1. Descent with Modification: A Darwinian View of Life
• The Origin of Species
– Focused biologists’ attention on the great
diversity of organisms
Figure 22.1
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2. • 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 (previously
proposed by other scientists like; Edward Blyth
and Patrick Matthew)
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3. 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 (with attempts to
replace the current worldview at the time with
its own worldview)
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4. 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 kinds were individually designed by
God (this is observable).
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5. • 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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6. 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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7. • 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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8. Theories of Gradualism
• Gradualism
– Is the idea that profound change can take
place through the cumulative effect of slow but
continuous processes
• Geologists Hutton and Lyell
– Perceived that changes in Earth’s surface can
result from slow continuous actions still
operating today (Uniformitarianism)
– Exerted a strong influence on Darwin’s thinking
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9. 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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10. • 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 (this
is an incorrect view of scripture because the
Bible never speaks of species, rather God
created ‘Kinds’ with built in variation).
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11. 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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12. • 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
EUROPE
NORTH
AMERICA
PACIFIC ATLANTIC
OCEAN OCEAN
Galápagos AFRICA HMS Beagle in port
Islands
SOUTH
Darwin in 1840, AMERICA
after his return
AUSTRALIA
Andes
Cape of
Good Hope
Tasmania
Cape Horn New
Tierra del Fuego Zealand
Figure 22.5
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13. • 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, (c) Seed eater. The large ground
sharp beak of the cactus finch (Geospiza magnirostris)
ground finch (Geospiza has a large beak adapted for
scandens) helps it tear cracking seeds that fall from
and eat cactus flowers plants to the ground.
and pulp.
Figure 22.6a–c (b) Insect eater. The green warbler
finch (Certhidea olivacea) uses its
narrow, pointed beak to grasp insects.
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14. • 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 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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15. 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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16. 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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17. • 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 Elephas Loxodonta Loxodonta
Hyracoidea (Manatees
maximus africana cyclotis
Years ago
(Hyraxes) and relatives) (Africa)
(Asia) (Africa)
Mammuthus
Stegodon
Mammut
Deinotherium
Platybelodon
Millions of years ago
Barytherium
Moeritherium
Figure 22.7
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18. 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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19. • Observation #1: For any species, population
sizes would increase exponentially
– If all individuals that are born reproduced
successfully
Figure 22.8
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20. • Observation #2: Nonetheless, 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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21. • Observation #4: Members of a population vary
extensively in their characteristics
– No two individuals are exactly alike
Figure 22.9
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22. • 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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23. • 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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24. 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 Lateral
bud buds
Cabbage Brussels sprouts
Flower Leaves
cluster
Cauliflower Kale
Flower
Stem
and
stems
Broccoli Wild mustard Kohlrabi
Figure 22.10
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25. Summary of Natural Selection
• Natural selection is Natural selection can produce
an increase over time in the
differential success in
adaptation of organisms to their
reproduction environment
– That results from (a) A flower mantid
in Malaysia
the interaction
between
individuals that
vary in heritable
traits and their (b) A stick mantid
in Africa
environment
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Figure 22.11

26. • If an environment changes over time
– Natural selection may result in adaptation to
these new conditions
– Researchers have observed natural selection
EXPERIMENT Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
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
Experimental
transplant of
Predator: Killifish; preys guppies
mainly on small 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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27. 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.
Weight of guppies
at maturity (mg)
at maturity (days)
Control Population: Guppies
Age of guppies
185.6
161.5 85.7 92.3
from pools with pike-cichlids
58.2 as predators
48.5
67.5 76.1
Experimental Population:
Guppies transplanted to
Males Females Males Females 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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28. 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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29. Anatomical Homologies
• Homology
– Is similarity resulting from common ancestry
• Homologous structures between organisms
– Are anatomical resemblances that represent variations on a structural
theme that was present in a common ancestor
Human Cat Whale Bat
Figure 22.14
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30. • Comparative embryology
– Reveals additional anatomical homologies not
visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo Human embryo
Figure 22.15
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31. • Vestigial organs
– Are some of the most intriguing homologous
structures
– Are remnants of structures that served
important functions in the organism’s
ancestors
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32. 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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33. • Anatomical resemblances among species
– Are generally reflected in their molecules, their
genes, and their gene products
Percent of Amino Acids That Are
Species Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Human 100%
Rhesus monkey 95%
Mouse 87%
Chicken 69%
Frog 54%
14%
Figure 22.16 Lamprey
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34. Biogeography
• Darwin’s observations of the geographic
distribution of species, biogeography
– Formed an important part of his theory of
evolution
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35. • Some similar mammals that have adapted to
similar environments
– Have evolved independently from different ancestors
So-Called NORTH
AMERICA
Sugar
glider
Convergent
Evolution AUSTRALIA
Flying
squirrel
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Figure 22.17

36. • The Darwinian view of life
– Predicts that evolutionary transitions should
leave signs in the fossil record (so called
missing-links)
• Paleontologists
– Have discovered some fossils of supposed
transitional forms (most are inconclusive)
Figure 22.18
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37. 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
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38. • Darwin’s theory of evolution by natural
selection
– Integrates diverse areas of biological study
and stimulates many new research questions
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