There are many theories to explain the process of evolution. Jean Baptiste Lamarck proposed the theory of inheritance of acquired character or the use and disuse theory which states that the modifications that an organism acquires as adaptations to the environment, are passed down to its descendants, thereby becoming a part of heredity. He explained the origin of species and adaptation to the environment in his book Philosophie Zoologique in 1809. According to Lamarck, there is a continuous increase in the size of a living organism and its body parts, as it grows older. Organisms produce new body movements and result in the formation of new organs. A change in the environment creates a special demand for certain organs. New needs lead to a greater use or disuse of certain organs. Vestigial organs are the non-functional organs present in the body that were functional in the ancestors. Acquired characteristics are acquired by an organism in its lifetime and inherited by the next generation. The evolution of long neck of giraffes, evolution of aquatic birds, evolution of snakes and the evolution of horse are the evidences that favour Lamarck. Besides, there have been certain contradictions to Lamarck’s prepositions. August weisman, Castle and Phillips, and Pavlov conducted few experiments in contradiction to Lamarck’s prepositions. Theory of germinal selection or Germplasm Theory was proposed by August Weismann in 1892. According to this theory, the proplasm differentiates into somatoplasm (body) and germplasm (sex cells). It is the germplasm passes hereditary material to progeny. However, scientists like F.B. Summer, P. Kammerer, Mc Dougall, Lindsey conducted experiments and supported the theories proposed by Lamarck. Gregor Mendel and August Weismann considered Lamarck’s theory of evolution as a hypothesis as acquired characteristics cannot be inherited.
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