Lamarck's Theory of Evolution - Practice Questions & MCQ

• Jean Baptiste Lamarck put forth the theory of inheritance of acquired characters, which is also known as Lamarckism. 
• It was published in ‘Philosophie Zoologique’ in the year 1809.
• The four propositions of Lamarckism are as follows:
  • Living organisms and their parts tend to increase in size continuously due to internal forces of life.
  • New organs are formed in the body of organisms in response to a new need which are influenced by the environment.
  • If an organ is used continuously and constantly, it tends to be highly developed, whereas misuse results in degeneration. This theory was called the use and disuse of organs.
  • Changes acquired during the lifetime of an individual are inherited by its offspring. This was called the inheritance of acquired characters.
• Lamarck explained his theory with an example of giraffe. 
• The ancestors of giraffes were bearing a small neck and forelimbs and were like horses. 
• But they were living in places with no surface vegetation so they had to stretch their neck and for-limbs to take the leaves for food, which resulted in slight elongation of these parts.
• Whatever they acquired in one generation was transmitted to the next generation with the result that a race of long-necked and long fore-limbed giraffes was developed.

Criticism of Lamarckism:

• August Weismann was the main opposer of the inheritance of acquired characters. He forwarded the theory of continuity of germplasm and provided that only those characters are inherited that affect the germplasm.
• Though the tendency to increase in size has been shown in many forms, there are also instances where there is a reduction in size. For example, trees that are primitive, are large in size, while the shrubs, herbs and grasses that evolved later are smaller in size.
• Mendel’s law of inheritance also disproved Lamarck’s theory.