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Evidence of Evolution

Evidence of Evolution. Voyage of the Beagle. Charles Darwin’s observations on a voyage around the world led to new ideas about species. Voyage of the Beagle. Darwin, Wallace, and Natural Selection.

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Evidence of Evolution

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  1. Evidence of Evolution

  2. Voyage of the Beagle • Charles Darwin’s observations on a voyage around the world led to new ideas about species

  3. Voyage of the Beagle

  4. Darwin, Wallace, and Natural Selection • In 1858, Charles Darwin and Alfred Wallace independently proposed a new theory, that natural selection can bring about evolution

  5. Variations in Traits • Darwin observed that variations in traits influence an individual’s ability to secure resources – to survive and reproduce

  6. Theory of Natural Selection • Natural selection • The differential in survival and reproduction among individuals of a population that vary in details of their shared traits • Can lead to increased fitness • Fitness • An individual’s adaptation to an environment, measured by its relative genetic contribution to future generations

  7. Fossil Evidence • Fossils • Physical evidence of life in the distant past • Found in stacked layers of sedimentary rock • Younger fossils in more recently deposited layers • Older fossils underneath, in older layers

  8. Stratification

  9. Fossilization

  10. Interpreting the Fossil Record • The fossil record is incomplete • Favors species with hard parts, dense populations with wide distribution, and that persisted a long time

  11. Plate Tectonics Theory • Movements of Earth’s tectonic plates rafted land masses to new positions • Pangea: First ancient supercontinent • Gondwana (later southern supercontinent) • Movements had profound impacts on the directions of life’s evolution

  12. Biogeographical Evidence

  13. Morphological Divergence • Homologous structures: Similar body parts that became modified differently in different lineages • Evidence of descent from a common ancestor

  14. Comparative Morphological Evidence

  15. Homologous Structures

  16. Analogous Structures

  17. DNA, RNA, and Proteins • Comparisons of DNA, RNA, and proteins reveal and clarify evolutionary relationships

  18. Populations Evolve • Population • Individuals of the same species in the same area • Generally the same number and kinds of genes for the same traits • Gene pool • All the genes of a population

  19. Variation in Alleles • Individuals who inherit different combinations of alleles vary in details of one or more traits • Mutations are the original source of new alleles • Lethal mutations result in death • Neutral mutations neither help nor hurt

  20. Phenotypic Variation in Populations

  21. Microevolution • Changes in allele frequencies of a population • Mutation • Natural selection • Genetic drift • Gene flow

  22. Natural Selection • Natural selection • Differential survival and reproduction among individuals of a population that show variations in details of their shared traits (alleles) • Allele frequencies • Maintained by stabilizing selection • Shifted by directional or disruptive selection

  23. Modes of Natural Selection

  24. Peppered Moth

  25. Pocket Mice

  26. Stabilizing Selection: Birth Weight

  27. Sexual Selection

  28. Evolution of sickle cell anemia

  29. Genetic Drift • Genetic drift • Random change in a population’s allele frequencies over time, due to chance • Can lead to loss of genetic diversity • Most pronounced in small or inbred populations • Bottleneck: Drastic reduction in population • Founder effect: Small founding group

  30. Gene Flow • Gene flow • Movement of alleles into or out of a population by immigration or emigration • Helps keep populations of same species similar • Counters processes that cause populations to diverge (mutation, natural selection, genetic drift)

  31. Gene Flow Between Oak Populations

  32. Reproductive Isolation • Individuals of a sexually reproducing species can produce fertile offspring, but are reproductively isolated • Reproductive isolating mechanisms evolve when gene flow between populations stops • Divergences may lead to new species

  33. Mechanical Isolation

  34. Behavioral Isolation

  35. Allopatric Speciation • A geographic barrier stops gene flow between two or more populations of a species • Example: Isolated continents or archipelagos • Genetic divergence and reproductive isolation give rise to new species

  36. Allopatric Speciations

  37. An Isolated Archipelago

  38. Patterns of Macroevolution • Coevolution • Close ecological interactions cause two species to act as agents of selection upon one another • Extinction • Irrevocable loss of species • Mass extinctions and recoveries have occurred several times in the history of life • Most species that ever existed are now extinct

  39. Coevolution

  40. Adaptation to What? • Evolutionary adaptation • Heritable traits that improve an individual’s chance of surviving and reproducing (under conditions that prevailed when genes evolved)

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