Chapter 15, 16, and 17 Lecture for Lab Bio.

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Biology
Chapter 15
Chapter 16
Section 17-4
EVOLUTION

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15-1 The Puzzle of Life's Diversity

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15-1 The Puzzle of Life's Diversity
Evolution is the process by which
modern organisms have descended
from ancient organisms.
A scientific theory is a well-
supported testable explanation of
phenomena that have occurred in
the natural world.

4. Voyage of the Beagle
In 1831, Darwin left England aboard
the H.M.S. Beagle for a voyage
around the world.
Darwin went ashore and collected plant and
animal specimens for his collection.
He studied the specimens, read the latest
scientific books, and filled many notebooks
with his observations and thoughts.

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Voyage of the Beagle

6. During his travels, Darwin made
numerous observations and
collected evidence that led him to
propose a hypothesis about the way
life changes over time.
That hypothesis has
become the theory of
evolution.

7. Darwin observed that many plants and
animals were well suited to the environments
they inhabited.
He was impressed by the ways in which
organisms survived and produced offspring.

8. Darwin was puzzled by where different
species lived and did not live.
Grasslands in some regions were similar to
one another but were inhabited by very
different animals.

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Living Organisms and Fossils
Darwin collected the preserved remains
of ancient organisms, called fossils.
Some of those fossils resembled
organisms that were still alive.
Others looked completely unlike any
creature he had ever seen.

10. The Galápagos Islands
Darwin observed that the Galápagos
Islands were close together but had very
different climates.
Darwin observed that the characteristics of
many animals and plants varied noticeably
among the different islands of the Galápagos.

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Darwin wondered if animals living on different
islands had once been members of the same
species.
These separate species would have evolved
from an original ancestor species.

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15–2
Ideas That Shaped Darwin's Thinking

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Hutton and Lyell helped scientists
recognize that Earth is many millions of
years old, and the processes that
changed Earth in the past are the same
processes that operate in the present.

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Hutton and Geological Change
In 1795, James Hutton published a hypothesis
about the geological forces that shaped Earth.
Most of these geological forces operate very
slowly, over millions of years.
Hutton proposed that Earth had to be very old.

15. Lyell’s work explained how geological
features could be built up or torn down over
long periods of time.

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This understanding of geology influenced
Darwin:
•If the Earth could change over time, life
might change as well.
•It would have taken many years for life to
change in the way Lyell suggested.
This would have been possible only if the
Earth were extremely old.

17. Lamarck's Evolution Hypotheses
Jean-Baptiste Lamarck recognized that:
•living things have changed over
time.
•all species are descended from
other species.
•organisms are adapted to their
environments.

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Population Growth
•In 1798, Thomas Malthus published a
book in which he noted that babies were
being born faster than people were
dying.
•The only forces he observed that worked
against this growth were war, famine,
and disease.

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Malthus reasoned that if the human
population continued to grow unchecked,
sooner or later there would be
insufficient living space and food for
everyone.

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When Darwin read Malthus’s work, he
realized that this reasoning applied to
plants and animals.
If all the offspring of almost any species
survived for several generations, they
would overrun the world.
This information was central to Darwin’s
explanation of evolutionary change.

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15-3 Darwin Presents His Case

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Publication of On the Origin of Species
•Darwin filled notebooks with his ideas
about species diversity and the evolution
process.
•Darwin was stunned and disturbed by his
discoveries.
•He shelved his manuscript for years and
told his wife to publish it in case he died.

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In 1858, Darwin received a short
essay from naturalist Alfred
Wallace.
The essay summarized Darwin’s
thoughts on evolutionary change.
Later that year, Wallace’s essay
was presented with some of
Darwin’s work.
In 1859, Darwin published his
book, On the Origin of Species.

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In his book, Darwin:
•proposed a mechanism for evolution
called natural selection.
•presented evidence that evolution has
been taking place for millions of years—
and continues in all living things.

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Inherited Variation and Artificial Selection
Members of each species vary from
one another in important ways.
•In Darwin’s day, variations were thought to
be unimportant, minor defects.
•Darwin argued that this variation mattered.

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Darwin noted that
plant and animal breeders breed
only the largest hogs or the cows
that produced the most milk.
Darwin termed this process
artificial selection.

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Artificial selection is the intentional
breeding for certain traits.

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Inherited Variation and Artificial Selection
Brussels
Sprouts
Kohlrabi
Ancestral
Species
Kale
Broccoli
Cauliflower

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Evolution by Natural Selection
•Darwin compared processes in nature to
artificial selection.
•By doing so, he developed a scientific
hypothesis to explain how evolution
occurs.

30. The Struggle for Existence
Darwin realized that high birth rates and
a shortage of resources would force
organisms to compete.

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The struggle for existence means
that members of each species
compete regularly to obtain food,
living space, and other necessities
of life.
The struggle for existence was central to
Darwin's theory of evolution.

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•The ability of an individual to survive
and reproduce in its specific
environment is fitness.
•Darwin proposed that fitness is the
result of adaptations.
•An adaptation is any inherited
characteristic that increases an
organism's chance of survival.

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Successful adaptations
enable organisms to
become better suited to
their environment and
better able to survive
and reproduce.

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Individuals with characteristics that
are not well suited to their environment
either die or leave few offspring.
Individuals that are better suited to
their environment survive and
reproduce most successfully.
Darwin called this process survival of
the fittest.

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Because of its similarities to artificial
selection, Darwin referred to the
survival of the fittest as natural
selection.
In natural selection, the traits being
selected contribute to an organism's
fitness in its environment.

36. Over time, natural selection results in
changes in the inherited characteristics
of a population.
These changes increase a species'
fitness in its environment.

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•Natural selection produces organisms
that have different structures, establish
different niches, or occupy different
habitats.
•Each living species has descended, with
changes, from other species over time.
•Darwin referred to this principle as
descent with modification.

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Descent with modification implies
that all living organisms are related
to one another, a principle known
as common descent.

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Evidence of Evolution
Darwin argued that living things have
been evolving on Earth for millions of
years.
Evidence for this process could be found
in the fossil record, the geographical
distribution of living species, homologous
structures of living organisms, and
similarities in early development, or
embryology.

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The Fossil Record
• Darwin saw fossils as a record of the history of life on Earth.
•By comparing fossils from older
rock layers with fossils from
younger layers, scientists could
document that life on Earth has
changed over time.

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Geographic Distribution of Living Species
•Darwin decided that all Galápagos
finches could have descended with
modification from a common mainland
ancestor.
•Darwin’s theory was that species now
living on different continents had each
descended from different ancestors.

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However, because some animals on each
continent were living under similar
ecological conditions, they were exposed to
similar pressures of natural selection.
Because of these similar selection
pressures, different animals ended up
evolving certain features in common.

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Evidence of Evolution
Similar, But Unrelated Species

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Evidence of Evolution
Homologous Body Structures
•Structures that have different
mature forms but develop from
the same embryonic tissues are
called homologous structures.
•Similarities and differences in homologous
structures help biologists group animals
according to how recently they last shared
a common ancestor.

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Homologous Structures
Turtle Alligator Bird Mammal
Ancient, lobe-
finned fish

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Not all homologous structures serve important
functions.
The organs of many animals are so reduced in
size that they are just vestiges, or traces, of
homologous organs in other species.
These organs are called vestigial organs.
Vestigal organs no longer work, they
are remnants of organs that ancestor
species once used.

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Similarities in Embryology
•The early stages, or embryos, of
many animals with backbones
are very similar.
• The same groups of embryonic
cells develop in the same order
and in similar patterns to
produce the tissues and organs
of all vertebrates.

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Summary of Darwin's Theory
Individual organisms differ, and some of
this variation is heritable.
Organisms produce more offspring than
can survive, and many that do survive do
not reproduce.
Because more organisms are produced
than can survive, they compete for limited
resources.

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Individuals best suited to their
environment survive and reproduce
most successfully.
These organisms pass their heritable
traits to their offspring. Other
individuals die or leave fewer offspring.
This process of natural selection
causes species to change over time.

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Species alive today are descended
with modification from ancestral
species that lived in the distant
past.
This process, by which diverse species
evolved from common ancestors, unites all
organisms on Earth into a single tree of
life.

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Evolutionary Theory
•Scientific advances in many fields of
biology, geology, and physics have
confirmed and expanded most of
Darwin’s hypotheses.
•Evolutionary theory continues to change
as new data are gathered and new ways
of thinking arise.

52. 52

53. 16-1 Genes and Variation16-1 Genes and Variation

54. How Common Is Genetic Variation?
Many genes have at least two forms, or alleles.
All organisms have genetic variation that is “invisible”
because it involves small differences in biochemical
processes.
An individual organism is heterozygous for many
genes.

55. Genetic variation is studied in populations.
A population is a group of individuals of the
same species that interbreed.
A gene pool consists of all genes, including all
the different alleles, that are present in a
population.

56. The relative frequency of an allele is the
number of times the allele occurs in a gene
pool, compared with the number of times
other alleles for the same gene occur.
Relative frequency is often expressed as a
percentage.

57. Gene Pool for Fur Color in Mice
Sample Population Frequency of Alleles
allele for
brown fur
allele for
black fur

58. Evolution is any change in
the relative frequency of
alleles in a population.

59. The two main sources of genetic
variation are mutations and the
genetic shuffling that results from
sexual reproduction.

60. A mutation is any change in a sequence of DNA.
Mutations occur because of
mistakes in DNA replication or
as a result of radiation or
chemicals in the environment.
Mutations do not always affect an organism’s
phenotype.

61. Most heritable differences are due to gene
shuffling.
Crossing-over increases the number of
genotypes that can appear in offspring.
Sexual reproduction produces
different phenotypes, but it does
not change the relative frequency
of alleles in a population.

62. Single-Gene and Polygenic Traits
The number of phenotypes produced for a
given trait depends on how many genes
control the trait.

63. A single-gene trait is controlled by
one gene that has two alleles.
Variation in this gene leads to only
two possible phenotypes.

64. The allele for a widow’s peak is dominant
over the allele for a hairline with no peak.
However, the presence of a widow’s peak
may be less common in a population.
In real populations, phenotypic ratios
are determined by the frequency of
alleles as well as by whether the
alleles are dominant or recessive.

65. Many traits are controlled by two
or more genes and are called
polygenic traits.
One polygenic trait can have many
possible genotypes and phenotypes.
Height in humans is a polygenic trait.

66. A bell-shaped curve is typical of
polygenic traits.
A bell-shaped curve is also called normal
distribution.

67. 16-2 Evolution as Genetic Change16-2 Evolution as Genetic
Change

68. 16-2 Evolution as Genetic
Change
Natural selection affects which individuals
survive and reproduce and which do not.
If an individual dies without
reproducing, its alleles are removed
from the population’s gene pool.
If an individual produces many
offspring, its alleles may increase in
frequency.

69. 16-2 Evolution as Genetic
Change
Evolution is any change over time in the
relative frequencies of alleles in a
population.
Populations, not individual organisms, can
evolve over time.
16-2 Evolution as Genetic
Change

70. Natural selection can lead to
changes in allele frequencies
and thus to evolution.

71. Organisms of one color may produce fewer
offspring than organisms of other colors.
For example, a lizard population is normally
brown, but has mutations that produce red
and black forms.
Red lizards are more visible to predators,
so they will be less likely to survive and
reproduce. Therefore, the allele for red
color will become rare.

72. Black lizards may warm up faster on cold
days. This may give them energy to avoid
predators. In turn, they may produce more
offspring.
The allele for black color will increase in
relative frequency.

74. Natural selection can affect the distributions
of phenotypes in any of three ways:
•directional selection
•stabilizing selection
•disruptive selection

75. Directional Selection
When individuals at one end of the
curve have higher fitness than
individuals in the middle or at the
other end, directional selection
takes place.
The range of phenotypes shifts as some
individuals survive and reproduce while
others do not.

76. In this case, birds with larger beaks have
higher fitness. Therefore, the average beak
size increases.

77. Stabilizing Selection
When individuals near the center
of the curve have higher fitness
than individuals at either end of
the curve, stabilizing selection
takes place.
This keeps the center of the curve at its
current position, but it narrows the overall
graph.

78. Human babies born at an average mass are
more likely to survive than babies born either
much smaller or much larger than average.

79. Disruptive Selection
When individuals at the upper and
lower ends of the curve have higher
fitness than individuals near the
middle, disruptive selection takes
place.
If the pressure of natural selection is strong
enough and long enough, the curve will split,
creating two distinct phenotypes.

80. If average-sized seeds become scarce, a
bird population will split into two groups:
one that eats small seeds and one that eats
large seeds.

81. A random change in allele
frequency is called genetic drift.

82. In small populations, individuals
that carry a particular allele may
leave more descendants than
other individuals do, just by
chance.
Over time, a series of chance
occurrences of this type can
cause an allele to become
common in a population.

83. Genetic drift may occur when a small group
of individuals colonizes a new habitat.
Individuals may carry alleles in different
relative frequencies than did the larger
population from which they came.
The new population will be genetically
different from the parent population.

84. Genetic Drift

87. Descendants
Population A Population B

88. When allele frequencies change
due to migration of a small
subgroup of a population it is
known as the founder effect.

89. Evolution Versus Genetic Equilibrium
The Hardy-Weinberg principle states
that allele frequencies in a population will
remain constant unless one or more
factors cause those frequencies to
change.
When allele frequencies remain constant
it is called genetic equilibrium.

90. Five conditions are required
to maintain genetic
equilibrium from generation
to generation:
• there must be random mating,
• the population must be very large,
• there can be no movement into or
out of the population,
• there can be no mutations, and
• there can be no natural selection.

91. Evolution Versus Genetic Equilibrium
Random Mating
Random mating ensures that each
individual has an equal chance of passing
on its alleles to offspring.
In natural populations, mating is rarely
completely random. Many species select
mates based on particular heritable traits.

92. Large Population
Genetic drift has less effect on large
populations than on small ones.
Allele frequencies of large populations are
less likely to be changed through the
process of genetic drift.
Evolution Versus Genetic Equilibrium

93. No Movement Into or Out of the Population
Because individuals may bring new alleles
into a population, there must be no
movement of individuals into or out of a
population.
The population's gene pool must be kept
together and kept separate from the gene
pools of other populations.
Evolution Versus Genetic Equilibrium

94. No Mutations
If genes mutate, new alleles may be
introduced into the population, and allele
frequencies will change.
Evolution Versus Genetic Equilibrium

95. No Natural Selection
All genotypes in the population must have
equal probabilities of survival and
reproduction.
No phenotype can have a selective
advantage over another.
There can be no natural selection operating
on the population.
Evolution Versus Genetic Equilibrium

96. 16-3 The Process of Speciation
16-3 The Process of Speciation

97. 16-3 The Process of Speciation
Natural selection and chance events can
change the relative frequencies of alleles in
a population and lead to speciation.
Speciation is the formation of new species.
A species is a group of organisms that
breed with one another and produce fertile
offspring.

98. Isolating Mechanisms
What factors are involved in the formation of new
species?
The gene pools of two
populations must become
separated for them to become
new species.

99. Isolating Mechanisms
Isolating Mechanisms
As new species evolve, populations
become reproductively isolated from
each other.
When the members of two populations
cannot interbreed and produce fertile
offspring, reproductive isolation has
occurred.

100. Isolating Mechanisms
Reproductive isolation can develop in a
variety of ways, including:
behavioral isolation
geographic isolation
temporal isolation

101. Isolating Mechanisms
Behavioral Isolation
Behavioral isolation occurs when two
populations are capable of interbreeding
but have differences in courtship rituals or
other reproductive strategies that involve
behavior.

102. Isolating Mechanisms
Geographic Isolation
Geographic isolation occurs when two
populations are separated by
geographic barriers such as rivers or
mountains.

103. Isolating Mechanisms
Geographic barriers do not guarantee the
formation of new species.
If two formerly separated populations can still
interbreed, they remain a single species.
Potential geographic barriers may separate
certain types of organisms but not others.

104. Isolating Mechanisms
Temporal Isolation
Temporal isolation occurs when two or
more species reproduce at different
times.

105. Testing Natural Selection
in Nature

106. Testing Natural Selection
in Nature

107. Speciation in Darwin's Finche
Speciation in Darwin's Finches
Speciation in the Galápagos finches occurred by:
founding of a new population
geographic isolation
changes in new population's gene pool
reproductive isolation
ecological competition

108. Speciation in Darwin's Finche
Founders Arrive
A few finches—
species A—travel
from South America
to one of the
Galápagos Islands.
There, they survive
and reproduce.

109. Speciation in Darwin's Finche
Geographic Isolation
Some birds from
species A cross to
a second island.
The two
populations no
longer share a
gene pool.

110. Speciation in Darwin's Finche
Changes in the Gene Pool
Seed sizes on the
second island favor
birds with large
beaks.
The population on
the second island
evolves into
population B, with
larger beaks.

111. Speciation in Darwin's Finche
Reproductive Isolation
If population B birds cross back to the
first island, they will not mate with birds
from population A.
Populations A and B are separate
species.

112. Speciation in Darwin's Finche
Ecological Competition
As species A and B compete for
available seeds on the first island, they
continue to evolve in a way that
increases the differences between
them.
A new species—C—may evolve.

113. Studying Evolution Since
Darwin
Studying Evolution Since Darwin
Scientific evidence supports the theory
that living species descended with
modification from common ancestors that
lived in the ancient past.
Scientists predict that as new fossils are
found, they will continue to expand our
understanding of how species evolved.

114. 17-4 Patterns of Evolution

115. Macroevolution refers to large-scale
evolutionary patterns and processes that
occur over long periods of time.

116. Six important topics in
macroevolution are:
•extinction
•adaptive radiation
•convergent evolution
•coevolution
•punctuated equilibrium
•changes in developmental
genes

117. Extinction
•More than 99% of all species that have
ever lived are now extinct.
•In the past, most researchers looked for
a single, major cause for each mass
extinction.
•Many paleontologists now think that
mass extinctions were caused by
several factors.

118. Extinction
What effects have mass extinctions had on
the history of life? Mass extinctions have:
•provided ecological opportunities for
organisms that survived
•resulted in bursts of evolution that
produced many new species

119. Adaptive Radiation
•Adaptive radiation is the process by
which a single species or a small
group of species evolves into several
different forms that live in different
ways.
•For example, in the adaptive radiation of
Darwin's finches, more than a dozen species
evolved from a single species.

120. Adaptive radiations can occur on a much
larger scale.
The disappearance of dinosaurs then
resulted in the adaptive radiation of
mammals.

121. Adaptive Radiation of Mammals
Artiodactyls
Cetaceans
Perissodactyls
Tubulidentates
Hyracoids
Sirenians
Proboscideans
Ancestral Mammals

122. Convergent Evolution
•Different organisms undergo adaptive
radiation in different places or at different
times but in similar environments.
•The process by which unrelated
organisms come to resemble one another
is called convergent evolution.
•Convergent evolution has resulted in
sharks, dolphins, seals, and penguins.

123. Structures that look and function similarly
but are made up of parts that do not share
a common evolutionary history are called
analogous structures.
A dolphin’s fluke and a fish’s tail fin are
analogous structures.

124. Coevolution
•Sometimes organisms that are closely
connected to one another by ecological
interactions evolve together.
•The process by which two species
evolve in response to changes in
each other over time
is called
coevolution. Watch vid

125. 125

126. Punctuated
Equilibrium
•Darwin felt that
biological
change was
slow and
steady, an idea
known as
gradualism.

127. Punctuated
equilibrium is a
pattern of evolution
in which long stable
periods are
interrupted by brief
periods of more
rapid change.

128. The concept of punctuated equilibrium has
generated debate and is still controversial
among some biologists today.
Evolution has often proceeded at different
rates for different organisms at different
times during the history of life on Earth.

129. Developmental Genes and Body Plans
•It is suspected that changes in genes for
growth and differentiation during
embryological development could
produce changes in body shape and
size.
•Small changes in the activity of control
genes can affect many other genes to
produce large changes in adult animals.

130. •Evolution of Wings in Insects
Ancient Insect Two Types of Modern Insects

131. Small changes in the timing of cell
differentiation and gene expression can
make the difference between long legs and
short ones.