Introduction

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In biology, classification is the process of arranging organisms, both living and extinct, into groups based on similar characteristics. The science of naming and classifying organisms is called taxonomy. The term is derived from the Greek taxis ("arrangement") and nomos ("constabulary").

Taxonomists classify organisms into a structural hierarchy—a multi-level arrangement in which each grouping is nested, or independent, within a larger grouping. Groups at the highest level are the largest and most full general and contain a wide diversity of living things. These groups are divided into smaller groups of similar organisms. Each smaller group is split into even smaller groups, which contain organisms with even more similar features: For case, a big group that includes all plants would contain smaller groups of that contain like types of plants, such as trees, bushes, mosses, flowering plants, and then forth. Each of these groups would incorporate nonetheless smaller groups; for example, the tree group might be divided into conifers and broadleaf trees.

Each group in biological classification—that is, each level in the hierarchy—is called a taxon (plural, taxa).The most basic taxon is the species, a group of closely related organisms that can breed and produce offspring that in turn tin can reproduce.

Scientific Names

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Organizing big amounts of information in a standardized way makes it easy to locate information and to communicate it to others. Scientists apply an internationally accustomed arrangement for classifying and naming organisms. The system is based on the classification method introduced in 1758 by Carolus Linnaeus, a Swedish botanist regarded as the founder of modern taxonomy.

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The Linnaean system assigns each species a ii-function scientific name composed of Greek or Latin words. The first role of the scientific proper noun is the organism'south genus, a taxon that includes closely related species. Wolves, dogs, coyotes, and jackals are all members of the genus Canis. Conventionally, scientific names are e'er italicized or underlined, and the genus name is always capitalized.

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The 2d role of the scientific name is chosen the species proper noun, and it is particular to each species in the genus. The species proper name of the coyote is latrans; that of the gray wolf is lupus. The species name is always written in lowercase and italicized.

Together, the genus name and the species name comprise the scientific name of the species. Thus, the coyote'southward scientific name is Canis latrans; the gray wolf's name is Canis lupus. The two-part scientific name is sometimes called a binomial—from the Latin words bi-, meaning two, and nomen, pregnant name.

Using scientific names helps scientists avert the confusion that tin ascend when referring to an organism by its common, or everyday, proper noun. For case, the proper name robin may refer to the European robin or to the American robin, or fifty-fifty to any of several other birds; all the same the robins' scientific names—Erithacus rubecula and Turdus migratorius (European robin and American robin, respectively)—conspicuously place the species beingness referenced. The scientific names show that the birds are distinct species and verify that they are not closely related, since each belongs to a different genus.

Levels of Classification

The classification system commonly used today is based on the Linnean system and has viii levels of taxa; from the most general to the most specific, these are domain, kingdom, phylum (plural, phyla), grade, gild, family, genus (plural, genera), and species. (For plants, the term partitioning is generally used instead of phylum.) Each level is contained, or nested, within the level higher up it. For instance, a genus contains i or more species; a family unit contains one or more genera; an order contains one or more families; then on. The domain is the highest level of organization and is the largest group.

Following are overviews of each taxonomic level in mod biological classification. (For a detailed clarification of domains and kingdoms, see "Classification of Living Things" in the article living things.)

Domain

The domain is the highest rank in biological classification. In that location are three domains—Archaea, Bacteria, and Eukarya. The Archaea and the Bacteria each contain prokaryotes (single-celled organisms that lack a truthful nucleus) but differ in structural, genetic, and biochemical characteristics. The domain Eukarya contains eukaryotes—organisms whose cells contain a nucleus and membrane-bound organelles.

Kingdom

Earlier the domain taxon was introduced during the 1990s, the kingdom ranked equally the highest taxonomic level in classification. Most scientists today recognize six kingdoms: Archaea (prokaryotes with singled-out cellular characteristics that adapt them to farthermost environments, such as deep-sea vents and hot springs); Bacteria (prokaryotes that are not archaeans); Protista (chiefly protozoa and algae); Fungi (mushrooms, molds, and yeasts); Plantae (plants); and Animalia (animals). The kingdoms Archaea and the Bacteria each constitute a carve up domain. The Protista, Fungi, Plantae, and Animalia all belong to the domain Eukarya.

Phylum

The phylum (plural, phyla) ranks below the kingdom and to a higher place the form in taxonomy. Scientists more often than not use the term phylum for archaea, leaner, protists, fungi, and animals, just they substitute the term division for plants.

Organisms are classified in a phylum or division based largely on full general body plan. For example, members of the Phylum Arthropoda have external skeletons, segmented bodies, and jointed legs. Insects, crabs, and arachnids are examples of arthropods. A muscular foot and a soft unsegmented body that may or may not be covered with a beat are hallmarks of the Phylum Mollusca; familiar mollusks include mussels, snails, and clams. Animals of the Phylum Chordata take an internal skeleton and a backbone or notochord (a primitive courage). Fish, amphibians, reptiles, birds, and mammals (including humans) are in this grouping. (Meet also vertebrate.)

Class

The course ranks below the phylum and higher up the gild in taxonomy. Members of a class share more characteristics with each other than they do with other organisms in the same phylum. Amphibians and reptiles both belong to the Phylum Chordata, but each belongs to a dissimilar class. Members of the Class Amphibia (chiefly frogs, toads, and salamanders) have moist, smooth skin and reproduce by laying large quantities of jellylike eggs in h2o. Members of the Class Reptilia (snakes, lizards, turtles, and tortoises) reptiles have dry scaly skin and reproduce by laying pocket-sized clutches of leathery eggs on country.

Order

The order ranks below the class and above the family in the taxonomic hierarchy. The groups in an order have more in common with each other than they practice with other members of the same class. Considering reindeer (caribou) and whales both belong to the Form Mammalia, they share the bones traits of mammals, such as feeding milk to their young; however, each belongs to a dissimilar order. Reindeer are function of the Social club Artiodactyla, which includes cloven-hoofed mammals; cows, pigs, antelope, and giraffes are fellow artiodactyls. Whales belong the Order Cetacea, a marine mammal order that counts porpoises and dolphins as members.

Family

In taxonomy, the family ranks below the lodge and higher up the genus. Members of the same taxonomic family are more closely related to each other than they are to other members of the aforementioned order. For example, foxes, coyotes, lions, cats, otters, and weasels all belong to the Order Carnivora. However, foxes and coyotes belong to the family Canidae. Lions and cats belong to the family Felidae; otters and weasels are part of the family Mustelidae.

Genus

The genus (plural, genera) is the taxonomic rank between family unit and species. The groups of organisms in a genus share many structural similarities and are very closely related. Members of a genus are more closely related to each other than they are to other genera in the same family. The true cat family, Felidae, includes lions, tigers, ocelots, domestic cats, bobcats, and lynx. However, lions and tigers belong to the genus Panthera, ocelots and domestic cats are part of the genus Felis, and lynx and bobcats are in the genus Lynx.

Species

The species is the most fundamental unit in taxonomy and ranks at the base of the biological nomenclature hierarchy. Members of the same species share the aforementioned evolutionary history and are more closely related to each other than they are to any other organisms, including other members of the aforementioned genus. Organisms are grouped into a species based on concrete and genetic similarities. All members of a species have the aforementioned number of chromosomes.

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The almost important factor in species classification is the power of members to successfully interbreed—that is, to mate and produce viable offspring (those that tin in plough brood and produce more offspring). Individuals of the same species can successfully interbreed with one another but almost never with members of other species. Different species within a genus have been known to produce hybrid offspring, simply the offspring are almost always sterile. An example of this is the mating of a equus caballus and a ass, which produces a mule. Considering mules are sterile, the interbreeding is not considered successful.

Each species has its ain scientific name, equanimous of the genus proper name and species epithet. The king of beasts'south scientific name is Lion, whereas the scientific name of the tiger is Panthera tigris.

Some species include groups with such distinctive traits that they are classified equally subspecies; in these cases, a subspecies proper noun is added to the cease of the species proper name. Subspecies of Panthera tigris include the Siberian tiger (Panthera tigris altaica) and the Indian, or Bengal, tiger (Panthera tigris tigris).

How Classification Works

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Modern scientists utilize both physical and genetic evidence to classify organisms into taxa. The coyote is classified as follows:

Domain Eukarya

Kingdom Animalia

Phylum Chordata

Class Mammalia

Gild Carnivora

Family Canidae

Genus Canis (coyotes, wolves, dogs, and jackals)

Species Canis latrans (coyotes)

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In general, the more levels species share, the more closely they are related. Coyotes, gray wolves (Canis lupus), domestic dogs (Dog), and jackals (4 Canis species) all belong to the same summit seven taxa (domain, kingdom, phylum, class, order, family unit, and genus). This indicates that these species share many concrete and genetic traits and are closely related.

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In dissimilarity, the red play a trick on (Vulpes vulpes), though a member of the family unit Canidae, belongs to the genus Vulpes. Thus—though the cherry-red fox is related to wolves, coyotes, dogs, and jackals— it is less closely related to them than they are to each other.

Changes in Classification Systems

In Linneaus's fourth dimension, scientists characterized organisms as either plants or animals. Linnaeus followed this full general rule, dividing all living things into two kingdoms—the Kingdom Plantae (plants) and the Kingdom Animalia (animals). His system was afterwards modified by other scientists, especially equally advances in microscopy revealed primal differences among organisms at the cellular level. For example, Linneaus classified fungi and algae in the plant kingdom. When later scientists noted key differences in the cell structures of these groups, algae and fungi were reclassified in different kingdoms.

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Over time, the Linnean classification organisation was expanded, first to iii kingdoms and then to 4. By the 1960s, scientists had organized living things into five kingdoms—the Monera (leaner), Protista (protozoa and algae), Fungi (mushrooms, yeasts, and molds), Plantae (plants), and Animalia (animals). The five-kingdom system was widely accepted and used for many years.

Encyclopædia Britannica, Inc.

Encyclopædia Britannica, Inc.

In the tardily 1970s, American microbiologist Carl Woese reported on several central genetic differences he had observed in prokaryotes. Woese's findings led scientists to split the Kingdom Monera into two kingdoms—the Bacteria and the Archaea. The vi-kingdom organization has been the standard used in taxonomy since the 1990s. Woese further proposed a major change in classification by placing all organisms into three domains—Eukarya, Bacteria, and Archaea—to reflect their three separate lines of evolution.