Darwins Theory

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Darwins Theory
Galapagos Islands
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Who is he?

• December 1831, HMS Beagle (British ship) went on
  a 5-year trip around the world
• 22 year old Charles Darwin naturalist
• - observed plants and animals
• - led him to develop the theory of evolution by
  natural selection

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I. Darwins Observations

• Included
• 1) the diversity of organisms,
• 2) remains of ancient organisms,
• 3) and characteristics of organisms on Galapagos
  Islands
• A) Diversity
• Saw tremendous diversity
• Scientists have now identified 1.7 million
  species
• Def. species organisms that can mate produce
  fertile offspring

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Darwins Observations (cont.)

• B) Fossils
• Def. fossil the preserved remains or traces of
  an organism that lived in the past
• Darwin saw bones of past sloths that were larger
  than when he lived.

Giant Sloth
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II. Galapagos Organisms

• Darwin found similarities between Galapagos
  organisms South American organisms
• A) Comparisons to S. American Organisms
• Many similarities as main land
• Important differences
• Small number of plants and animals had to reach
  island

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Galapagos Organisms (cont.)

• B) Comparisons Among Islands
• Saddle shape vs. dome shaped shells for tortoises
• The beaks of finches also differed (figure 3 p.
  227)
• C) Adaptation
• Def. adaptation a trait that helps an organism
  survive and reproduce in its environment
• Examples
• 1. Beak structure determines type of food.
• 2. Poisonous or bad tasting milkweed
• 3. Bright colored flowers attract insects

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III. Evolution

• A) Darwins Reasoning1. Plants animals on
  island face environmental factors different from
  mainland2. Species gradually change3. Species
  become better adapted to new environment

• Def. evolution gradual change in a species over
  time
• Def. Theory concept that explains wide range of
  observations

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Evolution (cont.)

• B) Selective BreedingWhen humans select a
  specific trait they want to pass to
  offspring(ex1) Sheep with fine wool(ex2)
  Pigeons with more than average number of feathers

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IV. Natural Selection

• Def individuals that are better adapted to
  environment and more likely to survive and
  reproduce
• Factors that affect process (fig. 5)1.
  Overproduction2. Variations3. Competition

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Natural Selection (cont.)

• A) Overproduction
• only strong survive since there isnt enough
  food, water and living space
• B) Variationsslight differences in traits(ex)
  Insects food choices
• C) Competitionfood and other resources are
  limited

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Natural Selection (cont.)

• D) Selection- some variations make individuals
  better adapted to their environment- environment
  selects organism with helpful trait- can cause
  change

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Natural Selection (cont.)

• E) Environmental Factors- can affect organisms
  ability to survive(ex1) Copper in soil with
  monkey flower(ex2) Smoke on trees with moths

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Natural Selection (cont.)

• F) Genes and Natural Selection- variations in
  organisms can result due to mutations in genes

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