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)