1. Unit 10: Speciation
10.5 Patterns of Evolution

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

3. Patterns of Evolution
Convergent Evolution: evolution towards similar traits in unrelated species due to a similar environment.
Example: Tuna (fish) and dolphins (mammals). Because they lived in the ocean (a similar environment) both faced similar evolutionary pressures and developed fins to navigate the water.

4. Patterns of Evolution
Divergent Evolution: evolution towards different traits in closely related species
Caused by different environments
Red Fox
Kit Fox
Ancestor

5. Patterns of Evolution
Coevolution: two or more species evolve in response to changes in each other.
Evolutionary paths become connected
Both species receive benefits from the other as a result of adaptations.
Example: Plants and Insects
Plants: provide insects with nectar
Insect: transfers pollen from one plant to another

6. Coevolution (cont.)
Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.
Example: Crab vs. Snail

7. Patterns of Evolution: Extinction
Background Extinctions
Mass Extinctions
Cause: local changes in the environment.
Forest fires, habitat destruction
Affects a few species in a small area
Less severe
Occurs at roughly the same rate as speciation
Cause: catastrophic events
Ice ages, meteorites
Destroys many species at a global level
Very severe
Rare but much more intense
At least 5 mass extinctions in Earth’s history

8. How Fast Does Evolution Occur? No Exact Time Frame!
Gradualism
Punctuated Equilibrium
Slow and steady change of one species into another
Small changes continually build over time
Long periods of little change are interrupted by shorter periods of rapid change.
Due to sudden environment change
Example: Mammal diversity exploded after the dinosaur extinction.

9. Gradualism of the Horse

10. How Fast Does Evolution Occur?
Adaptive Radiation: a process of evolution where one species can split into a number of different species.
Ancestral species diversifies into many descendent species
Each adapted to a different environment
Example: mammals