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Natural Selection and Speciation

Natural Selection and Speciation. Stabilizing Selection. favors the average individual reduces variation in a population. Examples. birth weight in humans Siberian husky- muscle mass “living fossils”- organisms that have remained unchanged for millions of years (sharks, crocs).

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Natural Selection and Speciation

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  1. Natural Selection and Speciation

  2. Stabilizing Selection • favors the average individual • reduces variation in a population

  3. Examples • birth weight in humans • Siberian husky- muscle mass • “living fossils”- organisms that have remained unchanged for millions of years (sharks, crocs)

  4. Birth Weight

  5. Directional Selection • favors one of the extreme variations • leads to rapid evolution of a population

  6. Examples PEPPERED MOTHS PESTICIDE/ANTIBIOTIC RESISTANCE

  7. Disruptive Selection • favors both extreme variations

  8. Examples • Darwin’s finches • small beaked birds could eat small seeds • large beaked birds could eat large seeds • medium beaked birds could not eat either seed efficiently

  9. STABILIZING DIRECTIONAL DISRUPTIVE

  10. Divergent Evolution • occurs when closely related species evolve to look differently • populations change to adapt to different environments • adaptive radiation- one species evolves into several different species

  11. Darwin’s Finches

  12. Hawaiian Island Honeycreepers

  13. Convergent Evolution • occurs when species of different ancestry evolve to look alike • occurs b/c species occupy similar environments • analogous traits

  14. Examples • whales and fish • birds and butterflies • marsupial and placental mammals

  15. Speciation • evolutionary formation of a new species

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