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3. Evolution and Natural Selection Continued

4. Evolution is… The gradual change in a species over time.

5. Things to keep in mind… Populations, not individuals, evolve. It’s all about the genes! Occurs over a LONG period of time.

6. Evidences of Evolution Fossil Record Biochemical - DNA Comparative Anatomy Biogeography Observable Events

7. Mechanisms of Evolution How does evolution occur?

8. Bottleneck Effect An event that kills off a large number of members of a species randomly by chance therefore reducing the genetic diversity.

9. Bottleneck Effect

10. Genetic Drift The alteration of allelic frequencies by chance events.

11. Genetic Drift

12. Mutations Random genetic changes that occur in a populations DNA.

13. Mutations • Most mutations are bad • Some are advantageous

14. Gene Flow The transfer of alleles from one population to another population through immigration or emigration of individuals.

15. Gene Flow

16. Natural Selection is… A mechanism for change in a population. Survival of the Fittest Organisms with favorable genetic variation survive to pass on their genes

17. Types of Natural Selection • Stabilizing • Directional • Disruptive

18. Stabilizing Selection: When the average is favored over either of the extremes in a population.

19. Stabilizing Selection:

20. Directional Selection: This happens when one of the “extremes” is favored in an environment over the other extreme or the old average.

21. Directional Selection:

22. Disruptive Selection: This situation happens when either extreme is favored over the average.

23. Disruptive Selection:

24. How are new species made? Speciation: the evolution of a new species

25. How are Species Made? Speciation is always caused by isolation Types of isolation: • Geographic • Reproductive

26. Types of Isolation • Geographic Isolation A single species can become two different species because they are isolated by mountains, rivers, canyons, etc.

27. Types of Isolation 2. Reproductive Isolation • Animals in different areas of the country may develop different actions and behaviors. • These different behaviors can cause groups to separate from each other and become different species.

28. Types of Isolation 2. Reproductive Isolation Organisms may develop different mating seasons which do not correspond to one another

29. Extinction Individuals die, species go extinct

30. Extinction As the environment changes, organisms must have variations that allow them to survive (adapt) to those changes or die If an entire population of a species cannot adapt, that species becomes extinct.

31. Mass Extinction There have been at least 5 MASS extinctions during Earth’s history where a huge % of the living species were destroyed At least one of these has been attributed to meteor impact and its consequences.

32. Mass Extinction