species

species, in biology, a category of classification, the original and still the basic unit in the demarcation of plant and animal types. The species marks the boundary between populations of organisms rather than between individuals. Because related species are not absolutely permanent (see evolution), a precise definition of the term is difficult. On the basis of genetics, scientists now include in a species all individuals that are potentially or actually capable of interbreeding and that share the same gene pool. The latter term refers to that collection of characteristics whose combination is unique in the species, although each individual of the group may not display every single one of the characteristics (see genetics). In the few cases where members of different species can interbreed, the offspring are usually sterile (e.g., the mule). Groups distinguished by lesser differences than those marking a species are called variously subspecies, varieties, races, or tribes.

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species

Subdivision of biological classification composed of related organisms that share common characteristics and can interbreed. Organisms are grouped into species according to their outer similarities, but more important in classifying organisms that reproduce sexually is their ability to interbreed successfully. To be members of the same species, individuals must be able to mate and produce viable offspring. Because genetic variations originate in individuals which then pass on their variations only within the species, it is at the species level that evolution takes place (see speciation). The international system of binomial nomenclature assigns new species a two-part name.

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species

1. Biology

a. any of the taxonomic groups into which a genus is divided, the members of which are capable of interbreeding: often containing subspecies, varieties, or races. A species is designated in italics by the genus name followed by the specific name, for example Felis domesticus (the domestic cat)

b. the animals of such a group

c. any group of related animals or plants not necessarily of this taxonomic rank

2. denoting a plant that is a natural member of a species rather than a hybrid or cultivar

3. Logic a group of objects or individuals, all sharing at least one common attribute, that forms a subdivision of a genus

4. Chiefly RC Church the outward form of the bread and wine in the Eucharist

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species [′spē·shēz]

(chemistry)

A chemical entity or molecular particle, such as a radical, ion, molecule, or atom. Also known as chemical species.

(nuclear physics)

nuclide

(systematics)

A taxonomic category ranking immediately below a genus and including closely related, morphologically similar individuals which actually or potentially interbreed.