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Darwin’s
Theory of
Evolution
Chapter 15
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15-1 The Puzzle of Life’s Diversity
Darwin’s observations
– Patterns of Diversity
Organism well suited to
live in particular habitat
Similar habitats in
different parts of the
world contained different
animals
– Fossils
Some similar to living
organism
Some completely different
than living organisms
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15-2 Ideas That shaped Darwin’s
Thinking
An Ancient, Changing Earth
– James Hutton 1795 – Earth is millions of years old
– Charles Lyell 1831 – geological process
The Earth is approximately 4.5 billion years old
Scientist use radioactive elements to date earth p. 420
Rock Layers help to set up geological time scale p.419
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Early Explanation of Evolutionary
Change
Jean
Baptiste de Lamarck (1744 – 1829)
– Realized organisms somehow adapted to their
environment
– Thought that organisms changed in response
to their environment
Due to an inborn urge to better themselves and
become more fit for their environment
Change occurred by using body part in a new way
A body part would become smaller and might
disappear if not used
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Lamarck continued
Lamarck also believed that acquired
characteristics were inherited by offspring.
We now know Lamarck was incorrect.
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Ideas That Shaped Darwin’s
Theory
Voyage on the HMS
Beagle
Diversity of Life
Geology
Age of the Earth
The Earth changed over
time
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Ideas That Shaped Darwin’s Theory
(continued)
Farmers – Artificial
Selection
– Farmers altered and improved
their live stock and crops
– Farmers could not cause
variations but could utilize
them once observed
Thomas Malthus –
Population Control
– The human birth rate
is higher than death
rate
– Eventually we will run
out of living space and
food
– However, famine,
disease and war would
limit endless
population growth
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15-3 Darwin Presents His Case
Evolution by Natural Selection
Struggle for Existence– Competition for life’s basic needs
Survival
of the fittest
– Darwin called the ability to survive Fitness
– Darwin also stated that fitness was result of
adaptations- inherited characteristics that
increase an organisms chance of survival
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Survival of the fittest
cont.
Individuals whose
characteristics are
well-suited for their
environment will
survive. Those
individuals whose
characteristics are not
well suited for their
environment either
die or produce fewer
offspring – survival of
the fittest.
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Continued
Descent with
modification– Over long periods of time
natural selection produced
varying organisms
Niches, habitats, structure
– Organisms look different
from ancestors
This is known as descent
with modification
Common Descent
– Descent with modification
also implies that all living
organisms are related
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Natural Selection in Action:
Peppered Moths
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Evidence of Evolution
The fossil Record
Fossils are the remains
of living organisms
Found in sedimentary
rock
The fossil record shows
life has changed over
time
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Evidence Continued
Beaver
Geographic Distribution
of Animals
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu and
Capybara
Similar habitats in
different parts of the
world contained different
animals
Different animals had
similar adaptations
Coypu
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Cont.
Similarities in
Embryology
Similarities in the
structure and
development of
embryos gives
evidence of a common
ancestor NOVA
Online/Odyssey of
Life/Morphing Embryos
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Homologous structures are evidence of a
common ancestor
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Vestigial Structures are also
evidence of a common ancestor
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Similarities in
biochemistry of
organisms is
evidence for a
common
ancestor.
DNA
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Summary of Darwin’s
Theory
Individual organisms
differ and some
variation is heritable
Organisms produce
more offspring than
survive
Organisms compete for
resources
Natural selection
Descent w/
Modification/Common
Descent
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Evolution of Populations
Chapter 16
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16-1 Genes and Variation
Variations and Gene Pools
Evolution is the change in the relative frequency
of alleles in a gene pool of a population
Population – collection of organisms of the same
species
Gene Pool – common group of genes in population
Relative Frequency – the number of times an allele
appears in a gene pool compared to the number of
times other alleles for the same gene appear
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Sources of Genetic Variation
Mutation- change in genetic information
Error during replication
Environmental factor – radiation, chemicals
Gene Shuffling – independent assortment,
crossing over, sexual reproduction
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Single – Gene and Polygenic Traits
The number of
phenotypes produced
for a given trait
depend on how many
genes control the
trait.
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16-2 Evolution as Genetic Change
Natural Selection on single- gene traits
can lead to changes in allele frequencies
and thus evolution. Pg. 397 fig 16-5
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Natural Selection of Polygenic
Traits
Natural selection can affect distribution of
phenotypes in three ways
Directional selection
Stabilizing selection
Disruptive selection
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Section 16-2
Figure 16–6 Graph of
Directional Selection
Key
Directional Selection
Food becomes scarce.
Individuals at one end of the graph have
higher fitness than individuals in the
middle or other end of the graph.
Low mortality,
high fitness
High mortality,
low fitness
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Figure 16–7 Graph of
Stabilizing Selection
Section 16-2
Key
Low mortality,
high fitness
High mortality,
low fitness
Percentage of Population
Individuals in
the center of
the curve
have a higher
fitness than
individuals at
the ends of
the curve.
Stabilizing Selection
Selection
against both
extremes keep
curve narrow
and in same
place.
Birth Weight
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Figure 16–8 Graph of
Disruptive Selection
Section 16-2
Disruptive Selection
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two subgroups
specializing in
different seeds.
Number of Birds
in Population
Key
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size
Beak Size
Individuals at the upper and lower ends of
the curve have higher fitness than
individuals near the middle.
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Genetic Drift
Genetic Drift –
Random change in
the frequency of a
alleles
Occurs most efficiently in a
small population
Can happen by chance
Natural disasters,
Chance, Migration
(Founder Effect)
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Evolution vs. Genetic Equilibrium
Hardy-Weinberg Principle
Allele frequency will remain constant unless one or
more factors causes those frequencies to change
Five conditions required to maintain equilibrium
Must be random mating
Large population
No movement into or out of population
No mutation
No Natural selection
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16-3 The Process of Speciation
Species
A group of similar looking
organisms that breed with
one another and produce
fertile offspring in a natural
environment
Speciation – is the
process of new species
evolving from old species
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Isolating Mechanisms
Reproductive Isolation
when members of two
populations cannot
interbreed, gene pools
become separated
React to natural selection
and genetic drift
independently
Behavior Isolation
Geographic isolation
Temporal Isolation
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Behavior Isolation
Organisms may be capable of interbreeding
but have different courtship rituals or other
reproductive strategies that involve behavior.
Great Horned Owl
Barred Owl
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Geographic Isolation
When two populations
are separated by
geographic boundaries
such a s river,
mountains or body of
water
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