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Darwin Explains Natural Selection - PowerPoint PPT Presentation

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Darwin Explains Natural Selection
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  1. Darwin ExplainsNatural Selection Ch 22.2

  2. Darwin’s Life • 1809-1831 • Lived in England & fascinated with nature • Went to school to became a physician • Dropped out (disgusted by surgery) • Became a clergyman • 1831-1836 • Invited on the HMS Beagle • Hydrographic survey of South America

  3. Darwin Observes • Documented • Kept a Journal: The Voyage of the Beagle • Collected • Thousands of plants, animals, & fossils

  4. On the Origin of Species • 1836-1859 • Thinks about the voyage, animal/plant collection, fossils, geology… • Begins to describe the most revolutionary idea in biology • Receives a letter from colleague Alfred Wallace with same idea • They publish their idea together • Then Darwin finishes his book

  5. We change organisms • Artificial Selection: • humans modify species over many generations by selecting and breeding individuals with desired traits

  6. Cabbage Brussels sprouts Kale Cauliflower Broccoli Wild mustard Kohlrabi We change organisms

  7. Artificial Selection Today • http://www.hhmi.org/biointeractive/evolution/dog_breeding.html • https://www.youtube.com/watch?v=0jFGNQScRNY

  8. Observations from the voyage • Galapagos islands, while close to each other, contained: • Various ecosystems • Organisms similar to, but different from each other • Each had adaptations to fit the environment

  9. Observations • For any species, population sizes would increase exponentially if all individuals born reproduce successfully • Populations tend to be stable in size, except for seasonal fluctuations • Resources are limited

  10. Inference #1 • Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

  11. Observations • Members of a population vary extensively in their characteristics • Much of this variation is heritable

  12. Inference #2 • Survival depends in part on inherited traits; individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

  13. Inference #3 • This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations

  14. Summary of Evolution by Natural Selection • Organisms better suited to the environment are more likely to survive & reproduce than organisms less suited to the environment Mutation  Variation  Selection Individuals do NOT change; populations change

  15. Evolution by natural selection There is a grandeur in this view of life…