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BIO190: The Class: Evolution: Lesson 9

Organic Evolution

Explore this web site to learn more about evolution: The Evolution Exhibit

Historical Developments

Pre-Darwin

Before the eighteenth century, speculation on the origin of species rested on myth and superstition.

Darwin

Charles Darwin's nineteenth century voyage on the Beagle led to the development of his theory of evolution. See figure 9-4.

The following are some observations made by Darwin on the voyage.

    1. Collected and observed flora and fauna are each stop.

    2. Noted the resemblance between extinct animal fossil in South American and fossils of North America.

    3. Observed ocean fossils in Andes in rock strata 13,000 ft above sea level

    4. Experienced an earthquake

    5. Observed erosion during tropical rains

    6. Developed the "…origins of all my views." (Darwin) during a visit to the Galapagos Islands.

    Observations at Galapagos

    a. tortoises

b. differences in Cape Verde Island' life and GIs' life

(see map p.153)

c. noted how GIs' flora/fauna related to South American

mainland

d. noted the differences and similarities in species on each island

7. Darwin was influenced by Lyell's book and by Malthus' essay.

8. Alfred Wallace

9. In 1859 Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

Darwin's Evolutionary Theory: The Evidence

Perpetual Change

The main premise underlying Darwinian evolution is that the living world is always changing. Perpetual change in the living world is can be seen through fossils.

1. Problems with interpreting fossil record

    1. biased records due to selective preservation (if bones/shells then best record)
    2. soft bodies difficult to fossilize (exception Burgess Shale)
    3. if perfect fossil beds, then oldest would be lowest in rock strata, most often not the case because of geological disturbances.

Geological Time Periods (see endpaper; inside back cover of text)

    1. Law of stratigraphy
    2. Radioactive clocks
    3. Dating methods are based on half-lifes of naturally occurring elements
      a. K-Ar
      b. U-Pb

      Visit this web site to learn more about geological time.

      Paleontology Without Walls

      Evolutionary trends

      Common descent

        1. proposed by Darwin that all plants and animals have descended from "…some one form into which life was first breathed"
        2. phylogency-organism's life history presented as a branching tree (fig. 9-15)
        3. homology (fig. 9-13)
        4. ontogency recapitulates phylogency or biogenetic law
          1. Haeckel proposed this idea but was based on flawed premise of acquired characteristics.

        Multiplication of species

        Darwin's theory postulates that the variation within species provides the material from which new species are produced.

          1. speciation (fig. 9-21)
          2. reproductive barriers
          3. allopatric speciation
          4. founder effect (vicariant speciation)
          5. hybridization
          6. hybrids
          7. sympatric speciation (fig. 9-20)
          8. adaptive radiation (fig. 9-22)

        Gradualism

        Darwin's theory of gradualism opposed arguments for the sudden origin of species.

          1. populational vs. phenotypic
          2. phyletic graduulism vs. punctuated equilibrium (fig. 9-24&9-25)

        Natural Selection

        Natural selection is the centerpiece of Darwin's theory of evolution

        It gives us a natural explanation for the origins of adaptation.

        Development of Darwin's Theory of Natural Selection

        Five observations of natural selection

          1. Organisms have great potential fertility
          2. Natural populations normally remain constant in size, except for minor fluctuations.
          3. Natural resources are limited
          4. All organisms show variation
          5. Some variations are heritable (note-Darwin did not understand this. It would have to wait for Mendel's work.)

          There is a differential survival and reproduction among varying organisms in a population.

          Over many generations, differential survival and reproductive generates new adaptations and new species.

          Revision of Darwin's Theory (Neo-Darwinism)

          Neo-Darwinism is the term used to describe August Weissmann's revision of Darwin's theory.

          This revision was caused by genetics

          Revision led to the emergence of population genetics

          Evolutionary biology divided into two subfields

          1. microevolution-changes of allelic forms within a population
          • polymorphism
            (measurement of electrophoretic apparatus-fig. 9-30)
          • gene pool
          • allelic frequency
          • genetic equilibrium<
            (Hardy-Weinberg equilibrium p.171)
          • upsetting genetic equilibrium
            genetic drift
            inbreeding
          • natural selection vs. sexual selection

          types of selection (fig. 9-31)
          1. stabilizing
          2. directional
          3. disruptive

          2. macroevolution-changes occurring on the grand scale

          • origin of new structures and designs
          • evolutionary trends
          • adaptive radiation
          • mass extinction (fig. 9-32)
            1. Permiam (225 mya)
            2. Cretaceous (65 mys)

            Once you have completed this lesson, you should go to Assignment 9-1.

            E-mail Sylvester Allred at Syl.Allred@nau.edu

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