1. Descent with Modification: A Darwinian View of Life
Chapter 22
Descent with Modification:
A Darwinian View of Life

2. Assignments:
- Study Chapter 22 - Do the MasteringBiology exercises for Chapt 22

3. Overview: Endless Forms Most Beautiful
A new era of biology began in 1859 when Charles Darwin published The Origin of Species
Darwin noted that current species are descendants of ancestral species
Evolution can be defined by Darwin’s phrase descent with modification
Evolution can be viewed as both a pattern and a process
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4. 1809
Lamarck publishes his
hypothesis of evolution.
1798
Malthus publishes
“Essay on the Principle
of Population.”
1812
Cuvier publishes his extensive studies of vertebrate fossils and
Proposed catastrophism.
1858
1795
While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection.
Hutton proposes
his principle of
gradualism.
1830
Lyell publishes
Principles of Geology.
1790
1870
1809
183136
1859
Charles Darwin
is born.
Darwin travels around the world on HMS Beagle.
On the Origin of Species is published.
Figure 22.2 The intellectual context of Darwin’s ideas.
1844
Darwin writes his essay on descent with modification.
Linnaeus developed
binomial naming for
species .
The Galápagos Islands

5. Paleontology Sedimentary rock layers (strata) Younger stratum
Figure 22.3 Formation of sedimentary strata with fossils.
Younger stratum
with more recent
fossils
Older stratum
with older fossils

6. 1809
Lamarck publishes his
hypothesis of evolution.
1798
Malthus publishes
“Essay on the Principle
of Population.”
1812
Cuvier publishes his extensive studies of vertebrate fossils and
Proposed catastrophism.
1858
1795
While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection.
Hutton proposes
his principle of
gradualism.
1830
Lyell publishes
Principles of Geology.
1790
1870
1809
183136
1859
Charles Darwin
is born.
Darwin travels around the world on HMS Beagle.
On the Origin of Species is published.
Figure 22.2 The intellectual context of Darwin’s ideas.
1844
Darwin writes his essay on descent with modification.
Linnaeus developed
binomial naming for
species .
The Galápagos Islands

7. © 2011 Pearson Education, Inc.

8. 1809
Lamarck publishes his
hypothesis of evolution.
1798
Malthus publishes
“Essay on the Principle
of Population.”
1812
Cuvier publishes his extensive studies of vertebrate fossils and
Proposed catastrophism.
1858
1795
While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection.
Hutton proposes
his principle of
gradualism.
1830
Lyell publishes
Principles of Geology.
1790
1870
1809
183136
1859
Charles Darwin
is born.
Darwin travels around the world on HMS Beagle.
On the Origin of Species is published.
Figure 22.2 The intellectual context of Darwin’s ideas.
1844
Darwin writes his essay on descent with modification.
Linnaeus developed
binomial naming for
species .
The Galápagos Islands

9. Figure 22.5 The voyage of HMS Beagle.
Darwin in 1840, after his return from the voyage
HMS Beagle in port
Great
Britain
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
PACIFIC
OCEAN
Pinta
Genovesa
Equator
Marchena
Malay Archipelago
Equator
SOUTH
AMERICA
PACIFIC
OCEAN
Santiago
Daphne
Islands
Chile
Brazil
AUSTRALIA
Fernandina
Pinzón
PACIFIC
OCEAN
Andes Mtns.
Isabela
Figure 22.5 The voyage of HMS Beagle.
Santa
Cruz
Cape of
Good Hope
Santa Fe
San
Cristobal
Argentina
Tasmania 20 40
Florenza
Española
Cape Horn
Kilometers
New
Zealand

10. (a) Cactus-eater (b) Insect-eater (c) Seed-eater Figure 22.6
Figure 22.6 Three examples of beak variation in Galápagos finches.
(c) Seed-eater

11. The Origin of Species Darwin explained three broad observations:
The unity of life
The diversity of life
The match between organisms and their environment
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12. Figure 22.8 Descent with modification. Elephas maximus (Asia)
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
†Moeritherium
†Barytherium
†Deinotherium
†Mammut
†Platybelodon
†Stegodon
†Mammuthus
Figure 22.8 Descent with modification.
Elephas maximus
(Asia)
Loxodonta africana
(Africa)
Loxodonta cyclotis
(Africa) 60 34 24
5.5 2
104
Millions of years ago
Years ago

13. Artificial Selection Cabbage Selection for apical (tip) bud Brussels
sprouts
Selection for axillary (side) buds
Broccoli
Selection for flowers and stems
Figure 22.9 Artificial selection.
Selection for stems
Selection for leaves
Kale
Wild mustard
Kohlrabi

14. Observation #1: Members of a population often vary in their inherited traits
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15. Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce
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16. Individuals in a population vary in their heritable characteristics.
Figure 22.UN02
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.
Figure 22.UN02 Summary figure, Concept 22.2
and
Over time, favorable traits accumulate in the population.

17. Natural Selection: A Summary
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

18. Evolution is supported by an overwhelming amount of scientific evidence
Direct Observations of Evolutionary Change
Homology
Fossil records
biogeography
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19. Direct Observations of Evolutionary Change
FIELD STUDY
Figure Inquiry: Can a change in a population’s food source result in evolution by natural selection?
Soapberry bug with beak inserted in balloon vine fruit

20. On native species, southern Florida
Figure 22.13b
RESULTS
Beak 10
On native species, southern Florida 8 6 4 2
Ballon vine fruit
Number of individuals
Museum-specimen average 10 8
On introduced species, central Florida
Figure Inquiry: Can a change in a population’s food source result in evolution by natural selection? 6 4 2 6 7 8 9 10 11
Goldenrain tree fruit
Beak length (mm)

21. Chromosome map of S. aureus clone USA300
Figure 22.14 1
2,750,000
250,000 base pairs
2,500,000
Chromosome map of S. aureus clone USA300
500,000
2,250,000
Key to adaptations
Methicillin resistance
Ability to colonize hosts
750,000
Increased disease severity
2,000,000
Increased gene exchange (within species) and toxin production
Figure Impact: The Rise of MRSA
1,000,000
1,750,000
1,250,000
1,500,000

22. CONCLUSION:
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
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23. Homology Homology is similarity resulting from common ancestry
Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor
Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor
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24. Mammalian forelimbs: homologous structures
Humerus
Radius
Ulna
Carpals
Metacarpals
Figure Mammalian forelimbs: homologous structures.
Phalanges
Human
Cat
Whale
Bat

25. Comparative embryology reveals anatomical homologies not visible in adult organisms
Pharyngeal pouches
Post-anal tail
Figure Anatomical similarities in vertebrate embryos.
Chick embryo (LM)
Human embryo

26. Vestigial structures are remnants of features that served important functions in the organism’s ancestors

27. Homologies and “Tree Thinking”
Evolutionary trees are hypotheses about the relationships among different groups
Homologies form nested patterns in evolutionary trees
Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
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28. Homologous characteristic
Figure 22.17
Branch point
Lungfishes
Amphibians 1
Tetrapods 2
Mammals
Digit- bearing
limbs
Amniotes 3
Lizards and snakes
Amnion 4
Crocodiles
Homologous characteristic
Figure Tree thinking: information provided in an evolutionary tree. 5
Ostriches 6
Birds
Feathers
Hawks and other birds

29. A Different Cause of Resemblance: 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

30. The Fossil Record
The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time
Fossils can document important transitions
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31. Transition from land to sea in the ancestors of cetaceans
Other even-toed ungulates
Hippopotamuses
†Pakicetus
†Rodhocetus
Common ancestor of cetaceans
Figure The transition to life in the sea.
†Dorudon
Living cetaceans 70 60 50 40 30 20 10
Key
Pelvis
Tibia
Millions of years ago
Femur
Foot

32. Biogeography
Present
Cenozoic
North America
Eurasia
65.5
Africa
Biogeography, the geographic distribution of species, provides evidence of evolution
Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift
South
America
India
Madagascar
Australia
Antarctica
Laurasia
135
Millions of years ago
Gondwana
Mesozoic
Figure The history of continental drift during the Phanerozoic eon.
251
Pangaea
Paleozoic

33. 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
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