Darwin’s theory of natural selection :
- Charles Darwin had collected innumerable specimens of plants and animals.
- Depending upon the observations of those specimens; he published the theory of natural selection which preaches the survival of fittest.
- Book titled ‘Origin of Species’.
- All the organisms reproduce prolifically.
- All the organisms compete with each other in a life--threatening manner.
- Only those organisms sustain which show the modifications essential for winning the competition.
- However, besides this, natural selection also plays important role.
- Nature selects only those organisms which are fit to live and the rest perish.
- Darwin’s theory of natural selection was widely accepted for long duration.
- Natural selection is not the only factor responsible for evolution.
- Darwin did not mention any explanation about useful and useless modifications.
- No explanation about slow changes and abrupt changes.
Lamarckism :
- Morphological changes occurring in living organisms are responsible for evolution.
- Reason - Activities or laziness of that organism.
- He called this concept as principle of ‘use or disuse of organs’.
- Further, he said that the neck of giraffe has become too long due to browsing on leaves of tall plants by extending their neck for several generations;
- similarly, shoulders of the ironsmith have become very strong due to frequent hammering movements.
- Wings of birds like ostrich and emu have become weak due to no use.
- Legs of the birds like swan and duck have become useful for swimming due to living in water
- snakes have lost their legs by modifications in their body for burrowing habit.
- All these examples are types of ‘acquired characters’ and are transferred from one to another generation. This is called as theory of inheritance of acquired characters or Lamarckism.
- Development of organs due to specific activities or their degeneration due to no use at all was widely accepted
- Transfer of those characters from generation to generation was rejected.
- Because it had been verified many times that modifications brought in us are not transferred to next generation and thereby Lamarck’s theory was disproved.
- The living organism can transfer the characters which it has acquired, to the next generation. This is called ancestry of acquired characters