1. Processes of Evolution
Chapter 12
Part 1

2. 12.1 Impacts/Issues Rise of the Super Rats
When humans tried to eradicate rats with warfarin, natural selection favored individuals with a mutation for warfarin resistance
Warfarin 一開始是註冊. 為老鼠藥（現名為殺鼠靈 ) Warfarin 為Wisconsin Alumni Research Foundation（贊助 Warfarin 合成的基金會）和 Coumarin（表示 Warfarin 是 coumarin 的衍生物）的縮寫。在上個世紀，大家慢慢注意「血栓」在西方國家是一個重要的死亡因子。「血栓」的產生會堵塞血管進而可能造成人體組織缺乏氧氣及養分。血栓的預防及治療極為重要，這也造成了口服抗凝血劑的廣泛運用。1940年從發霉的飼料中找到的劇毒生化物質，動物服用後數天後就會慢性出血而死亡，註冊為毒鼠藥使用。

3. Video: Rise of the super rats

4. 12.2 Making Waves in the Gene Pool
Individuals in a population share the same traits (phenotype) because they share the same genes (genotype)
Gene pool
All of the genes in a population

5. Alleles and Traits
Alleles of the same genes are the main source of variation in a population
Traits with two distinct forms are dimorphic
Traits with several distinct forms are polymorphic
Traits with continuous variation may have interactions of several genes or be influence by environment
Mutation is the source of new alleles

6. Sources of Variation in Traits

7. Phenotypic Variation in Humans

8. Mutation Revisited
Mutations are the original source of alleles, but many are lethal or neutral
Lethal mutation
Mutation that drastically alters phenotype; usually causes death
Neutral mutation
A mutation that has no effect on survival or reproduction

9. Allele Frequencies
Microevolution (change in allele frequencies) is always occurring in natural populations
Microevolution
Small-scale change in allele frequencies of a population or species
Allele frequency
Abundance of a particular allele among members of a population

10. Genetic Equilibrium Genetic equilibrium
Theoretical state in which a population is not evolving (allele frequencies do not change)
Only occurs if five conditions are met:
Mutations never occur, population is infinitely large, population is isolated from gene flow, mating is random, all individuals survive and reproduce equally

11. Processes of Microevolution
Genetic equilibrium does not occur in nature because processes that drive microevolution are always in play
Mutation
Natural selection
Genetic drift
Gene flow

12. Animation: Adaptation to what?

13. Animation: How to find out if a population is evolving

14. Animation: Sources of genotype variation

15. 12.3 Natural Selection Revisited
Natural selection occurs in different patterns depending on species and selection pressures
Directional selection
Stabilizing selection
Disruptive selection

16. Directional Selection
Mode of natural selection in which phenotypes at one end of a range of variation are favored
Allele frequencies shift in a consistent direction in response to selection pressure
Examples: peppered moths, rock pocket mice, antibiotic-resistant bacteria

17. Directional Selection

18. Number of individuals in population
Time 1
Number of individuals in population
Figure 12.3: Animated!
Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored.
Range of values for the trait
Fig. 12-3a, p. 219

19. Figure 12.3: Animated!
Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored.
Fig. 12-3b, p. 219

20. Time 2
Figure 12.3: Animated!
Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored.
Fig. 12-3b, p. 219

21. Time 3
Figure 12.3: Animated!
Directional selection. The bell curves indicate continuous variation in a butterfly wing-color trait. Red arrows indicate which forms are being selected against; green, forms that are being favored.
Fig. 12-3c, p. 219

22. Animation: Directional selection

23. Directional Selection in Peppered Moths
Predation pressure favors moths that are best camouflaged when the environment changes

24. Figure 12.4
Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color.
Fig. 12-4, p. 219

25. Figure 12.4
Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color.
Fig. 12-4a, p. 219

26. Figure 12.4
Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color.
Fig. 12-4b, p. 219

27. Figure 12.4
Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color.
Fig. 12-4c, p. 219

28. Figure 12.4
Directional selection of two forms of a trait in different settings. (A) Light peppered moths on a nonsooty tree trunk are hidden from predators. (B) Dark ones stand out. In places where soot darkens tree trunks, the dark color (C) is more adaptive than (D) the light color.
Fig. 12-4d, p. 219

29. Directional Selection in Rock Pocket Mice
Mice with coat colors that do not match their surroundings are more easily seen by predators
Rock Pocket Mice 黑腹絨鼠

30. Stabilizing Selection
Mode of natural selection in which intermediate phenotypes are favored and extreme forms are eliminated
Example: sociable weavers

31. Stabilizing Selection

32. Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6, p. 221

33. Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6a, p. 221

34. Number of individuals in population
Time 1
Number of individuals in population
Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Range of values for the trait
Fig. 12-6a, p. 221

35. Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6b, p. 221

36. Time 2
Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6b, p. 221

37. Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6c, p. 221

38. Time 3
Figure 12.6: Animated!
Stabilizing selection eliminates extreme forms of a trait, and maintains the predominance of an intermediate phenotype in a population. Red arrows indicate which forms are being selected against; green, forms that are being favored. Compare the data set from a field experiment shown in Figure 12.7.
Fig. 12-6c, p. 221

39. Animation: Stabilizing selection

40. Stabilizing Selection in Sociable Weavers
Body weight in sociable weavers is a trade off between starvation and predation
Sociable Weavers 織布鳥

41. Figure 12. 7 Stabilizing selection in sociable weavers (top)
Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season.
Figure It Out: What is the optimal weight of a sociable weaver bird?
Answer: About 29 grams.
Fig. 12-7, p. 221

42. Figure 12.7
Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season.
Figure It Out: What is the optimal weight of a sociable weaver bird?
Answer: About 29 grams.
Fig. 12-7a, p. 221

43. Figure 12.7
Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season.
Figure It Out: What is the optimal weight of a sociable weaver bird?
Answer: About 29 grams.
Fig. 12-7b, p. 221

44. 300
200
Number of survivors
100
Figure 12.7 Stabilizing selection in sociable weavers (top). Graph shows the number of birds (out of 977) that survived a breeding season.
Figure It Out: What is the optimal weight of a sociable weaver bird?
Answer: About 29 grams.
25.5
27.5
29.5
31.5
33.5
35.5
23.5
Body mass (grams)
Fig. 12-7b, p. 221

45. Disruptive Selection Disruptive selection
Mode of natural selection that favors extreme phenotypes in a range of variation
Intermediate forms are selected against
Example: African seedcrackers

46. Disruptive Selection

47. Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8, p. 222

48. Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8a, p. 222

49. Number of individuals in population
Time 1
Number of individuals in population
Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Range of values for the trait
Fig. 12-8a, p. 222

50. Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8b, p. 222

51. Time 2
Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8b, p. 222

52. Figure 12.8: Animated!
Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8c, p. 222

53. Time 3
Figure 12.8: Animated! Disruptive selection eliminates midrange forms of a trait, and maintains extreme forms.
Fig. 12-8c, p. 222

54. Animation: Disruptive selection

55. Disruptive Selection in African Seedcrackers
African seedcrackers tend to have either a large bill or a small one – but no sizes between

56. Figure 12. 9 Disruptive selection in African seedcrackers
Figure 12.9 Disruptive selection in African seedcrackers. Birds with bills that are about 12 or 15 millimeters wide are favored. The difference is a result of competition for scarce food during dry seasons.
lower bill 12 mm wide
Fig. 12-9a, p. 222

57. Figure 12. 9 Disruptive selection in African seedcrackers
Figure 12.9 Disruptive selection in African seedcrackers. Birds with bills that are about 12 or 15 millimeters wide are favored. The difference is a result of competition for scarce food during dry seasons.
lower bill 15 mm wide
Fig. 12-9b, p. 222

58. Animation: Change in moth population

59. Animation: Disruptive selection among African finches