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.

species (spee-shiz) n. the smallest unit used in the classification of living organisms. Members of the same species are able to interbreed and to produce fertile offspring. Similar species are grouped together within one genus.

species Group of physically and genetically similar individuals that interbreed to produce fertile offspring under natural conditions. In biological classification, species is the lowest level. Each species has a unique two-part Latin name, the first part being the capitalized genus name and the second part, the species. So far, more than 1.5 million plant and animal species have been identified. See also binomial nomenclature; taxonomy