In biology Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy, a species is one of the basic units of biological classification Biological classification, or scientific classification in biology, is a method by which biologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis. Modern biological classification and a taxonomic rank In biological classification, rank is the level in a taxonomic branched ordering of living things. The most specific level is species, the next most specific is genus, and then family, class, etc. Sometimes (but only rarely) the term "taxonomic category" is used and more often the term "rank" is used -- the ranking, or ordering,. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as similarity of DNA, morphology or ecological niche. Presence of specific locally adapted traits may further subdivide species into subspecies Subspecies in biological classification, is either a taxonomic rank subordinate to species, or a taxonomic unit in that rank (plural: subspecies). A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one.

The commonly used names for plant and animal taxa sometimes correspond to species: for example, "lion The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg (550 lb) in weight, it is the second-largest living cat after the tiger. Wild lions currently exist in Sub-Saharan Africa and in Asia with a critically endangered remnant population in Gir Forest National Park in India,," "walrus The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic Walrus (O. rosmarus rosmarus) which lives in the," and "Camphor tree Cinnamomum camphora is a large evergreen tree that grows up to 20–30 metres tall. The leaves have a glossy, waxy appearance and smell of camphor when crushed. In spring it produces bright green foliage with masses of small white flowers. It produces clusters of black berry-like fruit around one centimetre in diameter. It has a pale bark that is" – each refers to a species. In other cases common names do not: for example, "deer Deer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Male deer of all species but the Chinese Water deer and female reindeer grow and shed new antlers each year. In this they differ from permanently horned animals such as antelope; these are in the same order as deer and may" refers to a family What does and does not belong to each family is determined by a taxonomist. Similarly for the question if a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family of 34 species, including Eld's Deer Eld's Deer with the scientific name Cervus eldii M'Clelland, 1842, indigenous to Southeast Asia, Vulnerable as per IUCN 1990, has three recognized subspecies. The species was first discovered by westerners in Manipur in 1839. It was named Cervus eldi in 1844 in honour of Lt. Percy Eld – a British officer. The species categorization is based on, Red Deer The Red Deer is one of the largest deer species. The Red Deer inhabits most of Europe, the Caucasus Mountains region, Asia Minor and parts of western and central Asia. It also inhabits the Atlas Mountains region between Morocco and Tunisia in northwestern Africa, being the only species of deer to inhabit Africa. Red Deer have been introduced to and Elk The elk, or wapiti , is one of the largest species of deer in the world and one of the largest mammals in North America and eastern Asia. In the deer family (Cervidae), only the moose, Alces alces (called an "elk" in Europe), is larger, and Cervus unicolor (the sambar deer) can rival the C. canadensis elk in size. Elk are almost (Wapiti). The last two species were once considered a single species, illustrating how species boundaries may change with increased scientific knowledge.

Each species is placed within a single genus In biology, a genus is a low-level taxonomic rank (a taxon) used in the classification of living and fossil organisms, which is an example of definition by genus and differentia. The term comes from Latin genus "descent, family, type, gender", cognate with Greek: γένος – genos, "race, stock, kin". This is a hypothesis that the species is more closely related to other species within its genus than to species of other genera. All species are given a binomial name The formal system of naming species is called binomial nomenclature , binominal nomenclature (since 1953, the technically correct form in zoology), or binary nomenclature consisting of the generic name and specific name In zoological nomenclature, a specific name is the second part (second name) in the name of a species (a binomen). The first part is the name of the genus (or specific epithet). For example, Boa constrictor The Boa constrictor is a large, heavy-bodied species of snake. It is a member of the Boidae family found in Central America, South America and some islands in the Caribbean. A staple of private collections and public displays, its color pattern is highly variable yet distinctive. Ten subspecies are currently recognized, although some of these are, which is commonly called by its bionomial name, and is one of five species of the Boa genus.

A usable definition of the word "species" and reliable methods of identifying particular species are essential for stating and testing biological theories and for measuring biodiversity Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or on an entire planet. Biodiversity is one measure of the health of biological systems. Life on Earth today consists of many millions of distinct biological species. The year 2010 was declared the International Year of Biodiversity. Traditionally, multiple examples of a proposed species must be studied for unifying characters before it can be regarded as a species. Extinct species known only from fossils are generally difficult to give precise taxonomic rankings to.

Because of the difficulties with both defining and tallying the total numbers of different species in the world, it is estimated that there are anywhere between 2 and 100 million different species.[1]

Contents

Biologists' working definition

A usable definition of the word "species" and reliable methods of identifying particular species is essential for stating and testing biological theories and for measuring biodiversity Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or on an entire planet. Biodiversity is one measure of the health of biological systems. Life on Earth today consists of many millions of distinct biological species. The year 2010 was declared the International Year of Biodiversity. Traditionally, multiple examples of a proposed species must be studied for unifying characters before it can be regarded as a species. It is generally difficult to give precise taxonomic rankings to extinct species known only from fossils.

Some biologists may view species as statistical phenomena, as opposed to the traditional idea, with a species seen as a class of organisms. In that case, a species is defined as a separately evolving lineage that forms a single gene pool In population genetics, a gene pool is the complete set of unique alleles in a species or population. Although properties such as DNA-sequences and morphology are used to help separate closely related lineages, this definition has fuzzy boundaries.[2] However, the exact definition of the term "species" is still controversial, particularly in prokaryotes The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek πρό- (pro-) &,[3] and this is called the species problem The species problem is a mixture of difficult, related questions that often come up when biologists identify species and when they define the word "species".[4] Biologists have proposed a range of more precise definitions, but the definition used is a pragmatic choice that depends on the particularities of the species concerned.[4]

Common names and species

The commonly used names for plant and animal taxa sometimes correspond to species: for example, "lion The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg (550 lb) in weight, it is the second-largest living cat after the tiger. Wild lions currently exist in Sub-Saharan Africa and in Asia with a critically endangered remnant population in Gir Forest National Park in India,", "walrus The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic Walrus (O. rosmarus rosmarus) which lives in the", and "Camphor tree Cinnamomum camphora is a large evergreen tree that grows up to 20–30 metres tall. The leaves have a glossy, waxy appearance and smell of camphor when crushed. In spring it produces bright green foliage with masses of small white flowers. It produces clusters of black berry-like fruit around one centimetre in diameter. It has a pale bark that is" – each refers to a species. In other cases common names do not: for example, "deer Deer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Male deer of all species but the Chinese Water deer and female reindeer grow and shed new antlers each year. In this they differ from permanently horned animals such as antelope; these are in the same order as deer and may" refers to a family What does and does not belong to each family is determined by a taxonomist. Similarly for the question if a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family of 34 species, including Eld's Deer Eld's Deer with the scientific name Cervus eldii M'Clelland, 1842, indigenous to Southeast Asia, Vulnerable as per IUCN 1990, has three recognized subspecies. The species was first discovered by westerners in Manipur in 1839. It was named Cervus eldi in 1844 in honour of Lt. Percy Eld – a British officer. The species categorization is based on, Red Deer The Red Deer is one of the largest deer species. The Red Deer inhabits most of Europe, the Caucasus Mountains region, Asia Minor and parts of western and central Asia. It also inhabits the Atlas Mountains region between Morocco and Tunisia in northwestern Africa, being the only species of deer to inhabit Africa. Red Deer have been introduced to and Elk The elk, or wapiti , is one of the largest species of deer in the world and one of the largest mammals in North America and eastern Asia. In the deer family (Cervidae), only the moose, Alces alces (called an "elk" in Europe), is larger, and Cervus unicolor (the sambar deer) can rival the C. canadensis elk in size. Elk are almost (Wapiti). The last two species were once considered a single species, illustrating how species boundaries may change with increased scientific knowledge.

Because of the difficulties with both defining and tallying the total numbers of different species in the world, it is estimated that there are anywhere between 2 and 100 million different species.[1]

Placement within generation

Ideally, a species is given a formal, scientific name, although in practice there are very many unnamed species (which have only been described, not named). When a species is named, it is placed within a genus In biology, a genus is a low-level taxonomic rank (a taxon) used in the classification of living and fossil organisms, which is an example of definition by genus and differentia. The term comes from Latin genus "descent, family, type, gender", cognate with Greek: γένος – genos, "race, stock, kin". From a scientific point of view this can be regarded as a hypothesis that the species is more closely related to other species within its genus (if any) than to species of other genera. Species and genus are usually defined as part of a larger taxonomic hierarchy. The best-known taxonomic ranks are, in order: life Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes (biology) from those that do not, either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate, domain In biological taxonomy, a domain is the highest taxonomic rank of organisms, higher than a kingdom. According to the three-domain system of Carl Woese, introduced in 1990, the Tree of Life consists of three domains: Archaea, Bacteria and Eukarya. The arrangement of taxa reflects the fundamental differences in the genomes. There are some, kingdom In biology, kingdom or regnum is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany. The complete sequence of ranks is life, domain, kingdom, phylum, class, order, family, genus, and species, phylum In biology, a phylum [note 1] is a taxonomic rank below Kingdom and above Class. "Phylum" is equivalent to the botanical term division. Phylum is one of the major biological divisions called Taxa. Although "phylum" is often used as if it were a clearly defined term, no satisfactory definition of it exists. In fact, "phylum&, class The composition of each class is determined by a taxonomist. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing a class, but for well-known animals there is likely to be consensus. For example, dogs are usually assigned to the phylum, order The Latin suffix -formes meaning "having the form of" is used for the scientific name of orders of birds and fishes, but not for those of mammals and invertebrates, family What does and does not belong to each family is determined by a taxonomist. Similarly for the question if a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family, genus In biology, a genus is a low-level taxonomic rank (a taxon) used in the classification of living and fossil organisms, which is an example of definition by genus and differentia. The term comes from Latin genus "descent, family, type, gender", cognate with Greek: γένος – genos, "race, stock, kin", and species. This assignment to a genus is not immutable; later a different (or the same) taxonomist may assign it to a different genus, in which case the name will also change.

In biological nomenclature, the name for a species is a two-part name (a binomial name The formal system of naming species is called binomial nomenclature , binominal nomenclature (since 1953, the technically correct form in zoology), or binary nomenclature), treated as Latin Latin or sometimes Roman is an Italic language originally spoken in Latium and Ancient Rome. Although often considered a dead language, in view of the fact that it has no native speakers, a small number of scholars can fluently speak it and it continues to be taught in schools and universities and has been, and currently is, used in the process of, although roots from any language can be used as well as names of locales or individuals. The generic name In biology, a genus is a low-level taxonomic rank (a taxon) used in the classification of living and fossil organisms, which is an example of definition by genus and differentia. The term comes from Latin genus "descent, family, type, gender", cognate with Greek: γένος – genos, "race, stock, kin" is listed first (with its leading letter capitalized), followed by a second term, the specific name In zoological nomenclature, a specific name is the second part (second name) in the name of a species (a binomen). The first part is the name of the genus (or specific epithet). For example, the species commonly known as the Longleaf Pine is Pinus palustris The Longleaf Pine is a pine native to the southeast United States, found along the coastal plain from eastern Texas to southeast Virginia extending into northern and central Florida; gray wolves belong to the species Canis lupus, coyotes to Canis latrans, golden jackals to Canis aureus, etc., and all of those belong to the genus Canis Canis is a genus containing 7 to 10 extant species, including dogs, wolves, coyotes, and jackals, and many extinct species (which also contains many other species). The name of the species is the whole binomial The formal system of naming species is called binomial nomenclature , binominal nomenclature (since 1953, the technically correct form in zoology), or binary nomenclature, not just the second term (which may be called the specific name In zoological nomenclature, a specific name is the second part (second name) in the name of a species (a binomen). The first part is the name of the genus for animals).

This binomial naming convention, later formalized in the biological codes of nomenclature The Nomenclature Codes are the various rulebooks that govern biological nomenclature, each in their own area. They are united in that they use names of the type Neotragus batesi and Caesalpinia gilliesii for species. To an end-user who only deals with names of species, with some awareness that species are assignable to families, it may not be, was first used by Leonhart Fuchs Leonhart Fuchs , sometimes spelled Leonhard Fuchs, was a German physician and one of the three founding fathers of botany, along with Otto Brunfels and Hieronymus Bock (also called Hieronymus Tragus) and introduced as the standard by Carolus Linnaeus Carl Linnaeus [a 2] (Latinized as Carolus Linnaeus [a 3], also known after his ennoblement as Carl von Linné , 23 May[a 1] 1707 – 10 January 1778) was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of in his 1753, Species Plantarum (followed by his, 1758 Systema Naturae, 10th edition). At that time, the chief biological theory was that species represented independent acts of creation by God God is the English name given to the singular omnipotent being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism and were therefore considered objectively real and immutable, so the hypothesis of common descent did not apply.

Abbreviated names

Books and articles sometimes intentionally do not identify species fully and use the abbreviation "sp." in the singular or "spp." in the plural in place of the specific epithet: for example, Canis sp. This commonly occurs in the following types of situations:

In books and articles, genus and species names are usually printed in italics. If using "sp." and "spp.", these should not be italicized.

Difficulty of defining "species" and identifying particular species

Main article: Species problem The Greenish Warbler demonstrates the concept of a ring species.

It is surprisingly difficult to define the word "species" in a way that applies to all naturally occurring organisms, and the debate among biologists about how to define "species" and how to identify actual species is called the species problem.

Most textbooks follow Ernst Mayr's definition of a species as "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups".[4]

Various parts of this definition serve to exclude some unusual or artificial matings:

The typical textbook definition above works well for most multi-celled organisms, but there are several types of situations in which it breaks down:

Horizontal gene transfer makes it even more difficult to define the word "species". There is strong evidence of horizontal gene transfer between very dissimilar groups of prokaryotes, and at least occasionally between dissimilar groups of eukaryotes; and Williamson[5] argues that there is evidence for it in some crustaceans and echinoderms. All definitions of the word "species" assume that an organism gets all its genes from one or two parents that are very like that organism, but horizontal gene transfer makes that assumption false.

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