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

2. 1. What is our current working definition of evolution?
A new era of biology began in 1859 when Charles Darwin published The Origin of Species
Evolution can be defined by Darwin’s phrase descent with modification
It is also considered a change in allele frequencies.
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3. Fig. 22-1
Figure 22.1 How can this beetle survive in the desert, and what is it doing?

4. Examples of evolution.
Squirrel!

5. He developed the two-part, or binomial, system of naming species
Carolus Linnaeus ( ) was a Swedish physician and botanist who sought to classify life’s diversity “for the greater glory of God.”
He developed the two-part, or binomial, system of naming species
iInterpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose (clearly he did not support evolution)
Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms
He was not a proponent of evolution.
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6. A little fossil background.
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
Video: Grand Canyon
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7. 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

8. Briefly describe the beliefs of the following individuals:
Georges Cuvier ( ) observed that the older the stratum, the more dissimilar its fossils were to current life forms.
Also noted that from one layer to the next, some new species appeared while others disappeared.
He staunchly opposed evolution, but advocated catastrophism
Periodic catastrophes destroyed many of the species living in an area, and the area was repopulated by species immigrating in from other areas.

9. In contrast, other scientists suggested that profound change could take place through the cumulative effect of slow but continuous processes.

10. This view strongly influenced Darwin’s thinking
In 1795, Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today
Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time
This view strongly influenced Darwin’s thinking
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11. Lamarck’s Hypothesis of Evolution
Lamarck published his hypothesis in 1809, the year Darwin was born.
He proposed two ideas:
use and disuse
inheritance of acquired characteristics
The mechanisms he proposed are unsupported by evidence
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12. Fig. 22-4
Figure 22.4 Acquired traits cannot be inherited

13. Inheritance of Acquired Traits

14. Darwin’s Research
As a boy and into adulthood, Charles Darwin had a consuming interest in nature
Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University
After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle
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15. The Voyage of the Beagle
During his travels on the Beagle, Darwin collected specimens of South American plants and animals
He observed adaptations of plants and animals that inhabited many diverse environments
Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6000 years old
His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America
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16. His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
Figure 22.5 The voyage of HMS Beagle
For the Discovery Video Charles Darwin, go to Animation and Video Files.
AFRICA
Pinta
Genovesa
Marchena
Equator
SOUTH
AMERICA
Santiago
Daphne
Islands
Pinzón
AUSTRALIA
Fernandina
PACIFIC
OCEAN
Isabela
Andes
Cape of
Good Hope
Santa
Cruz
Santa Fe
San
Cristobal
Tasmania
Florenza
Española
Cape Horn
New
Zealand
Tierra del Fuego

17. Darwin observed geological phenomena that challenged the current idea that the Earth was only 6000 years old
He also observed finches that had very similar traits, but also differed in ways that made them more suitable for their environment.
He hypothesized that the Galapagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on various islands

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

19. Darwin’s Focus on Adaptation
An adaptation is an inherited characteristic of an organism that enhances its survival and reproduction in specific environments.
From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches
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20. In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar
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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21. Darwin developed two main ideas:
The Origin of Species
Darwin developed two main ideas:
Descent with modification
Natural selection
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22. Descent with Modification
Darwin never used the word evolution in the first edition of The Origin of Species
The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past
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23. 34 24 5.5 2 104 Millions of years ago Years ago 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

24. Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection
Darwin then described four observations of nature and from these drew two inferences
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25. Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters
Fig. 22-9
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

26. Fig
Observation #1: Members of a population often vary greatly in their traits
Figure Variation in a population

27. Observation #2: Traits are inherited from parents to offspring
Observation #3: All species are capable of producing more offspring than the environment can support
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28. Observation #4: Owing to lack of food or other resources, many of these offspring do not survive
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29. Therefore: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
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30. Cornucopians vs. Malthusians
Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources
Cornucopians vs. Malthusians
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31. 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
Video: Seahorse Camouflage
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32. (a) A flower mantid in Malaysia (b) A stick mantid in Africa
Fig
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Figure Camouflage as an example of evolutionary adaptation

33. Note that individuals do not evolve; populations evolve over time
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34. 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
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35. Direct Observations of Evolutionary Change
Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug-resistant HIV
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36. 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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37. Fig. 22-13 EXPERIMENT RESULTS 12 12 10 10 8 8 Area of colored
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”
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
RESULTS 12 12
Figure Can predation result in natural selection for color patterns in guppies? 10 10 8 8
Area of colored
spots (mm2)
colored spots
Number of 6 6 4 4 2 2
Source
population
Transplanted
population
Source
population
Transplanted
population

38. EXPERIMENT Experimental transplant of guppies Fig. 22-13a
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”

39. 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

40. As predicted, over time the population became less brightly colored
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
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41. The Evolution of Drug-Resistant HIV
The use of drugs to combat HIV selects for viruses resistant to these drugs
HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome
The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus
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42. Some individual HIV viruses have a variation that allows them to produce DNA without errors
These viruses have a greater reproductive success and increase in number relative to the susceptible viruses
The population of HIV viruses has therefore developed resistance to 3TC
The ability of bacteria and viruses to evolve rapidly poses a challenge to our society
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43. Fig
100
Patient
No. 1
Patient No. 2 75
Percent of HIV resistant to 3TC 50
Patient No. 3
Figure Evolution of drug resistance in HIV 25 2 4 6 8 10 12
Weeks

44. 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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45. The Fossil Record
The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time
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46. 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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47. Fig. 22-16 (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)

48. Homology is similarity resulting from common ancestry
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49. Anatomical and Molecular Homologies
Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor
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50. 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

51. Comparative embryology reveals anatomical homologies not visible in adult organisms
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52. 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

53. Vestigial structures are remnants of features that served important functions in the organism’s ancestors
Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor
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54. Homologies and “Tree Thinking”
The Darwinian concept of an evolutionary tree of life can explain homologies
Evolutionary trees are hypotheses about the relationships among different groups
Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
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55. Homologous characteristic
Fig
Branch point
(common ancestor)
Lungfishes 1
Amphibians
Tetrapods 2
Mammals
Tetrapod limbs
Amniotes 3
Lizards
and snakes
Amnion 4
Crocodiles
Figure Tree thinking: information provided in an evolutionary tree
Homologous
characteristic 5
Ostriches
Birds 6
Feathers
Hawks and
other birds

56. Convergent evolution does not provide information about ancestry
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
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57. NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Fig. 22-20
Figure Convergent evolution
Flying
squirrel

58. Biogeography
Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution
Islands have many endemic species that are often closely related to species on the nearest mainland or island
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59. Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift
An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved
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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
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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.

62. Fig. 22-UN2

63. Fig. 22-UN3

64. You should now be able to:
Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace
Describe Lamarck’s theories, and explain why they have been rejected
Explain what Darwin meant by “descent with modification”
List and explain Darwin’s four observations and two inferences
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65. Explain why an individual organism cannot evolve
Describe at least four lines of evidence for evolution by natural selection
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