organ is not used for a long time, it gradually degenerates. The ancestors of giraffe were provided with short neck and short forelimbs. Due to shortage of grass, they were forced to feed on leaves from trees. The continuous stretching of their neck and forelimbs resulted in the development of long neck and long forelimbs which is an example for constant use of an organ.
The degenerated wing of Kiwi is an example for organ of disuse. iv. Theory of Inheritance of acquired characters When there is a change in the environment, the animals respond to the change. They develop adaptive structures.
The characters developed by the animals during their life time, in response to the environmental changes are called acquired characters . According to Lamarck, the acquired characters are transmitted to the offspring by the process of inheritance. . .
Darwinism or Theory of Natural Selection Charles Darwin ( - ) was one of the great naturalist and philosopher of th century. He was born in England in . While studying in college through his friendship with Professor J.S.Henslow he was fascinated towards nature. At that time the British Admiralty planned a voyage of exploration for years on a ship named H.M.S.
Beagle around South America . Dr Henslow was asked to nominate a young naturalist for the voyage. Darwin was given the opportunity. During his five years ( – ) voyage he visited many parts of Flow chart showing the postulates of Lamarckism Organs of Use Environmental change Need for new structure Development of new structure Degeneration of the structure Inheritance of adaptive characters Origin of new species Organs of Disuse the world, a number of islands including the Galapagos island and Pacific island .
Darwin made elaborate observations on nature of the land, plants and animals of the regions he visited. He further worked for a period of years to develop the theory of natural selection. Darwin published his observations and conclusions under the name ‘ Origin of species ’ in . The book of Darwin demonstrates the fact of evolution.