Lamarckism Short Notes | Evolution Class 12 Notes

In this article we will discuss about Lamarckism :- 1. Effects of environment and new needs 2. Use and Disuse theory 3. Inheritance of acquired characters and 4. Speciation

  • First man to propose a theory for evolution
  • He coined the term biology
  • He published many book, Philosophic zoologique published in 1809


  1. Effect of environment and new needs
  2. Use and disuse of organs
  3. Inheritance of acquired characters
  4. Speciation
  1. Effect of Environment & New Needs
  • Environment influences all type of organisms
  • Changing environment gives rise to new needs
  • To fulfill these new needs, living organisms have to exert special efforts like changes in habits or behavior
  1. Use and Disuse of Organs
  • If an organ is constantly used over generations, it would be better developed
  • Whereas disuse of organ results in its degeneration
  1. Inheritance of Acquired Characters
  • During the life time of an organism, new characters develop due to effect of environment, new needs or use and disuse of organs
  • All these acquired characters are inherited from one generation to another
  • These offspring’s are fit to face the changed environmental conditions
  1. Speciation
  • Every generation new characters are acquired and transmitted to next generation
  • So that new characters accumulate generation after generation
  • After a number of generations a new species if formed


i) Evidence for use theory


  • Ancestors of giraffes are supposed to be deer like grazing upon the grasses in Africa
  • Due to disappearance of ground vegetation and availability of trees
  • Long necked and long fore limbed giraffe developed from short necked and small fore limbed deer like ancestors

Webbed Feet

  • Web feet aquatic birds evolved from non web feet birds
  • Aquatic birds float on water by propelling the water with their toes
  • After many generations web developed between the toes

Lamarckism Short Notes

ii) Evidence for disuse theory

Eyes of Cave Animals

  • Cave is characterized by complete darkness
  • In the absence of light cave animals cannot use their eyes
  • Eyes are not used many generations so the eyes become degenerated

Flightless Birds

  • Kiwi has descended from normal flying birds
  • When they first come to New Zealand they were good fliers
  • At the time there were no enemies on the land in New Zealand
  • Without enemies they had no chance to use their wings
  • This happened may generation resulting the degeneration of wings and loss of flight


i) Theory of Continuity of Germplasm

  • In 1892 this theory proposed by August Weismann
  • Multi cellular organism is formed of 2 types of cells
    • Germ cells: Have genes for inheritable characters to the offspring’s
    • Somatic cells: which have genes of particular organ during one’s life time only
  • Environment affects only somatic cells
  • Somatic cells are not transmitted to next generation so the acquired characters must be lost with the death of an organism
  • So these should have no role in evolution

ii) Pavlov Experiments

  • He is a Russian physiologist
  • Trained dog to come for food on hearing a bell
  • He reported that this training is not inherited and was necessary in each generation

iii) Whistler’s muscles

  • In Whistler’s a muscles are very well developed
  • Children’s of whistlers are not get this acquired characters from parents


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