Question

Explain Lamarck's theory of use and disuse of organs with suitable examples.

Answer 1

Hint:Lamarck wrote the theory of use and disuse of organs in his book named “Philosophic Zoologique”. Later his theory was criticized by August Weisman.

Complete answer:Lamarckism or Theory of Inheritance of Acquired Characters given by Jean Baptiste de Lamarck, 1809 in his book “Philosophic Zoologique”.
This theory is based on the comparison between the contemporary species of his time to the fossil record. Postulate given were:
1. New needs/doctrine of new needs or desires/ Appetency- The change in environmental factors like light, temperature, medium, food, air, etc. or migration, create new needs for the organisms. To fulfill these new needs, the organism has to put in some efforts which result in a change in habitat or habit of the organism.
2. Use and Disuse of Organs- The new habits involve greater use of certain organs and disuse/lesser use of other organs. Continuous use of certain organs makes them active and strong while disuse makes them inactive, reduced, and ultimately disappears.
Examples to support this postulate are: developed and strong biceps of a blacksmith, elongated limbless body of the snake, lengthening of the neck of Giraffe, vestigial organs of living animals, webbed feet of swimming birds, retractile claws in carnivorous, cave dwellers lost their eyesight, etc.
3. Inheritance of Acquired Characters- The change brought by the use and disuse of organs and environmental factors is called acquired characters. Lamarck believed that every generation acquires new characters which are transmitted to the new generation. After a few generations, new species are formed.

Note:Lamarckism was criticized by August Weisman. He experimented on rats. He cut tails of rats for many generations but no single rat was born without a tail in any generation. And then, he gave the theory of continuity of germplasm.