ch 22 notes
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 22
Descent with Modification: A
Darwinian View of Life
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Overview: Darwin Introduces a Revolutionary Theory
• 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
• The Origin of Species focused biologists’ attention
on the great diversity of organisms
Video: Galápagos Marine Iguana
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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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Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species
• To understand why Darwin’s ideas were
revolutionary, we must examine them in relation to
other Western ideas about Earth and its life
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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)
French Revolution U.S. Civil War
1900 1850 1800 1750
American Revolution
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.
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Resistance to the Idea of Evolution
• The Origin of Species
– Shook the deepest roots of Western culture
– Challenged a worldview that had been
prevalent for centuries
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The Scale of Nature and Classification of Species
• The Greek philosopher Aristotle viewed species
as fixed and unchanging
• The Old Testament holds that species were
individually designed by God and therefore perfect
• 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
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• 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
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Concept 22.2: In The Origin of Species, Darwin proposed that species change through natural selection
• As the 19th century dawned, it was generally
believed that species had remained unchanged
since their creation
• However, a few doubts about the permanence of
species were beginning to arise
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Darwin’s Research
• As a boy and into adulthood, Charles Darwin had
a consuming interest in nature
• After receiving his B.A. degree, he was accepted
on board the HMS Beagle, which was embarking
on a voyage around the world
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The Voyage of the Beagle
• 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
NORTH
AMERICA
SOUTH
AMERICA
AFRICA
EUROPE
AUSTRALIA
PACIFIC
OCEAN
ATLANTIC
OCEAN
England
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Galápagos
Islands
Darwin in 1840, after his return
HMS Beagle in port
Equator
Tasmania
New Zealand
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Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Galápagos Island Overview
Video: Galápagos Sea Lion
Video: Soaring Hawk
Video: Galápagos Tortoise
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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.
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• In 1844, Darwin wrote an essay on the origin of
species and natural selection but did not introduce
his theory publicly, anticipating an uproar
• In June 1858, Darwin received a manuscript from
Alfred Russell Wallace, who had developed a
theory of natural selection similar to Darwin’s
• Darwin quickly finished The Origin of Species and
published it the next year
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The Origin of Species
• Darwin developed two main ideas:
– Evolution explains life’s unity and diversity
– Natural selection is a cause of adaptive
evolution
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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
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives) 0
10,000
2
5.5
24
34
Elephas maximus
(Asia)
Loxodonta africana (Africa)
Loxodonta cyclotis (Africa)
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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
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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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Artificial Selection
• In artificial selection, humans have modified other
species over many generations by selecting and
breeding individuals with desired traits
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LE 22-10
Cabbage
Flower
clusters
Terminal
bud
Lateral
buds
Brussels sprouts
Leaves
Kale
Stem
Kohlrabi Wild mustard Broccoli
Cauliflower
Flowers
and
stems
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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
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LE 22-11 A flower mantid in Malaysia
A stick mantid in Africa
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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 drug-
resistant HIV
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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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LE 22-12a
Predator: Killifish; preys
mainly on small guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Experimental
transplant of
guppies
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
Pools with killifish
but no guppies prior
to transplant
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LE 22-12b
Control population:
Guppies from pools with
pike-cichlids as predators
Experimental population:
Guppies transplanted to
pools with killifish as
predators
92.3
Females
Ag
e o
f g
up
pie
s
at
ma
turi
ty (
da
ys
)
Males
85.7
58.2 48.5
100
80
60
40
20
185.6
Females
Ma
ss
of
gu
pp
ies
at
ma
turi
ty (
mg
)
Males
161.5
76.1 67.5
200
160
120
80
40
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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
Patient No. 3
Patient No. 2
Patient No. 1
100
75
50
25
0
0 2 4 6 8 10 12
Weeks
Perc
en
t o
f H
IV r
esis
tan
t to
3T
C
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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
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• Comparative embryology reveals anatomical
homologies not visible in adult organisms
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LE 22-15
Chick embryo (LM) Human embryo
Pharyngeal pouches
Post-anal tail
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• 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
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
100%
95%
87%
69%
54%
14%
Rhesus monkey
Species
Human
Mouse
Chicken
Frog
Lamprey
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Biogeography
• Darwin’s observations of biogeography, the
geographic distribution of species, formed an
important part of his theory of evolution
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• Some similar mammals that have adapted to
similar environments have evolved independently
from different ancestors
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LE 22-17
Sugar glider
Flying squirrel
NORTH AMERICA
AUSTRALIA
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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
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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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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