Scientific classification, or biological classification, lays down the scientific basis for how biologists group or categorize species belonging to living or extinct creatures. Modern classification is based on Carolus Linnaeus' system of classifying species according to their physical characteristics. This classification has undergone many modifications since Linnaeus, in the light of the general rules of the Darwinian principle. With the DNA analysis method used by molecular classification, many principles of this classification have also changed and continue to change. Scientific classification is associated with taxonomy or systematic as a science.