HL 1 Biology

5.4a Evidence of Evolution

AA-CC: 193-6


  • Evolution: the cumulative change in the heritable characteristics of a population
    • Charles Darwin: proposed theory of natural selection
    • Main types of evidence for evolution:
      • breeding domesticated animals/ crop plants
      • fossils
      • homologous structures
      • geographical distribution of animals/plants

<<Evidence for Evolution>>

  • Domesticated Animals
    • humans breed particular animal species = more variation
    • artificial selection: selecting particular species that are most suited to human use and are bred
    • shows it can cause evolution
    • does not prove evolution of species occur naturally/ that mechanism for evolution is natural selection
  • Fossils
    • radioisotope dating: reveals ages of rock strata/ fossils in them
    • strong evidence of evolution
      • sequence fossils appear match with sequence expected to evolve
      • sequence fits with ecology of groups. plant fossils appearing before animals, plants suitable for insect pollination than insect pollinators
      • many fossil sequences are known, lined with existing organisms (likely to be ancestors)
  • Homologous Structures
    • Analogous structures: similar function but having a different evolutionary origin (tail fins of whales and fish)
    • Convergent evolution: evolutionary interpretation that species have different origins but became similar because they perform the same/similar function
    • Homologous Structures:  structures that may loook superficially different and perform a different function (but have a “unity of type”)
    • Adaptive Radiation:  evolutionary explanation that species have same origins but became different because they perform different functions
      • e.g. small pelvis and thigh bone in body wall of whales and snakes


Domestication of corn (p.194)

1) 170-14/(14)*100 = (156/170)*100 =114%

2) 4100-150/(150)*100 = (3950/150)*100 = 2633%

3) Factors apart from the cob length, selected for by farmers includes the color and smoothness (texture) of the seeds as well as its starchiness.

4) Improvement slows down over generations of selection because as pure breeding continues throughout the generations, the selection of different traits are decreasing and become in a weakness.

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