Taxonomy is the scientific procedure for sorting things out. The first activity in the scientific investigation of a new field is to record detailed observations of as many phenomena in the field as possible. The second is to classify them by arranging the phenomena in groups together with the others which are most similar, or most closely related. In this way scientists look for patterns in the relationships among the phenomena they are investigating. These patterns help in the development of a theory (an explanation of how things work).
Classification (taxonomy) skills are most often taught in biology, but they are essential in every area of science. In chemistry, elements and compounds are classified. In geology, minerals and rocks are classified. In meteorology, cloud forms, wind systems, and climates are classified. However, in biology taxonomy is especially important because of the extremely large number of organisms to be sorted through.
There are a number of ways to classify living things, by habitat, position in the food web, or geographic distribution, among others. The "correct" system of classification is the one which works most conveniently for the purpose at hand. The "official" taxonomic system is designed to make it "easy" to identify any specimen with previous studies of the same species (kind), or to show that it is a "new" species, one not yet studied and classified by scientists. Before a new species name can be used an official description must be published, and the name approved by an international committee.
For most of history, scientists have divided all living things into two large groups, the kingdom of plants and the kingdom of animals. In everyday life most people see no difficulty deciding whether an organism is a plant or an animal, but the border is blurred, and in the past errors have been made (corals were long classified as plants instead of as animals). Especially with the use of the microscope, scientists found the two kingdoms less and less satisfactory. By the late 20th century the five kingdom taxonomy had been generally accepted. Monera (bacteria) - single celled organisms without nuclei, Protista (protists)- single celled organisms with nuclei, Protoctista (fungi) - multicelled organisms with cell walls which are not made of cellulose, Plantae (plants)- multicelled organisms with cell walls of cellulose, Animalae (animals)- multicelled organisms without cell walls. These are not official definitions of the kingdoms, but characteristics which work most of the time.
Living things are sorted into seven levels of classification, from largest to smallest they are; kingdom, phylum, class, order, family, genus, species. Because nature doesn't respect our esthetic of organization, sometimes we resort to sub levels or super levels. The scientific name of an organism is the combination of its genus name plus its species name. Example: The scientific name of the house cat is Felis domestica . "Felis", is the name of a genus, "domestica", is the name of a species. (For examples, see Back Yard Biology)
During the 19th century, organisms were sorted by apparent similarities,
and arranged to show presumed evolutionary relationships. That
is, those species which are most similar are expected to have had the
most recent "common ancestral species". By the end of the 20th century DNA comparisons were
used. The more similar their DNA, the more closely related the
species are. Surprisingly few changes in
taxonomic standings have resulted from the use of DNA.