2. Natural Selection (15.3)
State Standard
SB5D. Relate natural selection to changes in organisms

3. 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

4. Principles of Natural Selection
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.

5. Industrialization & the peppered moths
15.3 Natural Selection-Speciation-Resistance
Industrialization & the peppered moths

6. 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

7. 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.

8. 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

9. 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.

10. Can occur in a relatively short time when one species gives rise to
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

11. Associated with mutualism
Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
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

12. Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance
Convergent Evolution
Unrelated species evolve similar traits because of similar environmental pressures.

13. 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.

14. Chapter 15
Evolution
15.3 Natural Selection-Speciation-Resistance

15. directional evolution divergent evolution
Chapter 15
Evolution
15.3 Formative Questions
Which evolutionary pattern is represented by the similarities between these two organisms that live on separate continents?
coevolution
convergent evolution
directional evolution
divergent evolution A B C D
FQ 14

16. The divergent evolution of these cichlid fish is
Chapter 15
Evolution
Chapter Assessment Questions
The divergent evolution of these cichlid fish is
an example of what type of speciation?
coevolution
mutation
adaptive radiation
convergent evolution A B C D
CAQ 2

17. What tempo of evolution does this model represent?
Chapter 15
Evolution
Chapter Assessment Questions
What tempo of evolution does this model represent?
gradual
elevated
sequential
punctuated A B C D
CAQ 3

18. Standardized Test Practice
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
STP 5