Darwin

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Darwins Theory of Natural Selection

• Change Over Time

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Variation within Species

• Within a species, individuals have variations.
• Example Peppered moths vary from dark gray to
  light peppered appearance depending on the
  expression of the gene for melanin.

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Adaptation to Environmental Change

• Some individuals are more likely to survive than
  others because they have a variation that is
  better suited to the environment.
• If the environmental conditions change, other
  variations may have an advantage.

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Over-Production of Offspring

• The number of off-spring produced ensures
  survival of the species by replacing the parent
  generation and allowing an excess to be lost to
  predators, parasites, disease, and unfavorable
  temporary environmental changes such as drought
  or unusually hot or cold temperatures.

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Competition

• Over-production of offspring leads to competition
  for resources.
• Individuals who avoid predators, obtain food,
  find shelter, find a mate, and reproduce will
  pass on their traits to the next generation.
• Those that do not survive to reproduce, will not
  contribute genes to the next generation.

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Inheritance of Variation

• Offspring inherit traits from parents.
• Traits are determined by DNA.
• Genes are the mechanism by which traits are
  passed on.

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New Species Arise from Existing Species

• Over time, a new species may emerge with traits
  that are similar to the ancestor, but different
  enough to be considered a new species.

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Evidence for Evolution

• Change Over Time

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Homologous Structures

• Body parts that are structurally similar in
  related species and provide evidence that the
  structures were inherited from a common ancestor

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http//evolution.berkeley.edu/evosite/lines/Iihomo
logies.shtml
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http//evolution.berkeley.edu/evosite/lines/Iatran
sitional.shtml
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Branching Tree
A diagram that shows how scientists think
different groups of organisms are
related
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