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Theory of Evolution

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Theories of evolution
Theories of evolution
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Theory of Evolution

  1. 1. Darwin’s Theory of Evolution as a Mechanistic Process • Darwin’s Idea of Common Descent • Darwin’s Idea of Gradualism • Darwin’s Idea of Multiplication of Species • Darwin’s Idea of Natural Selection
  2. 2. Darwin’s Idea of COMMON DESCENT • evolution = descent with modification • All organisms are related through descent from some unknown ancestor that lived in the distant past. • As the descendants spilled into various habitats over time, they accumulated diverse modifications (adaptations) that fit them to specific ways of life. • The history of life is like a tree. • The Linnean classification scheme reflected the branching genealogy of the tree of life, with organisms at the different levels related through descent from common ancestors.
  3. 3. The evolutionary history of organisms can be portrayed as a tree growing through time.
  4. 4. Genealogy of the primates
  5. 5. Darwin’s Idea of GRADUALISM • The origin of new species and adaptation are closely related processes. • A new species would arise from an ancestral form by the gradual accumulation of adaptations to a different environment. • e.g. Darwin’s finches  ADAPTIVE RADIATION large ground finch small tree finch woodpecker finch
  6. 6. Darwin’s Idea of MULTIPLICATION of SPECIES  The existence of an enormous number of species  some species are very similar (not as distinct from each other!)  gradual changes in various characteristics as organisms became modified according to the conditions in which they lived
  7. 7. Darwin’s Idea of NATURAL SELECTION as the Mechanism for Evolution • Overproduction - All species have a tendency and the potential to increase at a geometric rate. 2. Competition - The conditions supporting life are limited. - Only a fraction of the offspring in a population will live to produce offspring, so that the number of individuals in a population remains fairly constant.  The environments of most organisms have been in constant change throughout geologic time.
  8. 8. 3. Variation - Individuals in a population vary greatly in their characteristics. 4. Adaptation - Some variations enable individuals to produce more offspring than other individuals. 5. Natural Selection - Individuals having favorable traits will produce more offspring, and those with unfavorable traits will produce fewer offspring. • Speciation - Given time, natural selection leads to the accumulation of changes that differentiate groups from one another, such that a new species may arise.
  9. 9. Industrial Melanism: The Peppered Moth (Biston betularia)
  10. 10.  Natural Selection  Survival of the Fittest Other examples: 1. Insecticide resistance 2. Drug resistance in bacteria  A population is the smallest unit that can evolve.  Natural selection acts on individuals, but individuals do not evolve.  Natural vs. Artificial Selection Camouflage as an example of evolutionary adaptation
  11. 11. Patterns of Evolution  Divergent evolution – from one species to several different forms; adaptive radiation  Convergent evolution – results in increased resemblance between unrelated species  Coevolution – occurs when two or more species evolve in response to each other
  12. 12. Darwin’s Theory of Evolution in a nutshell  Biological diversity is the product of evolution.  The mechanism of modification has been natural selection working continuously over long periods of time.
  13. 13. At the time, Darwin did not understand the genetic basis for evolution.  Variations arise from mutation and genetic recombination.  Much of the variation observed in the individuals of a population is heritable.
  14. 14. The Synthetic Theory of Evolution (Neo-Darwinism)  Variation mostly occurs as a result of gene mutations and genetic recombination.  Evolution is the change in allele frequency within a population over time. gene allele frequency gene pool Ernst Mayr

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