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Natural Selection

Natural Selection

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Natural Selection

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  1. Natural Selection

  2. Today’s Objectives: SOL BIO.8b-d • TSW investigate and understand how populations change through time, including: • How variation of traits, reproductive strategies, and environmental pressures impact on the survival of populations • Recognizing how adaptations lead to natural selection • How new species emerge

  3. Charles Darwin • On the Origin of Species • Sailed with the HMS Beagle • Observations made in the Galapogos Islands • These observations helped him form the theory of how species change over time called natural selection

  4. What is Natural Selection? • Natural selection is governed by the principles of genetics.

  5. Types of Adaptations • Protective Coloring • Camouflage • Mimicry • Physiological Adaptations • Reproductive Changes • Other changes • Behavioral Adaptations

  6. Evidence for Evolution • Fossil record • Anatomy • Homologous structures • Analagous structures • Vestigial structures • Embryology • Molecular biology (DNA differences)

  7. What is a Population? • Populations evolve over many generations, individuals don’t • Populations are groups of interbreeding individuals that live in the same place at the same time • Individuals in a population compete for resources with each other

  8. How Does Evolution Work? • Populations produce more offspring than the environment can support • The unequal ability of individuals to survive and reproduc leads to the gradual change in a population over many generations

  9. Mechanism for change in a population of organisms • Animals who have greater fitness survive in environment and live to reproduce • Random changes (mutations) can lead to greater or less fitness • Adaptations allow an organism to survive better in their environment

  10. Mutations & Variety Produced by Sexual Reproduction Allow for Diversity within a Population • Genetic drift (caused by chance) • Bottleneck • Founder effect • Genetic equilibrium • Hardy-Weinberg law • In H-W equilibrium, does not occur

  11. Adaptations • Can arise in response to environmental pressures • Temperature • Antibiotic resistance in bacteria • Pesticide resistance • Morphological changes in peppered moths

  12. Types of Selection • Directional • Extreme form favored by natural selection • Stabilizing • Middle form most successful • Disruptive • Two extreme forms successful in separate environments

  13. How are new species created? • Geographic isolation • Reproductive barriers • Change in chromosome numbers • Adaptive radiation

  14. Types of Evolution • Convergent evolution • Dolphins & fishes • Wings of bees & bats • Divergent evolution • Darwin’s finches • Adaptive radiation

  15. How fast does evolution occur? • Gradualism • Darwin • Species change slowly over time • Punctuated Equilibrium • Gould & Lewontin • Species can make rapid “leaps” in evolution • Modern Synthesis • Parts of both are correct