1. Patterns in Evolution

2. Key concept : 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. Convergent Evolution
Defined: evolution toward similar traits in unrelated species due to a similar environment.
Ex: Tuna (fish) and dolphins (mammals). They are an unrelated species living in a similar environment, the ocean.
Faced similar evolutionary pressures.

4. Kaibab Squirrel (Grand Canyon)
Divergent Evolution
Kaibab Squirrel (Grand Canyon)
ancestor
red fox
kit fox
Defined: Describes evolution toward different traits in closely related species.
Cause: Different environments

5. Coevolution
Defined: 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.
Ex: Plants and Insects
Plants: provide insects with nectar
Insect: transfers pollen from one plant to another

6. Coevolution Continued…
Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.
Example: Crab vs. Snail & Bacteria vs. Humans

7. Most bacteria killed
Strong Survive
Bacterial Resistance
Strong Reproduce

8. Extinction Defined: The elimination of a species from Earth.
Mass Extinctions:
Cause: Catastrophic events
Ice Age, Meteorites
Destroys many species at global level
Very severe
Rare but much more intense
At least 5 mass extinctions in last 600 million years
Background Extinctions:
Cause: Local changes in environment
Forest fires, habitat destruction.
Affects a few species in a small area
Less severe.
Occur at roughly the same rate as speciation

9. How Fast Does Evolution Occur?
No exact time frame
Punctuated Equilibrium: Long periods of little change are interrupted by shorter periods of rapid change.
Due to sudden environment change
Ex: Mammal diversity exploded after dinosaur extinction
Gradualism:
Slow & steady change of 1 species into another
Small changes continually build over time

10. Gradualism of the Horse

11. How Fast Does Evolution Occur?
To radiate = to s-p-r-e-a-d out
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
Ex: Mammals

12. Review How is convergent and divergent evolution different?
What is thought to bring different organisms such as fish and dolphins to have evolved a similar body plan?
What is coevolution?
What does a flower gain from a close relationship with a hummingbird?
What does the hummingbird gain?
How is gradualism and punctuated equilibrium different?