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Biological Evolution
A change in the genetic characteristics of a
population over time
 If any allele frequency in a population
changes w/ time, the population is evolving
 Most people think of evolution as Darwin’s
speciation, but this is not correct

© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Biological Evolution

Only populations can evolve; individuals
cannot
 (on
molecular level, genes can evolve)
Small scale change = microevolution
 Large scale change = macroevolution
 Macroevolution can lead to speciation, but
it does not have to

 macroevolution
that has occurred in dogs
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
2
Mechanisms of Evolution

Evolution occurs through two major
genetic forces:

Natural Selection (includes artificial seltn)
 Genetic Drift

What are the other two forces that can
change allele frequencies in a population?

Mutations
 Gene flow
 Do
not generally cause evolution, mutation is too rare
& gene flow tends to equalize the gene frequencies
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Natural Selection Occurs because:
Organisms with favorable traits have a
better chance at survival
 The longer an organism lives, the more
offspring it may produce
 More of the next generation will have the
favorable trait than the previous
generation

© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Genetic Drift


Differences in reproduction or survival between
organisms due to random chance
Environmental disturbances can cause genetic drift:

Hurricanes or Volcanic eruptions
 Clearing land for development or Over-hunting

Can be from random events
 seeds
from white flowers are blown to gravel, some
seeds from red flowers blown to good soil.
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Genetic Drift
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Result of Evolution

Evolution results in 3 major themes in
biology:
Adaptation of populations
2. Diversity of life
3. Shared inherited characteristics between
organisms
1.
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DISCOVER BIOLOGY 3/e
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Adaptations & Diversity

Adaptation –a characteristic that improves
the survival of an organism
 The

result of natural selection
Diversity is the result of speciation
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Impact of Evolutionary Thought

Understanding evolution has impacted
technology:
 Development
and use of pesticides
 Antibiotics and the development of drug resistance

Doonesbury cartoon?
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Readings on Evolution


I have assigned the readings, but I have only
lightly covered this topic
Want to spend more time on Life on Earth
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
10
Shared Inherited Characteristics

Characteristics
arise due to a
common ancestry:

Homologous
structures
 Vestigial structures
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Shared Non-Inherited
Characteristics
Convergent evolution in similar
adaptations
 These are considered analogous
structures


Thorns on roses and cactus
 Wings in birds and insects
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Evidence for Evolution

Fossils
© 2006 W.W. Norton & Company, Inc.
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Evidence for Evolution

Organisms contain evidence of their
evolutionary history:
 Vestigial
structures
 Embryological development
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Evidence for Evolution



Continental drift
The lungfish existed
before the break up of
the super continent,
Pangaea
Living representatives
of the lungfish are all
over the world
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
15
Evidence for Evolution

Direct observations of
genetic change in
populations

Artificial selection:
 Farming
crops
 Domesticated animals
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Evolution in Action

Medium ground finch
in the Galapagos

Changes in beak and
body size correlate
with rainfall over time
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Concept Quiz
Of the following situations that pertain to
evolution, which one is false?
A.
B.
C.
Organisms inherit traits from their parents.
Organisms can adapt to prepare their offspring
for future events.
Evolution can happen by chance.
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
18
Concept Quiz
Evolution is the change that occurs in
__________ over time.
A.
B.
C.
a population
an organism
the environment
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
19
Concept Quiz
Of the following, which term or phrase best
describes the process of natural selection?
A.
B.
C.
Genetic drift
Differential reproductive success
Speciation
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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