During the early period, people were not able to similarize or differentiate between the characteristics of different organisms. In 1758 Carl Linnaeus proposed a binomial nomenclature system. every single organism was given two names, i.e., genus and species. He then grouped genera into families- orders-classes-phyla-kingdoms. He also identified Animalia (animals) and Plantae (plants) kingdoms.
Thomas Whittaker proposed a "five kingdom" system in which three kingdoms were added to the animals and plants: Monera (bacteria), Protista, and Fungi.
Carl Woese proposed a radical reorganization of the 5 kingdoms into 3 domains.