Species
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).
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Famous quotes containing the word species:
“Let us guard against saying that death is opposed to life. The living is merely a species of the dead, and a very rare species.”
—Friedrich Nietzsche (1844–1900)
“The question that will decide our destiny is not whether we shall expand into space. It is: shall we be one species or a million? A million species will not exhaust the ecological niches that are awaiting the arrival of intelligence.”
—Freeman Dyson (b. 1923)
“There are minds so impatient of inferiority that their gratitude is a species of revenge, and they return benefits, not because recompense is a pleasure, but because obligation is a pain.”
—Samuel Johnson (1709–1784)