Key concept :Key concept : Evolution Evolution occurs in occurs in patternspatternsy py p pp• Evolution through natural selection is not random.
• Natural selection can have directionNatural selection can have direction.• The effects of natural selection add up over time.
Convergent Convergent EEvolution volution
Defined: Describes evolution toward similar traits in unrelated speciesspecies.
• Survival advantage to a particular environment.• Ex: Tuna (fish) and dolphins (mammals). They are an unrelatedEx: Tuna (fish) and dolphins (mammals). They are an unrelated
species living in a similar environment, the ocean.• Faced similar evolutionary pressures.
DivergentDivergent EEvolution volution
ancestor
red fox kit fox
• Defined: Describes evolution toward different l l l dtraits in closely related species.
– Cause: Different environments
CoevolutionCoevolution
• 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
CoevolutionCoevolution Continued…Continued…
• Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race.– Example: Crab vs. Snail & Bacteria vs. Humans
Evolutionary Arms Race Continued… Evolutionary Arms Race Continued… A tibi tiA tibi ti R i tR i tAntibiotic Antibiotic ResistanceResistance
GoodBad
• Antibiotics: chemicals designed to kill bacteria– Produced by other microorganisms to fight bacteria
• Antibiotic Resistance: Bacteria are adapting to the use of antibioticsAntibiotic Resistance: Bacteria are adapting to the use of antibiotics– Overuse & misuse speeds up the process– Importance: Bacteria infections are becoming harder to treat
Species Species CCan an BBecome ecome EExtinct xtinct • Defined: The elimination of a species from Earth• Defined: The elimination of a species from Earth.
• Background Extinctions:
– Cause: Local changes in environment
Forest fires habitat destruction
• Mass Extinctions:
– Cause: Catastrophic events
– Ice Age, Meteorites– Forest fires, habitat destruction.
– Less severe.
– Affects a few species in a small area
Ice Age, Meteorites
– Very severe
– Destroys many species at global level
R b t h i t– Occur at roughly the same rate as speciation
– 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
G d liGradualism of the Horseof the Horse
How Fast Does Evolution Occur?• Many species evolve from one species during adaptive radiation.
– Ancestral species diversifies into many descendent species
– Descendent speciesusually adapted towide range ofwide range ofenvironments
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