A way of organizing living things. In biology, plants and animals have traditionally been classified by the structure of their bodies, in a descending hierarchy of categories: kingdom, phylum, class, order, family, genus, and species. For example, human beings are classified as belonging to the animal kingdom, the phylum of chordates, the class of mammals, the order of primates, the genus Homo, and the species sapiens. The scheme is based on a system developed by the Swedish scientist Carolus Linnaeus in the eighteenth century.
There is a debate among scientists about whether the traditional classification system should be retained. Some argue that classifying living things by their descent, with all descendants of a single ancestor being grouped together, is more in keeping with the ideas of evolution (see cladistics). Others want to classify organisms by their genetic makeup, using sequences in DNA or RNA. Each of these schemes provides a different way of ordering living things, but there is no “right” way to accomplish this task.
| The classification of the Siberian tiger and romaine lettuce shown here are presented in descending order, beginning with the broadest category. Biologists who specialize in classification (called taxonomists) are constantly refining their terms as new relationships between organisms are recognized. | |
|
Kingdom
Animalia (animals) |
Kingdom
Plantae (plants) |
|
Phylum
Chordata (chordates) |
Division
Tracheophyta (vascular plants) |
|
Subphylum
Vertebrata (vertebrates) |
Class
Angiospermae (flowering plants) |
|
Class
Mammalia (mammals) |
Subclass
Dicotyledonae (dicotyledons) |
|
Order
Carnivora (carnivores) |
Order
Campanulales or Campanulatae (bellflowers, lobelias, composites) |
|
Family
Felidae (cats) |
Family
Compositae (composites) |
|
Genus
Panthera (lion, tiger, leopard, jaguar) |
Genus
Lactuca (lettuce) |
|
Species
Panthera tigris (tiger) |
Species
Lactuca sativa (cultivated lettuce) |
|
Subspecies
Panthera tigris altaica (Siberian tiger) |
Variety
Lactuca sativa longifolia (romaine lettuce) |