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Patterns in Evolution.

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Presentation on theme: "Patterns in Evolution."— Presentation transcript:

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?

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