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Chapter 22
Descent with Modification:
A Darwinian View of Life
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: Endless Forms Most Beautiful
• A new era of biology began in 1859 when
Charles Darwin published The Origin of
Species
• The Origin of Species focused biologists’
attention on the great diversity of organisms
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Darwin noted that current species are
descendants of ancestral species
• Evolution can be defined by Darwin’s phrase
descent with modification
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-1
Fig. 22-2
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1800
1900
1750
1850
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his hypothesis of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks.
1844 Darwin writes essay on descent with modification.
1858 Wallace sends his hypothesis to Darwin.
1859 The Origin of Species is published.
Ideas About Change over Time
• The study of fossils helped to lay the
groundwork for Darwin’s ideas
• Fossils are remains or traces of organisms
from the past, usually found in sedimentary
rock, which appears in layers or strata
Video: Grand Canyon
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Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
Fig. 22-4
Darwin’s Research
• Charles Darwin had an interest in nature
• First studied medicine (unsuccessfully), then
theology at Cambridge University
• Took a position as naturalist and companion to
Captain Robert FitzRoy for a 5-year around the
world voyage on the Beagle
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The Voyage of the Beagle
• Darwin collected specimens of S. American
plants & animals
• Observed adaptations of plants and animals
that inhabited many diverse environments
• Darwin was influenced by Lyell’s Principles of
Geology
– Earth more than 6000 yrs old
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Fig. 22-5
*Interest in geographic distribution of species peaked
while at the Galápagos Islands
*near the equator west of South America
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
Fig. 22-5a
Darwin in 1840
Fig. 22-5b
The
Galápagos
Islands
Pinta
Marchena
Santiago
Fernandina
Genovesa
Daphne
Islands
Pinzón
Isabela
Santa
Cruz Santa
Fe
Florenza
San
Cristobal
Española
Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
The Origin of Species
• Darwin developed two main ideas:
– Descent with modification explains life’s
unity and diversity
– Natural selection is a cause of adaptive
evolution
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Fig. 22-7
Fig. 22-8
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5
2 104 0
Years ago
Fig. 22-8a
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5
2 104 0
Years ago
Artificial Selection, Natural Selection, and
Adaptation
• Darwin noted that humans have modified
species
– selecting and breeding individuals with
desired traits
– called artificial selection
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Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Darwin made 4 observations, and drew 2 inferences
• Observation #1: Members of a population often
vary greatly in their traits
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• Observation #2: Traits are
inherited from parents to
offspring
• Observation #3: Species
are capable of producing
more offspring than the
environment can support
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• Observation #4: Lack of resources means
many of these offspring do not survive
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• Inference #1: Individuals with inherited traits
giving them a higher probability of surviving &
reproducing in a given environment tend to
leave more offspring than other individuals
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Inference #2: unequal ability of individuals to
survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• If some heritable traits are advantageous,
these will accumulate in the population, and the
frequency of individuals with adaptations will
increase
• This process explains the match between
organisms and their environment
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Natural Selection: A Summary
• Individuals with certain heritable characteristics
survive and reproduce at a higher rate than
other individuals
• Natural selection increases the adaptation of
organisms to their environment over time
• If an environment changes, natural selection
may result in adaptations to these new
conditions and may give rise to new species
Video: Seahorse Camouflage
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
• Individuals do not evolve
• Populations evolve over time
• Natural selection can only increase or
decrease heritable traits in a population
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Direct Observations of Evolutionary Change
• Two examples provide evidence for natural
selection: the effect of differential predation on
guppy populations and the evolution of drugresistant HIV
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Predation and Coloration in Guppies : Scientific
Inquiry
• John Endler has studied the effects of
predators on wild guppy populations
• Brightly colored males are more attractive to
females
• However, brightly colored males are more
vulnerable to predation
• Guppy populations in pools with fewer
predators had more brightly colored males
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-13
EXPERIMENT
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
RESULTS
12
Number of
colored spots
12
10
8
6
4
2
0
Source
population
Transplanted
population
10
8
6
4
2
0
Source
population
Transplanted
population
• Endler transferred brightly colored guppies
(with few predators) to a pool with many
predators
• As predicted, over time the population became
less brightly colored
• Endler also transferred drab colored guppies
(with many predators) to a pool with few
predators
• As predicted, over time the population became
more brightly colored
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The Evolution of Drug-Resistant HIV
• The use of drugs to combat HIV selects for
viruses resistant to these drugs
• HIV uses the enzyme reverse transcriptase to
make a DNA version of its own RNA genome
• The drug 3TC is designed to interfere and
cause errors in the manufacture of DNA from
the virus
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• Some individual HIV viruses have a variation
that allows them to produce DNA without errors
• These viruses have a greater reproductive
success and increase in number relative to the
susceptible viruses
• The population of HIV viruses has therefore
developed resistance to 3TC
• The ability of bacteria and viruses to evolve
rapidly poses a challenge to our society
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-14
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
• Natural selection does not create new traits,
but edits or selects for traits already present
in the population
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Fossil Record
• The fossil record provides evidence of the
extinction of species, the origin of new groups,
and changes within groups over time
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Fig. 22-15
0
2
4
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
12
3
2 Bristolia harringtoni
14
16
18 1 Bristolia mohavensis
3
2
1
Latham Shale dig site, San
Bernardino County, California
• The Darwinian view of life predicts that
evolutionary transitions should leave signs in
the fossil record
• Paleontologists have discovered fossils of
many such transitional forms
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Fig. 22-16
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Homology
• Homology is similarity in characteristics
resulting from common ancestry
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Anatomical and Molecular Homologies
• Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Embryological Homologies
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
• All vertebrates have pharyngeal pouches (gill
slits) and a tail at some stage in their
development
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Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
47
Embryological development
• Vestigial structures are remnants of features
that served important functions in the
organism’s ancestors
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Molecular Homologies
• All organisms have in
common:
– DNA and RNA
– ATP (energy molecule)
– Enzymes, amino acids,
proteins
• Provides evidence that all
organisms come from a
common ancestor
Homologies and “Tree Thinking”
• Evolutionary trees are hypotheses about the
relationships among different groups
• Evolutionary trees can be made using different
types of data
– for example, anatomical and DNA
sequence data
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Fig. 22-19
Branch point
(common ancestor)
Lungfishes
Amphibians
1
Mammals
2
Tetrapod limbs
Amnion
Lizards
and snakes
3
4
Homologous
characteristic
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
Convergent Evolution
• Convergent evolution is the evolution of
similar, or analogous, features in distantly
related groups
• Analogous traits arise when groups
independently adapt to similar environments in
similar ways
• Convergent evolution does not provide
information about ancestry
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Fig. 22-20
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Flying
squirrel
Biogeography
• Darwin’s observations of biogeography, the
geographic distribution of species, formed an
important part of his theory of evolution
• Islands have many endemic species that are
often closely related to species on the nearest
mainland or island
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Madagascar
• Madagascar is home to 5 percent of the world's
plant and animal species, 80 percent of which are
found nowhere else on Earth.
• Tremendous biodiversity and high rates of
endemic species: of more than 200,000 known
species found on Madagascar, about 150,000
exist nowhere else.
• Unique to the island are some 70 kinds of lemurs
• Earth’s continents were formerly united in a
single large continent, Pangaea
• Have since separated by continental drift
• An understanding of continent movement and
modern distribution of species allows us to
predict when and where different groups
evolved
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What Is Theoretical About Darwin’s View of Life?
• A theory accounts for many observations and
data
• Attempts to explain and integrate a great
variety of phenomena
• Darwin’s theory of evolution by natural
selection integrates diverse areas of biological
study and stimulates many new research
questions
• Ongoing research adds to our understanding of
evolution
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Fig. 22-UN1
Observations
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Inferences
Individuals that are well suited
to their environment tend to leave
more offspring than other individuals
and
Over time, favorable traits
accumulate in the population.
You should now be able to:
1. Describe the contributions to evolutionary
theory made by Linnaeus, Cuvier, Lyell,
Lamarck, Malthus, and Wallace
2. Describe Lamarck’s theories, and explain why
they have been rejected
3. Explain what Darwin meant by “descent with
modification”
4. List and explain Darwin’s four observations
and two inferences
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5. Explain why an individual organism cannot
evolve
6. Describe at least four lines of evidence for
evolution by natural selection
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings