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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. Fitness: Relative measure of reproductive success. Selective pressures: Environmental factors determine reproductive success. 3
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. 4
Natural selection operates on individuals but populations evolve 5
Antibiotic resistance in bacteria Selective pressure: use of antibiotics Selection for: higher resistance to antibiotics 6
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. 7
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 8
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 9
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 10
Natural selection 11
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