1. Descent with Modification19
Descent with Modification

2. Overview: Endless Forms Most Beautiful
Lepidopteran insects (moths and butterflies) have many features in common including a juvenile feeding stage called a caterpillar
Lepidopteran species also have many features that are distinct from each other in both the caterpillar and adult forms 2

3. Lepidopterans illustrate three key observations about life
The fit between organisms and their environment
The shared characteristics (unity) of life
The diversity of life 3

4. Figure 19.1
Figure 19.1 How is this caterpillar protecting itself from predators? 4

5. A new era of biology began in 1859 when Charles Darwin published The Origin of Species
The Origin of Species focused biologists’ attention on the great diversity of organisms 5

6. Darwin noted that current species are descendants of ancestral species
Evolution can be defined by Darwin’s phrase descent with modification
Evolution can be viewed as both a pattern and a process 6

7. Concept 19.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species
Darwin’s revolutionary ideas had deep historical roots 7

8. Figure 19.2
Figure 19.2 Unusual species inspired novel ideas. 8

9. Scala Naturae and Classification of Species
The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae
The Old Testament holds that species were individually designed by God and therefore perfect 9

10. Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a particular purpose
Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms
He developed the binomial format for naming species (for example, Homo sapiens) 10

11. Ideas About Change over Time
The study of fossils helped to lay the groundwork for Darwin’s ideas
Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata 11

12. Video: Grand Canyon

13. Younger stratum with more recent fossils Older stratum
Figure 19.3
Figure 19.3 Formation of sedimentary strata with fossils
Younger stratum
with more recent
fossils
Older stratum
with older fossils 13

14. Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier
Cuvier speculated that each boundary between strata represents a catastrophe that destroyed many species 14

15. This view strongly influenced Darwin’s thinking
Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow, continuous actions still operating today
Lyell further proposed that the mechanisms of change are constant over time
This view strongly influenced Darwin’s thinking 15

16. Lamarck’s Hypothesis of Evolution
Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
The mechanisms he proposed are unsupported by evidence 16

17. Figure 19.4
Figure 19.4 Acquired traits cannot be inherited. 17

18. Concept 19.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life
Some doubt about the permanence of species preceded Darwin’s ideas 18

19. Darwin’s Research
As a boy and into adulthood, Charles Darwin had a consuming interest in nature
Darwin first studied medicine (unsuccessfully) and then theology at Cambridge University
After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a five-year around-the-world voyage on the Beagle 19

20. The Voyage of the Beagle
During his travels on the Beagle, Darwin collected specimens of South American plants and animals
He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions
He experienced an earthquake in Chile and observed the uplift of rocks 20

21. Darwin was influenced by Lyell’s Principles of Geology and thought that Earth was more than 6,000 years old
His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands west of South America
He hypothesized that species from South America had colonized the Galápagos and speciated on the islands 21

22. Video: Albatross Courtship

23. Video: Boobies Courtship

24. Video: Galápagos Islands

25. Video: Marine Iguana

26. Video: Sea Lion

27. Video: Soaring Hawk

28. Video: Tortoise

29. Darwin in 1840, after his return HMS Beagle at sea from the voyage
Figure 19.5
Darwin in
1840, after
his return
from the
voyage
HMS Beagle at sea
Great
Britain
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
PACIFIC
OCEAN
AFRICA
Pinta
Genovesa
Equator
Marchena
SOUTH
AMERICA
Malay Archipelago
Equator
PACIFIC
OCEAN
Santiago
Daphne
Islands
Chile
Brazil
AUSTRALIA
Fernandina
Pinzón
PACIFIC
OCEAN
Andes Mtns.
Figure 19.5 The voyage of HMS Beagle
Isabela
Santa
Cruz
Santa Fe
San
Cristobal
Argentina
Cape of
Good Hope
Tasmania 20 40
Florenza
Española
Cape Horn
New
Zealand
Kilometers 29

30. Great Britain EUROPE NORTH AMERICA ATLANTIC OCEAN AFRICA SOUTH Equator
Figure 19.5a
Great
Britain
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
AFRICA
SOUTH
AMERICA
Equator
Malay Archipelago
PACIFIC
OCEAN
Chile
Brazil
AUSTRALIA
PACIFIC
OCEAN
Andes Mtns.
Figure 19.5a The voyage of HMS Beagle (part 1: full map)
Argentina
Cape of
Good Hope
Tasmania
Cape Horn
New
Zealand 30

31. Darwin in 1840, after his return from the voyage Figure 19.5b
Figure 19.5b The voyage of HMS Beagle (part 2: Darwin portrait)
Darwin in 1840,
after his return
from the voyage 31

32. The Galápagos Islands PACIFIC OCEAN Pinta Genovesa Marchena Equator
Figure 19.5c
The
Galápagos
Islands
PACIFIC
OCEAN
Pinta
Genovesa
Marchena
Equator
Santiago
Daphne
Islands
Pinzón
Fernandina
Isabela
Santa
Cruz
Santa Fe
Figure 19.5c The voyage of HMS Beagle (part 3: Galápagos map)
San
Cristobal 20 40
Florenza
Española
Kilometers 32

33. HMS Beagle at sea Figure 19.5d
Figure 19.5d The voyage of HMS Beagle (part 4: Beagle at sea)
HMS Beagle at sea 33

34. Darwin’s Focus on Adaptation
In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes
From studies made years after Darwin’s voyage, biologists have concluded that this is what happened to the Galápagos finches 34

35. (a) Cactus-eater (c) Insect-eater (b) Seed-eater Figure 19.6
Figure 19.6 Three examples of beak variation in Galápagos finches
(b) Seed-eater 35

36. (a) Cactus-eater Figure 19.6a
Figure 19.6a Three examples of beak variation in Galápagos finches (part 1: cactus-eater)
(a) Cactus-eater 36

37. (b) Seed-eater Figure 19.6b
Figure 19.6b Three examples of beak variation in Galápagos finches (part 2: seed-eater)
(b) Seed-eater 37

38. (c) Insect-eater Figure 19.6c
Figure 19.6c Three examples of beak variation in Galápagos finches (part 3: insect-eater)
(c) Insect-eater 38

39. In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification but did not introduce his theory publicly
Natural selection is a process in which individuals with favorable inherited traits are more likely to survive and reproduce
In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s
Darwin quickly finished The Origin of Species and published it the next year 39

40. Figure 19.7
Figure 19.7 Alfred Russel Wallace 40

41. Figure 19.7a
Figure 19.7a Alfred Russel Wallace (part 1: frog painting) 41

42. Figure 19.7b
Figure 19.7b Alfred Russel Wallace (part 2: Wallace portrait) 42

43. Ideas from The Origin of Species
Darwin explained three broad observations about life
The unity of life
The diversity of life
The match between organisms and their environment 43

44. Descent with Modification
Darwin never used the word evolution in the first edition of The Origin of Species
The phrase descent with modification summarized Darwin’s perception of the unity of life
The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past 44

45. In the Darwinian view, the history of life is like a tree with branches representing life’s diversity
Fossils of extinct species help to “fill in” the morphological gaps between present-day groups 45

46. Figure 19.8
Figure 19.8 “I think . . .” 46

47. Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Moeritherium † †
Figure 19.9
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium † †
Barytherium †
Deinotherium †
Mammut †
Platybelodon †
Stegodon
Mammuthus †
Figure 19.9 Descent with modification
Elephas maximus
(Asia)
Loxodonta africana
(Africa)
Loxodonta cyclotis
(Africa) 60 34 24
5.5 2
104
Millions of years ago
Years ago 47

48. Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) † Moeritherium †
Figure 19.9a
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium † †
Barytherium †
Deinotherium
Figure 19.9a Descent with modification (part 1) †
Mammut 48

49. † Platybelodon † Stegodon Mammuthus † Elephas maximus (Asia)
Figure 19.9b †
Platybelodon †
Stegodon
Mammuthus †
Elephas maximus
(Asia)
Loxodonta africana
(Africa)
Figure 19.9b Descent with modification (part 2)
Loxodonta cyclotis
(Africa) 60 34 24
5.5 2
104
Millions of years ago
Years ago 49

50. Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection
Darwin argued that a similar process occurs in nature 50

51. Cabbage Selection for apical (tip) bud Brussels sprouts Selection for
Figure 19.10
Cabbage
Selection for
apical (tip) bud
Brussels
sprouts
Selection for
axillary (side)
buds
Broccoli
Selection
for flowers
and stems
Figure Artificial selection
Selection
for stems
Selection
for leaves
Kale
Wild mustard
Kohlrabi 51

52. Figure 19.10a
Figure 19.10a Artificial selection (part 1: wild mustard)
Wild mustard 52

53. Kale Figure 19.10b Figure 19.10b Artificial selection (part 2: kale)53

54. Brussels sprouts Figure 19.10c
Figure 19.10c Artificial selection (part 3: brussels sprouts) 54

55. Figure 19.10d
Cabbage
Figure 19.10d Artificial selection (part 4: cabbage) 55

56. Figure 19.10e
Broccoli
Figure 19.10e Artificial selection (part 5: broccoli) 56

57. Figure 19.10f
Figure 19.10f Artificial selection (part 6: kohlrabi)
Kohlrabi 57

58. Darwin drew two inferences from two observations
Observation #1: Members of a population often vary in their inherited traits 58

59. Figure 19.11
Figure Variation in a population 59

60. Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce 60

61. Video: Sea Horses

62. Figure 19.12
Spore
cloud
Figure Overproduction of offspring 62

63. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals 63

64. Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations 64

65. Darwin was influenced by Thomas Malthus, who noted the potential for human population to increase faster than food supplies and other resources
If some heritable traits are advantageous, these will accumulate in a population over time, and this will increase the frequency of individuals with these traits
This process explains the match between organisms and their environment 65

66. Natural Selection: A Summary
Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals
Over time, natural selection increases the match between organisms and their environment
If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species 66

67. (a) A flower mantid in Malaysia (b) A leaf mantid in Borneo
Figure 19.13
Figure Camouflage as an example of evolutionary adaptation
(a) A flower mantid in Malaysia
(b) A leaf mantid in Borneo 67

68. (a) A flower mantid in Malaysia
Figure 19.13a
Figure 19.13a Camouflage as an example of evolutionary adaptation (part 1: flower mantid)
(a) A flower mantid in Malaysia 68

69. (b) A leaf mantid in Borneo
Figure 19.13b
Figure 19.13b Camouflage as an example of evolutionary adaptation (part 2: leaf mantid)
(b) A leaf mantid in Borneo 69

70. Note that individuals do not evolve; populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
Adaptations vary with different environments 70

71. Concept 19.3: Evolution is supported by an overwhelming amount of scientific evidence
New discoveries continue to fill the gaps identified by Darwin in The Origin of Species
There are four types of data that document the pattern of evolution
Direct observations
Homology
The fossil record
Biogeography 71

72. Direct Observations of Evolutionary Change
Two examples provide evidence for natural selection: natural selection in response to introduced plant species and the evolution of drug-resistant bacteria 72

73. Natural Selection in Response to Introduced Plant Species
Soapberry bugs use their “beak” to feed on seeds within fruits
In southern Florida soapberry bugs feed on balloon vine with larger fruit; they have longer beaks
In central Florida they feed on goldenrain tree with smaller fruit; they have shorter beaks
Correlation between fruit size and beak size has also been observed in Louisiana, Oklahoma, and Australia 73

74. These cases are examples of evolution by natural selection
In all cases, beak size has evolved in populations that feed on introduced plants with fruits that are smaller or larger than the native fruits
These cases are examples of evolution by natural selection
In Florida this evolution in beak size occurred in less than 35 years 74

75. Museum-specimen average
Figure 19.14
Field Study
Results 10
On native species,
balloon vine
(southern Florida)
Beak 8 6 4 2
Number of individuals
Museum-specimen average 10
On introduced
species,
goldenrain tree
(central Florida) 8
Soapberry bug with beak
inserted in balloon vine
fruit
Figure Inquiry: Can a change in a population’s food source result in evolution by natural selection? 6 4 2 6 7 8 9 10 11
Beak length (mm) 75

76. Soapberry bug with beak inserted in balloon vine fruit
Figure 19.14a
Field Study
Figure 19.14a Inquiry: Can a change in a population’s food source result in evolution by natural selection? (part 1: field study)
Soapberry bug with beak
inserted in balloon vine
fruit 76

77. Museum-specimen average
Figure 19.14b
Results 10
On native species,
balloon vine
(southern Florida)
Beak 8 6 4 2
Number of individuals
Museum-specimen average 10
On introduced
species,
goldenrain tree
(central Florida)
Figure 19.14b Inquiry: Can a change in a population’s food source result in evolution by natural selection? (part 2: results) 8 6 4 2 6 7 8 9 10 11
Beak length (mm) 77

78. Museum-specimen average
Figure 19.14c
Results 10
On native species,
balloon vine
(southern Florida) 8 6 4 2
Number of individuals
Museum-specimen average 10
On introduced
species,
goldenrain tree
(central Florida) 8
Figure 19.14c Inquiry: Can a change in a population’s food source result in evolution by natural selection? (part 3: results, detail) 6 4 2 6 7 8 9 10 11
Beak length (mm) 78

79. The Evolution of Drug-Resistant Bacteria
The bacterium Staphylococcus aureus is commonly found on people’s skin or in their nasal passages
Methicillin-resistant S. aureus (MRSA) strains are dangerous pathogens
S. aureus became resistant to penicillin in 1945, two years after it was first widely used
S. aureus became resistant to methicillin in 1961, two years after it was first widely used 79

80. MRSA bacteria use a different protein in their cell walls
Methicillin works by inhibiting a protein used by bacteria in their cell walls
MRSA bacteria use a different protein in their cell walls
When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains
MRSA strains are now resistant to many antibiotics 80

81. Annual hospital admissions
Figure 19.15
2,750,000 1
250,000 base pairs
400
2,500,000
350
Chromosome map
of S. aureus clone USA300
500,000
300
Key to adaptations
250
2,250,000
Annual hospital admissions
with MRSA (thousands)
Methicillin resistance
200
Ability to colonize hosts
750,000
150
Increased disease severity
100
Increased gene exchange
(within species) and
toxin production
2,000,000 50
1,000,000
’93
’94
’95
’96
’97
’98
’99
’00
’01
’02
’03
’04
’05
Figure The rise of methicillin-resistant Staphylococcus aureus (MRSA)
Year
1,750,000
1,250,000
1,500,000 81

82. Chromosome map of S. aureus clone USA300
Figure 19.15a 1
2,750,000
250,000 base pairs
2,500,000
Chromosome map
of S. aureus clone USA300
500,000
Key to adaptations
2,250,000
Methicillin resistance
Ability to colonize hosts
750,000
Increased disease severity
Increased gene exchange
(within species) and
toxin production
2,000,000
Figure 19.15a The rise of methicillin-resistant Staphylococcus aureus (MRSA) (part 1: chromosome map)
1,000,000
1,750,000
1,250,000
1,500,000 82

83. Annual hospital admissions
Figure 19.15b
400
350
300
250
Annual hospital admissions
with MRSA (thousands)
200
150
100
Figure 19.15b The rise of methicillin-resistant Staphylococcus aureus (MRSA) (part 2: hospitalization increases) 50
’93
’94
’95
’96
’97
’98
’99
’00
’01
’02
’03
’04
’05
Year 83

84. Natural selection does not create new traits, but edits or selects for traits already present in the population
The local environment determines which traits will be selected for or selected against in any specific population 84

85. Homology Evolution is a process of descent with modification
Related species can have characteristics with underlying similarity that function differently
Homology is similarity resulting from common ancestry 85

86. Anatomical and Molecular Homologies
Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor 86

87. Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat
Figure 19.16
Humerus
Radius
Ulna
Carpals
Figure Mammalian forelimbs: homologous structures
Metacarpals
Phalanges
Human
Cat
Whale
Bat 87

88. Comparative embryology reveals anatomical homologies not visible in adult organisms
Vestigial structures are remnants of features that served important functions in the organism’s ancestors 88

89. Pharyngeal arches Post-anal tail Chick embryo (LM) Human embryo
Figure 19.17
Pharyngeal
arches
Post-anal
tail
Figure Anatomical similarities in vertebrate embryos
Chick embryo (LM)
Human embryo 89

90. Pharyngeal arches Post-anal tail Chick embryo (LM) Figure 19.17a
Figure 19.17a Anatomical similarities in vertebrate embryos (part 1: chick embryo, LM)
Chick embryo (LM) 90

91. Pharyngeal arches Post-anal tail Human embryo Figure 19.17b
Figure 19.17b Anatomical similarities in vertebrate embryos (part 2: human embryo)
Human embryo 91

92. Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor
Homologous genes can be found in organisms as dissimilar as humans and bacteria 92

93. A Different Cause of Resemblance: Convergent Evolution
Convergent evolution is the evolution of similar, or analogous, features in distantly related groups
Analogous traits arise when groups independently adapt to similar environments in similar ways
Convergent evolution does not provide information about ancestry 93

94. NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Figure 19.18
Figure Convergent evolution
AUSTRALIA
Flying
squirrel 94

95. The Fossil Record The fossil record provides evidence of
The extinction of species
The origin of new groups
Changes within groups over time 95

96. Cetaceans and even-toes ungulates
Figure 19.19
Most mammals
Cetaceans and even-toes ungulates
Figure Ankle bones: one piece of the puzzle
(a) Canis (dog)
(b) Pakicetus
(c) Sus (pig)
(d) Odocoileus (deer) 96

97. (a) Canis (dog) Figure 19.19a
Figure 19.19a Ankle bones: one piece of the puzzle (part 1: Canis, dog)
(a) Canis (dog) 97

98. Figure 19.19b
Figure 19.19b Ankle bones: one piece of the puzzle (part 2: Pakicetus)
(b) Pakicetus 98

99. Figure 19.19c
Figure 19.19c Ankle bones: one piece of the puzzle (part 3: Sus, pig)
(c) Sus (pig) 99

100. (d) Odocoileus (deer) Figure 19.19d
Figure 19.19d Ankle bones: one piece of the puzzle (part 4: Odocoileus, deer)
(d) Odocoileus (deer)
100

101. Fossils can document important transitions
For example, the transition from land to sea in the ancestors of cetaceans
101

102. Other even-toed ungulates Hippopotamuses Pakicetus † Rodhocetus †
Figure 19.20
Other even-toed
ungulates
Hippopotamuses
Pakicetus †
Rodhocetus †
Common
ancestor
of cetaceans
Dorudon †
Figure The transition to life in the sea
Living
cetaceans 70 60 50 40 30 20 10
Key
Pelvis
Tibia
Millions of years ago
Femur
Foot
102

103. Pakicetus † Common ancestor of cetaceans Rodhocetus † Dorudon † Living
Figure 19.20a
Pakicetus †
Common
ancestor
of cetaceans
Rodhocetus †
Dorudon †
Living
cetaceans
Figure 19.20a The transition to life in the sea (detail) 50 40 30 20 10
Key
Pelvis
Tibia
Millions of years ago
Femur
Foot
103

104. 20 cm Diacodexis, an early even-toed ungulate Figure 19.UN01
Figure 19.UN01 In-text figure, Diacodexis, p. 377
Diacodexis, an early
even-toed ungulate
104

105. Biogeography
Biogeography, the geographic distribution of species, provides evidence of evolution
Earth’s continents were formerly united in a single large continent called Pangaea but have since separated by continental drift
An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved
105

106. Endemic species are species that are not found anywhere else in the world
Islands have many endemic species that are often closely related to species on the nearest mainland or island
Darwin explained that species on islands gave rise to new species as they adapted to new environments
106

107. What Is Theoretical About Darwin’s View of Life?
In science, a theory accounts for many observations and explains and integrates a great variety of phenomena
The predictions of a scientific theory must stand up to continual testing by experimentation and observation
Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions
Ongoing research adds to our understanding of evolution
107

108. Guppies transplanted Pools with pike-cichlids and guppies
Figure 19.UN02a
Guppies
transplanted
Pools with
pike-cichlids
and guppies
Figure 19.UN02a Skills exercise: making and testing predictions (part 1)
Pools with killifish,
but no guppies
prior to transplant
108

109. colored spots Number of Area of colored spots (mm2)
Figure 19.UN02b 12 12 10 10 8 8
colored spots
Number of
Area of colored
spots (mm2) 6 6 4 4 2 2
Figure 19.UN02b Skills exercise: making and testing predictions (part 2)
Source
population
Transplanted
population
Source
population
Transplanted
population
109

110. Individuals in a population vary in their heritable characteristics.
Figure 19.UN03
Observations
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Inferences
Individuals that are well suited
to their environment tend to leave more
offspring than other individuals.
Figure 19.UN03 Summary of key concepts: natural selection
and
Over time, favorable traits
accumulate in the population.
110

111. Figure 19.UN04
Figure 19.UN04 Test your understanding, question 6 (DDT resistance data)
111