Organic evolution is described as slow and continuous changes which occurs in organisms due to genetical modifications, natural selection , geographical isolation etc which pass from one generation to other .
Natural selection may be defined as the process by which the organisms which are better adaptive to a particular kind of environment tends to survive, leading in the elimination of the organism less adaptive to that environment. These organisms are naturally selected reproduce to pass on their genetic qualities suitable to that environment making their species best suitable to that particular environment.