Download Natural Selection Causes Evolution

Return of an Ancient Killer
 Tuberculosis has infected humans for 1000s
of years.
 Evidence of TB has been found in Egyptian
mummies.
 Hippocrates described a TB-like condition.
 In 1906, TB accounted for 2 out of every 1000 deaths
in the U.S.
 TB is caused by bacterium, Mycobacterium
tuberculosis.
 2 billion people carry TB.
 New infections occur at rate of 1 per second.
 TB causes roughly 2 million deaths per year.
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Return of an Ancient Killer - What is
Tuberculosis?
 Symptoms of TB include:
 Cough that produces blood
 Fever
 Fatigue
 Period of wasting – patient becomes weaker and
thinner
 Led to calling the disease “consumption”
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Return of an Ancient Killer - What is
Tuberculosis?
 Consumptive symptoms occur because of
damage to lung tissues.
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Return of an Ancient Killer - What is
Tuberculosis?
 Transmission of TB occurs through the air,
from infected individuals.
 A single sneeze can contain 40,000 droplets, all
containing infectious bacteria.
 Most individuals can fight off the infections,
except young children, elderly and immune
compromised individuals.
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Return of an Ancient Killer - Treatment – and
Treatment Failure
 In the 19th and early 20th century, TB treatment consisted of
“sanitariums.”
 The discovery of antibiotics revolutionized TB treatment.
 After 2 weeks of antibiotic treatment the individual is no
longer contagious.
 However, treatment with antibiotics needs to continue for 6
to 12 months to completely eliminate the organism.
 Since the 1980s, scientists have noticed an increase in TB
that is resistant to antibiotics.
 Because of resistance to antibiotics, the number of TB cases
worldwide is increasing.
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Return of an Ancient Killer - Treatment – and
Treatment Failure
 Since the 1980s, scientists have noticed an
increase in TB that is resistant to antibiotics.
 Because of resistance to antibiotics, the number of
TB cases worldwide is increasing.
 There is a strain of TB that is now resistant to both
the original treatment but also resistant to secondline drugs.
 1/3 of individuals with this extreme strain die of the
disease
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Natural Selection Causes Evolution
 Darwin discussed two ideas in Origin: common
descent and natural selection
 Natural selection is considered to be the primary
cause of evolution
 Other factors of evolution include genetic drift and
sexual selection
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Natural Selection Causes Evolution - Four
Observations and an Inference
 Natural selection is an inference based on four
observations:
1. Individuals within populations vary
2. Some of the variation within individuals can be
passed on to their offspring
3. Populations of organisms produce more offspring
than will survive
4. Survival and reproduction are not random
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Natural Selection Causes Evolution - Four
Observations and an Inference
1. Individuals within populations vary.
 This is true of human and non-human populations.
 Variation can include traits other than appearance,
such as blooming time in flowers.
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Natural Selection Causes Evolution - Four
Observations and an Inference
2. Some of the variation
within individuals can
be passed on to their
offspring.
 Darwin noticed that
animal breeders could
get exaggerated traits
through selective
breeding.
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Natural Selection Causes Evolution - Four
Observations and an Inference
3. Populations of organisms produce more offspring than
will survive.
 Even slow-breeding animals can produce large
populations quickly.
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Natural Selection Causes Evolution - Four
Observations and an Inference
4. Survival and reproduction are not random
 Fitness: Relative survival and reproduction of one
variant
 Adaptation: Traits that increase individual fitness in
an environment
 Individuals with adaptations for a particular
environment are more likely to survive and
reproduce.
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Natural Selection Causes Evolution - Four
Observations and an Inference
 Survival and reproduction are not random.
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Natural Selection Causes Evolution - Four
Observations and an Inference
 Adaptations do not only
affect survival.
 A flower’s reproduction is
impacted by traits that affect
the number of pollinators it
receives.
 Therefore, color or nectar
production might be
adaptations.
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Natural Selection Causes Evolution - Darwin’s
Inference: Natural Selection Causes Evolution
 Result of natural selection
 Favorable inherited variations tend to increase in
frequency
 Unfavorable variations tend to be lost
 End result is a change in the traits of individuals in
a population over generations
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Natural Selection Causes Evolution Testing Natural Selection
 Artificial selection: Selection
imposed by human choice
 Breeds of pigeons studied by
Darwin arose through artificial
selection
 Breeds of dog have been
artificially selected by humans
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Natural Selection Causes Evolution Testing Natural Selection
 In laboratory, environmental conditions can be
manipulated and effects on population examined
 Scientists examined alcohol metabolism in fruit flies
 Variations in ability to metabolize alcohol exist in
populations
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Natural Selection Causes Evolution - Testing
Natural Selection
 Natural selection in wild populations
 Many examples exist:
 Evolution of resistance of M. tuberculosis to
antibiotics
 Many other disease-causing pathogens have also
evolved resistance
 Galapagos finches provide another classic example
 Blue mussel has evolved the ability to thicken its
shell to protect against the invasive Asian crab
species.
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Animation: Natural Selection
Click “Go to Animation” / Click “Play”
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Natural Selection Since Darwin - The Modern
Synthesis
 The union of genetics and evolution is called “the
modern synthesis.”
 Knowledge of genetics facilitates understanding of
the mechanisms of evolution.
 Alleles are the basis of variation of traits.
 Half of the alleles carried by a parent are passed to
their offspring through their egg or sperm.
 Mutations can create new alleles and provide the
basis for new traits.
 Natural selection provides a filter that selects for or
against new traits.
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Natural Selection Since Darwin - The Modern
Synthesis
 Mutation and natural selection
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Natural Selection Since Darwin - Overview: The
Subtleties of Natural Selection
 Common misconceptions about natural selection
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Animation: Drug Resistance and Natural Selection
Click “Go to Animation” / Click “Play”
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Natural Selection Since Darwin - A Closer Look:
Subtleties of Natural Selection
 Natural selection cannot cause new traits to arise
 Not an issue of choice or “will” of organisms
 Selection can only act on variations that already exist
 For example, alcohol-rich environment in flies did not
cause a gene to arise, instead differential survival
caused allele to become more common
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Natural Selection Since Darwin - A Closer Look:
Subtleties of Natural Selection
 Natural selection does not result in perfection
 Natural selection does cause organisms to become
a better fit to their environment
 Organisms are not necessarily “better,” just better fit
to a particular situation
 Adaptation that is beneficial in one situation might
be a liability in another
 Adaptations are trade-offs between better fit in one
situation versus another
 Adaptations are constrained by underlying biology
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Natural Selection Since Darwin - A Closer Look:
Subtleties of Natural Selection
 Natural selection does not cause progression
towards a goal
 Natural selection favors variants with the most
appropriate adaptations for current environment
 Organisms do not choose to change or adapt
 Natural selection depends on the situation of the
population
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Natural Selection Since Darwin - Patterns of
Selection
 Different environmental conditions can lead to
different changes in populations
 Directional selection – change in population traits
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Natural Selection Since Darwin - Patterns of
Selection
 Different environmental conditions can lead to
different changes in populations
 Stabilizing selection – selection for the average traits
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Natural Selection Since Darwin - Patterns of
Selection
 Different environmental conditions can lead to
different changes in populations
 Diversifying selection – selection for extremes
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Natural Selection and Human Health Tuberculosis Fits Darwin’s Observations
 Mycobacterium tuberculosis has evolved resistance
to antibiotics because it fulfills the same
observations Darwin made
1. Organisms in the population vary
2. The variation among organisms can be passed on
to offspring
3. More organisms are produced than survive
4. An organism’s survival is not random
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Natural Selection and Human Health - Selecting for
Drug Resistance
 Simple antibiotic
treatment can
result in directional
selection in
bacteria.
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Natural Selection and Human Health - Stopping
Drug Resistance
 Combination therapy is a powerful tool against drug
resistance.
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Natural Selection and Human Health - Can
Natural Selection Save Us From Superbugs?
 If bacteria can evolve resistance to antibiotics, can
humans evolve resistance to bacteria?
 Humans do vary in their immune capacity
 To evolve resistance to superbugs would require
many humans to die
 Evolution of resistance requires exposure to
pathogens, most humans are never exposed
 Natural selection has also resulted in our brains,
giving us another tool to fight disease
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Natural Selection Causes Evolution - Four Observations
and an Inference
Natural selection is an inference based on
four observations
1. Individuals within populations vary
2. Some of the variation within individuals can be
passed on to their offspring
3. Populations of organisms produce more
offspring than will survive
4. Survival and reproduction are not random
© 2013 Pearson Education, Inc.
Natural Selection Causes Evolution - Testing Natural
Selection
Artificial Selection
Artificial selection
for dogs with
short legs
Artificial selection
for dogs with
short legs
Artificial selection
for dogs with
short legs
Dachshunds
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Figure 10.11
10.2 Natural Selection Causes Evolution
PLAY
Animation—Natural Selection
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What causes tuberculosis?
Virus
Bacteria
Spores
Pollution
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Which of the following is an example of artificial
selection?
A beetle’s acquired immunity to pesticide
Horse breeding
The average bill size increasing for finches due to
drought
None of the above
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Which of the following statements does not cause
natural selection?
Individuals within populations vary
Some of the variation within individuals can be
passed on to their offspring
Populations of organisms produce more offspring
than will survive
Survival and reproduction are random
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What type of selection results when the average
variant in the population has the highest fitness?
Directional selection
Stabilizing selection
Diversifying selection
Artificial selection
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True or False: Natural selection can cause new traits
to arise.
True
False
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What is often the result when people stop taking their
antibiotics when they feel better?
A drug-resistant strain is born
The person will have to restart the antibiotic course
The person will continue to feel fine
The person will be immune to that type of infection
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What type of selection is shown in this figure?
Directional selection
Artificial selection
Stabilizing selection
Diversifying selection
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What will the fly population look like after several
generations?
The frequency of the
mutant allele will
increase
The frequency of the
normal allele will
increase
There will be an equal
frequency of the
normal and mutant
alleles
There is no way to tell
what the population
will look like
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