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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.
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Patterns in Evolution
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.
Convergent Evolution
Defined: Describes evolution toward similar traits in unrelated species.• Survival advantage to a particular environment.• Ex: Tuna (fish) and dolphins (mammals). They are an
unrelated species living in a similar environment, the ocean.• Faced similar evolutionary pressures.
• Defined: Describes evolution toward different traits in closely related species.– Cause: Different environments
ancestor
red fox kit fox
Divergent Evolution
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
• Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.– Example: Crab vs. Snail & Bacteria vs. Humans
Coevolution Continued…
GoodBad
• Antibiotics: chemicals designed to kill bacteria– Produced by other microorganisms to fight bacteria
• Antibiotic Resistance: Bacteria are adapting to the use of antibiotics– Overuse & misuse speeds up the process– Importance: Bacteria infections are becoming harder to treat
Evolutionary Arms Race Continued… Antibiotic Resistance
Species Can Become Extinct • Defined: The elimination of a species from Earth.
• 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
• 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
How Fast Does Evolution Occur?
• No exact time frame• Gradualism: slow & steady change of 1 species into
another– Small changes continually build
• Punctuated Equilibrium: Rapid periods of evolution– Due to sudden environment change– Ex: Mammal diversity exploded after dinosaur extinction
• Examples of both models exist
• Adaptive radiation: A process of evolution where one species can split into a number of different species.
– Ancestral species diversifies into many descendent species
– Descendent speciesusually adapted todifferent (wide range of)environments
How Fast Does Evolution Occur?To radiate = to s-p-r-e-a-d out
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