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
Is a type of bird living in the Galápagos Islands

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

4. DARWIN’S THEORY OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory of evolution
On his visit to the Galápagos Islands, Charles Darwin observed many unique organisms
Figure 13.1A

5. Darwin’s main ideas
Can be traced back to the ancient Greeks
Aristotle and the Judeo-Christian culture believed that species are fixed (permanent) and do not evolve  

6. In the century prior to Darwin
The study of fossils suggested that life forms change
Geologists proposed that a very old Earth is changed by gradual processes
Lyell developed a theory of evolution nearly identical to Darwin's
The unifying theme of biology is evolution.

7. While on the voyage of the HMS Beagle in the 1830s
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
North America
Great Britain
Europe
Asia
ATLANTIC OCEAN
PACIFIC OCEAN
Africa
PACIFIC OCEAN
Equator
The Galápagos Islands
PACIFIC OCEAN
South America
Pinta
Genovesa
Marchena
Australia
Equator
Santiago
Andes
Cape of Good Hope
Daphne Islands
Fernandina
Pinzón
Tasmania
New Zealand
Isabela
Santa Cruz
Cape Horn
Santa Fe
San Cristobal
Tierra del Fuego
40 km
Figure 13.1B
Florenza
Española
40 miles

8. Main ideas that Darwin advanced in his works
Darwin’s experiences during the voyage of the Beagle helped him frame his ideas on evolution
Main ideas that Darwin advanced in his works
Species change over time  
Living species have arisen from earlier life forms  
Modern species arose through a process known as "descent with modification"  
New species arise by natural selection  

9. 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
The Earth is very old.  
Populations produce more offspring than their environment can support.  
Organisms compete for limited resources.  
Organisms vary in heritable ways.

10. 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

11. 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
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog (wolf)
Figure 13.2A
Figure 13.2B

12. 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
African wild dog
Coyote
Wolf
Fox
Jackal
Thousands to millions of years of natural selection
Ancestral canine
Figure 13.2C

13. 13.3 The study of fossils provides strong evidence for evolution
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
B Petrified tree
C Ammonite casts
D Dinosaur tracks
E Fossilized organic matter of a leaf
F Insect in amber
G “Ice Man”
Figure 13.3A–G

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

15. Fossils form the following processes
The remains of a dead organism are sometimes turned into stone by petrification.  
Actual organic material remains if an organism is buried in a medium that prevents bacteria and fungi from decomposing it.  
The hard parts of animals that are rich in minerals, such as teeth and the shells of clams, may remain as fossils.  
Whole organisms are sometimes preserved in ice or deep within acid bogs.  

16. Many fossils link early extinct species With species living today
Many fossils link early extinct species
With species living today
Figure 13.3I

17. The fossil record shows that
the earliest fossils of life are about 3.5 billion years old.  
younger strata are on top of older strata.  
within the vertebrates, fish were the first to evolve.  
some fossils represent an evolutionary series of changes that provide strong documentation of evolution.  

18. 13.4 A mass of other evidence reinforces the evolutionary view of life
13.4 A mass of other evidence reinforces the evolutionary view of life

19. Biogeography Biogeography, the geographic distribution of species
Biogeography
Biogeography, the geographic distribution of species
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

20. Comparative anatomy
Is the comparison of body structures in different species
Homology
Is the similarity in characteristics that result from common ancestry

21. Homologous structures
Homologous structures
Are features that often have different functions but are structurally similar because of common ancestry
Human
Cat
Whale
Bat
Figure 13.4A

22. Anatomy and Embryology
Analogous structures-have closely related functions but do not derive from the same ancestral form. (Different structure; same function.)
Ex. Bird, bat, and moth wings

23. Comparative Embryology
Comparative Embryology
Comparative embryology
Is the comparison of early stages of development among different organisms

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

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

26. 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
The smallest unit that can evolve.
A species is a group of populations
Whose individuals can interbreed and produce fertile offspring

27. 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

28. 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
Figure 13.7A
Webbing
No webbing

29. 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
Genotype frequencies
320
500
160
500 20
500
 0.64
 0.32
 0.04
Number of alleles in gene pool (total  1,000)
640 W
160 W  160 w
40 w
Allele frequencies
800
1,000
 0.8 W
200
1,000
 0.2 w
Figure 13.7B

30. 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

31. 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

32. 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

33. Genetic drift
Can cause the bottleneck effect (genetic drift resulting from a disaster that drastically reduces population size)or the founder effect
Original population
Bottlenecking event
Surviving population
Figure 13.9A
Figure 13.9B

34. Gene flow
Is the movement of individuals or gametes between populations
Can alter allele frequencies in a population
Tends to reduce genetic differences between populations

35. 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

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

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

38. 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

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

40. 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

41. 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

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

43. 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

44. 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

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

46. 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 13.17A
Figure 13.17B

47. Intrasexual selection-secondary sex structures may be used to compete with members of the same sex for mate.
Intersexual selection-mate choice-individuals of one sex (usually females) are choosy in selecting their mates.

48. 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