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Chapter 22
Descent with Modification: A
Darwinian View of Life
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Darwin made two major points in his book:
– Many current species are descendants of
ancestral species
– Natural selection is a mechanism for this
evolutionary process
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Concept 22.1: The Darwinian revolution
challenged traditional views of a young Earth
inhabited by unchanging species
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LE 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)
Mendel (inheritance)
Wallace (evolution, natural selection)
American Revolution
U.S. Civil War
French Revolution
1850
1900
1750
1800
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his theory of evolution.
1830 Lyell publishes Principles of Geology.
1831–1936 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks on the origin of species.
1844 Darwin writes his essay on the origin of species.
1858 Wallace sends his theory to Darwin.
1859 The Origin of Species is published.
1865 Mendel publishes inheritance papers.
The Scale of Nature and Classification of Species
• Carolus Linnaeus interpreted organismal
adaptations as evidence that the Creator had
designed each species for a specific purpose
• Linnaeus was a founder of taxonomy, the branch
of biology concerned with classifying organisms
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Fossils, Cuvier, and Catastrophism
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Paleontology, the study of fossils, was largely
developed by French scientist Georges Cuvier
• Cuvier advocated catastrophism, speculating that
each boundary between strata represents a
catastrophe
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Theories of Gradualism
• Gradualism is the idea that profound change can
take place through the cumulative effect of slow
but continuous processes
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• Geologists Hutton and Lyell perceived that
changes in Earth’s surface can result from slow
continuous actions still operating today
• This view strongly influenced Darwin’s thinking
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Lamarck’s Theory of Evolution
• Lamarck hypothesized that species evolve
through use and disuse and the inheritance of
acquired traits
• The mechanisms he proposed are unsupported by
evidence
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 22.2: In The Origin of Species,
Darwin proposed that species change
through natural selection
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Darwin’s Research
• After receiving his B.A. degree, he was accepted
on board the HMS Beagle, which was embarking
on a voyage around the world
• During his travels on the Beagle, Darwin
collected specimens of South American plants
and animals
• He observed adaptations of plants and animals
that inhabited many diverse environments
• His interest in geographic distribution of species
was kindled by a stop at the Galápagos Islands
near the equator west of South America
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LE 22-5
England
EUROPE
NORTH
AMERICA
PACIFIC
OCEAN
ATLANTIC
OCEAN
AFRICA
Galápagos
Islands
HMS Beagle in port
Equator
SOUTH
AMERICA
Darwin in 1840,
after his return
AUSTRALIA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
New
Zealand
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Galápagos Island Overview
Video: Galápagos Sea Lion
Video: Soaring Hawk
Video: Galápagos Tortoise
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Darwin’s Focus on Adaptation
• In reassessing his observations, Darwin perceived
adaptation to the environment and the origin of
new species as closely related processes
• From studies made years after Darwin’s voyage,
biologists have concluded that this is indeed what
happened to the Galápagos finches
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LE 22-6
Cactus eater. The long,
sharp beak of the
cactus ground finch
(Geospiza scandens)
helps it tear and eat
cactus flowers and
pulp.
Seed eater. The large
ground finch (Geospiza
magnirostris) has a large
beak adapted for cracking
seeds that fall from plants
to the ground.
Insect eater. The green warbler finch
(Certhidea olivacea) used its narrow,
pointed beak to grasp insects.
The Origin of Species
• Darwin developed two main ideas:
– Evolution explains life’s unity and diversity
– Natural selection is a cause of adaptive
evolution
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Descent with Modification
• The phrase descent with modification summarized
Darwin’s perception of the unity of life
• The phrase refers to the view that all organisms
are related through descent from an ancestor that
lived in the remote past
• In the Darwinian view, the history of life is like a
tree with branches representing life’s diversity
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LE 22-7
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
0
10,000
2
5.5
24
34
Elephas Loxodonta Loxodonta
cyclotis
maximus africana
(Africa)
(Africa)
(Asia)
Natural Selection and Adaptation
• Evolutionary biologist Ernst Mayr has dissected
the logic of Darwin’s theory into three inferences
based on five observations
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• Observation #1: For any species, population sizes
would increase exponentially if all individuals that
are born reproduced successfully
• Observation #2: Populations tend to be stable in
size, except for seasonal fluctuations
• Observation #3: Resources are limited
• Inference #1: Production of more individuals than
the environment can support leads to a struggle
for existence among individuals of a population,
with only a fraction of their offspring surviving
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• Observation #4: Members of a population vary
extensively in their characteristics; no two
individuals are exactly alike
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• Observation #5: Much of this variation is heritable
• Inference #2: Survival depends in part on inherited
traits; individuals whose inherited traits give them
a high probability of surviving and reproducing are
likely to leave more offspring than other individuals
• Inference #3: This unequal ability of individuals to
survive and reproduce will lead to a gradual
change in a population, with favorable
characteristics accumulating over generations
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Artificial Selection
• In artificial selection, humans have modified other
species over many generations by selecting and
breeding individuals with desired traits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-10
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Leaves
Flower
clusters
Kale
Cauliflower
Stem
Flowers
and
stems
Broccoli
Wild mustard
Kohlrabi
Summary of Natural Selection
• Natural selection is differential success in
reproduction from interaction between individuals
that vary in heritable traits and their environment
• Natural selection produces an increase over time
in adaptation of organisms to their environment
• If an environment changes over time, natural
selection may result in adaptation to these new
conditions
Video: Seahorse Camouflage
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-11
A flower mantid
in Malaysia
A stick mantid
in Africa
Concept 22.3: Darwin’s theory explains a wide
range of observations
• Darwin’s theory of evolution continues to be tested
by how effectively it can account for additional
observations and experimental outcomes
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Natural Selection in Action
• Two examples provide evidence for natural
selection: the effect of differential predation on
guppy populations and the evolution of drugresistant HIV
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Differential Predation in Guppy Populations
• Researchers have observed natural selection
leading to adaptive evolution in guppy populations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-12a
Pools with killifish
but no guppies prior
to transplant
Predator: Killifish; preys
mainly on small guppies
Experimental
transplant of
guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
200
160
120
80
40
185.6
161.5
67.5 76.1
Males
Females
Age of guppies
at maturity (days)
Mass of guppies
at maturity (mg)
LE 22-12b
100
80
60
40
20
85.792.3
58.2
48.5
Males
Females
Control population:
Guppies from pools with
pike-cichlids as predators
Experimental population:
Guppies transplanted to
pools with killifish as
predators
The Evolution of Drug-Resistant HIV
• The use of drugs to combat HIV selects for viruses
resistant to these drugs
• The ability of bacteria and viruses to evolve rapidly
poses a challenge to our society
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-13
Percent of HIV resistant to 3TC
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Homology, Biogeography, and the Fossil Record
• Evolutionary theory provides a cohesive
explanation for many kinds of observations
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Homology
• Homology is similarity resulting from common
ancestry
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Anatomical Homologies
• Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor
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LE 22-14
Human
Cat
Whale
Bat
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
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LE 22-15
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
• Vestigial organs are remnants of structures that
served important functions in the organism’s
ancestors
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Molecular Homologies
• Examples of homologies at the molecular level are
genes shared among organisms inherited from a
common ancestor
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Homologies and the Tree of Life
• The Darwinian concept of an evolutionary tree of
life can explain homologies
• Anatomical resemblances among species are
generally reflected in their molecules, genes, and
gene products
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LE 22-16
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Human
100%
Rhesus monkey
95%
87%
Mouse
69%
Chicken
54%
Frog
Lamprey
14%
Biogeography
• Darwin’s observations of biogeography, the
geographic distribution of species, formed an
important part of his theory of evolution
• Some similar mammals that have adapted to
similar environments have evolved independently
from different ancestors
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LE 22-17
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
The Fossil Record
• The succession of forms observed in the fossil
record is consistent with other inferences about
the major branches of descent in the tree of life
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
What Is Theoretical about the Darwinian View of
Life?
• In science, a theory accounts for many
observations and data and 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings