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
CONCEPTS OF LAMARCKISM
- Effect of environment and new needs
- Use and disuse of organs
- Inheritance of acquired characters
- Speciation
- 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
- 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
- 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
- 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
EVIDENCES OF LAMARCKISM
i) Evidence for use theory
Giraffe
- 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
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
CRITICISM OF LAMARCKISM
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
