The transformation of an unbranched lineage of organisms, sometimes to a state different enough from the ancestral population to justify renaming it as a new species.
Morphology is still the most common method used for describing species.
Modern taxonomists also consider genetic makeup and functional and behavior features when describing species. The biological species concept emphasizes reproductive isolation In 1942, Ernst Mayr proposed the biological species concept. B. Prezygotic and postzygotic barriers isolate the gene pools of biological species Any factor that impedes two species from producing viable, fertile hybrids contributes to reproductive isolation. Most species are genetically sequestered from other species by more than one type of reproductive barrier. Only intrinsic biological barriers to reproduction will be considered here.