In biology, a species (plural: species) is one of the basic units of biological classification and a taxonomic rank. 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, the difficulty of defining species is known as the species problem. 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 "infraspecific taxa" such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae).
Species hypothesized to have the same ancestors are placed in one genus, based on similarities. The similarity of species is judged based on comparison of physical attributes, especially their DNA sequences, where available. All species are given a two-part name, a "binomial name". The first part of a binomial name is the generic name, the genus of the species. The second part is either called the specific name (a term used only in zoology) or the specific epithet (the term used in botany, which can also be used in zoology). For example, Boa constrictor is one of four species of the Boa genus. The first part of the name is capitalized, and the second part has a lower case. The binomial name is written in italics when printed and underlined when handwritten.
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, though other taxonomic levels such as families may be considered in broad-scale studies. Extinct species known only from fossils are generally difficult to assign precise taxonomic rankings, which is why higher taxonomic levels such as families are often used for fossil-based studies.
The total number of non-bacterial and non-archaeal species in the world has been estimated at 8.7 million, with previous estimates ranging from two million to 100 million.
Read more about Species: Biologists' Working Definition, Difficulty of Defining "species" and Identifying Particular Species, Definitions of Species, Numbers of Species, Importance in Biological Classification, Implications of Assignment of Species Status, Historical Development of The Species Concept, See Also
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... Comprises 100 marine species ... Comprises about 400 species ... Includes seven species, of which six live as commensals in the mantle of large clams and one in that of a freshwater snail ...
... All species have a proboscis which lies in the rhynchocoel when inactive but everts (turns inside-out) to emerge just above the mouth and capture the animal's prey with venom ... A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host ... Most nemerteans have various chemoreceptors, and on their heads some species have a number of pigment-cup ocelli, which can detect light but not form ...
... An average of 30% more species inhabit organic farms ... Many weed species attract beneficial insects that improve soil qualities and forage on weed pests ... Species found in organic farms enhance sustainability by reducing human input (e.g ...
Famous quotes containing the word species:
“Both classically- and romantically-minded spirits—inasmuch as these two species always exist—occupy themselves with a vision of the future: but the former do so out of a strength of their age, the latter out of its weakness.”
—Friedrich Nietzsche (1844–1900)
“Thus all probable reasoning is nothing but a species of sensation. ‘Tis not solely in poetry and music, we must follow our taste and sentiment, but likewise in philosophy, When I am convinc’d of any principle, ‘tis only an idea which strikes more strongly upon me. When I give the preference to one set of arguments above another, I do nothing but decide from my feeling concerning the superiority of their influence.”
—David Hume (1711–1776)
“Books, gentlemen, are a species of men, and introduced to them you circulate in the “very best society” that this world can furnish, without the intolerable infliction of “dressing” to go into it. In your shabbiest coat and cosiest slippers you may socially chat even with the fastidious Earl of Chesterfield, and lounging under a tree enjoy the divinest intimacy with my late lord of Verulam.”
—Herman Melville (1819–1891)