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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
• Charles Darwin published The Origin of
Species
• Focused 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 according to Darwin:
– Dscent with modification
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-1
Fig. 22-2
Concept 22.1: The Darwinian revolution
vs traditional views
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.
Scala Naturae and Classification of Species
• Aristotle:
– Viewed species as fixed and
– Arranged on scala naturae
• The Old Testament:
– Species were individually designed by God
– Are therefore perfect
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• Carolus Linnaeus:
• Creator designed each species for a specific
purpose
• Adaptations is evidence for that
• Linnaeus was the founder of taxonomy
• Taxonomy:
• Branch of biology
• Concerned with classifying organisms
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Ideas About Change over Time
• Fossils:
• Remains/traces of organisms from the past
• Usually found in sedimentary rocks, which
appear in layers or strata
• Helped lay the groundwork for Darwin’s ideas
Video: Grand Canyon
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
• Paleontology:
– The study of fossils
– Largely developed by:
• The French scientist Georges Cuvier
• Cuvier advocated catastrophism:
– To explain the existence of fossil record
– Speculating that each boundary between
strata represents a catastrophe
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• James Hutton & Charles Lyell:
– Earth’s surface changes result from actions
that are:
• Slow
• Continuous
• Still operating today
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Lyell’s principle of uniformitarianism states
that:
– The mechanisms of change are constant
over time
• Lyell’s view strongly influenced Darwin’s
thinking
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Lamarck’s Hypothesis of Evolution
• Lamarck hypothesis:
– Species evolve through:
• The use and disuse of body parts
• The inheritance of acquired characteristics
• The mechanisms he proposed are unsupported
by evidence
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-4
Concept 22.2: Prior to Darwin
• The general belief in the 19th century:
– Species remained unchanged since their
creation
• However:
– A few doubts begin to rise about the
permanence of species
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The Voyage of the Beagle
• During his travels, Darwin collected:
– Specimens of plants and animals
• He observed:
– Adaptations of plants and animals
inhabiting diverse environments
• Influenced by Lyell’s Principles of Geology,
Darwin thought:
– The earth was more than 6000 years old
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Darwin’s interest in geographic distribution of
species was stimulated by:
– A stop at the Galápagos Islands (South America)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-5
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
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Darwin’s Focus on Adaptation
• Darwin perceived a close relationship between:
– Adaptation to the environment
&
– The origin of new species
• Biologists, from later studies, have concluded:
– Darwin’s perception is clearly observed in
the Galápagos finches
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Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
Fig. 22-6a
(a) Cactus-eater
Fig. 22-6b
(b) Insect-eater
Fig. 22-6c
(c) Seed-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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Descent with Modification
• Darwin’s phrase “descent with modification”
refers to:
– The perception of the unity of life
– The view that all organisms are related
through descent from an ancestor that lived
in the remote past
• Darwin’s theory meshed well with the hierarchy
of Linnaeus
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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 the modification of other species
by humans through:
– Selection & breeding for desired traits,
• This process is called artificial selection
• Darwin then:
– Described four observations of nature
– Drew two inferences from these observation
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Fig. 22-9
Artificial selection
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Artificial Selection, Natural Selection, and
Adaptation
• Observation #1:
– Trait variations among a population members
• Observation #2:
– Traits inheritance is parents to offspring
• Observation #3:
– Species capablity of producing more
offspring than the environment can support
• Observation #4:
– Diminished survival rate of offspring due to
lack of food or other resources
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-10
Variation in a population
Fig. 22-11
Overproduction of offspring
Spore
cloud
Artificial Selection, Natural Selection, and
Adaptation
• Inference #1:
– In a given environment, individuals with
better inherited traits for survival &
reproduction leave more offspring than
others
• Inference #2:
– This survival & reproductive inequality of
individuals will lead to the accumulation of
favorable traits in the population over
generations
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Darwin was influenced by the notion that:
– The potential for human population to
increase faster than food supplies & other
resources
– Advantageous heritable traits in a
population will accumulate increasing the
frequency of individuals with adaptations
• This process explains the match between
organisms and their environment
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Natural Selection: A Summary
• 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: Seahorse Camouflage
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-12a
(a) A flower mantid
in Malaysia
Fig. 22-12b
(b) A stick mantid
in Africa
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Concept 22.3: Evolution is supported by an
overwhelming amount of scientific evidence
• New discoveries:
– Continue to fill the gaps identified by Darwin
in The Origin of Species
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Direct Observations of Evolutionary Change
• Two examples provide evidence for natural
selection:
– The effect of differential predation on guppy
populations
– The evolution of drug-resistant 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
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Fig. 22-13a
EXPERIMENT
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
Fig. 22-13b
RESULTS
12
Number of
colored spots
12
10
8
6
4
2
0
Source
Transplanted
population population
10
8
6
4
2
0
Source
Transplanted
population 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• 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
• The fossil record provides:
– Evidence of the extinction of species
– The origin of new groups, and
– Changes within groups over time
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
Depth (meters)
Fig. 22-15b
12
2
Bristolia harringtoni
14
16
18 1 Bristolia mohavensis
2
1
Latham Shale dig site, San
Bernardino County, California
Fig. 22-15c
0
4
3
Depth (meters)
2
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
• 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)
Anatomical and Molecular Homologies
• Homologous structures:
– Are anatomical resemblances
– Represent variations on a structural theme
– The structural theme is present in a
common ancestor
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Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
• Comparative embryology:
– Reveals anatomical homologies
– Homologies are not visible in adult
organisms
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
• Vestigial structures:
– Remnants of features
– Served important functions in the ancestors
• Molecular level examples of homologies:
– Are genes shared among organisms
– Such genes are inherited from a common
ancestor
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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
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.