1. Evolution
Part 2

2. Evolution
Changes in gene pool over time

3. Evolution Includes populations diverging from one another over time
 may lead to new species

4. Mechanisms of Evolution
Genetic Drift
Population Bottlenecks
Founder Effect
Gene Flow
Immigration
Emigration
Mutations
Natural Selection

5. Genetic Drift
Changes in gene pool of populations due to random chance

6. Genetic Drift

7. Genetic Drift Image Credit: UC Museum of Paleontology's Understanding Evolution

8. Genetic Drift
Genetic drift has a bigger effect on small populations.

9. Bottleneck Effect
Changes in gene pool of populations due to some event
 drastically reduces population

10. Bottleneck Effect Survival is random
Whether an organism survives does not depend on any characteristic (allele)

11. Example of Bottleneck Effect
Population of plants on a mountain side
An avalanche wipes out all but a patch of plants behind the shelter of a large outcrop.

12. Example of Bottleneck Effect
Plants behind the outcrop survived only because they were out of the path of the avalanche.
There was nothing about the plants’ genes that influenced survival.

13. Example of Bottleneck Effect
Surviving population has an allele frequency different from the original population.

14. Bottleneck Effect

15. Bottleneck Effect: Cheetahs
10,000 years ago, cheetah populations worldwide crashed
Due to climate change
Photo Credit: Courtesy of Smithsonian National nationalzoo.si.edu

16. Cheetahs Only cheetahs in Africa & Eurasia survived
Location, not genes  Survival
Photo Credit: Kevin Walsh, 2006, Wikimedia Commons

17. Cheetahs Cheetahs today: Genetically identical
Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons

18. Bottleneck Effect: Northern Elephant Seals
Once numerous in the northern Pacific.
1800s: Hunted extensively for blubber
Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

19. Northern Elephant Seals
Only animals in a Mexican colony survived
Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

20. Northern Elephant Seals
Today: >100,000 individuals
Very little genetic diversity
Photo Credit: Mila Zinkova, 2008, courtesy of Wikimedia Commons

21. Founder Effect
New population established by very small number of individuals (“founders”)
By chance, founder group has a different allele mix than original population

22. Example of Founder Effect
200 German immigrants founded the Old Order Amish of Pennsylvania
Photo credit: : Matthew Trump, 2004, Wikimedia Commons

23. Old Order Amish
One couple brought allele polydactyly  Six fingers and toes
Photo credit: G. Baujat and M LeMerrer, 2007, Wikimedia Commons

24. Old Order Amish Inbreeding has  frequency of polydactyly
Click on this link: /3/l_063_03.html
Photo credit: gadjoboy, 2006, Wikimedia Commons

25. Gene Flow Movement of alleles between populations
Immigration: movement of alleles into a population
Emigration: movement of alleles out of population

26. Example of Gene Flow
Transfer of pollen from one population of sunflowers into another population of sunflowers
Photo Credit: Sunflower Pollen, Courtesy of Wikimedia Commons

27. Example of Gene Flow
Male juvenile Belding’s ground squirrels emigrate from their birthing population to new populations.
40-70% emigrate as juveniles. Remaining males leave by the end of their first year.
Photo Credit: Courtesy of Yathin at FlickR, /set /

28. Mutations Mutations can add new alleles to a population
Photo Credit for black Eastern Fox Squirrel: Jeffrey Pippen, Duke University
Photo Credit for wild-type Eastern Fox Squirrel: Calibas, 2007, Wikimedia Commons

29. Asexual Populations
Mutations are primary source of genetic variation in asexual populations
Photo Credit for E. coli 0157 colonies: Centers for Disease Control, 2005, Wikimedia Commons

30. Natural Selection
Environment determines which genes are passed onto the next generation
Based on which individuals successfully survive and reproduce

31. Natural Selection Requires: Genetic Variation
Overproduction of Offspring
Struggle for Existence
Differential Survival and Reproduction

32. View video at: http://www. pbs. org/wgbh/evolution/library/11/2/e_s_4
Photo credit: Dean E. Briggins, U.S. Fish and Wildlife Service,

33. Genetic Variation
Organisms in the population vary in their characteristics
Variations are heritable  Passed from parents to offspring

34. Variation in Snail Shells

35. Flower Variations

36. Natural Selection Flow Chart

37. How Natural Selection Works

38. View “Pocket Mouse and Predation” at http://www. hhmi
Photo Credit: Cheryl S. Brehme, USGS at

39. View “Pocket Mouse Evolution” at http://www. hhmi
Photo Credit: J. Harris, American Society of Mammalogy, at:

40. Artificial Selection
Humans select which genes are passed onto the next generation
Based on characteristics that humans find valuable or desirable

41. View “Dog Breeding” at http://www. hhmi
Photo credit: papillon.cz, courtesy of Wikimedia Commons (

42. Photo credit: USDA, 2005, courtesy of Wikimedia Commons
View “Breeding Teosinte” at
Photo credit: USDA, 2005, courtesy of Wikimedia Commons

43. Another Example of Artificial Selection

44. Sexual Selection
Some characteristics influence individual’s chance of mating
Photo Credit: Ian Sewell, 2006, Wikimedia Commons

45. Sexual Selection
Individual may have shorter life but will have better chances of mating and producing offspring
Photo Credit: David Dennis, 2007, Wikimedia Commons

46. Types of Sexual Selection
Mate Competition
One sex competes for access to the other sex
Other sex always “chooses” winner
Mate Choice
One sex chooses mate based on characteristics of other sex

47. Example of Mate Competition
Male bighorn sheep fight for mates
Male with largest horns usually wins
Photo Credit: Alan D. Wilson, naturespicsonline.com, courtesy of Wikimedia Commons

48. Photo Credit: Jon Sullivan, Wikimedia Commons
Video of Bighorn Sheep Fighting:
Photo Credit: Jon Sullivan, Wikimedia Commons

49. Example of Mate Choice Peacocks display their tails
Females choose male with showiest tail
Photo credit: Aaron Logan, courtesy of Wikimedia Commons

50. Example of Mate Choice Large tails decrease survival of peacocks
Natural selection favors small tails
Photo credit: Jörg Hempel, courtesy of Wikimedia Commons

51. Example of Mate Choice Peacocks with small tails do not mate
Mate choice favors large tails
Photo credit: Jyshah, 2007, courtesy of Wikimedia Commons

52. Photo credit: Myukii, courtesy of Wikimedia Commons
View the video at:
Photo credit: Myukii, courtesy of Wikimedia Commons

53. The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al Biology, 8th ed. Pearson Benjamin Cummings.