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Transcript
Chapter 13
How Populations Evolve
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Clown, Fool, or Simply Well Adapted?
• The blue-footed booby
– Is a type of bird living in the Galápagos
Islands
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Figure 13.1A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Darwin’s main ideas
– Can be traced back to the ancient
Greeks
• Aristotle and the Judeo-Christian culture
– Believed that species are fixed
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
North
America
Great
Britain
Europe
Asia
ATLANTIC
OCEAN
PACIFIC
OCEAN
Africa
PACIFIC
OCEAN
Equator
The
Galápagos
Islands
PACIFIC
OCEAN
Pinta
South
America
Genovesa
Equator
Santiago
Pinzón
Fernandina
Isabela
0
Figure 13.1B
0
40 km
Daphne
Islands
Cape of
Good Hope
Tasmania
Santa Santa
Cruz Fe
Florenza
40 miles
Australia
Andes
Marchena
Cape Horn
San
Cristobal
Tierra del Fuego
Española
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
New
Zealand
• 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
Hundreds to thousands
of years of breeding
(artificial selection)
Ancestral dog (wolf)
Figure 13.2A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Figure 13.2B
• Darwin proposed that living species
– Are descended from earlier life forms
and that natural selection is the
mechanism of evolution
African wild dog
Coyote
Wolf
Thousands to
millions of years
of natural selection
Figure 13.2C
Ancestral canine
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Fox
Jackal
13.3 The study of fossils provides strong
evidence for evolution
• Fossils and the fossil record
–
Strongly support the theory of evolution
A Skull of Homo
erectus
B Petrified tree
E Fossilized organic
matter of a leaf
Figure 13.3A–G
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C Ammonite casts
D Dinosaur tracks
F Insect in amber
G “Ice Man”
• The fossil record
– Reveals that organisms have evolved in
a historical sequence
Figure 13.3H
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• Many fossils link early extinct species
– With species living today
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
Figure 13.4A
Human
Cat
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Whale
Bat
Comparative Embryology
• Comparative embryology
– Is the comparison of early stages of
development among different organisms
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Many vertebrates
–
Have common embryonic structures
Pharyngeal
pouches
Post-anal
tail
Human embryo
Chick embryo
Figure 13.4B
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Molecular Biology
• Comparisons of DNA and amino acid
sequences between different organisms
– Reveal evolutionary relationships
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
A flower
mantid
in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Development of pesticide resistance in insects
– Is another example of natural selection in
action
Chromosome with gene
conferring resistance
to pesticide
Pesticide application
Survivor
Figure 13.5B
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
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POPULATION GENETICS AND THE MODERN
SYNTHESIS
• 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
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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
Figure 13.7A
Webbing
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No webbing
• Hardy-Weinberg equilibrium
–
States that the shuffling of genes during sexual
reproduction does not alter the proportions of
different alleles in a gene pool
Phenotypes
Genotypes
Number of animals
(total  500)
Genotype frequencies
Number of alleles
in gene pool
(total  1,000)
Allele frequencies
Figure 13.7B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
WW
320
320  0.64
500
640 W
800  0.8 W
1,000
Ww
ww
160
20
160  0.32
500
160 W  160 w
20  0.04
500
40 w
200  0.2 w
1,000
• We can follow alleles in a population
– To observe if Hardy-Weinberg equilibrium
exists
Recombination
of alleles from
parent generation
SPERM
W sperm
w sperm
p  0.8
q  0.2
WW
p2  0.64
Ww
pq  0.16
wW
qp  0.16
ww
q2  0.04
W egg
p  0.8
EGGS
w egg
q  0.2
Next generation:
Genotype frequencies
Allele frequencies
Figure 13.7C
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
0.64 WW
0.8 W
0.32 Ww
0.04 ww
0.2 w
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
CONNECTION
13.8 The Hardy-Weinberg equation is useful in
public health science
• Public health scientists use the HardyWeinberg equation
– To estimate frequencies of diseasecausing alleles in the human population
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Genetic drift
– Can cause the bottleneck effect or the
founder effect
Original
population
Bottlenecking
event
Surviving
population
Figure 13.9A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Figure 13.9B
• Gene flow
– Is the movement of individuals or
gametes between populations
– Can alter allele frequencies in a
population
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Natural selection
– Leads to differential reproductive
success in a population
– Can alter allele frequencies in a
population
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
CONNECTION
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
Figure 13.10
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VARIATION AND NATURAL SELECTION
13.11 Variation is extensive in most populations
• Many populations exhibit polymorphism
– Different forms of phenotypic
characteristics
Figure 13.11
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• Populations may also exhibit geographic
variation
– Variation of an inherited characteristic
along a geographic continuum
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Parents
A1
A1
X
A2
A3
Meiosis
Gametes
A2
A1
A3
Fertilization
Figure 13.12
Offspring,
with new
combinations
of alleles
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
A1
A2
A1
and
A3
CONNECTION
13.13 The evolution of antibiotic resistance in
bacteria is a serious public health concern
• The excessive use of antibiotics
Colorized
SEM 5,600
– Is leading to the evolution of antibioticresistant bacteria
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
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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Frequency of individuals
• Three possible effects of natural selection
Original
population
Figure 13.16
Evolved
population
Stabilizing selection
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Original
population
Phenotypes (fur color)
Directional selection
Disruptive selection
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
Figure 13.17A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Figure 13.17B
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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings