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Darwin’s theory of evolution
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Darwin’s theory of evolution

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  • 1.
    • 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. 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. The evolutionary history of organisms can be portrayed as a tree growing through time.
  • 4. Genealogy of the primates
  • 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.
    • 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
    Darwin’s Idea of MULTIPLICATION of SPECIES
  • 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.
    • 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.
    • 3. Variation
    • - Individuals in a population vary greatly in their characteristics.
    • 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. Industrial Melanism: The Peppered Moth ( Biston betularia)
  • 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.  
  • 12.  
  • 13.
    • 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
  • 14.
    • Biological diversity is the product of evolution.
    • The mechanism of modification has been natural selection working continuously over long periods of time.
  • 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 .
  • 16.
    • 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
  • 17.