This theory was given by Jean Baptiste Lamarck in 1809. His theory is known as Theory of Acquired traits. According to Lamarck due to changes in environment, more frequently used organ strengthened and organ that was less frequently used disappeared. Giraffes are found in Africa. It has long legs and neck. It lives by eating the leaves of tall trees. According to Lamarck ancestors of giraffe were not so tall. They could easily eat weeds. Gradually, due to changes in the environment, desert extended and grassland perished.

To get the leaves of the tress which were at height, legs and neck had to use more frequently. That’s why its legs and neck become too long. These traits are inherited from generation and generation. Snakes live in holes. Due to inconvenience legs were use less and gradually disappeared. Drawbacks of Lamarck: Some scientists denied the theory of Lamarck. They said,”if the tail of a mouse is cut generation to generation, there is no chance of birth of a mouse with out tail. In the same manner, girls do not take with a prick in their earlobe even after girls are having it from generations.