Theory of Natural Selection:

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Theory of Natural Selection

• Darwins explanation for HOW evolution works.

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VOYAGE OF THE HMS BEAGLE 1831 - 1836
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7 Steps to Natural Selection

• Overpopulation (overproduction)- animals produce
  more offspring than survive.
• Variation- animals of the same species are
  different
• Change in environment-
• a) Biological - food, predators, shelter, etc.
• b) Physicalwater, oxygen, temp, etc.

• 4. Struggle for existence- competition for water,
  food, shelter
• 5. Survival of the fittest- the best adapted
  strongest tend to survive longer produce more
  offspring
• 6. Inheritance- favored/best fit/selected
  variations (characteristics) are passed on to
  offspring.
• 7. New species arise- selected individuals grow
  in number and become a new species that cannot
  reproduce with original species

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Darwins Observation 13 or so species of
finches on different Galapagos islands these
finches resembled the South American (mainland)
finches more than say finches in Asia.
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Same process for other species!
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Jean Baptiste Lamarck the outcaste!

• used the fossil record as evidence
• proposed a theory of evolution where organisms
  became better and better
• Mechanism - use and disuse leads to
• inheritance of acquired characteristics (you
  acquire a phenotype in your lifetime and pass
  it on to your kids)
• also means environmental influences can be
  inherited
• DONT BE LAMARCKIAN!

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Hugo DeVries Mutation Theory

• New Characteristics suddenly appear
• Mutation
• These can be passed on and may or may not help a
  species become more fit
• Helped to modify Darwins Theory

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Evidences for Darwins theory

• Fossil record - horse lab
• Homologous Structures
• Vestigial structures
• Artificial selection

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• Natural selection in action the evolution of
  insecticide-resistance occurs in nature -
  individuals with the best fit genes that can
  resist the insecticide will survive.

Fig. 22.12
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B) HOMOLOGIES

• Similarities in characteristics resulting from
  common ancestry is known as homology.
• 1) Homologous Structures Same skeletal elements,
  but different functions

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Human hand, cat limb, whale flipper, bat wing -
they all have the same basic bone structure and
design So they have ALL evolved from a common
ancestor with a similar limb design.
B) HOMOLOGIES
HOMOLOGOUS STRUCTURES
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C) Vestigial organs, structures that are not
used, but which had important functions in
ancestors - still retained in descendents, so
evolution/change has occurred.
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C) Vestigial organs spurs in snakes, hind leg
bones in whales.
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Artificial Selection
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• Artificial Selection The selective breeding of
  domesticated plants and animals to encourage the
  occurrence of desirable traits.
• Short period of time needed for Artificial
  Selection

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Heredity Characteristics that are passed down to
offspring
Mutations Changes that occur in the hereditary
material
Mutant The new form that survives a mutation and
passes this trait on to offspring
Adaptation A favorable variation within a
species that may help an organism survive
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• Natural selection - Predators/famine/space
  shortage/disease/ environmental changes

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Origin of life and Stanley Millers Experiment
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Abiotic synthesis of organic monomers

• Stanely Miller - simulated conditions on early
  Earth (no oxygen, reducing environment with
  inorganic gases like H2, CO2, NH3, CH4
  lightning/UV with no ozone. Favored the
  synthesis of organic compounds from
  inorganicmaterial

• The Miller-Urey experiments produced a variety of
  amino acids and other organic molecules
  (monomers).