Darwin’s theory of evolution


Published on

  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Darwin’s theory of evolution

  1. 1. <ul><li>Darwin’s Idea of Common Descent </li></ul><ul><li>Darwin’s Idea of Gradualism </li></ul><ul><li>Darwin’s Idea of Multiplication of </li></ul><ul><li>Species </li></ul><ul><li>Darwin’s Idea of Natural Selection </li></ul>
  2. 2. Darwin’s Idea of COMMON DESCENT <ul><li>evolution = descent with modification </li></ul><ul><li>All organisms are related through descent from some unknown ancestor that lived in the distant past. </li></ul><ul><li>As the descendants spilled into various habitats over time, they accumulated diverse modifications ( adaptations ) that fit them to specific ways of life. </li></ul><ul><li>The history of life is like a tree. </li></ul><ul><li>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. </li></ul>
  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 <ul><li>The origin of new species and adaptation are closely related processes. </li></ul><ul><li>A new species would arise from an ancestral form by the gradual accumulation of adaptations to a different environment. </li></ul><ul><li>e.g. Darwin’s finches  ADAPTIVE RADIATION </li></ul>large ground finch small tree finch woodpecker finch
  6. 6. <ul><li>The existence of an enormous number of species </li></ul><ul><li> some species are very similar (not as distinct from each other!) </li></ul><ul><li> gradual changes in various characteristics as organisms became modified according to the conditions in which they lived </li></ul>Darwin’s Idea of MULTIPLICATION of SPECIES
  7. 7. Darwin’s Idea of NATURAL SELECTION as the Mechanism for Evolution <ul><li>Overproduction </li></ul><ul><li>- All species have a tendency and the potential to increase at a geometric rate. </li></ul><ul><li>Competition </li></ul><ul><li>- The conditions supporting life are limited. </li></ul><ul><li>- 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. </li></ul><ul><li> The environments of most organisms have been in constant change throughout geologic time. </li></ul>
  8. 8. <ul><li>3. Variation </li></ul><ul><li>- Individuals in a population vary greatly in their characteristics. </li></ul><ul><li>Adaptation </li></ul><ul><li>- Some variations enable individuals to produce more offspring than other individuals. </li></ul><ul><li>5. Natural Selection </li></ul><ul><li>- Individuals having favorable traits will produce more offspring, and those with unfavorable traits will produce fewer offspring. </li></ul><ul><li>Speciation </li></ul><ul><li>- Given time, natural selection leads to the accumulation of changes that differentiate groups from one another, such that a new species may arise. </li></ul>
  9. 9. Industrial Melanism: The Peppered Moth ( Biston betularia)
  10. 10. <ul><li>Natural Selection  Survival of the Fittest </li></ul><ul><li>Other examples: </li></ul><ul><li>1. Insecticide resistance </li></ul><ul><li>2. Drug resistance in bacteria </li></ul><ul><li>A population is the smallest unit that can evolve. </li></ul><ul><li> Natural selection acts on individuals, but individuals do not evolve. </li></ul><ul><li>Natural vs. Artificial Selection </li></ul>Camouflage as an example of evolutionary adaptation
  11. 13. <ul><li>Divergent evolution – from one species to several different forms; adaptive radiation </li></ul><ul><li>Convergent evolution – results in increased resemblance between unrelated species </li></ul><ul><li>Coevolution – occurs when two or more species evolve in response to each other </li></ul>
  12. 14. <ul><li>Biological diversity is the product of evolution. </li></ul><ul><li>The mechanism of modification has been natural selection working continuously over long periods of time. </li></ul>
  13. 15. 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. 16. <ul><li>Variation mostly occurs as a result of gene mutations and genetic recombination. </li></ul><ul><li>Evolution is the change in allele frequency within a population over time. </li></ul><ul><li>gene </li></ul><ul><li>allele </li></ul><ul><li>frequency </li></ul><ul><li>gene pool </li></ul>Ernst Mayr