In order to effectively study plants and animals, all scientists need to use the same names. Using the same names keeps scientists from getting confused about what species is being referred to.
The current classification system was created by Swedish botanist Carl Linnaeus in 1757. Scientists often refer to this system as taxonomy. The Linnaean taxonomic system is quite useful as a classification system. Not only does it provide official names for every plant and animal, it also helps scientists understand how objects are related to one another.
Showing off your genus about the species
This scientific classification system notes the relationships and similarities among organisms. Each organism is given a scientific name that consists of two words (usually derived from Latin) — the genus and the species of the organism. The genus is the first word, and the species is the second word in this name. Thus, Homo sapiens refers to humans. Canis familiaris is the family dog, and Canis lupus is the family wolf. Because wolves and dogs share many similarities, they share the same genus (no, no, not the same genes, the same genus).
When writing a scientific name, the genus name is capitalized, and the species name is all lowercase. Both names are italicized.
Counting down the classification system
The classification system consists of seven levels:
- Kingdom: A kingdom is the broadest level. It contains the most kinds of organisms. The relationships among organisms in a kingdom are extremely loose.
- Phylum: Phylum is the major taxonomic group of animals and plants. Within the kingdoms, organisms are divided by general characteristics. For example, in the Animal Kingdom, animals with backbones are placed in a separate phylum from animals without backbones.
- Class: Organisms in a phylum are divided into classes that further group similarities. In the Animal Kingdom, for example, birds, mammals, and fish all group in their own classes. Among plants, the angiosperm class comprises all flowering plants, and all conifers, such as pines and spruces, make up the conifer class.
- Order: Scientific groupings don't follow hard and fast rules. After you get to the "order" of a living thing, there's disagreement about where it belongs. You may find that different scientific organizations group creatures in different orders or families.
- Family: Families further divide organisms of the same class by similar characteristics. Not all scientific organizations may agree to the exact family an organization should be classified in.
- Genus: Two or more species that share unique body structures or other characteristics are considered to be closely related and are placed together in a genus. Sometimes a genus may include only a single species if there's nothing else in the world that has similarities with it.
- Species: A species is the most specific level. It contains the fewest organisms. The relationship between organisms in a species is very close.
A mess of mnemonic devices are floating around out there to help you remember the order of the Linnaean taxonomic system, from Kant Provides Crazy Ontology For Graduate Students to King Philip Cut Open Five Green Snakes. You can use one of these or make up your own, as long as you can remember the correct classification order: Kingdom, Phylum, Class, Order, Family, Genus, Species.
In order to get a better idea of how the scientific classification system works, here's how the average lion is classified:
- Kingdom Animalia: This kingdom includes all animals.
- Phylum Chordata: All vertebrate animals belong to the phylum Chordata. (Think "spinal cord.")
- Class Mammalia: All mammals belong to this class.
- Order Carnivora: All mammals that eat meat belong to the order Carnivora.
- Family Felidae: The family Felidae includes all cats.
- Genus Panthera: This genus includes all the roaring cats, such as lions, tigers, jaguars, and leopards.
- Species leo: Lion.
Although not every scientist agrees (scientists never agree on any subject), in general, most lab-coated individuals settle on five as the number of kingdoms:
- Animals: One of the two largest kingdoms. Includes many-celled organisms that, unlike plants, don't have cellulose cell walls, chlorophyll, or the capacity to convert light into energy (photosynthesis); members of this kingdom can move and respond to stimuli. The Animal kingdom includes more than 1,000,000 species.
- Plants: One of the two largest kingdoms. Includes organisms that can't move, don't have obvious nervous or sensory systems, and possess cellulose cell walls. Over 250,000 species belong to the Plant Kingdom.
- Monerans and viruses: Includes bacteria and algae — one-celled organisms that don't have a nucleus. Viruses don't have a true cell structure either — that's why they're stuck in this kingdom. More than 10,000 species have been discovered and classified in the Monera kingdom.
- Protists: One-celled organisms that have a nucleus, like the protozoa (you may remember from biology class). This kingdom consists of more than 250,000 species.
- Fungi: Complex, many-celled organisms that don't photosynthesize (use light to create energy) like plants. Mushrooms are the most famous fungi. Over 100,000 species belong to the Fungi kingdom.
Thirty-three phyla (the plural of phylum) make up the Animal kingdom, and 17 main phyla make up the Plant kingdom. Monerans consist of three phyla; Protists have seven phyla, and Fungi are made up from four phyla. Numerous classes, orders, families, genera, and species fall under each phylum.
Humans belong to the kingdom Animalia, the phylum Chordata, the class Mammalia, the order Primata, the family Hominidae, the genus Homo, and the species sapiens. You know, just in case you were wondering.