1. KEY CONCEPTS Evolution occurs in patterns:
Evolution through natural selection is not random
Species can shape each other over time
Species can become extinct
Speciation often occurs in patterns

2. Evolution through natural selection is not random.
Natural selection can have direction.
The effects of natural selection add up over time.

3. Convergent evolution: The process whereby unrelated species become more and more similar in appearance as they adapt to the same kind of lifestyle.

4. Question Break
Two unrelated species both live near the north pole. How might the appearance of the unrelated species be similar? Explain how this is an example of convergent evolution.

5. Divergent evolution: The process whereby organisms within a population diverge so much that they no longer look similar.
How do convergent and divergent evolution illustrate the directional nature of natural selection?
ancestor
red fox
kit fox

6. Question Break
Analogous structures are often examples of convergent evolution. What types of structures would likely be examples of divergent evolution?

7. Species can shape each other over time.
Coevolution: Two or more species can evolve together in response to changes in each other.
evolutionary paths become connected

8. Coevolution can occur in beneficial relationships: Both species receive benefits from the other as a result of adaptations that each species has evolved over many generations.

9. Coevolution can occur in Evolutionary Arms Races: Both species respond to competitive pressure from the other through adaptations over many generations.

10. How does coevolution shape two species over time?
Question Break
How does coevolution shape two species over time?

11. Punctuated Equilibrium
Gradualism
Species evolve slowly over long periods of time.
Each generation is a tiny bit different than the previous one
Punctuated Equilibrium
Proposes that species show no evolutionary change for many years, followed by periods of rapid change.

12. Species can become extinct.
Extinction: is the elimination of a species from Earth.
Background extinctions: occur randomly but at a very low rate.
Usually affects only a few species
caused by local changes in the environment.

13. Mass extinctions are rare but very intense.
destroy many species at global level
thought to be caused by catastrophic events (Ice Age)
at least five mass extinctions in last 600 million years

14. Speciation often occurs in patterns.
A pattern of punctuated equilibrium exists in the fossil record.
episodes of speciation occur suddenly in geologic time
followed by long periods of little evolutionary change
revised Darwin’s idea that species arose through gradual transformations

15. Many species evolve from one species during adaptive radiation:
Diversification of one ancestral species into many descendent species.
Descendent species usually adapted to wide range of environments

16. Question Break
What is the relationship between speciation and punctuated equilibrium?