1. How Populations Evolve
Chapter 13
How Populations Evolve

2. “Nothing in Biology Makes Sense Except in the light of evolution. ” T
“Nothing in Biology Makes Sense Except in the light of evolution.” T. Dobzhansky

3. Clown, Fool, or Simply Well Adapted?
Clown, Fool, or Simply Well Adapted?
The blue-footed booby
Is a type of bird living in the Galápagos Islands

4. This type of bird possesses many specialized characteristics, called evolutionary adaptations
Evolutionary adaptations are inherited traits that enhance its ability to survive and reproduce in its particular environment.

5. What are some of the characteristics that show evolutionary adaptations for the blue footed booby?
The blue-footed booby has:
enormous webbed feet
an oil producing gland that keeps the booby afloat
a nostril that can close under water that prevents water from entering the lungs
a gland that secrets salt from consumed sea water
and a torpedo-like body
All adaptations that make life on the sea feasible.

6. If you look at any organism critically, you are first struck by the differences from other organisms.
Further observations often reveals that an organism’s features show some relationship to where the organism lives and what it does in its environment

7. DARWIN’S THEORY OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory of evolution
On his visit to the Galápagos Islands: (VIDEO)
Charles Darwin observed many unique organisms
Iguana
Note: Special structures or behaviors help the organism survive and reproduce in a particular environment.
Figure 13.1A

8. Living species have arisen from earlier life forms and that species change over time.
Darwin’s main ideas can be traced back to the ancient Greeks.
Anaximander (about 2,500 years ago) suggested that life arose in water and that simpler forms preceded more complex forms of life.
Aristotle believed that species were fixed and did not evolve.
Judeo-Christian tradition that all species were created in a single act of creation about 6,000 years ago.

9. In the century prior to Darwin
In the century prior to Darwin
Buffon (mid-1700s) suggested that Earth was much older than 6,000 years, and raised the possibility that different species arose from common ancestors, although he later argued against this point.
The study of fossils suggested that life forms change
Video
Lamarck (early 1800s) was the first to strongly support the idea of evolution, but he believed the mechanism for change was the inheritance of acquired characteristics.
He proposed that by using or not using its body parts, an individual may develop certain traits that are passed on to its offspring.

10. While on the voyage of the HMS Beagle in the 1830s
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
While on the voyage of the HMS Beagle in the 1830s
Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands.
Web 13A Darwin and the Galapagos Islands

11. Darwin’s experiences during the voyage of the Beagle helped him frame his ideas on evolution
Species evolve as a result of their interactions with their environment.
Darwin was influenced by Lyell’s Principles of Geology, in which he promoted the idea of continual, gradual, and consistent geological change.
Darwin coined the term, decent with modification,
A unity among organisms related through descent from an ancestor that lived in the remote past.
Over millions of years they accumulated diveses adaptations that allowed them to survive.

12. What was Darwin’s Phrase for evolution? What does it mean?
Activity 13B: The Voyage of the Beagle: Darwin's Trip Around the World (13.1)

13. 13.2 Darwin proposed natural selection as the mechanism of evolution
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 characteristics that can be inherited

14. Darwin reasoned that natural selection
Darwin reasoned that natural selection
Results in favored traits being represented more and more and unfavored ones less and less in ensuing generations of organisms
Darwin observed that species tend to produce excessive numbers of offspring, that the expression of traits varies among the individuals of a population, and that many of these traits are heritable.

15. What do overproduction of offspring, and heritable variations have to do with organisms becoming adapted to their environment?
1. Every environment has a limited supply of resources. 2. Survival in a limited environment depends in part on the features the organisms inherit from their parents. 3. Those with characteristics favored the environment went on to reproduce 4. Darwin referred to this process as Natural Selection

16. Hundreds to thousands of years of breeding (artificial selection)
Darwin found convincing evidence for his ideas in the results of artificial selection
The selective breeding of domesticated plants and animals (modifying species)
Figure 13.2A
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog (wolf)
Figure 13.2B

17. Thousands to millions of years of natural selection
Darwin proposed that living species
Are descended from earlier life forms and that natural selection is the mechanism of evolution
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog (wolf)
Thousands to millions of years of natural selection
Ancestral canine
African wild dog
Coyote
Wolf
Fox
Jackal
Figure 13.2C

18. Two important points can be drawn from Darwin’s theory of natural selection:
1.Ancestral species gave rise to the diverse life forms by transfer of heritable traits to offspring that best promote reproduction. He called this “descent with modification.”
2.Over vast amounts of time, the gradual accumulation of changes in the characteristics among the individuals in a population occurs.

19. 13.3 The study of fossils provides strong evidence for evolution
Fossils and the fossil record
Strongly support the 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

20. The fossil record
Reveals that organisms have evolved in a historical sequence
Figure 13.3H

21. Many fossils link early extinct species with species living today
Basilosaurus, an extinct whale whose hind legs link living whales with their land-dwelling ancestors.
Figure 13.3I

22. 13.4 A mass of other evidence reinforces the evolutionary view of life.
Biogeography
Biogeography, the geographic distribution of species
Species at different geographical regions are similar to each other
This suggested to Darwin that organisms evolve from common ancestors
Darwin noted that Galápagos animals
Resembled species of the South American mainland more than animals on similar but distant islands

23. Comparative anatomy Homology
Comparative anatomy
Is the comparison of body structures in different species
Anatomical similarities between many species give signs of common decent.
For example, all mammals have the same basic limb structure.
Homology
Is the similarity in characteristics that result from common ancestry

24. Homologous structures
Homologous structures
Are features that often have different functions but are structurally similar because of common ancestry
Evolution is a remodeling process. Web activity
Vestigial organs
Organs that have no know function that are remains from ancestors.
Human
Cat
Whale
Bat
Figure 13.4A

25. Comparative Embryology
Comparative Embryology
Comparative embryology is the comparison of early stages of development among different organisms.

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

27. Molecular Biology
Comparisons of DNA and amino acid sequences between different organisms
Reveal evolutionary relationships
Table 13.4

28. CONNECTION 13.5 Scientists can observe natural selection in action
13.5 Scientists can observe natural selection in action
Camouflage adaptations that evolved in different environments are examples of the results of natural selection.
A flower mantid in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A

29. Development of pesticide resistance in insects
Is another example of natural selection in action
These two examples illustrate that natural selection is an editing process, not a creative mechanism. They also show that natural selection is regional, timely, and can occur rapidly.
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

30. In what sense is natural selection more of an editing process than a creative process?

31. POPULATION GENETICS AND THE MODERN SYNTHESIS
13.6 Populations are the units of evolution
Population
Is a group of individuals of the same species living in the same place at the same time
Species is a group of populations
Whose individuals can interbreed and produce fertile offspring
A population is the smallest unit that can evolve
The increase of resistant insects in areas sprayed with pesticides is a good example of a population evoloving.
Natural selection favored genes that were resistant
These insects left more offspring
The population changed or evolved.

32. The modern synthesis (1940’s)
Population genetics (1920’s) – combined the teachings of Darwin and Mendel
Studies how populations change genetically over time
The modern synthesis (1940’s)
Connects Darwin’s theory with population genetics
i.e. populations are the unit of evolution.
Key Features of Populations:
Populations may be isolated from others of the same species, with little interbreeding and thus little exchange of genes.
Islands, mountain ranges

33. A gene pool Microevolution
A gene pool
Is the total collection of genes in a population at any one time
Alleles in all the individuals within a population.
Microevolution
Is a change in the relative frequencies of alleles in a gene pool
i.e. alleles for pesticide resistance

34. Why can’t an individual evolve?

35. 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.
No matter how many times alleles are shuffled , the frequency of each allele is the gene pool remains the same.
Webbing
No webbing
Figure 13.7A

36. 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
Genetic make up of the original population.
From the genotype frequency we can calculate the frequency of each allele in this population.
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

37. We can follow alleles in a population
To observe if Hardy-Weinberg equilibrium exists
P2 + 2pq + q2 = allows us to determine the frequency of genotypes in a gene pool
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

38. 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
These 5 conditions are rarely met. In many populations the rate of evolution is so slow that the population appears close to equilibrium.

39. Freshman Biology Skip to 13.9 Slide 40

40. 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

41. 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
The smaller the population the more likely genetic drift will occur.
Can alter allele frequencies in a population
Genetic drift tend to reduce genetic variation through the loss in alleles

42. Genetic drift Can cause the bottleneck effect or the founder effect
Genetic drift
Can cause the bottleneck effect or the founder effect
Bottleneck effect is an event that drastically reduces the population
Founder effect caused by the colonization of new locations by smaller population.
The smaller the group the less likely the genetic makeup will represent the population they left.
Original population
Bottlenecking event
Surviving population
Figure 13.9A
Figure 13.9B

43. Gene flow
Is the movement of individuals or gametes (pollen grains) between populations
Gene flow tends to reduce differences between populations
Can alter allele frequencies in a population

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

45. List three causes of microevolution
List three causes of microevolution. Which one will adapt a population to its environment?

46. CONNECTION 13.10 Endangered species often have reduced variation
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

47. Skip to 13.18 Natural Selection cannot fashion perfect organisms
Slide 59

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

50. 13.12 Mutation and sexual recombination generate variation
13.12 Mutation and sexual recombination generate variation
Mutations, or changes in the nucleotide sequence of DNA
Can create new alleles

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

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

53. 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

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

55. 13.15 The perpetuation of genes defines evolutionary fitness
13.15 The perpetuation of genes defines evolutionary fitness
An individual’s fitness
Is the contribution it makes to the gene pool of the next generation

56. 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

57. 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

58. 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

59. 13.18 Natural selection cannot fashion perfect organisms
13.18 Natural selection cannot fashion perfect organisms
There are at least four reasons why natural selection cannot produce perfection
Organisms are limited by historical constraints
Adaptations are often compromises
Chance and natural selection interact
Selection can only edit existing variations