1. Chapter 22 Part 3 Descent with Modification
A Darwinian View of Life

2. 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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3. 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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4. Direct Observations Color patterns in guppies Drug resistant HIV
Beak size in Birds
Others

5. 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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6. Color Pattern in Guppies
Field Experiment (see text for full details)
Changed the selection pressure on male guppies
Result – color pattern change in 15 generations (22 months).

8. 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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9. HIV Drug Resistance Drug resistance strains selected for by treatments
Result – resistant strains became 100% dominant in 4-5 weeks.

10. 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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11. 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12. 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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14. Beak Size
Field Study – measured the beak size of all birds in a population over several years.
Result – drought and food competition changed beak size.

16. Fossils Relics or impressions of organisms from the past. Problem:
Show changes over time from simple to complex.
Many fossils don't have descendants.

17. Evolution Viewpoint Life has changed over time.
Many species failed to survive and became extinct.

18. Comments 1. Fossilization is a rare event.
2. Only hard parts fossilize well.
3. Problem in finding fossils.
4. Interpretation.
5. Missing Links.

19. 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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20. 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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21. The Fossil Record
The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. Fig. 22-15 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 102 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

23. 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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24. 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)

25. Homology Homology is similarity resulting from common ancestry
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26. Homology Mammal forelimbs
Homologous Structures - Common "building plan” with divergent functions.

27. 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

28. 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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29. Vestigial Organs Whale Legs
Rudimentary structures of marginal, if any, use.

30. Human Example

31. Human Example

32. Evolution Viewpoint
Remodeling of ancestral structures as their functions or adaptations changed.

33. Homology in Embryos
Closely related organisms go through similar stages in their embryonic development.
Ex: Gill pouches in vertebrates

34. Comparative embryology reveals anatomical homologies not visible in adult organisms
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36. 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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37. 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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38. 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
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39. Convergent Evolution Unrelated organisms show similar adaptations.
Cause – lived in a similar environment with similar selection pressures.

42. 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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43. 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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44. Evolution Viewpoint
Biogeographical patterns reflect descent from the ancestors that colonized that area.

46. Molecular Biology Study of Evolution at the DNA or protein levels.
Related species have similar DNA sequences.

48. Evolution Viewpoint
Related species share a common ancestrial DNA. The closer the relationship, the more similar the DNA sequences should be.

49. 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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50. 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.

51. Fig. 22-UN2

52. Fig. 22-UN3

53. 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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54. Explain why an individual organism cannot evolve
Describe at least four lines of evidence for evolution by natural selection
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55. Summary Darwin's ideas now a "Theory”.
Predictions of a Theory are tested by experiments and observations.
Be familiar with the pre-Darwin views of evolution.

56. Summary Know Darwin’s “observations” and “inferences”.
Be able to discuss the various evidences of Darwinian evolution.