BIOLOGY 105 SPRING 2001

LECTURE 3.1 AND 3.2

Outline: Evolution and natural selection

  1. 1-minute paper: change over time

    2.  
  2. What is evolution?
    1. Why should ecologists understand evolution?
  3.     Charles Darwin (1809 -1882)
    1.  Biography
    2. full text of Darwin's Voyage of the Beagle
    3. Return to England to develop ideas, publishes Origin of Species in 1859
  4. Darwin's ideas and observations led him to propose the theory of evolution by natural selection.
    1. The principle of common descent
    2. Natural selection and adaptation
    3. Darwinian logic
      1. First three observations and the inference Darwin drew from them
        1. Observations 1-3
          1. Fertility would lead to exponential population increase (2, 4, 8, 16, 32, 64, 128 etc.)   if all individuals born reproduce successfully.
          2. Most populations are normally stable in size, except for seasonal fluctuations.
          3. Natural resources are limited.
        2. Inference 1
          1. production of more individuals than the environment can support leads to a struggle for existence among individuals of a population:  only a fraction of offspring that are born in each generation survive to reproduce.
      1. Two more observations and two more inferences
        1. Observations 4-5
          1. Individuals of a population vary, no 2 individuals are exactly alike.
          2. Much of this variation is heritable.
        2. Inference 2
          1. Individuals whose inherited characteristics fit them best to their environment are likely to leave more offspring than less fit individuals.
        3. Inference 3
          1. Unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over the generations.
      2. Darwin called this natural selection: differential success in reproduction (contrast to artificial selection, or selective breeding of plants and animals to achieve desired characteristics)
        1. The product of natural selection is adaptation of organisms to their environment.
        2. Natural selection occurs from the interaction between the environment and the inherent variability in a population.
        3. Variations in a population arise by chance, but natural selection is not a chance phenomenon since environmental factors set definite criteria for reproductive success.
    1. Evolution
      1. Definition:  change in gene frequency over time.
      2. How do we know that evolution occurs?
        1. Biogeography. = geographic distribution of species.
          1. ex: Quino Checkerspot Butterfly    distribution of Quino Checkerspot in Western Riverside County
        2. Fossil Record
          1.    ex:  fossils of cat species
        3. Comparative anatomy--homologous structures
          1. ex:  forelimbs in vertebrates
        4. Comparative embryology--similar early developmental stages
          1. example:  pharyngeal slits in vertebrate embryos
        5. Molecular biology
          1. every living organism employs DNA and uses an almost identifcal genetic code
          2. close similarity of genetic sequences between closely related organisms
            1. e.g. cytochrome C structure
      3. Evolution does not make perfect organisms
        1. Historical constraints
        2. Adaptations are often compromises
        3. Not all evolution is adaptive
        4. Selection can only work on variations that exist
    2. Change in biodiversity over time
      1. History of life
      2. Evolutionary timeline
      3. Movement of tectonic plates
      4. New biodiversity
        1. Ex: Lake Victoria cichlids: 500 species in 12,000 yrs
        2. Mutations
        3. Natural selection
          1. Conditions for n.s. to work
          2. Types of selection
            1. Directional
            2. Stabilizing
            3. Disruptive
        4. Speciation:  the production of new species via evolution
          1. Allopatric speciation
          2. Sympatric speciation
            1. Behavioral differences in courtship/mating
            2. Host races
            3. Polyploidy
          3. Adaptive radiation
            1. Hawaiian honeycreepers
            2. Darwin’s finches
        5. Convergent evolution
          1. Definition
          2. Examples
            1. nectar-feeding birds:  hummingbirds from Americas, sunbirds from Africa
            2. evolution of flight in unrelated groups of vertebrates:  mammals, birds, and pterodactyls
            3. saber-tooth cat from N.A. and sabre-tootherd marsupial cat from South America
            4. desert-dwelling succulents:  cactus from America, euphorbias from Africa
      5. Change in biodiversity over recent time:  Cape Cod