BIOLOGICAL EVOLUTION

BIOLOGICAL EVOLUTION:

  • The essence of Darwinian Theory about evolution is natural selection.
  • The rate of appearance of new forms is linked to the life cycle or the life span.
  • There must be a genetic basis for getting selected and to evolve.
  • Some organisms are better adapted to survive in an otherwise hostile environment.
  • Adaptive ability is inherited.
  • It has genetic basis.
  • Fitness is the end result of the ability to adapt and get selected by nature.
  • Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.

Lamark theory of evolution: (theory of inheritance of acquired characters)

  • French Naturalist Lamark had said that evolution of life forms had occurred but driven by use and disuse of organs.
  • He gave the example of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks.
  • They passed on this acquired character of elongated neck to succeeding generations.
  • Giraffes, slowly over the years, came to acquire long necks.

 

MECHANISM OF EVOLUTION:

Variation:

  • In the first decade of twentieth century, Hugo de Vries based on his work on evening primrose brought fourth the idea of mutations.
  • Mutation is the large difference arising suddenly in a population.

Hugo de Vries theory of mutation differs from Darwin’s theory of natural selection?

  • It is the mutation which causes evolution and not the minor variations that Darwin talked about.
  • Mutations are random and directionless while Darwinian variations are small and directional.
  • Evolution for Darwin was gradual while de Vries believed mutation caused speciation and hence called it saltation (single step large mutation).

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