I. 1.4 (b) Theories of Organic Evolution (Pre- Darwinian, Darwinian and Post- Darwinian)

Evolution

It is slow, progressive, continuous and irreversible change of organisms from simple and undeveloped form to complex and developed form in long course of time.

Definition organic evolution

Organic evolution is biological evolution. It is the gradual process of change in gene frequency of a population.

Concept of organic evolution

Organism undergo the process of change in response to changing environmental conditions and genetic make-up. Organic evolution  means gradual changes in the gene frequency or decent with modification. It is a result of interplay between organisms and environment.

Basic premises of organic evolution

  1. Environmental conditions in nature are ever changing.
  2. Organism have inherent character to change in order to adjust to the with the changing conditions.
  3. Adaption is process of change in organism to changing conditions.
  4. New species are always better adapted than earlier ones.
  5. Organic evolution is time consuming process.
  6. All the present species originate from existing species thus they have common ancesters.

Methods of study of organic evolution

  1. Evidences from palaeontology
  2. Evidences from molecular biology
  3. Evidences from comparative anatomy
  4. Evidences from geographical distribution
  5. Evidences from taxonomy
  6. Evidences from antibiotics resistance and pesticide resistances

Theories of Organic Evolution

  1. Pre- Darwinian
    1. Lamarkism- Inheritance of acquired characters
    2. August Weismann- Theory of continuity of Germplasm
    3. Neo-Lamarkism – Morgan and Cope
  2. Darwinian – Theory of Natural selection
    1. Herbert Spencer-
    2. B. Summer
    3. McDougail
    4. Lindsey
    5. Tower
  3. Post- Darwinian
    1. Hugo De-Vries- The mutation theory
    2. Synthetic theory of organic evolution

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