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Natural Selection

Today's objectives include investigating how populations change over time due to traits variation, environmental pressures, and reproductive strategies. Learn about natural selection, adaptations, evidence for evolution, and mechanisms for change in populations.

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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

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