Lamarckism: Jean Baptiste de Lamarck proposed the first theory of evolution.
Book: Philosophic Zoologique (1809)
Basic Concepts of Lamarckism:
(i) Effect of environment and new needs: The environment influences all types of organisms. Changing the environment gives rise to new needs. New needs or desires produce new structures (doctrine of desired) and change habits of the organism.
(ii) Use and disuse of organs: If an organ is constantly used, it would be better developed whereas the disuse of organs results in its degeneration.
(iii) Inheritance of acquired character: During the lifetime of an organism new characters develop due to internal vital forces, effects of the environment, new needs, and use and disuse of organs. These characters that are acquired by one generation are inherited to another. By continuous inheritance, through many generations, these acquired characters tend to make new generations quite different from their ancestors resulting in the formation of new species.
Examples in support of Lamarckism :
1. The long neck and high forelimb of giraffe.
2. Aquatic birds stretched their toes and developed the web.
3. Snakes lost their legs.
4. Deers became good runners by the development of strong limbs and a streamlined body.
5. Retractile claws of carnivorous animals.