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Figure 13.0-1
DARWIN’S THEORY OF EVOLUTION
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I Can…
1. Explain how Darwin’s voyage on the Beagle
influenced his thinking.
2. Explain why the concept of evolution is regarded as
a theory with great significance.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• Charles Darwin is best known for his book On the
Origin of Species by Means of Natural Selection,
commonly referred to as The Origin of Species,
which launched the era of evolutionary biology.
• Darwin’s early career gave no hint of his future
fame.
• He enrolled in but left medical school.
• Then he entered Cambridge University to become a
clergyman.
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Figure 13.1a-0
HMS Beagle in port
Darwin
in 1840
North
America
Great
Britain
Asia
Europe
ATLANTIC
OCEAN
Africa
Pinta
Marchena
Santiago
Galápagos
Islands
Genovesa
Equator
Daphne Islands
Pinzón
Fernandina
Isabela
0
0
40 km
South
America
Santa
Cruz
Florenza
40 miles
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Santa
Fe
San
Cristobal
Española
PACIFIC
OCEAN
Andes
PACIFIC
OCEAN
PACIFIC
OCEAN
Equator
Australia
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Tasmania
New
Zealand
13.1 A sea voyage helped Darwin frame his
theory of evolution
• Darwin’s observations indicated that geographic
proximity is a better predictor relationships
between organisms than similarity of environment.
• Darwin was particularly intrigued by the geographic
distribution of organisms on the Galápagos
Islands, including
• marine iguanas
• giant tortoises
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• While on his voyage, Darwin was strongly
influenced by the newly published Principles of
Geology, by Scottish geologist Charles Lyell.
• The book presented the case for an ancient Earth
sculpted over millions of years by gradual geologic
processes that continue today.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• By the time Darwin returned to Great Britain five
years after the Beagle first set sail, he had begun
to seriously doubt that Earth and all its living
organisms had been specially created only a few
thousand years earlier.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• As he reflected on his observations, analyzed his
collections, and discussed his work with
colleagues, Darwin hypothesized:
• Present-day species are the descendants of
ancient ancestors that they still resemble in some
ways.
• As the descendants of a remote ancestor spread
into various habitats millions of years, they
accumulated diverse modifications, or
adaptations.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• By the early 1840s, Darwin had
composed a long essay describing the
major features of his theory of evolution
by natural selection.
• But he delayed publishing his essay,
continued to compile evidence, and
finally released his essay when learning
of the work of another British naturalist,
Alfred Wallace, who had a nearly
identical hypothesis as Darwin.
© 2015 Pearson Education, Inc.
13.1 A sea voyage helped Darwin frame his
theory of evolution
• The next year, Darwin published The Origin of Species, a
book that supported his hypothesis with immaculate logic
and hundreds of pages of evidence from observations and
experiments in biology, geology, and paleontology.
• The hypothesis of evolution generated predictions that have
been tested and verified by more than 150 years of
research and millions of experiments.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• Consequently, scientists regard Darwin’s concept
of evolution by means of natural selection as a
theory, a widely accepted explanatory idea that
• is broader in scope than a hypothesis,
• generates new hypotheses, and
• is supported by a large body of evidence.
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13.1 A sea voyage helped Darwin frame his
theory of evolution
• Darwin’s theory of evolution states that:
• living species are descendants of ancestral
species (different from present-day) and that
natural selection is the mechanism for evolutionary
change.
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Evidence of Evolution
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I Can…
1. Explain how homologies, the fossil record, and molecular
biology support evolution.
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13.2 The study of fossils provides strong
evidence for evolution
• Fossils
• are the imprints or remains of
organisms that lived in the past,
• document differences between past
and present organisms, and
• reveal that many species have
become extinct.
• For example, the fossilized skull of
one of our early relatives, Homo
erectus, represents someone who
lived 1.5 million years ago in Africa.
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13.2 The study of fossils provides strong
evidence for evolution
• The sequence in which fossils
appear within strata, layers of
sedimentary rocks, is a historical
record of life on Earth.
• The fossil record is the
chronicle of evolution over
millions of years of geologic time
engraved in the order in which
fossils appear in rock strata.
Upper strata have younger
fossils, deeper strata host older
fossils.
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13.2 The study of fossils provides strong
evidence for evolution
• The fossil record is incomplete because
• many of Earth’s organisms did not live in areas that
favor fossilization,
• fossils that did form were in rocks later distorted or
destroyed by geologic processes, and
• not all fossils that have been preserved are
accessible to paleontologists.
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13.3 SCIENTIFIC THINKING: Fossils of
transitional forms support Darwin’s theory of
evolution
• In The Origin of Species, Darwin predicted the
existence of fossils of transitional forms linking
very different groups of organisms.
• Thousands of fossil discoveries have since shed
light on the evolutionary origins of many groups of
plants and animals, including
• the transition of fish to amphibian,
• the origin of birds from a lineage of dinosaurs, and
• the evolution of mammals from a reptilian ancestor.
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13.4 Homologies provide strong evidence for
evolution
• Evolution is a process of descent with
modification.
• Characteristics present in an ancestral organism
are altered over time by natural selection as its
descendants face different environmental
conditions.
• Related species can have characteristics that have
an underlying similarity yet function differently.
• Similarity resulting from common ancestry is known
as homology.
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13.4 Homologies provide strong evidence for
evolution
• Darwin cited the anatomical similarities among
vertebrate forelimbs as evidence of common
ancestry.
• Biologists call anatomical similarities in different
organisms homologous structures.
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13.4 Homologies provide strong evidence for
evolution
• Darwin’s boldest hypothesis was that all life-forms
are related. Molecular biology, comparing
similarities in DNA, RNA, or Amino Acids between
diverse organisms, provides strong evidence for
this claim.
• All forms of life use the same genetic language of
DNA and RNA.
• The genetic code—how RNA triplets are translated
into amino acids—is essentially universal.
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13.4 Homologies provide strong evidence for
evolution
• An understanding of homology helps explain why
• early stages of development in different species reveal
similarities not visible in adults
• at some point in their development, all vertebrate
embryos have
• a tail
• pharyngeal (throat) pouches.
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13.4 Homologies provide strong evidence for
evolution
• Some of the most interesting homologies are
“leftover” structures that are of marginal or perhaps
no importance to the organism.
• These vestigial structures are remnants of
features that served important functions in the
organism’s ancestors.
Sci Show Vestigial Structures: https://www.youtube.com/watch?v=OAfw3akpRe8
Stated Clearly Evidence for Evolution: https://www.youtube.com/watch?v=lIEoO5KdPvg
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13.5 Homologies indicate patterns of descent
that can be shown on an evolutionary tree
• Darwin was the first to view the history of life as a
tree, with multiple branches from a common
ancestral trunk to the descendant species at the
tips of the twigs.
• Today, biologists represent these patterns of
descent with an evolutionary tree or phylogenic
tree.
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13.5 Homologies indicate patterns of descent
that can be shown on an evolutionary tree
• Homologous structures, including anatomical structure and/or
molecular structure, can be used to determine the branching
sequence of an evolutionary tree.
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Evolution by Natural Selection
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I Can…
•
•
•
Describe Darwin’s observations and inferences in
developing the concept of natural selection.
Explain how the work of Thomas Malthus and the
process of artificial selection influenced Darwin’s
development of the idea of natural selection.
Explain why individuals cannot evolve and why
evolution does not lead to perfectly adapted
organisms.
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13.6 Darwin proposed natural selection as
the mechanism of evolution
• Darwin’s greatest contribution to biology was his
explanation of how life evolves.
• Because he thought that species formed gradually
over time, he knew that he would not be able to
study evolution by direct observation.
• However, examples of incremental change can be
seen in artificial selection, in which humans have
modified species through selective breeding.
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Artificial Selection
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13.6 Darwin proposed natural selection as
the mechanism of evolution
• Darwin knew that individuals in natural
populations have small but measurable
differences. But forces led to the choosing
of which individuals became the breeding
stock for the next generation?
• Darwin found inspiration from economist
Thomas Malthus, who said that human
suffering—disease, famine, and war—was
the result of human populations increasing
faster than their resources (food, etc.).
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13.6 Darwin proposed natural selection as
the mechanism of evolution
• Darwin deduced that the production of more
individuals than the limited resources can support
leads to a struggle for existence, with only some
offspring surviving in each generation.
• The essence of natural selection is this unequal
reproduction.
• Individuals whose traits better enable them to
obtain food or escape predators or tolerate physical
conditions will survive and reproduce more
successfully, passing these adaptive traits to their
offspring.
• Show Booby Chick Fight
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Natural Selection =
Heritable Variation + Differential Reproductive Success
© 2015 Pearson Education, Inc.
13.6 Darwin proposed natural selection as
the mechanism of evolution
• Darwin reasoned that if artificial selection can bring
about so much change in a relatively short period
of time, then natural selection could modify species
considerably over hundreds or thousands of
generations.
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13.6 Darwin proposed natural selection as
the mechanism of evolution
• Three key points about evolution by natural
selection.
1. Although natural selection occurs through interactions
between individuals and the environment, individuals
do not evolve. Rather, it is the population that evolves
over time.
2. Natural selection can amplify or diminish only
heritable traits. Traits gained during an organisms
lifetime can not be inherited.
3. Evolution is not goal directed; it does not lead to
perfectly adapted organisms. Traits that are “good
enough” to allow an organism to survive and
reproduced will get passed on.
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13.7 Scientists can observe natural selection
in action
• An example of
natural selection in
action is the
evolution of
pesticide resistance
in insects.
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13.7 Scientists can observe natural selection
in action
• These examples of evolutionary adaptation
highlight two important points about natural
selection.
1. Natural selection is more of an editing process
than a creative mechanism.
2. Natural selection is contingent on time and place,
favoring those heritable traits in a varying
population that fit the current, local environment.
If the environment changes so too can the forces
of natural selection.
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• Video 1
http://www.youtube.com/watch?v=zuqqnTOM1po
• Video 2
• https://www.youtube.com/watch?v=rltZfejDVuw
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THE EVOLUTION OF POPULATIONS
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I can…
•
Explain how mutation and sexual reproduction produce
genetic variation.
•
Describe the five conditions required for the HardyWeinberg equilibrium.
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13.8 Mutation and sexual reproduction
produce the genetic variation that makes
evolution possible
• Organisms typically show individual variation.
• However, in The Origin of Species, Darwin could
not explain
• the cause of variation among individuals or
• how variations were passed from parents to
offspring.
• Just a few years after the publication of The Origin
of Species, Gregor Mendel wrote a
groundbreaking paper on inheritance in pea plants.
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13.8 Mutation and sexual reproduction
produce the genetic variation that makes
evolution possible
• Individual variation occurs in all species and it is
essential for evolution.
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13.8 Mutation and sexual reproduction
produce the genetic variation that makes
evolution possible
• Mutations are
• changes in the nucleotide sequence of DNA and
• the ultimate source of new alleles.
• Thus, mutation is the ultimate source of the
genetic variation that serves as raw material for
evolution.
• A change as small as a single nucleotide in a
protein-coding gene can have a significant effect
on phenotype.
© 2015 Pearson Education, Inc.
13.8 Mutation and sexual reproduction
produce the genetic variation that makes
evolution possible
• On rare occasions, however, a mutated allele may
actually improve the adaptation of an individual to
its environment and enhance its reproductive
success.
• Rock Pocket Mice
• http://www.hhmi.org/biointeractive/making-fittestnatural-selection-and-adaptation
© 2015 Pearson Education, Inc.
13.8 Mutation and sexual reproduction
produce the genetic variation that makes
evolution possible
• Genetic variation of existing alleles arise every
generation from three random components of
sexual reproduction:
1. crossing over,
2. independent orientation of homologous
chromosomes at metaphase I of meiosis, and
3. random fertilization.
© 2015 Pearson Education, Inc.
Animation: Genetic Variation from Sexual
Recombination
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13.9 Evolution occurs within populations
• A population is a group of individuals of the same
species, that live in the same area, and interbreed.
• Different populations of the same species may be
geographically isolated from each other to such an
extent that an exchange of genetic material never
occurs, or occurs only rarely.
• A gene pool consists of all copies of every type of
allele, at every locus, in all members of the
population.
© 2015 Pearson Education, Inc.
13.9 Evolution occurs within populations
• Microevolution is
• change in the relative frequencies of alleles in a
population over a number of generations and
evolution occurring on its smallest scale.
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13.10 The Hardy-Weinberg equation can test
whether a population is evolving
• If a population is in Hardy-Weinberg equilibrium,
allele and genotype frequencies will remain
constant, generation after generation.
• The Hardy-Weinberg principle tells us that
something other than the reshuffling processes of
sexual reproduction is required to change allele
frequencies in a population.
© 2015 Pearson Education, Inc.
13.10 The Hardy-Weinberg equation can test
whether a population is evolving
• For a population to be in Hardy-Weinberg equilibrium and
not evolving, it must satisfy five main conditions. There must
be
1.
2.
3.
4.
5.
a very large population,
no gene flow between populations,
no mutations,
random mating, and
no natural selection.
• Rarely are all five conditions met in real populations, and
thus allele and genotype frequencies often do change.
© 2015 Pearson Education, Inc.
13.10 The Hardy-Weinberg equation can test
whether a population is evolving
• Rarely are all five conditions met in real
populations, and thus allele and genotype
frequencies often do change.
TED Ed: 5 Fingers of Evolution
http://ed.ted.com/lessons/five-fingers-of-evolution
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
MECHANISMS OF MICROEVOLUTION
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I Can…
• Define genetic drift and gene flow. Explain how the
bottleneck effect and the founder effect influence
microevolution.
• Distinguish between stabilizing selection, directional
selection, and disruptive selection. Describe an example of
each.
© 2015 Pearson Education, Inc.
13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
• The three main causes of evolutionary change are
1. natural selection,
2. genetic drift, and
3. gene flow.
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13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
1. Natural selection
• If individuals differ in their survival
and reproductive success,
natural selection will alter allele
frequencies.
• Genetic equilibrium would be
disturbed as the frequency of the
beneficial allele increased in the
gene pool from one generation to
the next.
© 2015 Pearson Education, Inc.
13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
2. Genetic drift
• In a process called genetic drift, chance events
can cause allele frequencies to fluctuate
unpredictably from one generation to the next.
• The smaller the population, the more impact
genetic drift is likely to have.
• Catastrophes (hurricanes, floods, or fires) may kill a
lot of individuals, leaving a small population that is
unlikely to have the same genetic makeup as the
original population.
© 2015 Pearson Education, Inc.
13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
• The bottleneck effect leads to a loss of genetic
diversity when a population is greatly reduced.
• Human activities such as overhunting and habitat
destruction may create severe bottlenecks for other
species.
© 2015 Pearson Education, Inc.
13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
• Genetic drift is also likely when a few individuals
colonize an island or other new habitat, producing
what is called the founder effect.
• The smaller the group, the less likely the genetic
makeup of the colonists will represent the gene
pool of the larger population they left.
© 2015 Pearson Education, Inc.
13.12 Natural selection, genetic drift, and
gene flow can cause microevolution
3. Gene flow
• Where a population may gain or lose alleles when
fertile individuals move into or out of a population or
when gametes (such as plant pollen) are
transferred between populations.
• Gene flow tends to reduce differences between
populations.
© 2015 Pearson Education, Inc.
13.13 Natural selection is the only mechanism that
consistently leads to adaptive evolution
• Genetic drift, gene flow, and mutations could each result in
microevolution, but only by chance could these events
improve a population’s fit to its environment.
• In natural selection, only the genetic variation produced by
mutation and sexual reproduction results from random
events.
• The process of natural selection, in which some
individuals are more likely than others to survive and
reproduce, is not random.
• Because of this sorting, only natural selection
consistently leads to adaptive evolution.
© 2015 Pearson Education, Inc.
13.13 Natural selection is the only mechanism that
consistently leads to adaptive evolution
• Relative fitness is the contribution an individual
makes to the gene pool of the next generation
relative to the contributions of other individuals.
© 2015 Pearson Education, Inc.
13.14 Natural selection can alter variation in a
population in three ways
• Natural selection can affect the distribution of
phenotypes in a population.
• Stabilizing selection favors intermediate
phenotypes.
• Directional selection shifts the overall makeup of
the population by acting against individuals at one
of the phenotypic extremes.
• Disruptive selection typically occurs when
environmental conditions vary in a way that favors
individuals at both ends of a phenotypic range over
individuals with intermediate phenotypes.
© 2015 Pearson Education, Inc.
Figure 13.14
Frequency of
individuals
Original population
Original
population
Evolved
population
Stabilizing selection
© 2015 Pearson Education, Inc.
Phenotypes (fur color)
Directional selection
Disruptive selection
© 2015 Pearson Education, Inc.
I Can…
• Define and compare intrasexual selection and
intersexual selection.
© 2015 Pearson Education, Inc.
13.15 Sexual selection may lead to
phenotypic differences between males and
females
• Sexual selection is a form of natural selection in
which individuals with certain characteristics are
more likely than other individuals to obtain mates.
• Booby Dance
• In many animal species, males and females may
have secondary sexual characteristics, noticeable
differences not directly associated with reproduction
or survival, called sexual dimorphism.
• Peacocking
© 2015 Pearson Education, Inc.
13.15 Sexual selection may lead to
phenotypic differences between males and
females
• In some species, individuals compete directly with
members of the same sex for mates.
• This is called intrasexual selection (within the
same sex, most often the males).
© 2015 Pearson Education, Inc.
13.15 Sexual selection may lead to
phenotypic differences between males and
females
• In a more common type of sexual selection, called
intersexual selection (between sexes) or mate
choice, individuals of one sex (usually females) are
choosy in selecting their mates.
• Human Sexual Selection
© 2015 Pearson Education, Inc.
Giraffe Clips
http://www.arkive.org/giraffe/giraffacamelopardalis/video-09e.html
http://www.arkive.org/giraffe/giraffacamelopardalis/video-09a.html
© 2015 Pearson Education, Inc.
Sexual Selection: Giraffe
• Males use the flehmen (urine test) sequence to determine which
females are in estrus
• According to Pratt (1985), female giraffes prefer older, more
dominant males.
• When approached for urine-testing, Pratt found that females
urinated more often for dominant males than subordinate
males.
• Thus, dominant males have more success in determining which
females are receptive.
• This advantageous for the female because it allows her to get the
best genes for her offspring: the most dominant male is the one
who ultimately fertilizes her eggs
© 2015 Pearson Education, Inc.
13.15 Sexual selection may lead to
phenotypic differences between males and
females
• What is the advantage to females of being
choosy?
• One hypothesis is that females prefer male traits
that are correlated with “good genes.”
• In several bird species, research has shown that traits preferred by
females, such as bright beaks or long tails, are related to overall
male health.
• The “good genes” hypothesis was also tested in gray tree frogs.
Female frogs prefer to mate with males that give long mating calls.
© 2015 Pearson Education, Inc.
13.16 EVOLUTION CONNECTION: The
evolution of drug-resistant microorganisms
is a serious public health concern
• In the same way that pesticides
select for resistant insects,
antibiotics select for resistant
bacteria.
• Again we see both the random and
nonrandom aspects of natural
selection:
• random genetic mutations in
bacteria
• nonrandom selective effects as
the environment favors the
antibiotic-resistant phenotype.
© 2015 Pearson Education, Inc.
13.16 EVOLUTION CONNECTION: The
evolution of drug-resistant microorganisms
is a serious public health concern
• Each year in the United States nearly 100,000
people die from infections they contract in the
hospital, often because the bacteria are resistant
to multiple antibiotics.
• A formidable “superbug” known as MRSA
(methicillin-resistant Staphylococcus aureus) can
cause “flesh-eating disease” and potentially fatal
systemic (whole-body) infections.
© 2015 Pearson Education, Inc.
13.17 Diploidy and balancing selection
preserve genetic variation
• In some cases, genetic variation is preserved
rather than reduced by natural selection.
• Balancing selection occurs when natural
selection maintains stable frequencies of two or
more phenotypic forms in a population.
© 2015 Pearson Education, Inc.
13.17 Diploidy and balancing selection
preserve genetic variation
• Heterozygote advantage is a type of balancing
selection in which heterozygous individuals have
greater reproductive success than either type of
homozygote, with the result that two or more
alleles for a gene are maintained in the population.
© 2015 Pearson Education, Inc.
13.17 Diploidy and balancing selection
preserve genetic variation
• Frequency-dependent selection is a type of
balancing selection that maintains two different
phenotypic forms in a population.
• In this case, selection acts against either
phenotypic form if it becomes too common in the
population.
• Scale-eating fish in Lake Tanganyika, Africa, which attacks other
fish from behind, darting in to remove a few scales from the side of
its prey.
© 2015 Pearson Education, Inc.
13.18 Natural selection cannot fashion
perfect organisms
• The evolution of organisms is constrained.
1.
2.
3.
4.
Selection can act only on existing variations. New,
advantageous alleles do not arise on demand.
Evolution is limited by historical constraints.
Evolution co-opts existing structures and adapts
them to new situations.
Adaptations are often compromises. The same
structure often performs many functions.
Chance, natural selection, and the environment
interact. Environments often change
unpredictably.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
You should now be able to
1.
Explain how Darwin’s voyage on the Beagle influenced
his thinking.
2.
Explain why the concept of evolution is regarded as a
theory with great significance.
3.
Explain how fossils form and why the fossil record is
incomplete.
4.
Explain how homologies, the fossil record, and
molecular biology support evolution.
5.
Explain how evolutionary trees are constructed and
used to represent ancestral relationships.
© 2015 Pearson Education, Inc.
You should now be able to
6.
Describe Darwin’s observations and inferences in
developing the concept of natural selection.
7.
Explain how the work of Thomas Malthus and the
process of artificial selection influenced Darwin’s
development of the idea of natural selection.
8.
Explain why individuals cannot evolve and why
evolution does not lead to perfectly adapted organisms.
9.
Describe two examples of natural selection known to
occur in nature.
© 2015 Pearson Education, Inc.
You should now be able to
10. Explain how mutation and sexual reproduction produce
genetic variation.
11. Explain why prokaryotes can evolve more quickly than
eukaryotes.
12. Describe the five conditions required for the HardyWeinberg equilibrium.
13. Explain why the Hardy-Weinberg equilibrium is
significant to understanding the evolution of natural
populations and to public health science.
14. Define genetic drift and gene flow. Explain how the
bottleneck effect and the founder effect influence
microevolution.
© 2015 Pearson Education, Inc.
You should now be able to
15. Distinguish between stabilizing selection, directional
selection, and disruptive selection. Describe an example
of each.
16. Define and compare intrasexual selection and
intersexual selection.
17. Explain how antibiotic resistance has evolved.
18. Explain how genetic variation is maintained in
populations.
19. Explain why natural selection cannot produce
perfection.
© 2015 Pearson Education, Inc.
Figure 13.UN01
Heritable variations
in individuals
Observations
Overproduction
of offspring
Inferences
Individuals well-suited to the environment tend to leave more offspring
and
Over time, favorable traits accumulate in the population
© 2015 Pearson Education, Inc.
Figure 13.UN02
Allele frequencies
p
+ q = 1
Genotype frequencies
p2 + 2pq
+ q2 = 1
Dominant
Heterozygotes
homozygotes
© 2015 Pearson Education, Inc.
Recessive
homozygotes
Figure 13.UN03
Original
population
Stabilizing selection
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Evolved
population
Directional selection
Pressure of
natural selection
Disruptive selection
Figure 13.UN04
Microevolution
is the
may result from
change in allele
frequencies in a
population
(a)
(c)
(b)
random fluctuations
due to
more likely in a
movement of
individuals
or gametes
(d)
may be result of
(e)
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(f)
due to
leads to
(g)
of individuals
best adapted
to environment
adaptive
evolution
Figure 13.UN05
© 2015 Pearson Education, Inc.