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Evolution: Natural Selection & Adaptation

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Evolution: Natural Selection & Adaptation. Chapters 15 and 16. Evolution is the Unifying Principle of all Biology forms foundation for all other concepts answers all “why” questions explains context of boil. phenomena two major aspects:

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Evolution is the Unifying Principle of all Biology

    • forms foundation for all other concepts
      • answers all “why” questions
      • explains context of boil. phenomena
    • two major aspects:
      • descent from a common ancestor  why org. have similar characteristics
      • adaptation to environment  explains diversity of life
  • Charles Darwin
    • developed theory of evolution
      • 1859: The Origin of Species
    • descent with modification
      • “change through time”
    • evol. occurs through natural selection
      • env. determines which ind. will survive and reproduce
        • are fittestind.  possess best adaptations
      • adaptations
        • characteristics that increase chance of survival and reproduction

Natural Selection

    • mechanism of evol.
    • based on five key points:
      • ind. vary within pops.
      • some variation is inherited and affects survival
      • more offspring are produced than env. can support
      • offspring with most adaptive traits will survive better and produce more of their own offspring
        • offspring will also have the adaptive traits
      • over time, the pop. changes
        • more adaptive traits become more prevalent
    • environmental forces affect an individual’s phenotype
      • to survive, an org’s. phenotype must become adapted to env.
        • but, genotype determines phenotype
      • orgs. with most adaptive genotypes survive better and pass their genes onto their offspring
        • their genotypes produce a more fit and adaptive phenotype
          • such organisms are “selected for”
      • variation in pop.  small genetic changes  produce new genotypes  lead to new, better adapted phenotypes
      • continued phenotypic change  development of new species


    • occurs in pops. in many different traits
      • behavioral, biochemical, physical
      • must be genetically based
      • two primary sources
        • mutation
          • source of new variations
        • crossing over
          • source of new combinations of traits
      • is very beneficial to a pop. evol. cannot occur without it
    • maintained through a wide variety of mechanisms
      • dispersal of young
      • masking recessive alleles
      • heterozygote advantage
      • others

Fig. 15.7 Variation in a human population


Modern Synthesis – Today’s Theory of Evolution

      • incorporates genetics into evolution
  • nat. sel. causes populations to change, not individuals
  • selection is not a random process
  • evol. is not based on the needs of organisms
    • mutations  acted on by nat. sel.  adaptation to local env. conditions
  • selection has been tested and confirmed many times in many organisms
  • fittest ind. are those more likely to survive, based on adaptations
      • evolution is not “survival of the fittest”
      • survival not as important as reproduction

Fig. 16.3

Natural selection in peppered moths


Evidence and Examples of Evolution

    • fossil record
      • radioactive dating
      • hard-bodied vs. soft-bodied organisms
      • phylogenetic trees

Fig. 17.17 Evolutionary history of Equus



    • study of where organisms are found on earth
    • provides evidence of past evol. history
    • isolated regions have their own types of plants and animals
    • similarity of unrelated species in similar environments

Page 274 Biogeographical regions

Fig. 15.5 An example of evidence through biogeography – the European hare and the Patagonian (S.A.) hare


Fig. 15.14 Biogeography. Some mammals of Australia and their North and South American counterparts.


comparative anatomy

    • homologous vs. analogous structures
    • adult and embryological evidence
    • transitional organisms
    • vestigial structures

Fig. 15.16 Developmental homologies

Fig. 15.15 Homologous structures


Fig. 15.13 Ambulocetus – an ancestor of whales and a transitional fossil

Fig. 15.12 Transitional fossils - Archaeopteryx


Some vestigial structures

Fig. 17.1 Whale evolution, showing transitional organisms


molecular biology

    • genetic code and cellular structure
    • DNA and amino acid similarities
    • number of mutations
    • phylogenetic trees

Fig. 15.17 Biochemical differences – evidence from molecular biology


artificial selection

    • selective breeding

Fig. 15.9 Artificial selection in plants

Fig. 15.8 Artificial selection in animals