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Theory of Evolution
Darwin’s theory of evolution
Cause of evolution
Evidence of evolution theory
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Darwin’s theory of evolution
Question: origin of the organisms
(plants, animals, bacteria, etc.)
Evolution – descent with modification
All species are descendants of ancestral species.
Species changes.
Charles Darwin
( )
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Before Darwin, 18th century:
Species were created by God
Aristotle: species do not change
Lamarck, 1809: species evolved
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II. Cause of evolution
Darwin: characteristics of animal and plants
suit to environment - adaptation
Beak
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What causes the fit to environment?
Lamarck: innate drive causes evolution
Darwin: natural selection causes evolution
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6. 1859: On the Origin of Species by Means of Natural Selection
Observations:
member difference,
traits inherited,
capable of over producing,
competing for resources
→ individuals with traits favoring surviving and
reproducing tend to leave more offspring
→ accumulation of favorable traits
Adaptation is caused by selection

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Mantid
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8. Darwinian theory of evolution
• Adaptation is caused by selection
• New species develop if environment changes
or organisms migrate to new environment
• Adaptation to variety of environment → diversity
of life
• All species are from a common ancestor
(unity of life)
Note that
• Individuals do not evolve, although they may change.
• Acquired characteristics do not pass to offspring.
• Natural selection amplifies/diminishes Inheritable traits.

9. III. Evidence of evolution theory 1. From direct observation
Example: virus evolution %
100
Patient
No. 1
Patient No. 2 75 50
Patient No. 3
Percent of HIV resistant to 3TC 25 2 4 6 8 10 12
Weeks

10. III. Evidence of evolution theory 2. From fossil record of
changes over time 2 4
Bristolia
insolens 6 4 8 3
Bristolia
bristolensis 10
Depth (meters) 12 2
Bristolia
harringtoni 14 16 18 1
Bristolia
mohavensis
San Bernardio, California
Deposited 500 mya

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III. Evidence of
evolution theory
2. From fossil record
of changes over time
and origin of new
species
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
Cetaceans
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
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Fossils provide
evidence of evolution
evidence for origin of new species
evidence for chronological order
Fossils show pattern of evolution
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13. III. Evidence of evolution theory
3. From homology of species: closely related
species are similar in structure
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Mammals evolve form a common ancestor - unity of life

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Anatomical and molecular homology show
characteristics from deep ancestor shared by
more species;
Newly evolved characteristics are shared by
small group of species.
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Darwin: Species evolve Cause of evolution: natural selection with evidence direct observation fossil record homology
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