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

2. 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

3. Darwin noted that:
Current species are descendants of ancestral species
Evolution according to Darwin:
Dscent with modification

4. Fig. 22-1
Figure 22.1 How can this beetle survive in the desert, and what is it doing?

5. Concept 22.1: The Darwinian revolution vs traditional views
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
1750
1800
1850
1900
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.
Figure 22.2 The historical context of Darwin’s life and ideas
1831–1836
Darwin travels around the world on HMS Beagle.
1837
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.

6. 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

7. 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

8. 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

9. Layers of deposited sediment Younger stratum with more recent fossils
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Figure 22.3 Formation of sedimentary strata with fossils
Older stratum
with older fossils

10. 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

11. James Hutton & Charles Lyell:
Earth’s surface changes result from actions that are:
Slow
Continuous
Still operating today

12. Lyell’s principle of uniformitarianism states that:
The mechanisms of change are constant over time
Lyell’s view strongly influenced Darwin’s thinking

13. 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

14. Fig. 22-4
Figure 22.4 Acquired traits cannot be inherited

15. 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

16. 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

17. Darwin’s interest in geographic distribution of species was stimulated by:
A stop at the Galápagos Islands (South America)

18. Figure 22.5 The voyage of HMS Beagle
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Marchena
Equator
SOUTH
AMERICA
Santiago
Daphne
Islands
Pinzón
AUSTRALIA
Fernandina
PACIFIC
OCEAN
Isabela
Figure 22.5 The voyage of HMS Beagle
For the Discovery Video Charles Darwin, go to Animation and Video Files.
Santa
Cruz
Andes
Cape of
Good Hope
Santa Fe
San
Cristobal
Tasmania
Florenza
Española
Cape Horn
New
Zealand
Tierra del Fuego

19. Fig. 22-5a
Figure 22.5 The voyage of HMS Beagle
Darwin in 1840

20. The Galápagos Islands Pinta Genovesa Marchena Santiago Daphne Islands
Fig. 22-5b
The
Galápagos
Islands
Pinta
Genovesa
Marchena
Santiago
Daphne
Islands
Pinzón
Fernandina
Isabela
Santa
Cruz
Santa Fe
Figure 22.5 The voyage of HMS Beagle
San
Cristobal
Florenza
Española

21. 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

22. 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

23. (a) Cactus-eater (c) Seed-eater (b) Insect-eater Fig. 22-6
Figure 22.6 Beak variation in Galápagos finches
(b) Insect-eater

24. (a) Cactus-eater Fig. 22-6a
Figure 22.6 Beak variation in Galápagos finches
(a) Cactus-eater

25. (b) Insect-eater Fig. 22-6b
Figure 22.6 Beak variation in Galápagos finches
(b) Insect-eater

26. Fig. 22-6c
Figure 22.6 Beak variation in Galápagos finches
(c) Seed-eater

27. Darwin developed two main ideas:
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

28. 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

29. Figure 22.8 Descent with modification
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) 34 24
5.5 2
104
Millions of years ago
Years ago

30. 34 24 5.5 2 104 Millions of years ago Years ago Platybelodon Stegodon
Fig. 22-8a
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Figure 22.8 Descent with modification
Loxodonta cyclotis
(Africa) 34 24
5.5 2
104
Millions of years ago
Years ago

31. 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

32. Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters
Fig. 22-9
Artificial selection
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Figure 22.9 Artificial selection
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi

33. 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

34. Variation in a population
Fig
Figure Variation in a population
Variation in a population

35. Spore cloud Overproduction of offspring Fig. 22-11
Figure Overproduction of offspring

36. 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

37. 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

38. 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

39. (a) A flower mantid in Malaysia Fig. 22-12a
Figure Camouflage as an example of evolutionary adaptation
(a) A flower mantid
in Malaysia

40. (b) A stick mantid in Africa Fig. 22-12b
Figure Camouflage as an example of evolutionary adaptation
(b) A stick mantid
in Africa

41. 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

42. 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

43. 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

44. 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

45. EXPERIMENT Experimental transplant of guppies
Fig a
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”
Figure Can predation result in natural selection for color patterns in guppies?
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”

46. Area of colored spots (mm2) colored spots Number of
Fig b
RESULTS 12 12 10 10 8 8
Area of colored
spots (mm2)
colored spots
Number of 6 6 4 4 2 2
Figure Can predation result in natural selection for color patterns in guppies?
Source
population
Transplanted
population
Source
population
Transplanted
population

47. 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

48. 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

49. The Fossil Record
The fossil record provides:
Evidence of the extinction of species
The origin of new groups, and
Changes within groups over time

50. Bristolia bristolensis
Fig 2 4 4 6 4
Bristolia insolens 8 3
Bristolia bristolensis 10 12 3
Depth (meters) 2
Bristolia harringtoni 14 16 18 1
Bristolia mohavensis 3
Figure Fossil evidence of evolution in a group of trilobites 2 1
Latham Shale dig site, San
Bernardino County, California

51. Bristolia harringtoni 14
Fig b 12
Depth (meters)
Bristolia harringtoni 2 14 16 18
Bristolia mohavensis 1 2
Figure Fossil evidence of evolution in a group of trilobites
Latham Shale dig site, San
Bernardino County, California 1

52. 2 4 6 Depth (meters) 4 Bristolia insolens 4 8 Bristolia bristolensis 3
Fig c 2 4 4 6
Bristolia insolens 4
Depth (meters) 8
Bristolia bristolensis 3
Figure Fossil evidence of evolution in a group of trilobites 10 3

53. 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

54. (a) Pakicetus (terrestrial)
Fig
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Figure The transition to life in the sea
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)

55. Anatomical and Molecular Homologies
Homologous structures:
Are anatomical resemblances
Represent variations on a structural theme
The structural theme is present in a common ancestor

56. Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat
Fig
Humerus
Radius
Ulna
Carpals
Metacarpals
Figure Mammalian forelimbs: homologous structures
Phalanges
Human
Cat
Whale
Bat

57. Comparative embryology:
Reveals anatomical homologies
Homologies are not visible in adult organisms

58. Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo
Fig
Pharyngeal
pouches
Post-anal
tail
Figure Anatomical similarities in vertebrate embryos
Chick embryo (LM)
Human embryo

59. 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

60. 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

61. Individuals in a population vary in their heritable characteristics.
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.