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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
Learning Targets:
1. Describe the contributions to evolutionary theory
made others beside Darwin.
2. Describe Lamarck’s theories, and explain why
they have been rejected
3. Explain “descent with modification”
5. Explain why an individual organism cannot
evolve
6. Describe at least four lines of evidence for
evolution by natural selection
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Evolution time line
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.
Philosopher Aristotle
• 384 BC - 322 BC
• Viewed species as fixed and arranged them on
a scala naturae
– All living things are organized from most
perfect, at the top, to least perfect, at the
bottom
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Carolus Linnaeus
• 1707-1778
• Interpreted organismal adaptations as
evidence that the “Creator had designed each
species for a specific purpose”
• Founder of taxonomy, the branch of biology
concerned with classifying organisms
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Georges Cuvier
• 1769 – 1832
• Developed Paleontology, the study of fossils,
• Advocated catastrophism, speculating that
each boundary between strata represents a
catastrophe
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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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Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
James Hutton and Charles Lyell
• 1726 - 1796
• Two geologists who believed that changes in
Earth’s surface can result from slow continuous
actions still operating today
• Lyell’s principle of uniformitarianism states
that the mechanisms of change are constant
over time
• This view strongly influenced Darwin’s thinking
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Lamarck’s Hypothesis of
Evolution
• 1744 – 1896
• Lamarck hypothesized that
species evolve through use
and disuse of body parts
and the inheritance of
acquired characteristics
• The mechanisms he
proposed are unsupported by
evidence
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Darwin’s Research
• 1809 - 1888
• As a boy and into adulthood, Charles Darwin
had a consuming interest in nature
• Darwin first studied medicine (unsuccessfully),
and then theology at Cambridge University
• After graduating, he took an unpaid 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
• 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
• Darwin was influenced by Lyell’s Principles of
Geology and thought that the earth was more
than 6000 years old
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Darwin’s interest in geographic distribution
of species was kindled by a stop at the
Galápagos Islands near the equator west of
South America
AUSTRALIA
The
Galápagos
Islands
Equator
SOUTH
AMERICA
Video: Galápagos Islands Overview
Video: Blue-footed Boobies Courtship Ritual
Video: Albatross Courtship Ritual
Video: Galápagos Sea Lion
Video: Soaring Hawk
Video: Galápagos Tortoises
Video: Galápagos Marine Iguana
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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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Darwin’s Finches
Cactus-eater
Seed-eater
Insect-eater
The Origin of Species and Natural Selection
• Darwin wrote an essay on the origin of species and
natural selection in 1844.
• 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 his book 1 year later which
included two main ideas:
1. Descent with modification explains life’s unity and
diversity
2. Natural selection is a cause of adaptive evolution
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1. Descent with Modification
• Darwin never used the word evolution in the
first edition of The Origin of Species
• 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
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In the
Darwinian
view, the
history of
life is like a
tree with
branches
representin
g life’s
diversity.
This
messes
well with
the ideas of
Linnaeus
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
2. Artificial Selection
• Darwin noted that humans have modified other
species by selecting and breeding individuals
with desired traits, a process called artificial
selection
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Darwin then described four observations of nature
1. Members of a population often vary greatly in
their traits
2. Traits are inherited from parents to offspring
3. All species are capable of producing more
offspring than the environment can support
4. Owing to lack of food or other resources, many of
these offspring do not survive
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From his observations he drew two inferences
• Inference #1: Individuals whose inherited traits
give them a higher probability of surviving and
reproducing in a given environment tend to
leave more offspring than other individuals
• Inference #2: This unequal ability of individuals
to survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
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Thomas Malthus
• Influenced Darwin by noteing the potential for
human population to increase faster than food
supplies and other resources
• If some heritable traits are advantageous,
these will accumulate in the population, and
this will increase the frequency of individuals
with adaptations
• This process explains the match between
organisms and their environment
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Natural Selection
• 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 over time, natural
selection may result in adaptation to these new
conditions and may give rise to new species
Video: Octopus Camouflage
Video: Seahorse Camouflage
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Natural Selection
A flower mantid in Malaysia
A stick mantid in Africa
Natural Selection
• Note that individuals do not evolve; populations
evolve over time
• Natural selection can only increase or
decrease heritable traits in a population
• Adaptations vary with different environments
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Direct Observations of Evolutionary Change
• Two examples provide evidence for natural
selection
1. The effect of differential predation on guppy
populations
2. The evolution of drug-resistant HIV
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Predation and Coloration in Guppies
• 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
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Predation and Coloration in Guppies
• Transferred brightly colored guppies (with few
predators) to a pool with many predators
• As predicted, over time the population became
less brightly colored
• 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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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
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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The Evolution of Drug-Resistant HIV
• 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
100
Patient
No. 1
Patient No. 2
75
50
Patient No. 3
25
0
0
2
4
6
Weeks
8
10
12
Natural Selection
• Natural selection does not create new traits,
but edits or selects for traits already present in
the population
• The local environment determines which traits
will be selected for or selected against in any
specific population
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The fossil
record
provides
evidence
of the
extinction
of
species,
the origin
of new
groups,
and
changes
within
groups
over time
0
2
The Fossil Record
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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Pakicetus (terrestrial)
Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
Dorudon (fully aquatic)
Pelvis and
hind limb
(Balaena
(recent whale ancestor)
Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Comparative embryology reveals anatomical
homologies not visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo
Vestigial structures
• Remnants of features that served important
functions in the organism’s ancestors
The Appendix
Wisdom teeth
The Tail Bone
The Arrector Pili
• Examples of homologies at the molecular level
are genes shared among organisms inherited
from a common ancestor
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Homologies and “Tree Thinking”
• The Darwinian concept of an evolutionary
tree of life can explain homologies
• 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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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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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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• Earth’s continents were formerly united in a
single large continent called Pangaea, but
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?
• 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
• Ongoing research adds to our understanding of
evolution
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings