Origin and Evolution of Life: Mechanism of Evolution and Darwin՚s Theory of Natural Selection (For CBSE, ICSE, IAS, NET, NRA 2022)

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Mechanism of Evolution

  • Mechanism of evolution is proposed by various theories and in that Landmark ′ s theory of “Inheritance of acquired characters” , De Vries ′ Mutation theory and Evolutionary by Natural selection (Darwinism) .
  • Darwin՚s theory of Natural selection still holds ground but was modified with progress in genetics and developed into the Modern synthetic theory which is regarded as the most valid theory of evolution.

Darwin՚s Theory of Natural Selection

  • Natural selection is a process in which individuals that are well suited to their environment will survive and reproduce better than their individuals.
  • Charles Darwin suggested that all kind of organisms are related through ancestry and a mechanism for evolution and named it natural selection. According Darwin, organisms produce more offspring than can survive because environmental resources are limited ant there ensues struggle for existence. Organisms with advantageous variations are protected and allowed to reproduce while the disadvantageous variants are limited from nature. This is the termed of natural selection by Darwin.
  • According to Darwin when the environment changes, new adaptations get selected in nature and after many generations sufficient characteristics will have been changed so as to alter the species into a new one (origin of species) .
  • Darwin talked about variation but did not know about the sources of variation. With progress in genetics the sources of variation were discovered, and Darwin՚s original theory of Natural Selection modified. This new theory was termed Neo-Darwinism or Modern Synthetic Theory.

According to this theory:

  • The unit of evolution is population which has its own gene pool. Gene pool is the group of all different genes of a population.
  • Heritable genetic changes appear in the individuals of a population. These heritable changes or variations occur due to small mutations in the genes or in the chromosomes and their recombination՚s
  • Natural selection selects the variation which helps in adapting to the environment.
  • A change in the genetic constitution of a population selected by natural selection is responsible for evolution of a new species, since through interaction of variation and Natural Selection more offspring՚s with favorable genetic changes are born. This is called differential reproduction.
  • Once evolved, Reproductive Isolation helps in keeping species distinct.
Different Species Come from a Common Ancestor

Salient Features of Darwin՚s Theory of Natural Selection

  • Over production (Rapid Multiplication)
  • Limited Food and Space
  • Struggle for Existence
  • Appearance of Variations
  • Natural Selection or Survival of the Fittest
  • Inheritance of useful variations
  • Speciation (Formation of new species)

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