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Descent with Modification via Natural Selection

Darwinism. Descent with Modification via Natural Selection. Darwin’s Inspirations. Geology Earth’s current features are the result of billions of years of gradual change. Darwin’s Inspirations. Fossil Record Extant species are not the only ones to have existed on Earth.

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Descent with Modification via Natural Selection

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  1. Darwinism Descent with Modification via Natural Selection

  2. Darwin’s Inspirations Geology Earth’s current features are the result of billions of years of gradual change

  3. Darwin’s Inspirations Fossil Record Extant species are not the only ones to have existed on Earth

  4. Darwin’s Inspirations • Fossil Record • Some fossils indicate missing links between extant groups

  5. Darwin’s Inspirations • Morphology • Homologous structures’ underlying similarities indicate common ancestry • Analogous structures have a similar function but are likely coincidental • Vestigial structures are remnants of ancestors that have no apparent use in a particular current organism.

  6. Homologous Structures

  7. Analogous Structures

  8. Vestigial Structures

  9. Beyond Darwin • Embryological Homologies • Similarity in early development indicates common ancestry Sponge Jellyfish Clam Insect Human

  10. Beyond Darwin • Molecular Homologies • Molecular comparisons indicate relations (closer match = closer relation) • DNA Hybridization • Protein Comparison (amino acid sequence) A+B A B A B C

  11. Natural SelectionEnvironment determines success of traits • Overproduction of offspring and scarcity of resources

  12. Natural SelectionEnvironment determines success of traits 2. Genetic variation within populations

  13. Natural SelectionEnvironment determines success of traits 3. Orgs with adaptations will survive and reproduce in greater numbers.

  14. Natural SelectionEnvironment determines success of traits 4. Subsequent generations will contain more orgs with these adaptations.

  15. Adaptation • Inherited trait • Increases chance of survival/reproduction • Environment-specific

  16. Natural Selection • Orgs produce more offspring than can possibly survive. • Orgs within a species possess different genetic traits. • Orgs with adaptations will survive and reproduce in greater numbers. • The next generation will contain more individuals with these adaptations.

  17. Natural Selection

  18. Modes of Selection • Stabilizing • Environment is stable • Initially adaptive form becoming more numerous from many generations of natural selection MOST ADAPTIVE FORM RANGE OF PHENOTYPES

  19. Modes of Selection • Directional • Environment is changing (or has changed) • Formerly adaptive form is no longer adaptive • Pop evolves toward newly adaptive form MOST ADAPTIVE FORM RANGE OF PHENOTYPES

  20. Modes of Selection • Disruptive (Diversifying) • Intermediate form is undesirable and decreases in # RANGE OF PHENOTYPES MOST ADAPTIVE FORMS MOST ADAPTIVE FORMS

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