The Effect of Natural Selection

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Topic 4

• The Effect of Natural Selection

The unit of evolution is an episode of variation
followed by an episode of selection." Graham Bell
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Fitness (w)
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Adaptation
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Selection Differential (s)
S
NOT SELECTED
SELECTED
mean
mean
overall
survivors
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Types of Natural Selection
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Natural selection requires variation. Where does
it come from?
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Case Studies of Natural Selection in the Wild
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1. Industrial Melanism (Biston betularia)
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Kettlewells Peppered Moth Data Mark and Recpture
Survival Rate
Observed
Expected
Birmingham Polluted
typica carbonaria
18 140
36 121
0.5 1.15
Deanend Woods Unpolluted
1.23 0.68
typica carbonaria
67 32
54 47
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2. Natural Selection on Beak Size in Galapagos
Finches
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Darwins Finches
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Testing Darwins four postulateswith the finches
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(No Transcript)
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1. Are populations variable?
Bill size varies
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2. Is variation heritable?
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Bill size is heritable
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3. Are more offspring produced than survive?
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4. Is survival and reproduction random?
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Bill depth of birds born lt and gt drought
Bill depth lt and gt drought
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30 years of evolution
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Proof in the Opposite Direction