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History of Evolution

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Intellectual history of evolution from Greek philosophers to catastrophists of medieval times to the Darwinist Revolution to the history of genetics

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History of Evolution

  1. 1. History of Evolutionary Theory Anaximander to Austrian Monks
  2. 2. The Evolutionary Model <ul><li>Evolution is based on two models of population change </li></ul><ul><li>Mutation—Change In DNA Structure—involves the creation of new life forms </li></ul><ul><li>Natural selection involves environmental pressures that favor, restrict, or eliminate life forms </li></ul><ul><li>Other factors may favor population change: gene flow (migration) or genetic drift (changes as the product of chance </li></ul>
  3. 3. Overview of Evolutionary Change <ul><li>First, we look at the history of evolutionary thought from the Greek philosophers to the Darwinist model </li></ul><ul><li>Then we look at the mechanisms of evolutionary change </li></ul><ul><li>Biological, Molecular, and Population Genetics </li></ul><ul><li>Natural Selection </li></ul><ul><li>Other Mechanisms of Population Change </li></ul><ul><li>Speciation and Taxonomy </li></ul>
  4. 4. Overview of Evolution of Evolutionary Thought <ul><li>History of Evolutionary Concepts </li></ul><ul><li>Greek Precursors </li></ul><ul><li>17 th Century Theologians </li></ul><ul><li>18 th Century Catastrophists </li></ul><ul><li>18 th Century Uniformitarians </li></ul><ul><li>Uniformitarianism of Hutton and Lyell </li></ul><ul><li>Darwin and Wallace </li></ul><ul><li>Gregor Mandel </li></ul><ul><li>Key concepts in evolutionary history </li></ul><ul><li>Essentialism/Chain of Being </li></ul><ul><li>Natural Selection/Mutation </li></ul>
  5. 5. Early Theorists: The Classical Greeks <ul><li>Anaximander: (6 th Century BC) </li></ul><ul><li>Argued that men arose from fishes, setting the stage of </li></ul><ul><li>He relied on reasoning, not supernatural explanations </li></ul><ul><li>Plato and Aristotle: Set the stage for two models of existence </li></ul><ul><li>Essentialism, or the ideal type of biological lifeforms </li></ul><ul><li>Great Chain of Being, which placed all lifeforms in a hierarchical system of existence from lowest to highest. </li></ul>
  6. 6. Early Models: Essentialism <ul><li>Essentialism: The ideal reality against which the perceived reality is compared and contrasted </li></ul><ul><li>Plato (above) was the first to come up with the ideal entity (including the human), against which the perceived entity was compared </li></ul><ul><li>Aristotle (below) also accepted the idea of a perfect universe, but did not accept the dichotomy that Plato posited. Rather, he saw the essential as the properties of each lifeform and other entities. </li></ul><ul><li>Greek gods and goddesses represented the ideal human male and female forms, as reflected in sculpture and other representational art. </li></ul><ul><li>Any deviation from the essential reflected some defect in any lifeform, animal or plant. </li></ul>
  7. 7. Early Models: The Great Chain of Being <ul><li>A hierarchy of entities from the simplest to most complex anticipated the later rise of taxonomy; Karl von Linn é (discussed below) drew on this model. </li></ul><ul><li>In this view, the human race was the most complex and perfect of all living forms </li></ul><ul><li>Humans, however, were below the divine beings (including demons in the model depicted here. </li></ul>
  8. 8. Catastrophism <ul><li>Earth’s history is product of sudden change </li></ul><ul><li>Example: Creation of Earth in six days (upper left), including Adam </li></ul><ul><li>Example: Flood (Noah’s Ark), which eliminated all life except Noah’s family and the male and female animals he allowed into the ark </li></ul><ul><li>Catastrophism does have some basis of reality: an asteroid that struck the earth 65 million years ago (lower left) nearly destroyed all life </li></ul>
  9. 9. Early Theorists: 17 th Century Catastrophists <ul><li>James Ussher (1581-1656): Argued that humankind created noon, Oct. 23, 4004;(Upper left) </li></ul><ul><li>He based his calculations on biblical history and astronomy </li></ul><ul><li>Nicholas Steno (1638-1686): </li></ul><ul><li>Stratigraphy—sediments deposited by water in a sequence </li></ul><ul><li>Robert Hooke (1635-1703) </li></ul><ul><li>Described fossils (mineralized remains of lifeforms) </li></ul><ul><li>Recognized them as of extinct or early formative creatures </li></ul><ul><li>He also described the cell as the basic unit of life and invented the microscope </li></ul><ul><li>Adaptation : creatures changed as earth changed </li></ul><ul><li>All three explained history of earth as a catastrophic creation. </li></ul>
  10. 10. Early Theorists: 18 th Century Catastrophists <ul><li>Carolus Linnaeus (Carl Linn é; 1707-1778) </li></ul><ul><li>Inventor of taxonomy —classification of lifeforms based on similarities and differences (Sample taxonomy next slide) </li></ul><ul><li>Viewed system as divinely ordained </li></ul><ul><li>He also classified human races as being of separate species with their own personality traits </li></ul><ul><li>Georges Cuvier (1769-1832) </li></ul><ul><li>Developed the science of comparative anatomy </li></ul><ul><li>Compared the Anatomy of present lifeforms with those of the fossils forms </li></ul><ul><li>Catastrophism: He concluded that the lifeforms of the world changed but they did not evolve </li></ul>
  11. 11. Carolus Linnaeus (Linn é)
  12. 12. Early Theorists: 18 th Century Uniformitarians <ul><li>Uniformitarianism : Processes occur at same rate through time—present and past </li></ul><ul><li>Georges-Louis Leclerc (Comte de Buffon; 1707-1788) </li></ul><ul><li>He observed that the tides and currents of seas are uniform through time </li></ul><ul><li>He concluded that the earth had to be older than 6000 years </li></ul><ul><li>James Hutton (1726-1797): Discovered uniformity in 3 processes: </li></ul><ul><li>Deposit of strata under oceans </li></ul><ul><li>Uplifting seabeds to above sea level by volcanic action </li></ul><ul><li>Land erosion by water, wind, and decay </li></ul><ul><li>He too concluded that the earth had to be older than 6000 years </li></ul>
  13. 13. Uniformitarianism According to Charles Lyell <ul><li>Charles Lyell (1797-1875) </li></ul><ul><li>Espoused extreme form of uniformitarianism by denying catastrophism ( Principles of Geology ) </li></ul><ul><li>Three aspects hold up today </li></ul><ul><li>Geological processes of past are the same as today </li></ul><ul><li>Stratigraphy serves to reconstruct history of the earth </li></ul><ul><li>Immense amount of time necessary for geological processes to effect change in the landscape </li></ul><ul><li>Age of earth: The current estimate is 4.5 billion years </li></ul>
  14. 14. Counterevidence to Lyell’s Model <ul><li>Five global catastrophes are known to have occurred. </li></ul><ul><li>Example: collision of asteroid with earth 65 m.y.a. wiped out 75% of world’s marine species) </li></ul><ul><li>Mississippi Delta is less than 100,000 years old—and has been shrinking since 3400 BCE </li></ul>
  15. 15. Evolutionary Theories: Acquired Characteristics <ul><li>Jean-Baptiste de Lamarck (1744-1829) </li></ul><ul><li>Traits acquired in organism’s lifetime </li></ul><ul><li>Acquired Characteristics : </li></ul><ul><li>Are passed down to offspring </li></ul><ul><li>Product of adaptation to changing environment </li></ul><ul><li>Progress from simple to complex organisms </li></ul><ul><li>Example: elongation of giraffes’ necks to get at leaves of taller trees </li></ul><ul><li>Shortcoming: </li></ul><ul><li>No example to support theory; natural selection coupled with mutation better explain the lengthening of giraffes’ necks </li></ul><ul><li>Counterexamples abound; for example, generations of docking sheep's’ tails in rural Spain did not eliminate them. </li></ul>
  16. 16. Evolutionary Theories: Natural Selection <ul><li>Natural selection Defined: </li></ul><ul><li>Evolutionary change by </li></ul><ul><li>Differential reproductive success of individuals </li></ul><ul><li>within a species (group of organism able to reproduce fertile offspring) </li></ul><ul><li>Through successful adaptation to an environment </li></ul>
  17. 17. Charles Darwin (1809-1882) Origin of Species <ul><li>Charles Darwin (above) observed that pigeons, dogs, and horses were subjected to artificial selection in order to improve their breeding </li></ul><ul><li>On Galapagos Islands in 1832, Darwin observed that 14 species of finches adapted in different niches descented from a common ancestor (next slide) </li></ul><ul><li>He conceived the idea of natural selection and after years of dithering finally published his conclusions in The Origin of Species in 1859 </li></ul><ul><li>Alfred Russel Wallace (below) drew the same conclusions—but Darwin published the results first </li></ul><ul><li>(Wallace made a bad career move: he sent his results to Darwin asking for comments. Oops!) </li></ul>
  18. 18. Charles Darwin and Natural Selection
  19. 19. Natural Selection: Definition and Implications <ul><li>Variations are already present when selection occurs </li></ul><ul><li>Natural selection has no particular direction—change is random </li></ul><ul><li>Therefore, not all evolution is from the simple to the complex </li></ul><ul><li>Species can and do become extinct </li></ul><ul><li>New species can and do arise (Darwin had no way of explaining how the originated, however.) </li></ul><ul><li>Reproductive isolation makes for new species </li></ul><ul><li>New species fill new niches, as the finches showed </li></ul><ul><li>Thus, dark-winged moths filled a new environment in a soot-darkened coal-fired steel city; birds did not pick them off </li></ul><ul><li>The dark colored pepper moth is to the lower part of the photo </li></ul>
  20. 20. Evolutionary Theories: Genetics <ul><li>It was up to the Austrian monk Gregor Mendel to discover the principle that would lead to the explanation how species originated. </li></ul><ul><li>He experimented with peas in monastery garden </li></ul><ul><li>In so doing, he found that smooth and wrinkled peas when combined produced offspring resembling their parents </li></ul><ul><li>Nothing but smooth peas appeared in generation 2 </li></ul><ul><li>A ratio of 3 smooth peas to one wrinkled pea appeared in generation 3 </li></ul><ul><li>The experiments provided the hereditary foundation for “origin” of species: mutation or genetic change </li></ul>
  21. 21. Gregor Mendel and Genetics <ul><li>Mendel experimented with six other traits: color of peas, texture of pea pods, color of flowers </li></ul><ul><li>He found the same outcomes over three generations </li></ul><ul><li>The traits were each determined by variants (alleles) of a pair of genes. </li></ul><ul><li>Mendelian traits were thereby discovered </li></ul><ul><li>Later, it would be discovered that multiple genes could determine a single trait, such as eye and skin color </li></ul>
  22. 22. Molecular Genetics <ul><li>The final step to understanding origins of species came with the discovery by James Watson (left) and Francis Crick (right) of a double helix molecule that determine traits of all species </li></ul><ul><li>Called DNA, they found that mutations could change the traits of a species—any species of a plant or animal. </li></ul><ul><li>Details of this process are discussed in the next set of slides. </li></ul>
  23. 23. Conclusion <ul><li>Trends in history of evolutionary thought have been reviewed </li></ul><ul><li>Creationism to evolutionary models of change </li></ul><ul><li>Catastrophism to uniformitarianism </li></ul><ul><li>Essentialism to natural selection </li></ul><ul><li>Chain of being to variation by random mutation </li></ul><ul><li>Evidence fits evolutionary change better than model of creation </li></ul><ul><li>How evolutionary change occurs is covered in the next sets of slides. </li></ul>

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