Natural Selection (15.3)
State Standard
SB5D. Relate natural selection to changes in
organisms
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Natural Selection
 Nature acts to
select the
individuals that
are best
adapted for
survival and
reproduction in a
particular
environment
Chapter 15
Evolution
Principles of Natural Selection
Natural selection takes place when…
 Individuals in the population show variations.
 The variations are inheritable.
 Members of the population have more offspring
than can survive on available resources
(overproduction).
 Variations that increase reproductive success
have a greater chance of being passed on.
15.3 Natural Selection-Speciation-Resistance
• Industrialization
& the peppered
moths
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
 Stabilizing selection operates to eliminate
extreme expressions of a trait when the
average expression leads to higher fitness.
Ex: Peppered Moths before the Industrial Revolution
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
 Directional selection makes an organism
more fit by selecting against one extreme.
Ex: Pollution from the Industrial Revolution caused
directional selection in the peppered moths.
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
 Disruptive selection
is a process that
splits a population
into two groups.
Ex: Different rock types in
the same biome will favor
different coat varieties of
these mice
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
 Sexual selection operates in populations
where males and females differ significantly
in appearance.
 Qualities of
sexual
attractiveness
appear to be the
opposite of
qualities that
might enhance
survival.
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Adaptive Radiation – AKA Divergent Evolution/Speciation
 Can occur in a relatively short time when one species
gives rise to
many different
species in
response to the
creation of new
habitat or some
other ecological
opportunity
Chapter 15
Evolution
15.3 Natural Selection-SpeciationResistance
Coevolution
 The relationship between two species might
be so close that the evolution of one species
affects the evolution of the other species.
 Associated with mutualism
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Convergent Evolution
 Unrelated
species evolve
similar traits
because of
similar
environmental
pressures.
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Rate of Speciation
 Evolution proceeds in small, gradual steps
according to a theory called gradualism.
 Punctuated equilibrium explains rapid spurts
of genetic change causing species to diverge
quickly.
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Chapter 15
Evolution
15.3 Formative
Questions
Which evolutionary pattern is
represented by the similarities
between these two organisms
that live on separate continents?
0%
B
A
0%
A
B
C
D
0%
0%
D
1.
2.
3.
4.
C
A. coevolution
B. convergent evolution
C. directional evolution
D. divergent evolution
Chapter 15
Evolution
Chapter Assessment
Questions
The divergent evolution
of these cichlid fish is
an example of what
type of speciation?
0%
B
A
0%
A
B
C
D
0%
0%
D
1.
2.
3.
4.
C
A. coevolution
B. mutation
C. adaptive radiation
D. convergent evolution
Chapter 15
Evolution
Chapter Assessment
Questions
What tempo of evolution
does this model represent?
0%
B
A
0%
A
B
C
D
0%
0%
D
1.
2.
3.
4.
C
A. gradual
B. elevated
C. sequential
D. punctuated
Chapter 15
Evolution
Standardized Test
Practice
Within a population of squirrels, those that live higher in the
mountains where it is cooler have long fur. Squirrels that live in
the foothills where it is warmer have short fur. The original
population is believed to have had intermediate fur length. Which
graph represents this type of natural selection?
A
B
C
0%
0%
0%
C
1.
2.
3.
B
C.
B.
A
A.