that helps an organism
  be more suited to its environment.
• Natural selection results in the adaptation of
  populations to their specific environments.

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Industrial MelanismAn Example of Natural
Selection

• The Peppered Moths of Manchester, England come in
  two varieties, one darker than the other.
• Before the industrial revolution, the dark moth
  was rare however, during the industrial
  revolution the light moth seldom appeared.
• Why?

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Natural selection acts on phenotype, not
genotype.

• Natural Selection reduces, but does not
  eliminate, the range of phenotypes.
• Natural selection works directly on the
  expression or appearance of an inherited trait
  rather than on the gene combination that produces
  that trait.

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Selection against unfavorable recessive alleles
is slow

• Alleles that are lethal in a homozygous recessive
  individual may be carried in a heterozygote and
  thus maintained in a gene pool.

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Genetic Drift Drastic change in a population due
to a chance event.

• Genetic drift works to reduce the variation in a
  population.
• Genetic Drift works the best in small populations.

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Genetic Drift at Work

• An example of genetic drift is the Founder Effect
  the colonization of a new area by a few
  individuals. These new individual may not
  represent the original population.

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SPECIATIONSplitting of one species into two
species
Isolation leads to species formation

• Geographic isolation physically separates groups
  within a population. 
• When populations become separated, different
  environmental pressures can create differences
  between the two groups.

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Allopatric speciation is created by a geographic
barrier
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Sympatric speciation is when populations develop
a genetic difference

• If these differences become so extreme that the
  two populations can no longer interbreed they
  can, at that point, be considered two different
  species.

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Reproductive isolation keeps newly forming
species from interbreeding
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Why is species diversity beneficial?

• Increased diversity among species increases the
  chances that some species will adapt to survive
  future environmental changes.

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Fossils Tell The Story Fossils - preserved or
mineralized remains or traces of an
organism that lived long ago.
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THE FOSSIL RECORD

• Provides evidence for succession of life over
  time (example the evolution of the horse).
• - Provides transitional links between groups
  of organisms (example Archaeopteryx - links
  reptiles to birds).

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Biological diversity within a species is
difficult to study because preserved organic
material is rare as a source of DNA in fossils.

• The study of biological diversity from the fossil
  record is generally limited to the study of the
  differences among species instead of the
  differences within species.

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Biological Diversity and the Fossil
RecordNumbers and Geologic Age of Fossil Species

• The width of the column represents the diversity
  of the group. The depth reflects the age of the
  group.
• The top line is the most current time period.

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What is a Mass Extinction?

• Periods when a large percentage of existing
  species becomes extinct within a relatively short
  period of time.
• Is All life wiped out during a Mass Extinction?
• No, but one mass extinction lost as much as 95
  of the life on earth.

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What can cause a Mass Extinction?

• Environmental changes, diseases, loss of
  resources, predation, extraterrestrial events 

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What do Mass Extinction do in terms of evolution?

• - Mass Extinctions allow evolution to take a new
  direction.  
• - Episodes of speciation are the most dramatic
  after a mass extinction has cleared the way for
  new species take over recently vacated areas.