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Overview:
Chapter 22
• 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
(Species: a group whose members possess
similar anatomical characteristics and have the
ability to interbreed, and produce viable
offspring)
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The Origin of Species
• Focused biologists’ attention on the great
diversity of organisms
Figure 22.1
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• Darwin made two major points in his book
– He presented evidence that the many species
of organisms presently inhabiting the Earth are
descendants of ancestral species
– He proposed a mechanism for the evolutionary
process, natural selection
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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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The historical context of Darwin’s life and ideas
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)
American Revolution
1750
Wallace (evolution, natural selection)
French Revolution
U.S. Civil War
1800
1850
1900
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.
1831–1836 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.
Figure 22.2
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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 of the Bible
– Holds that species were individually designed
by God and therefore perfect
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Carolus Linnaeus
• Interpreted organismal adaptations as evidence
that the Creator had designed each species for a
specific purpose
• Was a founder of taxonomy, classifying life’s
diversity “for the greater glory of God”
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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
Figure 22.3
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• Paleontology, the study of fossils
– Was largely developed by French scientist
Georges Cuvier
• Cuvier opposed the idea of gradual
evolutionary change
– And instead 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
• Exerted a strong influence on 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
– But the mechanisms he proposed are
unsupported by evidence
Figure 22.4
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Concept 22.2: Darwin and Natural Selection
• As a boy and into adulthood, Charles Darwin
– Had a consuming interest in nature
• Soon after Darwin received his B.A. degree
– He was accepted on board the HMS Beagle,
which was about to embark on a voyage
around the world
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The Voyage of the Beagle
• During his travels on the Beagle
– Darwin observed and collected many
specimens of South American plants and
animals
• Darwin observed various adaptations of plants
and animals
– That inhabited many diverse environments
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• Darwin’s interest in the geographic distribution
of species
– Was kindled by the Beagle’s stop at the Galápagos
Islands near the equator west of South America
England
NORTH
AMERICA
EUROPE
ATLANTIC
OCEAN
PACIFIC
OCEAN
Galápagos
Islands
AUSTRALIA
Cape of
Good Hope
Cape Horn
Figure 22.5
HMS Beagle in port
SOUTH
AMERICA
Andes
Darwin in 1840,
after his return
AFRICA
Tierra del Fuego
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Tasmania
New
Zealand
Darwin’s Focus on Adaptation
• As Darwin reassessed all that he had observed
during the voyage of the Beagle
– He began to perceive adaptation to the
environment and the origin of new species as
closely related processes
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• From studies made years after Darwin’s
voyage
– Biologists have concluded that this is indeed
what happened to the Galápagos finches
(a) Cactus eater. The long,
sharp beak of the cactus
ground finch (Geospiza
scandens) helps it tear
and eat cactus flowers
and pulp.
Figure 22.6a–c
(c) Seed eater. The large ground
finch (Geospiza magnirostris)
has a large beak adapted for
cracking seeds that fall from
plants to the ground.
(b) Insect eater. The green warbler
finch (Certhidea olivacea) uses its
narrow, pointed beak to grasp insects.
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• In 1844, Darwin wrote a long essay on the origin
of species and natural selection
– But he was reluctant to introduce his theory
publicly, anticipating the uproar it would cause
• In June 1858 Darwin received a manuscript from
Alfred Russell Wallace
– Who had independently 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
– States 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 multiple branchings from a common trunk to
the tips of the youngest twigs, that represent the
diversity of living organisms
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
Elephas Loxodonta Loxodonta
maximus africana
cyclotis
(Africa)
(Asia)
(Africa)
Figure 22.7
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Artificial Selection
• In the process of artificial selection
– Humans have modified other species over
many generations by selecting and breeding
individuals that possess desired traits
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower
cluster
Leaves
Cauliflower
Kale
Flower
and
stems
Broccoli
Stem
Wild mustard
Figure 22.10
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Kohlrabi
Summary of Natural Selection
• Natural selection is differential success in
reproduction
– That results from the interaction between
individuals that vary in heritable traits and their
environment
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• Natural selection can increase the adaptation of
organisms to their environment, over time
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Figure 22.11
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• If an environment changes over time
– Natural selection may result in adaptation to
these new conditions
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Concept 22.3:
• Natural Selection in Action
– Two examples provide evidence for natural
selection
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Differential Predation in Guppy Populations
• Researchers have observed natural selection
leading to adaptive evolution in guppy populations
Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
EXPERIMENT
and measured the average age and size of guppies at maturity over an 11-year period (30 to
60 generations).
Pools with killifish,
but not 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”
Figure 22.12
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RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
185.6
161.5
85.7 92.3
48.5
58.2
Control Population: Guppies
from pools with pike-cichlids
as predators
67.5 76.1
Males
Females
Males
Females
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.
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The Evolution of Drug-Resistant HIV
• In humans, the use of drugs selects for pathogens
that through chance mutations are resistant to the
drugs’ effects
• Natural selection is a cause of adaptive evolution
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• Researchers have developed numerous drugs
to combat HIV
– But using these medications selects for
viruses resistant to the drugs
Patient
No. 1
Patient No. 2
Patient No. 3
Weeks
Figure 22.13
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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 between organisms
– Are anatomical resemblances that represent
variations on a structural theme that was
present in a common ancestor
Human
Cat
Figure 22.14
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Whale
Bat
• Comparative embryology
– Reveals additional anatomical homologies not
visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Figure 22.15
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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
• Biologists also observe homologies among
organisms at the molecular level
– Such as genes that are shared among
organisms inherited from a common ancestor
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• Anatomical resemblances among species
– Are generally reflected in their molecules, their
genes, and their gene products
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
100%
Human
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Frog
Figure 22.16
Lamprey
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54%
14%
Biogeography
• Darwin’s observations of the geographic
distribution of species, biogeography
– 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
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
Figure 22.17
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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
Figure 22.18
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