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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 13
How Populations Evolve
Modules 13.1 – 13.3
From PowerPoint® Lectures for Biology: Concepts & Connections
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Clown, Fool, or Simply Well Adapted?
• All organisms have evolutionary adaptations
– Inherited characteristics that enhance their
ability to survive and reproduce
• The blue-footed booby of the
Galápagos Islands has features
that help it succeed in its
environment
– Large, webbed feet help
propel the bird through
water at high speeds
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EVIDENCE OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory
of evolution
• Aristotle and the culture of the 1800’s believed
that species are fixed
• Fossils suggested that life forms change
– This idea was embraced by Lamarck in the early
1800s
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• While on the voyage of the HMS Beagle in the
1830s, Charles Darwin observed
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as blue-footed boobies and giant tortoises
Figure 13.1A
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• The voyage of the Beagle
Great
Britain
Europe
North
America
Pacific
Ocean
Atlantic
Ocean
Africa
Galápagos
Islands
Equator
South
America
Australia
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Figure 13.1B
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• Darwin became convinced that the Earth was
old and continually changing
– He concluded that living things also change, or
evolve over generations
– He also stated that living species descended
from earlier life-forms: descent with
modification
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13.2 The study of fossils provides strong evidence
for evolution
• Fossils and the fossil record
strongly support the theory of
evolution
– Hominid skull
– Petrified trees
Figure 13.2A, B
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– Scorpion in amber
– “Ice Man”
Figure 13.2E, F
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• The fossil record shows that
organisms have appeared in a
historical sequence
• Many fossils link
early extinct species
with species living
today
– These fossilized
hind leg bones link
living whales with
their land-dwelling
ancestors
Figure 13.2G, H
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13.3 A mass of evidence validates the evolutionary
view of life
• Other evidence for evolution comes from
– Biogeography
– Comparative
anatomy
– Comparative
embryology
Human
Cat
Whale
Bat
Figure 13.3A
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– Molecular biology
Human
Rhesus monkey
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
Mouse
Chicken
Frog
Lamprey
80 MYA
275 MYA
330 MYA
450 MYA
Figure 13.3B
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DARWIN’S THEORY AND THE MODERN
SYNTHESIS
13.4 Darwin proposed natural selection as the
mechanism of evolution
• Darwin observed that (Natural Selection)
– organisms produce more offspring than the
environment can support
– organisms vary in many characteristics
– these variations can be inherited
– organisms that are better adapted leave more
offspring
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Darwin’s Four Criteria for Natural
Selection to Occur
• Overproduction of offspring leads to more
offspring than environment can support
• Variation in those offspring
• Variations are inherited
• Offspring that are better adapted to
environment leave subsequently more
offspring
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• Darwin concluded that individuals best suited
for a particular environment are more likely to
survive and reproduce than those less well
adapted
• Darwin saw natural selection as the basic
mechanism of evolution
– As a result, the proportion of individuals with
favorable characteristics increases
– Populations gradually change in response to the
environment
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Darwin also saw that when
humans choose organisms
with specific
characteristics as breeding
stock, they are performing
the role of the environment
– This is called artificial
selection
Adopt me!!
Figure 13.4A
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13.5 Connection: Scientists can observe natural
selection in action
• Evolutionary adaptations have been observed
in populations of birds, insects, and many other
organisms
– Example: camouflage adaptations of mantids
that live in different environments
Figure 13.5A
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• The evolution of insecticide resistance is an
example of natural selection in action
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Figure 13.5B
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13.6 Populations are the units of evolution
• A species is a group of
populations whose individuals
can interbreed and produce
fertile offspring
• A population is a group of
interbreeding individuals
living in same place and same
time.
– Populations evolve, not
individuals!!!
Figure 13.6
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13.7 Microevolution is change in a population’s
gene pool over time
• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool
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13.8 The gene pool of a nonevolving population
remains constant over the generations
• Hardy-Weinberg equilibrium
states that the shuffling of
genes during sexual
reproduction does not alter
the proportions of different
alleles in a gene pool
– To test this, let’s look at an
imaginary, nonevolving
population of blue-footed
boobies
Webbing
No webbing
Figure 13.8A
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• We can follow alleles in a population to observe
if Hardy-Weinberg equilibrium exists
Phenotypes
Genotypes
WW
Ww
ww
Number of animals
(total = 500)
320
160
20
Genotype frequencies
320/
500
= 0.64
Number of alleles
in gene pool
(total = 1,000)
640 W
Allele frequencies
800/
1,000
160/
500
20/
= 0.32
160 W + 160 w
= 0.8 W
200/
1,000
500
= 0.04
40 w
= 0.2 w
Figure 13.8B
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Recombination
of alleles from
parent generation
SPERM
EGGS
WW
p2 = 0.64
WW
qp = 0.16
Ww
pq = 0.16
ww
q2 = 0.04
Next generation:
Genotype frequencies
0.64 WW
Allele frequencies
0.32 Ww
0.8 W
0.04 ww
0.2 w
Figure 13.8C
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13.10 Five conditions are required for HardyWeinberg equilibrium
• The population is very large
• The population is isolated
• Mutations do not alter the gene pool
• Mating is random
• All individuals are equal in reproductive success
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What is Hardy-Weinberg Equilibrium????
• It just means that the gene pool is in
equilibrium.
• Allele frequency is not changing
• POPULATION IS NOT EVOLVING!!!
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13.11 There are several potential causes of
microevolution
• Genetic drift is
a change in a
gene pool due
to chance
– Genetic drift
can cause the
bottleneck
effect
Original
population
Bottlenecking
event
Surviving
population
Figure 13.11A
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– or the founder effect
Figure 13.11B, C
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• Gene flow can change a gene pool due to the
movement of genes into or out of a population
• Mutation changes alleles
• Natural selection leads to differential
reproductive success
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Five Fingers of Evolution
(Causes of Microevolution)
• Small population size
• Non-random mating
• Mutations
• Gene flow (migration)
• Natural selection
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13.12 Adaptive change results when natural
selection upsets genetic equilibrium
• Natural selection results in the accumulation of
traits that adapt a population to its environment
– If the environment should change, natural
selection would favor traits adapted to the new
conditions
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VARIATION AND NATURAL SELECTION
13.13 Variation is extensive in most populations
• Phenotypic variation may be environmental or
genetic in origin
– But only genetic changes result in evolutionary
adaptation
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• Many populations exhibit polymorphism and
geographic variation
Figure 13.13
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13.14 Connection: Mutation and sexual
recombination generate variation
A1
Parents
A1
A2
A3
MEIOSIS
A1
A2
A3
Gametes
FERTILIZATION
Offspring,
with new
combinations
of alleles
A1
A2
A1
A3
and
Figure 13.14
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13.15 Overview: How natural selection affects
variation
• Natural selection tends to reduce variability in
populations
– The diploid condition preserves variation by
“hiding” recessive alleles
– Balanced polymorphism may result from the
heterozygote advantage
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13.16 Not all genetic variation may be subject to
natural selection
• Some variations may be neutral, providing no
apparent advantage or disadvantage
– Example: human fingerprints
Figure 13.16
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13.17 Connection: Endangered species often have
reduced variation
• Low genetic variability may reduce the capacity
of endangered species to survive as humans
continue to alter the environment
– Studies have shown that cheetah populations
exhibit extreme genetic uniformity
– Thus they may have a
reduced capacity to
adapt to environmental
challenges
Figure 13.17
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13.18 The perpetuation of genes defines
evolutionary fitness
• An individual’s Darwinian fitness is the
contribution it makes to the gene pool of the
next generation relative to the contribution
made by other individuals
• Production of fertile offspring is the only score
that counts in natural selection
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13.19 There are three general outcomes of natural
selection
Frequency of
individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19
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13.20 Sexual selection may produce sexual
dimorphism
• Sexual selection leads to the evolution of
secondary sexual characteristics
– These may give individuals an advantage in
mating
Figure 13.20A, B
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13.21 Natural selection cannot fashion perfect
organisms
• This is due to:
– historical constraints
– adaptive compromises
– chance events
– availability of variations
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