Evolutionary theory, evidence of evolution

• Darwin's theory of natural selection: 3 inferences based on 5 observations
  • observation 1: great reproductive potential of species
  • observation 2: populations tend to remain stable
  • inference 1: struggle for existence among individuals in a population, with only a fraction of offspring surviving each generation
  • observation 3: individuals in a population vary
  • observation 4: much of this variation is heritable
  • inference 2: survival is not random, but depends in part on the hereditary constitution of surviving individuals, individuals whose characteristics best fit them to the environment are more likely to leave offspring than less fit individuals
  • inference 3: unequal ability of individuals to survive and reproduce will lead to a gradual change in the population
• Artificial selection
  • examples: wild mustard (cabbage, cauliflower, etc), selective breeding of dogs
• Points to remember about natural selection
  • population is smallest unit that can evolve
  • natural selection can amplify or diminish only heritable variations
  • specifics of natural selection are situational- a change in environmental conditions may result in selection of different characteristics
• Natural selection in action- examples
  • guppies with different predators ( killifish prey mainly on small guppies, pike-cichlid prey mainly on large guppies)
  • finches on Galapagos Islands, change in beak size depending on food availability
• Evidence of evolution
  • biogeography- geographical distribution of species
  • fossil record- succession of fossil forms
  • comparative anatomy- e.g. homologous structures
  • comparative embryology
  • molecular biology

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