Pace of Speciation

• Speciation


  Evolution that occurs across the species barrier (macroevolution)
• Models of evolution via speciation


  • Phyletic gradualism
  • Punctuated equilibrium
• Phyletic gradualism


  • Speciation occurs uniformly, via the steady and gradual transformation of whole lineages
  • Speciation is seen as a smooth and continuous process (big changes result from many cumulative small changes)
• Phyletic gradualism


  • Fossil record of the horse, with many intermediate forms connecting the ancestral species to the modern equivalent
• Punctuated equilibrium

  • Species remain stable for long periods before undergoing abrupt and rapid change (speciation)
  • Speciation is seen as a periodic process (big changes occur suddenly, followed by long periods of no change)
• The general lack of transitional fossils for most species could be explained by the relatively rare and irregular conditions required for fossilisation
• Evolution occurs both within a species (microevolution) and across the species barrier (macroevolution = speciation)