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Biogeography is study of distribution of animals and plants in different parts of the earth. Wallace (1876) divided the earth in six biogeographical realms : Oriental, Ethiopian, Palaearctic, Australian, Nearctic and Neotropical. It is suggested that all the continents have originated from a single land mass, Gondwana, due to movements of crustal plates of the earth. Main biogeographical evidences are Darwin's finches, discontinuous distribution of alligators, magnolias differences in between the island and mainland fauna due to isolation and consequent adaptation to new environment.