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- Ch. 2 Scientific thought and Darwin's
theory of natural selection
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Office hours Tuesdays and Thursdays, 12-1 pm 1 Ch. 2 Scientific - - PowerPoint PPT Presentation
Office hours Tuesdays and Thursdays, 12-1 pm 1 Ch. 2 Scientific - - PowerPoint PPT Presentation
Office hours Tuesdays and Thursdays, 12-1 pm 1 Ch. 2 Scientific thought and Darwin's theory of natural selection 2 Important terms for evolution by natural selection Reproductive success: # of reproductively viable offspring produced.
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Reproductive success: # of reproductively viable offspring produced. Fitness: Relative measure of reproductive success. Selective pressures: Environmental factors determine reproductive success.
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Important terms for evolution by natural selection
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Darwin's theory of natural selection
- Mechanism of evolutionary change
- All species have variation of heritable traits among individuals.
- Traits are advantageous (increase reproductive success) relative
to the environment.
- Gradual accumulation of advantageous traits leads to speciation.
- New species also arise due to geographic isolation.
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Natural selection operates on individuals but populations evolve
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Antibiotic resistance in bacteria
Selective pressure: use of antibiotics Selection for: higher resistance to antibiotics
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Fundamentals of natural selection:
- I. Only acts on heritable traits.
- II. Only acts on already existing variation.
- III. Fitness is relative to environmental changes.
- IV. Only acts on traits that affect reproduction.
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Constraints on Darwin's theory of natural selection
Constraint: Didn't know why biological variation occurs Constraint: Didn't know how traits were inherited Eventually overcame these constraints using:
- Advancements in technology, cell biology, and genetics
- The rediscovery of Mendel's principles of inheritance
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Conditions needed for natural selection
- I. Only acts on heritable traits
- II. Only acts on already existing variation
- III. Fitness is relative to environmental changes
- IV. Only acts on traits that affect reproduction
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Examples of natural selection: Galapagos finches
- Local environmental conditions varied from island to island
Beak sizes differ between species Heavy beaks = ate hard seeds Long stout beaks = ate insects (like a woodpecker) Long thin beaks = ate flying insects
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