Chapter 13 How Populations Evolve

Notes for my AP Biology course

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PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Chapter 13
How Populations Evolve
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Clown, Fool, or Simply Well Adapted?
•The blue-footed booby
–Is a type of bird living in the Galápagos
Islands
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•This type of bird possesses many specialized
characteristics, called evolutionary adaptations
–Which are inherited traits that enhance its
ability to survive and reproduce in its
particular environment
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DARWIN’S THEORY OF EVOLUTION
13.1 A sea voyage helped Darwin frame his
theory of evolution
•On his visit to the Galápagos Islands
–Charles Darwin observed many unique
organisms
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Figure 13.1A

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•Darwin’s main ideas
–Can be traced back to the ancient
Greeks
•Aristotle and the Judeo-Christian culture
–Believed that species are fixed
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•In the century prior to Darwin
–The study of fossils suggested that life
forms change
•Geologists proposed that a very old Earth
–Is changed by gradual processes
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•While on the voyage of the HMS Beagle in the
1830s
–Charles Darwin observed similarities
between living and fossil organisms and the
diversity of life on the Galápagos Islands
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North
America
Europe
Great
Britain
Africa
Equator
Asia
Australia
Tasmania
New
Zealand
PACIFIC
OCEAN
ATLANTIC
OCEAN
PACIFIC
OCEAN
PACIFIC
OCEAN
The
Galápagos
Islands
South
America
Tierra del Fuego
Cape Horn
Cape of
Good HopeAndes
Pinta
Marchena
Genovesa
Equator
Santiago
Isabela
Fernandina
Florenza
Española
San
Cristobal
Santa
Cruz
Santa
Fe
Pinzón
Daphne
Islands
40 miles
40 km
0
0 Figure 13.1B

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•Darwin’s experiences during the voyage of the
Beagle
–Helped him frame his ideas on evolution
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13.2 Darwin proposed natural selection as the
mechanism of evolution
•Darwin observed that organisms
–Produce more offspring than the
environment can support
–Vary in many characteristics that can be
inherited
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•Darwin reasoned that natural selection
–Results in favored traits being
represented more and more and
unfavored ones less and less in ensuing
generations of organisms
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•Darwin found convincing evidence for his ideas
in the results of artificial selection
–The selective breeding of domesticated
plants and animals
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Figure 13.2A
Hundreds to thousands
of years of breeding
(artificial selection)
Ancestral dog (wolf)
Figure 13.2B

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•Darwin proposed that living species
–Are descended from earlier life forms and
that natural selection is the mechanism
of evolution
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Thousands to
millions of years
of natural selection
Ancestral canine
African wild dog Coyote Wolf Fox Jackal
Figure 13.2C

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13.3 The study of fossils provides strong
evidence for evolution
•Fossils and the fossil record
–Strongly support the theory of evolution
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A Skull of Homo
erectus
D Dinosaur tracksC Ammonite castsB Petrified tree
E Fossilized organic
matter of a leaf
G “Ice Man”
Figure 13.3A–G
F Insect in amber

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•The fossil record
–Reveals that organisms have evolved in
a historical sequence
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Figure 13.3H

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•Many fossils link early extinct species
–With species living today
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Figure 13.3I

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13.4 A mass of other evidence reinforces the
evolutionary view of life
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Biogeography
•Biogeography, the geographic distribution of
species
–Suggested to Darwin that organisms
evolve from common ancestors
•Darwin noted that Galápagos animals
–Resembled species of the South
American mainland more than animals
on similar but distant islands
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Comparative anatomy
•Comparative anatomy
–Is the comparison of body structures in
different species
•Homology
–Is the similarity in characteristics that
result from common ancestry
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•Homologous structures
–Are features that often have different
functions but are structurally similar
because of common ancestry
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Human Cat Whale BatFigure 13.4A

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Comparative Embryology
•Comparative embryology
–Is the comparison of early stages of
development among different organisms
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•Many vertebrates
–Have common embryonic structures
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Post-anal
tail
Pharyngeal
pouches
Chick embryo Human embryo
Figure 13.4B

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Molecular Biology
•Comparisons of DNA and amino acid
sequences between different organisms
–Reveal evolutionary relationships
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Table 13.4

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CONNECTION
13.5 Scientists can observe natural selection in
action
•Camouflage adaptations that evolved in
different environments
–Are examples of the results of natural
selection
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A flower
mantid
in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A

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•Development of pesticide resistance in insects
–Is another example of natural selection in
action
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Pesticide application
Survivor
Chromosome with gene
conferring resistance
to pesticide
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will growFigure 13.5B

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•13.6 Populations are the units of evolution
–A population
•Is a group of individuals of the same
species living in the same place at the
same time
–A species is a group of populations
•Whose individuals can interbreed and
produce fertile offspring
0POPULATION GENETICS AND THE MODERN
SYNTHESIS

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•Population genetics
–Studies how populations change
genetically over time
•The modern synthesis
–Connects Darwin’s theory with population
genetics
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•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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13.7 The gene pool of a nonevolving population
remains constant over the generations
•In a nonevolving population
–The shuffling of alleles that accompanies
sexual reproduction does not alter the
genetic makeup of the population
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Webbing No webbingFigure 13.7A

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•Hardy-Weinberg equilibrium
–States that the shuffling of genes during sexual
reproduction does not alter the proportions of
different alleles in a gene pool
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Phenotypes
Genotypes WW Ww ww
Number of animals
(total = 500)
320 160 20
320
500
Genotype frequencies = 0.64
160
500
= 0.32
20
500
= 0.04
Number of alleles
in gene pool
(total = 1,000)
Allele frequencies
800
1,000
= 0.8 W = 0.2 w
640 W 160 W + 160 w 40 w
Figure 13.7B
200
1,000

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•We can follow alleles in a population
–To observe if Hardy-Weinberg
equilibrium exists
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Recombination
of alleles from
parent generation
EGGS
Genotype frequencies
Allele frequencies
0.64 WW 0.32 Ww 0.04 ww
0.8 W 0.2 w
Next generation:
W egg
p = 0.8
w egg
q = 0.2
W sperm
p = 0.8
w sperm
q = 0.2
SPERM
WW
p
2
= 0.64
Ww
pq = 0.16
wW
qp = 0.16
ww
q
2
= 0.04
Figure 13.7C

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•For a population to be in Hardy-Weinberg
equilibrium, it must satisfy five main conditions
–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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13.8 The Hardy-Weinberg equation is useful in
public health science
•Public health scientists use the Hardy-
Weinberg equation
–To estimate frequencies of disease-
causing alleles in the human population
0CONNECTION

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13.9 In addition to natural selection, genetic drift
and gene flow can contribute to evolution
•Genetic drift
–Is a change in the gene pool of a
population due to chance
–Can alter allele frequencies in a
population
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•Genetic drift
–Can cause the bottleneck effect or the
founder effect
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Original
population
Bottlenecking
event
Surviving
population
Figure 13.9A Figure 13.9B

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•Gene flow
–Is the movement of individuals or
gametes between populations
–Can alter allele frequencies in a
population
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•Natural selection
–Leads to differential reproductive
success in a population
–Can alter allele frequencies in a
population
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13.10 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
0CONNECTION
Figure 13.10

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13.11 Variation is extensive in most populations
•Many populations exhibit polymorphism
–Different forms of phenotypic
characteristics
0VARIATION AND NATURAL SELECTION
Figure 13.11

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•Populations may also exhibit geographic
variation
–Variation of an inherited characteristic
along a geographic continuum
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13.12 Mutation and sexual recombination
generate variation
•Mutations, or changes in the nucleotide
sequence of DNA
–Can create new alleles
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•Sexual recombination
–Generates variation by shuffling alleles during
meiosis
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A
1
A
2
A
1
A
3
A
1
A
1
A
2
A
3
A
2
A
1
A
3
and
X
Parents
Meiosis
Gametes
Fertilization
Offspring,
with new
combinations
of allelesFigure 13.12

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13.13 The evolution of antibiotic resistance in
bacteria is a serious public health concern
•The excessive use of antibiotics
–Is leading to the evolution of antibiotic-
resistant bacteria
0CONNECTION
Colorized SEM 5,600
´
Figure 13.13

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13.14 Diploidy and balancing selection variation
•Diploidy preserves variation
–By “hiding” recessive alleles
•Balanced polymorphism
–May result from the heterozygote
advantage or frequency-dependent
selection
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•Some variations may be neutral
–Providing no apparent advantage or
disadvantage
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Figure 13.14

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13.15 The perpetuation of genes defines
evolutionary fitness
•An individual’s fitness
–Is the contribution it makes to the gene
pool of the next generation
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13.16 Natural selection can alter variation in a
population in three ways
•Stabilizing selection
–Favors intermediate phenotypes
•Directional selection
–Acts against individuals at one of the
phenotypic extremes
•Disruptive selection
–Favors individuals at both extremes of the
phenotypic range
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•Three possible effects of natural selection
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Original
population
Stabilizing selection
Original
population
Evolved
population
Frequency of individuals
Phenotypes (fur color)
Directional selection Disruptive selectionFigure 13.16

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13.17 Sexual selection may produce sexual
dimorphism
•Sexual selection leads to the evolution of
secondary sexual characteristics
–Which may give individuals an advantage
in mating
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Figure 13.17A Figure 13.17B

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13.18 Natural selection cannot fashion perfect
organisms
•There are at least four reasons why natural
selection cannot produce perfection
–Organisms are limited by historical
constraints
–Adaptations are often compromises
–Chance and natural selection interact
–Selection can only edit existing variations
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