1. How Populations Evolve
Chapter 13
How Populations Evolve

2. Clown, Fool, or Simply Well Adapted?
Clown, Fool, or Simply Well Adapted?
The blue-footed booby
bird living in the Galápagos Islands

3. many “specialized characteristics”: evolutionary adaptations ... ???
many “specialized characteristics”:
evolutionary adaptations ... ???
inherited traits, enhance its ability to survive and reproduce in particular environment

4. DARWIN’S THEORY OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory of evolution
Galápagos Islands
many unique organisms
Figure 13.1A

5. In century prior to Darwin
study of fossils suggested: life forms change
Geologists proposed a very old Earth
changed by gradual processes

6. HMS Beagle, 1830s Darwin observed
North America
Europe
Great Britain
Africa
Equator
Asia
Australia
Tasmania
New Zealand
PACIFIC OCEAN
ATLANTIC OCEAN
The Galápagos Islands
South America
Tierra del Fuego
Cape Horn
Cape of Good Hope
Andes
Pinta
Marchena
Genovesa
Santiago
Isabela
Fernandina
Florenza
Española
San Cristobal
Santa Cruz
Santa Fe
Pinzón
Daphne Islands
40 miles
40 km
Figure 13.1B
HMS Beagle, 1830s
Darwin observed
similarities btwn living & fossil organisms
diversity of life on Galápagos Islands

7. His experiences during the voyage
His experiences during the voyage
Helped him frame his ideas on evolution

8. 13.2 Darwin proposed natural selection as the mechanism of evolution
Darwin observed that organisms
Produce more offspring than the environment can support
Vary in many heritable characteristics

9. Darwin reasoned that natural selection
Results in favored traits being represented more and more and
unfavored ones less and less
in future generations of organisms

10. Hundreds to thousands of years of breeding (artificial selection)
Artificial selection supports his ideas
selective breeding of domesticated plants and animals
Figure 13.2A
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog (wolf)
Figure 13.2B

11. Thousands to millions of years of natural selection
Darwin proposed
living species descended from earlier life forms
natural selection is the mechanism of evolution
Thousands to millions of years of natural selection
Ancestral canine
African wild dog
Coyote
Wolf
Fox
Jackal
Figure 13.2C

12. 13.3 fossils: strong evidence for evolution
fossil record strongly supports theory of evolution
A Skull of Homo erectus
D Dinosaur tracks
C Ammonite casts
B Petrified tree
E Fossilized organic matter of a leaf
G “Ice Man”
Figure 13.3A–G
F Insect in amber

13. http://media. pearsoncmg. com/bc/bc_0media_bio/bioflix/bioflix. htm

14. organisms have evolved in a historical sequence
Fossil record
organisms have evolved in a historical sequence
Figure 13.3H

15. Many fossils link early extinct species with species living today
Figure 13.3I

16. 13.4 A mass of other evidence reinforces the evolutionary view of life

17. 1. Biogeography geographic distribution of species
Suggests (to Darwin): organisms evolve from common ancestors
Darwin: Galápagos animals
Resembled species of South American mainland more than animals on similar but distant islands

18. 2. Comparative anatomy body structures, different species Homology
Similarity, results from common ancestry

19. Homologous structures
Homologous structures
features often w/different functions but structurally similar
because of common ancestry
Human
Cat
Whale
Bat
Figure 13.4A

20. 3. Comparative Embryology
early stages of development, different organisms

21. Many vertebrates -- common embryonic structures
Post-anal tail
Pharyngeal pouches
Chick embryo
Human embryo
Figure 13.4B
Many vertebrates -- common embryonic structures

22. 4. Molecular Biology
DNA, amino acid sequences between different organisms
 evolutionary relationships
Table 13.4

23. 13.5 Scientists observe natural selection in action
CONNECTION
13.5 Scientists observe natural selection in action
Camouflage adaptations evolved in different environments
A flower mantid in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A

24. Development of pesticide resistance in insects
Pesticide application
Survivor
Chromosome with gene conferring resistance to pesticide
Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow
Figure 13.5B

25. 1.6 review...

26. 1.6 Evolution explains the unity and diversity of life
Charles Dar win
Synthesized theory of evolution by natural selection
Figure 1.6A

27. Natural selection is an editing mechanism
occurs when populations/organisms, having inherited variations,
exposed to environmental factors that favor the reproductive success of some individuals over others 1 2 3
Populations with varied inherited traits
Elimination of individuals with certain traits
Reproduction of survivors
Figure 1.6B

28. All organisms have adaptations
have evolved by means of natural selection
Killer whale
Pangolin
Figure 1.6C

29. 13.12 Mutation & sexual recombination generate variation
changes in nucleotide sequence of DNA
Can create new alleles

30. shuffling alleles during meiosis  variation!
Sexual recombination
shuffling alleles during meiosis  variation! A1 A2 A3
and X
Parents
Meiosis
Gametes
Fertilization
Offspring, with new combinations of alleles
Figure 13.12

31. CONNECTION
13.13 The evolution of antibiotic resistance in bacteria is a serious public health concern
excessive use of antibiotics
evolution of antibiotic-resistant bacteria
Colorized SEM 5,600
Figure 13.13

32. 13.15 The perpetuation of genes defines evolutionary fitness
An individual’s fitness ???
contribution it makes to gene pool of next generation

33. 13.18 Natural selection cannot fashion perfect organisms
At least 4 reasons why
Organisms limited by historical constraints
Adaptations often compromises
Chance and natural selection interact
Selection can only edit existing variations

34. Review ?s
Articles
Go over Quiz

35. POPULATION GENETICS AND THE MODERN SYNTHESIS
13.6 Populations are the units of evolution
A population
Is a group of individuals of the same species living in the same place at the same time
A species is a group of populations
Whose individuals can interbreed and produce fertile offspring

36. Population genetics
Studies how populations change genetically over time
The modern synthesis
Connects Darwin’s theory with population genetics

37. A gene pool
Is the total collection of genes in a population at any one time
Microevolution
Is a change in the relative frequencies of alleles in a gene pool

38. 13.7 The gene pool of a nonevolving population remains constant over the generations
In a nonevolving population
The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population
Webbing
No webbing
Figure 13.7A

39. Hardy-Weinberg equilibrium
Hardy-Weinberg equilibrium
States that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool
Phenotypes
Genotypes WW Ww ww
Number of animals (total  500)
320
160 20
500
Genotype frequencies
 0.64
 0.32
 0.04
Number of alleles in gene pool (total  1,000)
Allele frequencies
800
1,000
 0.8 W
 0.2 w
640 W
160 W  160 w
40 w
Figure 13.7B
200

40. We can follow alleles in a population
We can follow alleles in a population
To observe if Hardy-Weinberg equilibrium exists
Recombination of alleles from parent generation
EGGS
Genotype frequencies
Allele frequencies
0.64 WW
0.32 Ww
0.04 ww
0.8 W
0.2 w
Next generation:
W egg p  0.8
w egg q  0.2
W sperm p  0.8
w sperm q  0.2
SPERM
WW p2  0.64
Ww pq  0.16
wW qp  0.16
ww q2  0.04
Figure 13.7C

41. For a population to be in Hardy-Weinberg equilibrium, it must satisfy five main conditions
The population is very large
The population is isolated
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive success

42. 13.8 The Hardy-Weinberg equation is useful in public health science
CONNECTION
13.8 The Hardy-Weinberg equation is useful in public health science
Public health scientists use the Hardy-Weinberg equation
To estimate frequencies of disease-causing alleles in the human population

43. 13.9 In addition to natural selection, genetic drift and gene flow can contribute to evolution
Genetic drift
Is a change in the gene pool of a population due to chance
Can alter allele frequencies in a population

44. Can cause the bottleneck effect or the founder effect
Genetic drift
Can cause the bottleneck effect or the founder effect
Original population
Bottlenecking event
Surviving population
Figure 13.9A
Figure 13.9B

45. Gene flow
Is the movement of individuals or gametes between populations
Can alter allele frequencies in a population

46. Natural selection
Leads to differential reproductive success in a population
Can alter allele frequencies in a population

47. 13.10 Endangered species often have reduced variation
CONNECTION
13.10 Endangered species often have reduced variation
Low genetic variability
May reduce the capacity of endangered species to survive as humans continue to alter the environment
Figure 13.10

48. VARIATION AND NATURAL SELECTION
13.11 Variation is extensive in most populations
Many populations exhibit polymorphism
Different forms of phenotypic characteristics
Figure 13.11

49. Populations may also exhibit geographic variation
Variation of an inherited characteristic along a geographic continuum

50. 13.14 Diploidy and balancing selection variation
13.14 Diploidy and balancing selection variation
Diploidy preserves variation
By “hiding” recessive alleles
Balanced polymorphism
May result from the heterozygote advantage or frequency-dependent selection

51. Some variations may be neutral
Some variations may be neutral
Providing no apparent advantage or disadvantage
Figure 13.14

52. 13.16 Natural selection can alter variation in a population in three ways
Stabilizing selection
Favors intermediate phenotypes
Directional selection
Acts against individuals at one of the phenotypic extremes
Disruptive selection
Favors individuals at both extremes of the phenotypic range

53. Stabilizing selection Directional selection
Three possible effects of natural selection
Original population
Stabilizing selection
Evolved population
Frequency of individuals
Phenotypes (fur color)
Directional selection
Disruptive selection
Figure 13.16

54. 13.17 Sexual selection may produce sexual dimorphism
13.17 Sexual selection may produce sexual dimorphism
Sexual selection leads to the evolution of secondary sexual characteristics
Which may give individuals an advantage in mating
Figure 13.17B
Figure 13.17A