Introduction to Bio Science

1. Evolution and
Natural Selection
BIOL 108
Intro to Bio Sci
Chapter 8
Rob Swatski
Assoc Prof Biology
HACC-York

2. Learning Goals
Be able to
explain
evolution in
action.
Be able to
explain
Darwin’s
journey to an
idea.
Be able to
describe and
explain the
four
mechanisms
that can give
rise to
evolution.
Be able to
explain how
populations of
organisms can
adapt to their
environment
through
natural
selection.
Be able to
explain how
the evidence
for the
occurrence of
evolution is
overwhelming.
2

3. 8·1
Evolution is an
ongoing process.

4. Evolution in Action
8.1 We can see evolution occur right before us.
Could you breed fruit
flies who could live
longer than 20 hours on
average?
4

5. 5

6. When these eggs hatch, do you think
the flies in this new generation will live
longer than 20 hours without food?
6

7. 7

8. What Happened?
Evolution
A genetic change in
the population
Natural
Selection
The consequence of
certain individual
organisms in a population
being born with
characteristics that enable
them to survive better and
reproduce more than the
offspring of other
individuals in the
population
8

9. Does
Evolution
Occur?
The answer is an
unambiguous YES
We can watch it
happen in the lab
whenever we want.
9

10. Evolution
How does
evolution occur?
What types of
changes can
evolution cause in
a population?
Five primary lines
of evidence
Evolution by
natural selection
10

11. Take-Home Message 8.1
The characteristics of
individuals in a
population can
change over time.
We can observe such
change in nature and
can even cause such
change to occur.
11

12. 8.2–8.5
Darwin
journeyed to a
new idea.

13. 13

14. Darwin’s Journey to an Idea
8.2 Before Darwin, most people
believed that all species had
been created separately and
were unchanging.14

15. 15

16. Jean-
Baptiste
Lamarck
Early 1800s:
Species evolve
through the use
& disuse of
body parts
Characteristics
acquired during
life are inherited
Unsupported by
evidence
16

17. Lamarck’s Hypothesis
17

18. 18

19. Aren’t you glad
Lamarck was wrong? 19

20. Charles Lyell
Principles of Geology (1830) 20

21. Charles
Lyell
Early 1800s
geologist:
Principles of
Geology (1830)
Geological forces
had shaped the
earth and were
continuing to do
so.
Gradual but
constant
change
21

22. “The
mechanisms of
change are
constant over
time”
Uniformitarianism
22

23. Take-Home Message 8.2
People used to think
that the earth was
6,000 years old and
that species were
unchanging.
We can observe such
change in nature and
can even cause such
change to occur.
These changes helped
shape Darwin’s
thinking.
23

24. Darwin’s
Research
Darwin always
had a deep
interest in science
& nature
Was a student of
medicine &
theology at
Cambridge
5-year voyage on
the Beagle after
graduation
24
8.3

25. Don’t Listen to
Your Parents
“You care for
nothing but
shooting, dogs, and
rat-catching. You
will be a disgrace to
yourself and your
family.”
- DR. ROBERT DARWIN25

26. Voyage of
the Beagle
Collected
specimens of South
American plants &
animals
Observed
adaptations to
many diverse
environments
Became interested
in the geographic
distribution of
species after a stop
at the Galápagos
Islands 26

27. 27

28. Take-Home Message 8.3
After initially training in
medicine and theology,
Charles Darwin studied
the natural world on a
‘round-the-world voyage.
28

29. 8.4 Observing geographic similarities and differences
among fossils and living plants and animals, Darwin
developed a theory of evolution.
29

30. Two important and unexpected patterns:
1. Traits exhibited by species
30

31. 2. Similarity between the fossils of extinct
species and the living species in that same area
31

32. 32

33. Thomas
Malthus
An economist who
had a major
influence on Darwin
Malthus wrote about
the potential for
human population to
increase faster than
food supplies &
other resources
33

34. 34

35. Take-Home Message 8.4
Darwin noted unexpected
patterns among fossils he
found and living organisms
he observed while on the
voyage of the Beagle.
Fossils resembled but were
not identical to the living
organisms in the same
area.
Finch species on the
Galapagos Islands differed
in small but significant
ways.
These observations helped
him to develop his theory
of how species might
change over time.
35

36. If you had an idea that
was going to outrage
society…
would you keep
it to yourself?36

37. Alfred
Russell
Wallace
37

38. 8.5 In 1859, after
decades of mulling
and procrastinating,
Darwin published his
thoughts on natural
selection.
38

39. 39

40. 40

41. Take-Home Message 8.5
After putting off publishing his
thoughts on natural selection for
more than 15 years, Darwin did
so only after Alfred Russel
Wallace independently came up
with the same idea.
They published a joint
presentation on their ideas in
1858 and Darwin published a
much more detailed treatment in
The Origin of Species in 1859,
sparking wide debate and
discussion of natural selection.
41

42. 8.6–8.11
Four mechanisms
can give rise to
evolution.

43. 8.6 Evolution occurs when the allele
frequencies in a population change.
43

44. Witnessing Evolution
Alter the
population
Increase the
white phenotype
through breeding
As the
generations go
by…
Higher proportion
of white tigers
Evolution =
Change in the
allele frequencies
of a population
44

45. Individuals do not
evolve.
Populations
evolve.
45

46. Natural
Selection
An efficient
mechanism of
evolution…
… and a powerful
force in adapting
populations to
their environment
Evolution and
natural selection
are not the same
thing.
46

47. Agents of Evolutionary
Change
1.
Mutation
2.
Genetic
drift
3.
Migration
4.
Natural
selection
47

48. 48

49. Take-Home Message 8.6
Evolution is a change in
allele frequencies
within a population.
It can occur by four
different mechanisms:
mutation, genetic drift,
migration, and natural
selection.
49

50. 8.7 Mutation—a direct change in the
DNA of an individual—is the ultimate
source of all genetic variation.
50

51. 51
Mutation
An alteration of
the base-pair
sequence of an
individual’s DNA
When this
alteration occurs
in a gene…
…the change in
the DNA
sequence may
change the allele.

53. 53

54. 54
Causes of
Mutations
The process of
cells dividing
can go awry
Environmental
phenomena:
mutagens
Mutations are
random

55. Mutation is the ultimate
source of genetic variation
in a population.

56. Nearly all mutations reduce
an organism’s fitness.
Suppose that
you have
written a
ten-page
paper.
Randomly
select one
letter in the
paper and
change it to
another
letter
Is the change
more likely
to make your
paper better
or worse?
56

57. Take-Home Message 8.7
Mutation is an alteration of
the base-pair sequence in
an individual’s DNA.
This constitutes evolution if
it changes an allele the
individual carries.
Mutations can be caused by
high-energy sources or
chemicals in the
environment and also can
appear spontaneously.
Mutation is the only way
that new alleles can be
created within a population,
and so generates the
variation on which natural
selection can act.
57

58. 8.8 Genetic drift is a random change
in allele frequencies
in a population.
58

59. 59

60. The important factor that distinguishes
genetic drift from natural selection:
The change in allele frequencies is not related to
the alleles’ influence on reproductive success.
60

61. The impact of genetic drift is much
greater in small populations than in
large populations.
61

62. 62
Fixation
Genetic drift can lead
to fixation for one
allele for a gene in a
population.
If this happens, there
is no more variability
in the population for
this gene.
Genetic drift reduces
the genetic variation
in a population.

63. Two special cases of genetic drift, the
founder effect and population
bottlenecks, are important in the
evolution of populations.
63

64. 64
Founder
Effect
A small number of
individuals may leave
a population…
…and become the
founding members of
a new, isolated
population.
The founders may have
different allele
frequencies than the
original “source”
population, particularly if
they are a small sample.

65. 65

66. 66

67. Take-Home Message 8.8
Genetic drift is a random
change in allele frequencies
within a population,
unrelated to the alleles’
influence on reproductive
success.
Genetic drift is a significant
agent of evolutionary
change primarily in small
populations.
67

68. 8.9 Migration into or out of a population may
change allele frequencies.
Migration (gene flow) is the
movement of some individuals of a
species from one population to
another.68

69. Take-Home Message 8.9
Migration, or gene flow,
leads to a change in allele
frequencies in a population
as individuals move into or
out of the population.
69

70. 8.10 When three simple conditions are
satisfied, evolution by natural selection
occurs.
1. There must be
variation for the
particular trait
within a
population.
2. That variation
must be
inheritable.
3. Individuals
with one version
of the trait must
produce more
offspring than
those with a
different version
of the trait.
70

71. 71

72. Condition 1: Variation for a Trait
Variation is all around us and is the raw material
on which evolution feeds.
72

73. Condition 2: Heritability
We call the transmission of traits from parents to
their children through genetic information
inheritance or heritability.
73

74. Condition 3: Differential
Reproductive Success
1. There are
more
organisms
born than can
survive.
2. Organisms
are
continually
struggling for
existence.
3. Some
organisms
are more
likely to win
this struggle
& survive and
reproduce.
74

75. Differential Reproductive Success
From all the variation existing in a population, individuals with
traits most suited to reproduction in their environment
generally leave more offspring than individuals with other
traits. 75

77. Most agricultural pests evolve
resistance to pesticides.
How does this happen?

78. 78

79. Take-Home Message 8.10
Natural selection is a mechanism of
evolution that occurs when there is
heritable variation for a trait, and
individuals with one version of the
trait have greater reproductive
success than individuals with a
different version of the trait.
It can also be thought of as the
elimination of alleles from a
population that reduce the
reproductive rate of individuals
carrying them relative to the
reproductive rate of individuals who
do not carry the alleles.
79

80. 8·12–8·17
Through natural
selection,
populations of
organisms can
become adapted to
their environments.

81. 8.12 Traits causing some
individuals to have more offspring
than others become more
prevalent in the population.
81

82. 82
“Survival of
the Fittest”
Reproductive
success
Fitness
A measure of the relative amount of
reproduction of an individual with a
particular phenotype, as compared with
the reproductive output of individuals
with alternative phenotypes

83. Fruit Fly Example
One fly carries
the genes for a
version of a trait
that allows it to
survive a long
time without
food.
The other fly has
the genes for a
different version
of the trait that
allows it to
survive only a
short while
without food.
Which fly has
the greater
fitness?
83

84. The alleles carried by an individual with
high fitness will increase their market
share in a population over time and the
population will evolve.
84

85. 3 important elements to an
organism’s fitness:
1. An individual’s
fitness is
measured
relative to other
genotypes or
phenotypes in
the population.
2. Fitness
depends on the
specific
environment in
which the
organism lives.
3. Fitness
depends on an
organism’s
reproductive
success
compared to
other organisms
in the
population.
85

86. 86

87. Take-Home Message 8.12
Fitness is a measure of the
relative amount of reproduction
of an individual with a particular
phenotype, as compared with
the reproductive output of
individuals with alternative
phenotypes.
An individual’s fitness can vary,
depending on the environment
in which the individual lives.
87

88. 8.13 Organisms in a population can become better
matched to their environment through natural
selection.
88

89. Take-Home Message 8.13
Adaptation—the process by
which organisms become better
matched to their environment
and the specific features that
make an organism more fit—
occurs as a result of natural
selection.
89

90. 8.14 Natural selection does not lead to
perfect organisms.
90

91. 91
Organisms
aren’t “perfect”
Evolution in general,
and natural selection
specifically, do not
guide organisms toward
“better-ness” or
perfection.
If the environment
changes, the alleles
causing the traits
favored by natural
selection may change,
too.
Why doesn’t natural
selection lead to the
production
of perfect organisms?

92. Factors that Prevent Populations from
Progressing Inevitably toward Perfection
1.
Environments
change quickly.
2. Variation is
needed as the
raw material of
selection.
3. There may
be multiple
different alleles
for a trait, each
causing an
individual to
have the same
fitness.
92

93. Take-Home Message 8.14
Natural selection does
not lead to organisms
perfectly adapted to
their environment
because:
1. Environments can
change more quickly
than natural selection
can adapt organisms to
them.
2. All possible alleles
are not produced by
mutation.
3. There is not always a
single optimum
adaptation for an
environment.
93

94. 8.15 Artificial selection is just a
special case of natural selection.
94

95. Take-Home Message 8.15
Animal breeders and farmers
utilize natural selection when
they modify their animals
and crops because the three
conditions for natural
selection are satisfied.
Because the differential
reproductive success is
determined by humans and
not nature, this type of
natural selection is also called
artificial selection.
95

96. 8.16 Natural
selection can
change the
traits seen in a
population in
several ways.
96

97. Directional Selection
Individuals with one extreme from the range of
variation in the population have higher fitness.
97

98. Stabilizing Selection
Individuals with intermediate phenotypes are most fit.
98

99. Disruptive Selection
Individuals with extreme phenotypes experience the highest
fitness, and those with intermediate phenotypes have the
lowest.
99

100. Take-Home Message 8.16
Natural selection can
change populations in
several ways:
1. Directional selection, in
which the average value for
the trait increases or
decreases
2. Stabilizing selection, in
which the average value of a
trait remains the same
while extreme versions of
the trait are selected against
3. Disruptive selection, in
which individuals with
extreme phenotypes have
the highest fitness
100

101. 8.17 Natural selection can cause the
evolution of complex traits and behaviors.
101

103. 103

104. Often, structures
appear because they
serve some other
purpose.
Functional Shifts

105. Take-Home Message 8.17
Natural selection can
change allele frequencies
for genes involving complex
physiological processes and
behaviors.
This sometimes involves a
trait that has been selected
for one function being
modified at a later time to
serve a completely different
function.
105

106. 8.18–8.22
The evidence for
evolution is
overwhelming.

107. Five primary lines of
evidence:
1. The fossil
record
2.
Biogeography
3.
Comparative
anatomy &
embryology
4. Molecular
biology
5. Laboratory
& field
experiments
107

108. 108
8.18 The fossil record
documents the process
of natural selection.

109. 109

112. Take-Home Message 8.18
Radiometric dating confirms that
the earth is very old and makes it
possible to determine the age of
fossils.
Analysis of fossil remains enables
biologists to reconstruct what
organisms looked like long ago,
learn how organisms were
related to each other, and
understand how groups of
organisms evolved over time.
112

113. 8-19 Geographic patterns of species’
distributions reflect their evolutionary
histories.
113

115. 115
History
Matters
Who arrived
first?
Are numerous
different habitats
available?

116. 116

117. Take-Home Message 8.19
Observing geographic patterns of
species distributions—noting similarities
and differences among species living
close together but in very different
habitats and among species living in
similar habitats but located far from one
another—helps us understand the
evolutionary histories of populations.
117

118. 8.20 Comparative anatomy and embryology
reveal common evolutionary origins.
118

119. Homologous Structures
119

120. Vestigial
Structures
120

121. Convergent
Evolution
Analogous
structures all
developed from
different original
structures. 121

122. Take-Home Message 8.20
Similarities in how
organisms look and
develop shows their
common evolutionary
origins.
122

123. 8.21 Molecular biology reveals that
common genetic sequences link all
life forms.
The genetic code provides our fourth line
of evidence that evolution occurs.
123

124. 124
DNA Similarities
and Differences
Related vs.
unrelated
individuals
The more distantly
you and another
individual are
related…
…the more your
DNA differs.

125. 125
DNA Similarity
between Two
Species
Compare their DNA
sequences for
individual genes.
In Rhesus monkeys,
138 amino acids are
the same as those
found in human
hemoglobin.

126. 126
Recency of
Common
Ancestry
Estimates of
evolutionary
relatedness are
made from:
Comparative
anatomy,
embryology, &
the fossil record
“Molecular
clocks”

127. Take-Home Message 8.21
All living organisms are share
the same genetic code.
The degree of similarity in the
DNA of different species can
reveal how closely related they
are and the amount of time
that has passed since they last
shared a common ancestor.
127

128. 8.22 Laboratory and field experiments
enable us to watch evolution in progress.
A fifth line of evidence for the occurrence of
evolution comes from multigeneration
experiments and observations.
128

129. Changes in the
Frequency
of the Various
Alleles
129

130. 130

131. 131

132. Take-Home Message 8.22
Replicated, controlled
laboratory selection
experiments and long-term field
studies of natural populations
allow us to watch and measure
evolution as it occurs.
132