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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
A new era of biology began on November 24, 1859,
the day Charles Darwin published On the Origin of
Species by Means of Natural Selection
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• 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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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.
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
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
Galapagos Islands
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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.
Descent with Modification
• The phrase descent with modification
summarized Darwin’s perception of the unity of life
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
0
10,000
2
5.5
24
34
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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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Natural Selection and Adaptation
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• Observation #1: For any species, population
sizes would increase exponentially if all individuals
that are born reproduced successfully
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• 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
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• 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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Natural Selection
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Artificial Selection
• In artificial selection, humans have modified other
Lateral by selecting and
species over manyTerminal
generations
buds
bud
breeding individuals with desired traits
Brussels sprouts
Cabbage
Leaves
Flower
clusters
Kale
Cauliflower
Stem
Flowers
and
stems
Wild
Broccoli
Copyright
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mustard
Kohlrabi
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Differential Predation in Guppy Populations
• Researchers have observed natural selection
leading to adaptive evolution in guppy populations
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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”
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
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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
Anatomical Homologies
• Homologous structures are anatomical resemblances that
represent variations on a structural theme present in a common
ancestor
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Anatomical Homologies
Turtle
Alligator
Ancient, lobefinned fish
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Bird
Mammal
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
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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
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
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14%
Biogeography
• Darwin’s observations of biogeography, the
geographic distribution of species, formed an
important part of his theory of evolution
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• 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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Whales
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Modern Tetrapod Lineage
They are all Middle–
Late Devonian in age,
ranging from 385 million
years (Panderichthys) to
365 million years
(Acanthostega,
Ichthyostega).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings