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The Evidence for Evolution
Chapter 15-18
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
The Fossil Record
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Case for evolution based on two pillars:
 Evidence natural selection can produce
evolutionary change.
 Evidence from fossil record that evolution
has occurred.
Three events of fossilization:
 Organism buried in sediment.
 Calcium in material must mineralize.
 Surrounding sediment hardens.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Evidence 1-The Fossil Record
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Dating Fossils
Radioactive isotopes
have decayed more in
older rocks.
Steady decay rate
allows measurement.
History
The Fossil Record
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Arraying fossils
according to age
provides evidence of
successive
evolutionary change
(gradual change over
time)
One of strongest lines
of evidence for
evolution.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
The Evolution of Horses
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Modern members of
Equidae (horses, zebras,
donkeys) are descendents
of lineage originating in the
Eocene Period 55 mya.
 Earliest known members
were species in genus
Hyracotherium.
- Small size
- Multiple toes
- Small, simple teeth.
 Evolutionary change
has not occurred at a
constant rate.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Evidence 2-Natural Selection Changes
Populations
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Evidence of branching evolution
Darwin collected a closely related
group of 13 finch species in the
Galapagos Islands.
 All similar except for beak
characteristics.
- Beak correspondence
suggested to Darwin that
they were shaped by
evolution.
 Nature of available food
supply.
Example: Beaks of
Darwin’s Finches
Natural selection continued
Peppered Moths and Industrialized Melanism
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Until the mid-nineteenth century,
Peppered Moths, Biston
betularia, had predominately
light-colored wings.
 Industrial smog helped turn
lichens on tree trunks dark.
 Subsequently, dark
individuals became
predominant.
- Predators see them!
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Second half of the twentieth
century saw widespread
implementation of pollution
controls, thus trends reversed
and light colored moths again
dominated.
But, caution must be taken, as
the selective agent could be
some factor other than wing
coloration.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Artificial Selection
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Agriculture
 Kernel characteristics of corn.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Artificial Selection
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Domestication
 Breeds and characteristics of dogs.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Evidence 3-The Anatomical Record
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Homology
 Evidence of branching evolution
 Structures with different appearances and
functions that all derived from a common
ancestor.
The Anatomical Record
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Development
 Evidence of branching evolution
 Different organisms exhibit similar
embryological forms.
The Anatomical Record
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Vestigal Structures

Organs with no apparent
modern function, but
resemble ancestral
structures.

Evidence of branching
evolution and branching
evolution
Evidence 4-The Molecular Record
(DNA, RNA, proteins)
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Distantly related
organisms are
expected to
accumulate a greater
number of evolutionary
differences than closely
related species.
Evidence of branching
evolution and common
descent
Types of Evolution
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Convergent Evolution - Selection that favors
changes making two or more groups more
similar.
 Similar solutions to similar problems.
- Marsupial-Placental Convergence
Divergent Evolution - Selection that favors
changes making two or more groups less
similar.
 Exposure to different selective pressures.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
When two groups of the same species are
separated, changes may occur in each population
that eventually causes them to be so different that
speciation occurs
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Geographic Isolation
 separated by land formations such as rivers, mountains,
valleys, etc
Reproductive Isolation
 separated due to inability to mate with each other
- Structural, mating time is different, etc
Temporal Isolation
 Separated by time factors such as circadian rhythms
Behavioral Isolation
 Separated by behavioral differences such as courtship
dances or sounds
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Darwin’s Critics
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Evolution is not solidly demonstrated.
There are no fossil intermediates.
Intelligent Design.
Evolution violates Second Law of
Thermodynamics.
Proteins are too improbable.
Natural Selection does not imply evolution.
The irreducible complexity argument.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Review
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The Fossil Record
The Evolution of Horses
Beak’s of Darwin’s Finches
Peppered Moths and Industrial Melanism
Artificial Selection
The Anatomical Record
The Molecular Record
Convergent and Divergent Evolution
Darwin’s Critics
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies