Taxonomy

In the past, biologists classified all organisms into the plant kingdom or animal kingdom. Fungi were placed into the plant kingdom and single-celled organisms were rather arbitrarily placed into one kingdom or the other. Very few biologists currently use this simple two kingdom system. In recent years, biologists have proposed a great variety of classification systems, based on as many as 13 separate kingdoms of organisms. The five kingdom system, based on proposals by ecologist Robert Whittaker in 1959 and 1969, is widely used as a framework for discussing the diversity of life in most modern biology textbooks.