Before 1969, there was two-kingdom classification, in which life was divided into two kingdoms such as, Animal Kingdom and the Plant Kingdom. The two-kingdom classification system did not last too long because this two-kingdom classification can not differentiate between the eukaryotes and prokaryotes; neither unicellular and multicellular; nor photosynthetic and the non-photosynthetic. Between 1969 – 1990 the five-kingdom classification system was introduced. In this classification system life was divided into five-kingdom such as Monera, Protista, Plantae, Fungi, Animalia. This classification system divides the life based on their anatomy, morphology, embryology, and cell structure. There were several limitations of five kingdom classification such as this classification system does not mention about viruses, even this classification does not mention about how organisms within Kingdoms or between kingdoms may be related to each other via evolutionary relationships among the kingdoms. After 1990, The Domain kingdom classification system or Carl Woese’s Classification or Six Kingdoms and Three Domains Classification was introduced. This classification system is based on the genetic characteristics (rather than phenotypic ones) with respect to evolutionary relatedness (phylogeny) of organisms that may prove more stable and predictable. There were several limitations or drawbacks of these classifications that is why they don't last too long. (Follow my previous articles )