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Evolution by Means of
NATURAL SELECTION
Chapter 22
In the 1830’s, what was known
about…
• Geology?
– The Earth is very old
– Slow change can build and result in
profound geologic changes over time
– Darwin brought work by Lyell (1830) with
him on his voyage
In the 1830’s, what was known
about…
• Classification?
– Carolus Linnaeus (1707-1778)
– founder of taxonomy and binomial
nomenclature
– Clustered similar organisms into
categories, he did not assume any
evolutionary relationship based on
this classification scheme
In the 1830’s, what was known
about…
• Paleontology?
– developed by Cuvier (1769-1832)
– He noticed that species appear and
disappear in the fossil record
In the 1830’s, what was known
about…
• Heredity?
– Mendel didn’t publish his work until 1865,
and it wasn’t recognized until the early
1900’s
In the 1830’s, what was known
about…
• Molecular genetics?
– 100 years before Griffith’s pneumococcus
transforming factor experiment
Relating environmental
change to biological evolution:
• Theories of biological evolution begin in
the late eighteenth century
• Jean Baptiste Lamarck was the first to
propose a mechanism that related
environment to biological changes
(1809)
– Use and Disuse
– Inheritance of Acquired Characteristics
Darwin
• Sails on Beagle at 22
• Noted that organisms of islands off of
SA were more like continental species
than those of other islands with similar
climate and habitats
• Contributions of Lyell and others along
with his observations lead him to his
mechanism for evolution
LE 22-6
Cactus eater. The long,
sharp beak of the
cactus ground finch
(Geospiza scandens)
helps it tear and eat
cactus flowers and
pulp.
Seed eater. The large
ground finch (Geospiza
magnirostris) has a large
beak adapted for cracking
seeds that fall from plants
to the ground.
Insect eater. The green warbler finch
(Certhidea olivacea) used its narrow,
pointed beak to grasp insects.
Evolution
• What is evolution?
• Change in the gene pool of a population
over generations (often in response to
environmental changes)
• All of the accumulated changes that have
occurred over time
• Darwin’s definition: Descent with
modification
• Life’s history is a tree with different branches
• Darwin used Linnaeus’ taxonomic
classification scheme to connect
diversity of life
• Domain > Kingdom > phylum > class >
order > family > genus > species
Mechanism : Natural Selection
• Fact 1: Over-reproduction occurs in
nature
• Fact 2: Populations do not increase
exponentially
• Fact 3: There are limited natural
resources (food, shelter)
• Inference 1:
• struggle for survival ensues
• Fact 4: Variation exists in populations
• Fact 5: Much of the variation is heritable
• Fact 4 was physically observed. Darwin’s
weakness (at that time) was the 5th fact
• Inference 2:
• Organisms with the best variations survive the
struggle for life
• Inference 3:
• Unequal survival of organisms with different
variations leads to favorable variations
accumulating over time
Key Concepts
• What is the raw material necessary for
the mechanism of Natural Selection?
• Heritable variations !!!
• What is the smallest unit of evolution?
• Populations !!!
Examples of Natural Selection
• Grants on the island of Daphne Major
– observed shifts in the frequency of beak
sizes over short periods of time
• Antibiotic resistance in bacteria
• Pesticide/herbicide resistance
• How do genetic variations arise in
nature?
What is
wrong
with this
idea?
Evidence for Evolution
• Artificial selection
• Island biogeography: closely related species
tend to be found in the same geographical
region, species found at a distance tend to be
less related even if they occupy similar niches
• Fossil record
• Comparative Anatomy
• Vestigial Structures
• Comparative Embryology/Evo Devo biology
• Molecular Biology
– all organisms have DNA, common genetic code,
ATP, other enzymes
LE 22-15
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Eye sockets in blind salamanders
LE 22-16
Species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
Human
100%
Rhesus monkey
95%
87%
Mouse
69%
Chicken
54%
Frog
Lamprey
14%
200
160
120
80
40
185.6
161.5
67.5 76.1
Males
Females
Age of guppies
at maturity (days)
Mass of guppies
at maturity (mg)
LE 22-12b
100
80
60
40
20
85.792.3
58.2
48.5
Males
Females
Control population:
Guppies from pools with
pike-cichlids as predators
Experimental population:
Guppies transplanted to
pools with killifish as
predators
LE 22-17
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
•Forks of the tree
represent
common
ancestors
•Most closely
related organisms
share common
paths on the
branching tree