Transcript Adaptive Evolutionx

The Smallest Unit of Evolution
• One misconception is that organisms evolve
during their lifetimes
• Natural selection acts on individuals, but only
populations evolve
• Consider, for example, a population of medium
ground finches on Daphne Major Island
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Average beak depth (mm)
Figure 23.2
10
9
8
0
1978
1976
(similar to the (after
prior 3 years) drought)
• Microevolution is a change in allele
frequencies in a population over generations
• Three mechanisms cause allele frequency
change:
– Natural selection
– Genetic drift
– Gene flow
• Only natural selection causes adaptive
evolution
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Natural Selection
• Differential success in reproduction results in
certain alleles being passed to the next
generation in greater proportions
• For example, an allele that confers resistance
to DDT increased in frequency after DDT was
used widely in agriculture
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Figure 23.9-1
CRCR
CRCR
CRCW
CWCW
CRCR
CRCW
CRCR
CRCR
CRCW
CRCW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW) = 0.3
Figure 23.9-2
CRCR
CRCR
CRCW
CWCW
5
plants
leave
offspring
CRCR
CWCW
CRCW
CRCR
CWCW
CRCR
CRCW
CRCW
CRCR
CRCR
CRCW
CRCW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW) = 0.3
CWCW
CRCW
CRCR
CRCW
Generation 2
p = 0.5
q = 0.5
Figure 23.9-3
CRCR
CRCR
CRCW
CWCW
5
plants
leave
offspring
CRCR
CWCW
CRCW
CRCR
CWCW
CRCR
CRCW
CRCW
CRCR
CRCR
CRCW
CRCW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW) = 0.3
CWCW
CRCW
2
plants
leave
offspring
CRCR
CRCR
CRCR
CRCR
CRCR
CRCR
CRCR
CRCW
Generation 2
p = 0.5
q = 0.5
CRCR
CRCR
CRCR
CRCR
Generation 3
p = 1.0
q = 0.0
Figure 23.11c
Pre-bottleneck
(Illinois, 1820)
Greater prairie chicken
Range
of greater
prairie
chicken
Post-bottleneck
(Illinois, 1993)
A Closer Look at Natural Selection
• Natural selection brings about adaptive
evolution by acting on an organism’s
phenotype
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Relative Fitness
• The phrases “struggle for existence” and
“survival of the fittest” are misleading as they
imply direct competition among individuals
• Reproductive success is generally more
subtle and depends on many factors
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• Relative fitness is the contribution an
individual makes to the gene pool of the next
generation, relative to the contributions of other
individuals
• Selection favors certain genotypes by acting on
the phenotypes of certain organisms
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• Natural selection increases the frequencies of
alleles that enhance survival and reproduction
• Adaptive evolution occurs as the match between
an organism and its environment increases
• Because the environment can change, adaptive
evolution is a continuous process
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Why Natural Selection Cannot Fashion
Perfect Organisms
1.
2.
3.
4.
Selection can act only on existing variations
Evolution is limited by historical constraints
Adaptations are often compromises
Chance, natural selection, and the
environment interact
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Storytelling!
Character + Predicament + Attempted Extrication
Edward Bloom (aka current Homo sapiens)
• Practice and rehearsal of
ideas
• Pleasure
• Escape from ‘life’
• Nostalgic memories
• His son finishes his (life)
story
Early Homo sapiens
• Survival communication
• Purpose
• Escape from death
• Building “mental muscle,”
enhancing neural pathways
• ‘Fitness’ is transmitting
information (including
genes) to the next
generation
Write your own Fiction
Using the story equation – the
adaptive evolutionary model