The first theory of evolution was proposed by Jean Baptiste de Lamarck Lamarckism proposed, Some internal forces are present in all organisms. Due to the presence of these forces, the organism has the tendency to increase the size of their organs or the entire body.
Environment influences all type of organisms. Changing environment give rise to new needs. New needs or desires produce new structure and change habits of the organism.
If an organ is constantly used, it would be better developed whereas disuse of organ results in its degeneration.