Review: Why Evolution Is True

7. The Origin of Species

• How do species arise from natural selection?
  • A species get split by geographical isolation
    “the theory of geographic speciation”
  • Both groups continue to evolve independently
• Different species cannot exchange genes
  • They are “reproductively isolated”
  • Biological Species Concept (BSC)
    • “a reproductive gene pool”
• Species are “evolutionary accidents”
• Species do not arise to fill empty niches
• There has been enough time for speciation to create millions of species
• Sister species tend to be geographically close
• Speciation can be seen happening
  • “Creationists often claim that if we can’t see a new species evolve during our lifetime, then speciation doesn’t occur. But this argument is fatuous: it’s like saying that because we haven’t seen a single star go through its complete life cycle, stars don’t evolve, or because we haven’t seen a new language arise, languages don’t evolve.”
• Reproductive isolation increases over time
• Sympatric speciation is rare as expected
  Sympatric speciation: Different species occur in close proximity to each other
  • Subset: Hybridisation can produce new species
    Chromosomes are doubled—a random event with low frequency, but not low probability in species (usually plants) that produce millions of eggs/sperm.
    • Allopolyploid speciation
    • Polyploid speciation

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