Natural Selection

Natural Selection

  1. 1. •You will be able to describe Darwin’s theory of natural selection as well as give examples that support the theory. •You will be able to describe the conditions required for natural selection.
  2. 2. Recall •Evolution: changes that transform life over an immense time. •Darwin published , The Origins of Species making two main points for the mechanisms of evolution… 1. Descent with modification 2. Natural selection
  3. 3. Decent with Modification  Species living today descended from ancestral species  Species spread into various habitats over millions of years  Species accumulated different modifications, or adaptations, to diverse ways of life  Results in diversity of species
  4. 4. Natural Selection  Process by which individuals with inherited characteristics well-suited for their environment leave more offspring on average than do other individuals  Survival and reproduction of the fittest
  5. 5. Theory of Natural Selection Flow Chart Population of Organisms Overproduction Variation Struggle for existence Differences in reproductive success Evolution of adaptations
  6. 6. What have you learned?  What are the two main points that Darwin made in is book to ague the mechanisms of evolution?  Descent with modification and natural selection  What is natural selection?  Process by which individuals with inherited characteristics well-suited for their environment leave more offspring on average than do other individuals  Describe some conditions that could lead to a struggle for existence among individuals in a population.  Over population, limited resources, changes occurring in the environment
  7. 7. Natural Selection Game http://www.sciencechannel.com/games-and- interactives/charles-darwin-game/
  8. 8. Evidence of Evolution  The fossil record= shows patterns of evolution over millions of years  Comparative Anatomy  Comparative Embryology  Comparative Biochemistry: amino acid tables  Geographic Distribution: similar organisms separated by land
  9. 9. Fossil Record  Fossils provide a record of species that lived long ago.  Fossils show that ancient species share similarities with species that now live on Earth.
  10. 10. Comparative Anatomy  Homologous structures= anatomically similar structures inherited from a common ancestor
  11. 11. Comparative Embryology  Similar phases of development
  12. 12. Comparative Biochemistry  Common ancestry can be seen in the complex metabolic molecules that many different organisms share.  Organisms with closely related morphological features have more closely related molecular features.
  13. 13. Geographical Distribution  The distribution of plants and animals that Darwin saw first suggested evolution to Darwin.  Patterns of migration were critical to Darwin when he was developing his theory.  Evolution is intimately linked with climate and geological forces.
  14. 14. What have you learned?  What are the five things that provide evidence for evolution?  Fossil Record  Comparative anatomy  Comparative embryology  Comparative biochemistry  Geographical Distribution  In your foldable if you missed something update it with the new information.
  15. 15. You will be able to discuss mechanisms of evolution other than natural selection such as genetic drift and gene flow.
  16. 16. Gene Pool Consists of all the alleles in all the individuals that make up a population. The process of meiosis (specifically crossing over) and fertilization shuffle alleles in the gene pool giving us genetic diversity
  17. 17. Genetic Drift  A change in the population due to chance  All populations are subject to some genetic drift; however, the smaller the population the greater the impact.  Bottleneck effect- disasters can reduce the size of a population. By chance some alleles are represented more than others while others are completely eliminated  Founder effect- when a few individuals colonize an isolated habitat. There is low genetic make- up
  18. 18. Demonstration for Genetic Drift  Hypothesis:  What would the populations look like generations from now if there were no environmental changes and the gene pool remained the same?  Analysis:  What are some deadly “chance” events?  How did the removal of some of the marbles (change in the gene pool) affect each population?  How did the impact of genetic drift contrast between the small population and the larger population?
  19. 19. Gene Flow  The exchange of genes with another population  Occurs when fertile individuals or their gametes migrate between populations  Tends to reduce genetic differences between populations
  20. 20. What have you learned?  What is a gene pool?  All of the alleles in all of the organisms that make up a population  What are the two main forces of evolutionary change in gene pools other than natural selection?  Genetic drift and gene flow  How can genetic drift cause a substantial change in allele frequencies in small populations?  It can reduce genetic variations
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