Extinction

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Extinction

• Historical and Current

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Extinction and Evolution

• All species go extinct (99 of all species)
• Many die out completely
• Others evolve into new species
• Historical record involves five mass extinctions

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Mass Extinctions

• Ordovician
• Devonian
• Permian
• Triassic
• Cretaceous

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Source of Mass extinctions

• Random fluctuations-no cause
• Caused by catastrophes such as
• asteroid impact
• Massive loss of species followed by development
  of new types of species

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Rate of Evolution

• Darwin argued for gradual change gradualism
• Mendelians and others argued for more rapid
  change saltations or jumps
• Gaps in fossil record make it difficult to
  determine rate of evolution

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Rate of evolution

• Hopeful monsters are new species formed
  instantly from large mutations
• Idea discredited
• Some species show stasis (no change) such as
  horseshoe crabs and sturgeon

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Punctuated Equilibrium

• Punctuated equilibrium proposed in 1970s
• Idea is that species form rapidly but not
  instantaneously
• In between rapid change, species change very
  little (stasis)
• Rapid means 5,000-50,000 years (usually too
  little time for fossils to form)

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Mass extinction-Human caused

• Currently in sixth great extinction crisis
• Caused by human population
• overhunting and overfishing
• introduced species (outcompeting natives)
• habitat loss
• toxic poisoning
• trade in exotic animals

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Habitat Loss
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