1. Taxonomy employs a hierarchical system of classification.
A. The Classification of Organisms
1. Early naming of organisms
a. Classification of organisms started about 2000 years ago with Aristotle, who had a simple classification system (plant or animal).
b. After Aristotle the system was continued and expanded by the Greeks and Romans.
2. The Binomial System
a. Developed by Carolus Linnaeus (1707-1778)
b. Linnaeus categorized and named thousands of species that he found in his travels.
c. He gave each organism a 2-part name, what we now know as the Latin name, which consists of the Genus and Species names.
d. Example: Humans are Homo sapiens. Homo is the Genus and sapiens is the species.
e. Linnaeus grouped species into the same genus if they seemed related based on their appearance and structure. Almost all of these classifications of Linnaeus are still used today-he was very accurate in his classifications.
B. Under the binomial system, each species is assigned a two-part latinized name, a binomial.
1. No 2 species have the same name.
2. All names are Latin or latinized-all countries use the same names.
3. First word is the genus; second word is the species.
4. Writing Latin names:
a. Genus name is capitalized, Species name is not capitalized.
b. Both Genus and Species are italicized (Homo sapiens) OR underlined (Homo sapiens) (not both).
c. If you have written the full name out as in b above, it is permissable to abbreviate the Genus name subsequently in the same paper or document as follows: H. sapiens.
d. All other taxonomic unit names are capitalized, but no distinctive print style.
C. The Taxonomic Hierarchy
1. Organisms are grouped into larger and larger categories: Species, Genus, Family, Order, Class, Phylum, Kingdom, Domain.
2. Groupings larger than Genus were added after Linnaeus.
3. Each level is a taxon (plural form is taxa).
4. For example, the leopard, Panthera pardus, belongs to a genus that includes the African lion (Panthera leo) and the tiger (Panthera tigris) (Fig. 25.7).
D. Major Categories of the Current Classification System (Fig. 26.16)
1. Domains
a. Archaea are very different from other organisms. They were discovered in the 1980's and prokaryotic cells that live in extreme environments like the hot springs at Yellowstone. They caused the adoption of a taxonomic level higher than Kingdom, the Domain level.
b. Bacteria is a second Domain and includes all other prokaryotic cells.
c. Eukarya is a third Domain and contains all organisms with eukaryotic cells.
2. Kingdoms
a. Archaea-only Kingdom in Domain Archaea-all are unicellular prokaryotes.
b. Bacteria (sometimes called Eubacteria)-only Kingdom in Domain Bacteria-all are unicellular prokaryotes.
c. Kingdoms in Domain Eukarya:
1. Kingdom Protista-unicellular and multicellular eukaryotes. Consists of eukaryotes that don't fit into the plant, animal or fungus kingdoms.
2. Kingdom Fungi-contains multicellular forms like mushrooms and unicellular yeasts.
3. Kingdom Plantae (plants)-all are multicellular organisms.
4. Kingdom Animalia (animals)-all are multicellular organisms.
E. There will be much more research before there is anything close to a new consensus for how the three domains of life are related and how many kingdoms there are.
1. New data will undoubtedly lead to further taxonomic modeling.
2. Keep in mind that phylogenetic trees and taxonomic groupings are hypotheses that fit the best available data.