Evolution Unit

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Evolution Unit

• 15-1 Notes Adaptations and Natural Selection

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Adaptations

• A hereditary characteristic that helps an
  organism survive and reproduce in its
  environment.

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Fitness

• Measure of ability to survive and produce more
  offspring relative to other members of a
  population

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Animal Observation
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So how did these organisms become so well adapted
to their environment?
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Darwins Explanation

• Darwin proposed that animals evolved to fit their
  environments.

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Evolution

• The change in a population of organisms over time
  

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Darwins Explanation

• Darwin realized that animals have many offspring
  and some dont survive.
• The survivors are better suited to their
  environment.

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He called this process.
Natural Selection
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Natural Selection

• Mechanism by which the environment is the
  selective agent
• Mechanism by which evolution occurs

Darwin said that in nature, environment creates
selective pressure
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Steps of Natural Selection

• Overproduction
• -organisms have many offspring, but not all
  will survive.

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Steps of Natural Selection

• 2. Genetic Variation
• --Individuals vary within a population
• --New traits appear due to genetic mutations

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Steps of Natural Selection

• 3. Struggle to Survive
• --Organisms compete for resources (food, water,
  shelter, and mates)
• --Organisms have to get away from predators

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Steps of Natural Selection

• 3. Struggle to Survive
• --Some adaptations allow organism to survive at
  higher rate and individuals are naturally
  selected to survive and produce offspring

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Steps of Natural Selection

• 4. Descent with Modification
• --Organisms with the best adaptations will
  survive and reproduce passing these good traits
  down to their offspring

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• Natural Selection acts on phenotypes not
  genotypes
• As environment changes, different traits will
  become beneficial.

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Examples of Natural Selection
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Insects become resistant to insecticides.

• Insecticide kills off most insects.

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• Those insects that survive have a gene that makes
  them resistant.

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• Resistant insects reproduce with other resistant
  insects.

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• Their offspring have the resistant gene.
• Insecticides dont work very well over time!

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Other examples of evolution

• Bacteria become resistant to antibiotics
• Dont take antibiotics unless you have a
  bacteria infection!

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Other Examples of Natural Selection

• Peppered Moths in England
• There were more light moths
• (on light trees) before 1850.
• There were more dark moths
• (on light trees) after 1850.