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Darwinian Evolution
Ch. 16
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Darwin’s Achievement
 Darwin’s Theory of Evolution is
one of the greatest intellectual
achievements in history of
science.
 Why? And how did he do it? That
is the topic of this presentation.
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Brief Darwin (1809 – 1882)
 Darwin’s ideas formed the basis for
modern evolutionary theory.
 Poor student, he was a challenge for his
father.
 In l831, when Darwin was only 22 he
signed on as the ship’s naturalist aboard
the Beagle on a 5-year expedition around
the world.
 Darwin studied and collected many
different and usual specimens which
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contributed to his theory.
Darwin’s Voyage to the
Galapagos Islands
 Some of Darwin’s most important
observations were made on the
Galapagos Islands.
 The islands are near the equator,
1000km off the west coast of South
America.
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More Animals of the
Galapagos Islands:
Blue Footed Boobies in the Galapagos
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Assumptions at that time:
 Species are fixed (do not change)
 Aristotle’s Scala naturae-He believed that
species were fixed creations that never
changed and they were arranged from least
complex to most complex-worms on the
bottom and man on the top.
 Earth is only a few thousand years old.
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Darwin’s Revolutionary
Ideas:
On the Origin of Species published
1859
1) Species change (they are not fixed)
2) Species changed or evolved from
common ancestry over time
(implying a much older Earth)
3) Natural Selection is the mechanism
for change
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Why species change?
 Darwin observes organisms with
slight differences
or variations
 Ex: Galápagos
finches with
different beaks
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Why Common Ancestry?
 Darwin also finds fossils of organisms
unlike any that live today.
 Ex: giant sloth in Argentina
(modern armadillos and
sloths related, but MUCH
smaller)
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There are many Common
Ancestry Implications
noted by Darwin:
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Why Earth had to be older
than 6,000 years?
 He read geology papers (Lyell’s
work showed growing evidence
for gradual change of landforms)
 Found evidence of long extinct
habitats (fossil sea shells in
Andes Mountains)
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How does change happen?
 Ideas for selection started with
interviewing pigeon breeders
 artificial
selection in
animals and
plants
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What about in nature?
 What force “selects” which organisms
reproduce? The Environment
 What does the environment include?
 Influenced by Malthus (economist)
writing about competition for scarce
resources.
 If organisms must compete for
survival, the survivors would
reproduce more.
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Darwin’s Natural Selection
1) Overproduction-Organisms produce
more offspring than can survive
because of competition for resources.
2) Variety within a population or species
3) Selection-having a particular trait can
make individuals more or less likely to
survive and produce offspring
4) Adaptation–over time, the traits that
aid survival and reproduction become 14
common
Darwin’s Natural Selection
Summary:
 Given: Too many organisms +
scarce resources = fierce
competition
 Given: Individuals have heritable
variations
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Darwin’s Natural Selection
 Conclusion: Individuals with
beneficial variations outreproduce others
 Conclusion: Over many
generations, many in the
population have beneficial trait
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Does natural selection
occur now?
 Goal – study a model organism
with fast life cycle
 How about bacteria?
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Bacterial Evolution
 Resistance to antibiotic
medicines
 First wide use of antibiotic
penicillin in 1940s
 Open books to p. 484 to figure 12
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Darwin vs. Lamarck
Darwinian evolution
Lamarckian evolution
 Genetic variation
 Individuals change
traits by use and disuse
 Individuals with
beneficial variations
reproduce more
 Individuals pass
acquired changes
throughout life to
offspring
 Population evolves,
NOT individuals
 Individuals evolve
because they “want”
change
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Lamark’s Theory
“
Use and Disuse”
1. Use of structure
results in
Evolution
2. Does not take
into account
DNA or sex cell
Mutations
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Did Evolution occur in
history?
 Yes … transitional fossil evidence
 Archaeopteryx – reptile / bird
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Transitional Fossils
 Tiktaalik – fish / amphibian
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Homologous Structures
 Homo = ?
 Same
evolutionary
history
 Different
functions in
different
environments
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Homologous DNA
Most powerful evidence for a common
ancestor
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Homologous Development
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Homologous Cell Processes
 Respiration / photosynthesis
pathways are similar processes in
most species
 Mitosis process is the same in all
eukaryotes
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Vestigial structures-lost
over time
“use it or lose it”
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Vestigial Structures
“use it or lose it”28
See Page
382 for Whale
Evolution

Ambulocetus natans in action. A reconstruction of an
early close cousin of whales.
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Adaptations: Camouflage
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Adaptations: Mimicry
We think this mimicry has evolved so that
potential predators, such as fish, learn more
quickly that red spots are a sign that the
animal has large glands of distasteful
chemicals in their mantle.
Owl butterfly
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Vestiges and Selection
 Natural selection not only
changes populations over time…
 Selection also preserves crucial
traits needed for survival
 Example: The Wolf’s sense of
smell.
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Misconceptions
 Evolution does not just add
complexity, it can take it away as well
 Great example: tapeworm-lacks many
organ systems
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Imperfections in Humans
 Evolution does not “finish” with a “perfect
trait”
incoming light
 Eye photoreceptor setup and blind spots
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Complex Changes-How?
 How does random mutation lead to
complex changes?
 The icefish below is able to withstand
the Anarctic freeze. How?
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Evolution of Complexity
 Organisms often “borrow” from
pre existing, successful genes,
which are adapted for new
purposes.
 Example: Icefish antifreeze protein is
closely related to fish trypsinogen protein
already produced by the fish. The antifreeze
protein is simply modified from typsinogen.36
Patterns of Evolution
 Populations are not isolated, and
often evolve in response to each
other
 Coevolution – two species are
competing to “one up” each other
with adaptations
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Coevolution
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Divergent
evolution
Convergent
evolution
Also called Adaptive
Radiation
See Page 383, Figure 8
new organisms
common
ancestor
some similar organisms
develop in similar environments
in different parts of the world
different
ancestries
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Adaptive Radiation
Special
case of
divergent
evolution when
many
niches are
available
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Patterns of Evolution
 Gradualism vs. punctuated
equilibrium
Slow, even change Long periods of no change
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with bursts of rapid change
The End
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